@article{yang_ye_tran_liu_cao_dong_portale_liu_zhang_loi_et al._2024, title={Impact of Oligo(Ethylene Glycol) Side Chains on the Thermoelectric Properties of Naphthalenediimide-Dialkoxybithiazole Polymers}, volume={2}, ISSN={["2639-4979"]}, DOI={10.1021/acsmaterialslett.4c00068}, abstractNote={Organic thermoelectric materials have garnered significant interest as promising candidates for energy harvesting applications. In recent years, ethylene-glycol side-chain engineering in organic semiconductors has gradually become an efficient approach to boost the performance of organic thermoelectrics. Although this strategy is widely utilized, the impact of their volume and branching structure remains unknown. This contribution describes a trade-off phenomenon between the oligo(ethylene glycol) (OEG) side chains and thermoelectric properties based on the n-type doped low-bandgap conjugated polymers, achieved through the modification of the volume and structure of side chains. Three conjugated polymers comprising a naphthalenediimide-dialkoxybithiazole backbone and different linear length or branched OEG side chains exhibit good host/dopant miscibility after doping. We find that, in the linear OEG side-chain-based polymers, the increased volume of side chains slightly influences the planarity of backbones, thereby leading to similar and satisfactory thermoelectric performances. The high fraction of side chains does not consistently yield enhanced performance, as the branched OEG side-chain introduces steric hindrance. Consequently, the accordingly conjugated backbones become less planar and rigid, resulting in critical molecular packing changes and low charge carrier mobility and doping efficiency and thus low thermoelectric performance. Our work provides a unique insight into the fundamental understanding of the relationship between molecular packing and thermoelectric properties and guides the future rational design of efficient n-type organic semiconductors.}, journal={ACS MATERIALS LETTERS}, author={Yang, Xuwen and Ye, Gang and Tran, Karolina and Liu, Yuru and Cao, Jiamin and Dong, Jingjin and Portale, Giuseppe and Liu, Jian and Zhang, Ping and Loi, Maria Antonietta and et al.}, year={2024}, month={Feb} }
 @article{soni_werner_aidi_moors_mthembu_zharnikov_havenith_monakhov_chiechi_2023, title={Influence of Polyoxovanadate and Phthalocyanine on 4f Electron Transfer in Gold-Confined Monolayers Probed with EGaIn Top Contacts}, volume={6}, ISSN={["2574-0970"]}, url={https://doi.org/10.1021/acsanm.3c05021}, DOI={10.1021/acsanm.3c05021}, abstractNote={This work describes the effects of dodecavanadate anions and phthalocyanine ligands as well as the identity of lanthanide centers on the charge transport characteristics of heterometallic complexes (nBu4N)3[HV12O32Cl(LnPc)] and (nBu4N)2[HV12O32Cl(LnPc)2] for SmIII–ErIII, LuIII, and YIII on gold surfaces. In molecular ensemble junctions with eutectic Ga–In top contacts, the complexes containing two phthalocyanine ligands are highly conductive but show no clear effect of varying the lanthanide. By contrast, the complexes that omit phthalocyanine but include 4f-functionalized dodecavanadate building blocks show clear trends in conductance, rectification, and transition voltages. Density functional theory calculations show that the occupied and unoccupied frontier orbitals in the heterometallic complexes are delocalized on the phthalocyanine ligand and dodecavanadate anion, respectively, suggesting strong lanthanide–ligand electronic coupling. Near-edge X-ray absorption fine structure spectroscopy on these complexes further suggests that the phthalocyanine ligands are arranged such that their edges are in contact with the electrodes, creating tunneling transmission channels that bypass the lanthanide, effectively obviating the electronic contributions of the lanthanide centers to charge transport. These results separate the influence of the individual constituents of these metal–ligand complexes on the tunneling charge-transport properties. These results demonstrate how strongly coupled ligands such as phthalocyanine can dominate charge transport, from which we construct design rules for harnessing the properties of f-block elements in redox-active molecular heterojunctions.}, number={24}, journal={ACS APPLIED NANO MATERIALS}, author={Soni, Saurabh and Werner, Irina and Aidi, Michael and Moors, Marco and Mthembu, C. Lungani and Zharnikov, Michael and Havenith, Remco W. A. and Monakhov, Kirill Yu. and Chiechi, Ryan C.}, year={2023}, month={Dec}, pages={22643–22650} }
 @article{pitaro_alonso_di mario_romero_tran_kardula_zaharia_johansson_johansson_chiechi_et al._2023, title={Tuning the Surface Energy of Hole Transport Layers Based on Carbazole Self-Assembled Monolayers for Highly Efficient Sn/Pb Perovskite Solar Cells}, volume={8}, ISSN={["1616-3028"]}, url={https://doi.org/10.1002/adfm.202306571}, DOI={10.1002/adfm.202306571}, abstractNote={Recently, carbazole‐based self‐assembled monolayers (SAMs) have been utilized as hole transport layers (HTLs) in perovskite solar cells. However, their application in Sn or mixed Sn/Pb perovskite solar cells has been hindered by the poor wettability of the perovskite precursor solution on the carbazole surface. Here a self‐assembled bilayer (SAB) comprising a covalent monolayer (Br‐2PACz) and a noncovalent wetting layer (4CzNH3I) as the HTL in a Cs0.25FA0.75Sn0.5Pb0.5I3 perovskite solar cell is proposed. It is demonstrated that the wetting layer completely solves the problem due to the higher polarity of the surface and, furthermore, the ammonium groups help in the passivation of trap states at the buried SAB/perovskite interface. The introduction of the SAB enhances the device reproducibility with an average efficiency of 18.98 ± 0.28% (19.45% for the best device), compared to 11.54 ± 9.36% (19.34% for the best device) for the SAM‐only devices. Furthermore, the improved perovskite processability on the SAB helps to increase the reproducibility of larger size device, where, a 12.5% efficiency for a 0.8 cm2 active area device compared to 0.68% for the best SAM‐based solar cell is demonstrated. Finally, the device's operational stability is also improved to 358 hours (T80%), compared to 220 hours for the SAM‐based solar cell.}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Pitaro, Matteo and Alonso, Javier E. Sebastian and Di Mario, Lorenzo and Romero, David Garcia and Tran, Karolina and Kardula, Jane and Zaharia, Teodor and Johansson, Malin B. and Johansson, Erik M. J. and Chiechi, Ryan C. and et al.}, year={2023}, month={Aug} }
 @article{rahimichatri_liu_jahani_qiu_chiechi_hummelen_koster_2022, title={A method for identifying the cause of inefficient salt-doping in organic semiconductors}, volume={10}, url={https://doi.org/10.1039/D1TC06062G}, DOI={10.1039/D1TC06062G}, abstractNote={Doping to enhance the electrical conductivity of organic semiconductors is not without its challenges: The efficacy of this process depends on many factors and it is not always clear how to remedy poor doping. In the case of doping with salts, one of the possible causes of poor doping is a limited yield of integer charge transfer resulting in the presence of both cations and anions in the film. The charge of such ions can severely limit the electrical conductivity, but their presence is not easily determined. Here we introduce a set of simple conductivity measurements to determine whether poor doping in the case where the dopant is a salt is due to limited integer charge transfer. By tracking how the conductivity changes over time when applying a bias voltage for an extended amount of time we can pinpoint whether unwanted ions are present in the film. Firstly, we introduce the principle of this approach by performing numerical simulations that include the movement of ions. We show that the conductivity can increase or decrease depending on the type of ions present in the film. Next, we show that the movement of these dopant ions causes a build-up of space-charge, which makes the current–voltage characteristic non-linear. Next, we illustrate how this approach may be used in practice by doping a fullerene derivative with a series of organic salts. We thus provide a tool to make the optimization of doping more rational.}, number={36}, journal={Journal of Materials Chemistry C}, author={Rahimichatri, A. and Liu, J. and Jahani, F. and Qiu, L. and Chiechi, R. C. and Hummelen, J. C. and Koster, L. J. A.}, year={2022}, pages={13093–13098} }
 @article{zhang_doremaele_ye_stevens_song_chiechi_burgt_2022, title={Adaptive Biosensing and Neuromorphic Classification Based on an Ambipolar Organic Mixed Ionic-Electronic Conductor}, volume={4}, ISSN={["1521-4095"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85128209600&partnerID=MN8TOARS}, DOI={10.1002/adma.202200393}, abstractNote={Organic mixed ionic–electronic conductors (OMIECs) are central to bioelectronic applications such as biosensors, health‐monitoring devices, and neural interfaces, and have facilitated efficient next‐generation brain‐inspired computing and biohybrid systems. Despite these examples, smart and adaptive circuits that can locally process and optimize biosignals have not yet been realized. Here, a tunable sensing circuit is shown that can locally modulate biologically relevant signals like electromyograms (EMGs) and electrocardiograms (ECGs), that is based on a complementary logic inverter combined with a neuromorphic memory element, and that is constructed from a single polymer mixed conductor. It is demonstrated that a small neuromorphic array based on this material effects high classification accuracy in heartbeat anomaly detection. This high‐performance material allows for straightforward monolithic integration, which reduces fabrication complexity while also achieving high on/off ratios with excellent ambient p‐ and n‐type stability in transistor performance. This material opens a route toward simple and straightforward fabrication and integration of more sophisticated adaptive circuits for future smart bioelectronics.}, number={20}, journal={ADVANCED MATERIALS}, author={Zhang, Yanxi and Doremaele, Eveline R. W. and Ye, Gang and Stevens, Tim and Song, Jun and Chiechi, Ryan C. and Burgt, Yoeri}, year={2022}, month={Apr} }
 @article{talsma_ye_liu_duim_dijkstra_tran_qu_song_chiechi_loi_2022, title={Efficient Selective Sorting of Semiconducting Carbon Nanotubes Using Ultra-Narrow-Band-Gap Polymers}, volume={8}, ISSN={["1944-8252"]}, url={https://doi.org/10.1021/acsami.2c07158}, DOI={10.1021/acsami.2c07158}, abstractNote={Conjugated polymers with narrow band gaps are particularly useful for sorting and discriminating semiconducting single-walled carbon nanotubes (s-SWCNT) due to the low charge carrier injection barrier for transport. In this paper, we report two newly synthesized narrow-band-gap conjugated polymers (PNDITEG-TVT and PNDIC8TEG-TVT) based on naphthalene diimide (NDI) and thienylennevinylene (TVT) building blocks, decorated with different polar side chains that can be used for dispersing and discriminating s-SWCNT. Compared with the mid-band-gap conjugated polymer PNDITEG-AH, which is composed of naphthalene diimide (NDI) and head-to-head bithiophene building blocks, the addition of a vinylene linker eliminates the steric congestion present in head-to-head bithiophene, which promotes backbone planarity, extending the π-conjugation length and narrowing the band gap. Cyclic voltammetry (CV) and density functional theory (DFT) calculations suggest that inserting a vinylene group in a head-to-head bithiophene efficiently lifts the highest occupied molecular orbital (HOMO) level (−5.60 eV for PNDITEG-AH, −5.02 eV for PNDITEG-TVT, and −5.09 eV for PNDIC8TEG-TVT). All three polymers are able to select for s-SWCNT, as evidenced by the sharp transitions in the absorption spectra. Field-effect transistors (FETs) fabricated with the polymer:SWCNT inks display p-dominant properties, with higher hole mobilities when using the NDI-TVT polymers as compared with PNDITEG-AH (0.6 cm2 V–1 s–1 for HiPCO:PNDITEG-AH, 1.5 cm2 V–1 s–1 for HiPCO:PNDITEG-TVT, and 2.3 cm2 V–1 s–1 for HiPCO:PNDIC8TEG-TVT). This improvement is due to the better alignment of the HOMO level of PNDITEG-TVT and PNDIC8TEG-TVT with that of the dominant SWCNT specie.}, number={33}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Talsma, Wytse and Ye, Gang and Liu, Yuru and Duim, Herman and Dijkstra, Sietske and Tran, Karolina and Qu, Junle and Song, Jun and Chiechi, Ryan C. and Loi, Maria Antonietta}, year={2022}, month={Aug} }
 @article{carlotti_soni_kovalchuk_kumar_hofmann_chiechi_2022, title={Empirical Parameter to Compare Molecule–Electrode Interfaces in Large-Area Molecular Junctions}, volume={2}, url={https://doi.org/10.1021/acsphyschemau.1c00029}, DOI={10.1021/acsphyschemau.1c00029}, abstractNote={This paper describes a simple model for comparing the degree of electronic coupling between molecules and electrodes across different large-area molecular junctions. The resulting coupling parameter can be obtained directly from current–voltage data or extracted from published data without fitting. We demonstrate the generalizability of this model by comparing over 40 different junctions comprising different molecules and measured by different laboratories. The results agree with existing models, reflect differences in mechanisms of charge transport and rectification, and are predictive in cases where experimental limitations preclude more sophisticated modeling. We also synthesized a series of conjugated molecular wires, in which embedded dipoles are varied systematically and at both molecule–electrode interfaces. The resulting current–voltage characteristics vary in nonintuitive ways that are not captured by existing models, but which produce trends using our simple model, providing insights that are otherwise difficult or impossible to explain. The utility of our model is its demonstrative generalizability, which is why simple observables like tunneling decay coefficients remain so widely used in molecular electronics despite the existence of much more sophisticated models. Our model is complementary, giving insights into molecule–electrode coupling across series of molecules that can guide synthetic chemists in the design of new molecular motifs, particularly in the context of devices comprising large-area molecular junctions.}, number={3}, journal={ACS Physical Chemistry Au}, author={Carlotti, Marco and Soni, Saurabh and Kovalchuk, Andrii and Kumar, Sumit and Hofmann, Stephan and Chiechi, Ryan C.}, year={2022}, month={May}, pages={179–190} }
 @article{torabi_rousseva_chen_ashrafi_kermanpur_chiechi_2022, title={Graphene oxide decorated with gold enables efficient biophotovolatic cells incorporating photosystem I}, volume={12}, ISSN={["2046-2069"]}, url={https://doi.org/10.1039/D1RA08908K}, DOI={10.1039/D1RA08908K}, abstractNote={This paper describes the use of reduced graphene oxide decorated with gold nanoparticles as an efficient electron transfer layer for solid-state biophotovoltic cells containing photosystem I as the sole photo-active component. Together with polytyrosine–polyaniline as a hole transfer layer, this device architecture results in an open-circuit voltage of 0.3 V, a fill factor of 38% and a short-circuit current density of 5.6 mA cm−2 demonstrating good coupling between photosystem I and the electrodes. The best-performing device reached an external power conversion efficiency of 0.64%, the highest for any solid-state photosystem I-based photovoltaic device that has been reported to date. Our results demonstrate that the functionality of photosystem I in the non-natural environment of solid-state biophotovoltaic cells can be improved through the modification of electrodes with efficient charge-transfer layers. The combination of reduced graphene oxide with gold nanoparticles caused tailoring of the electronic structure and alignment of the energy levels while also increasing electrical conductivity. The decoration of graphene electrodes with gold nanoparticles is a generalizable approach for enhancing charge-transfer across interfaces, particularly when adjusting the levels of the active layer is not feasible, as is the case for photosystem I and other biological molecules.}, number={14}, journal={RSC ADVANCES}, publisher={Royal Society of Chemistry (RSC)}, author={Torabi, Nahid and Rousseva, Sylvia and Chen, Qi and Ashrafi, Ali and Kermanpur, Ahmad and Chiechi, Ryan C.}, year={2022}, month={Mar}, pages={8783–8791} }
 @article{zhang_ye_van der pol_dong_van doremaele_krauhausen_liu_gkoupidenis_portale_song_et al._2022, title={High‐Performance Organic Electrochemical Transistors and Neuromorphic Devices Comprising Naphthalenediimide‐Dialkoxybithiazole Copolymers Bearing Glycol Ether Pendant Groups}, volume={32}, ISSN={1616-301X 1616-3028}, url={http://dx.doi.org/10.1002/adfm.202201593}, DOI={10.1002/adfm.202201593}, abstractNote={Organic electrochemical transistors (OECTs) have emerged as building blocks for low power circuits, biosensors, and neuromorphic computing. While p‐type polymer materials for OECTs are well developed, the choice of high‐performance n‐type polymers is limited, despite being essential for cation and metabolite biosensors, and crucial for constructing complementary circuits. N‐type conjugated polymers that have efficient ion‐to‐electron transduction are highly desired for electrochemical applications. In this contribution, three non‐fused, planar naphthalenediimide (NDI)‐dialkoxybithiazole (2Tz) copolymers, which systematically increase the amount of polar tri(ethylene glycol) (TEG) side chains: PNDI2OD‐2Tz (0 TEG), PNDIODTEG‐2Tz (1 TEG), PNDI2TEG‐2Tz (2 TEG), are reported. It is demonstrated that the OECT performance increases with the number of TEG side chains resulting from the progressively higher hydrophilicity and larger electron affinities. Benefiting from the high electron mobility, excellent ion conduction capability, efficient ion‐to‐electron transduction, and low‐lying lowest unoccupied molecular orbital energy level, the 2 TEG polymer achieves close to 105 on‐off ratio, fast switching, 1000 stable operation cycles in aqueous electrolyte, and has a long shelf life. Moreover, the higher number TEG chain substituted polymer exhibits good conductance state retention over two orders of magnitudes in electrochemical resistive random‐access memory devices, highlighting its potential for neuromorphic computing.}, number={27}, journal={Advanced Functional Materials}, publisher={Wiley}, author={Zhang, Yanxi and Ye, Gang and van der Pol, Tom P. A. and Dong, Jingjin and van Doremaele, Eveline R. W. and Krauhausen, Imke and Liu, Yuru and Gkoupidenis, Paschalis and Portale, Giuseppe and Song, Jun and et al.}, year={2022}, month={Apr} }
 @article{rousseva_raul_kooij_kuevda_birudula_hummelen_pshenichnikov_chiechi_2022, title={Investigating the dielectric properties and exciton diffusion in C-70 derivatives}, volume={24}, ISSN={["1463-9084"]}, url={https://doi.org/10.1039/D2CP00791F}, DOI={10.1039/d2cp00791f}, abstractNote={In recent years, the dielectric constant (εr) of organic semiconductors (OSCs) has been of interest in the organic photovoltaic (OPV) community due to its potential influence on the exciton binding energy. Despite progress in the design of high εr OSCs and the accurate measurement of the εr, the effects of the synthetic strategies on specific (opto)electronic properties of the OSCs remain uncertain. In this contribution, the effects of εr on the optical properties of five new C70 derivatives and [70]PCBM are investigated. Together with [70]PCBM, the derivatives have a range of εr values that depend on the polarity and length of the side chains. The properties of the singlet excitons are investigated in detail with steady-state and time-resolved spectroscopy and the exciton diffusion length is measured. All six derivatives show similar photophysical properties in the neat films. However, large differences in the crystallinity of the fullerene films influence the exciton dynamics in blend films. This work shows that design principles for OSCs with a higher εr can have a very different influence on the performance of traditional BHJ devices and in neat films and it is important to consider the neat film properties when investigating the optoelectronic properties of new materials for OPV.}, number={22}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Rousseva, Sylvia and Raul, Benedito A. L. and Kooij, Felien S. and Kuevda, Alexey V. and Birudula, Srikanth and Hummelen, Jan C. and Pshenichnikov, Maxim S. and Chiechi, Ryan C.}, year={2022}, month={Jun}, pages={13763–13772} }
 @article{ye_talsma_tran_liu_dijkstra_cao_chen_qu_song_loi_et al._2022, title={Polar Side Chains Enhance Selection of Semiconducting Single-Walled Carbon Nanotubes by Polymer Wrapping}, volume={55}, ISSN={["1520-5835"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85124494851&partnerID=MN8TOARS}, DOI={10.1021/acs.macromol.1c01842}, abstractNote={This paper describes the effectiveness of donor–acceptor (D-A) conjugated polymers to disperse and select for semiconducting single-walled carbon nanotubes (s-SWCNTs) when enhanced by the inclusion of polar oligoethylene glycol-based side chains, without altering the D–A backbone. We designed and synthesized two sets of naphthalenediimide(NDI)-alt-bithiophene(T2)-based conjugated polymers with one of two alkyl side chains (decyl and dodecyl chains) of different lengths and with or without polar triethylene glycol side chains. The resulting low-band-gap copolymers all effectively disperse and select for s-SWCNT, but the inclusion of polar side chains enhances the interactions between the polymer backbone and the walls of the s-SWCNTs relative to the polymers with only alkyl side chains. As a result, the wrapping and selection efficiency of the polymer-SWCNT systems with polar side chains are both significantly enhanced. We further optimized the binding energy and surface coverage by combining glycol ether and dodecyl side chains to maximize wrapping efficiency, leading to a field-effect mobility of 2.82 cm2 V–1 s–1 and on/off current ratios of ∼2 × 107 in polymer-wrapped SWCNTs. Our results provide insight into the role of the side-chain interactions in the polymer wrapping and dispersion technique, and, because we focus on manipulating side chains, they can be generalized for other conjugated polymer backbones.}, number={4}, journal={MACROMOLECULES}, author={Ye, Gang and Talsma, Wytse and Tran, Karolina and Liu, Yuru and Dijkstra, Sietske and Cao, Jiamin and Chen, Jianhua and Qu, Junle and Song, Jun and Loi, Maria Antonietta and et al.}, year={2022}, month={Feb}, pages={1386–1397} }
 @article{qiu_chiechi_2022, title={Printable logic circuits comprising self-assembled protein complexes}, volume={13}, ISSN={["2041-1723"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85128965842&partnerID=MN8TOARS}, DOI={10.1038/s41467-022-30038-8}, abstractNote={This paper describes the fabrication of digital logic circuits comprising resistors and diodes made from protein complexes and wired together using printed liquid metal electrodes. These resistors and diodes exhibit temperature-independent charge-transport over a distance of approximately 10 nm and require no encapsulation or special handling. The function of the protein complexes is determined entirely by self-assembly. When induced to self-assembly into anisotropic monolayers, the collective action of the aligned dipole moments increases the electrical conductivity of the ensemble in one direction and decreases it in the other. When induced to self-assemble into isotropic monolayers, the dipole moments are randomized and the electrical conductivity is approximately equal in both directions. We demonstrate the robustness and utility of these all-protein logic circuits by constructing pulse modulators based on AND and OR logic gates that function nearly identically to simulated circuits. These results show that digital circuits with useful functionality can be derived from readily obtainable biomolecules using simple, straightforward fabrication techniques that exploit molecular self-assembly, realizing one of the primary goals of molecular electronics.}, number={1}, journal={NATURE COMMUNICATIONS}, author={Qiu, Xinkai and Chiechi, Ryan C.}, year={2022}, month={Apr} }
 @article{khandan_boerkamp_jabermoradi_fontana_hohlbein_verpoorte_chiechi_mathwig_2022, title={Viscophoretic particle transport}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85144972047&partnerID=MN8TOARS}, DOI={10.48550/arXiv.2212.11503}, abstractNote={Viscosity is a fundamental property of liquids. It determines transport and diffusion of particles in solution. Nonetheless, it is an open question how a gradient of viscosity - causing a gradient in diffusivity - can lead to viscophoretic transport, i.e., directed transport of particles and molecules in solution. Here, we determine viscophoretic drift experimentally. We generate steep, stable viscosity gradients in a microfluidic device and image transport of suspended nanoparticles in these gradients using high-resolution microscopy. We observe high viscophoretic drift velocities which significantly exceed theoretical predictions. In addition, we demonstrate a new method for trapping and concentrating particles by using the interplay of viscophoresis and diffusiophoresis. We believe that a quantification of viscophoresis will advance the understanding and application of transport processes of gradients of viscosity occurring in very diverse fields such as cell biology, chromatography, and membrane technology.}, journal={arXiv}, author={Khandan, V. and Boerkamp, V. and Jabermoradi, A. and Fontana, M. and Hohlbein, J. and Verpoorte, E. and Chiechi, R.C. and Mathwig, K.}, year={2022} }
 @article{liu_qiu_soni_chiechi_2021, title={Charge transport through molecular ensembles: Recent progress in molecular electronics}, volume={2}, url={https://doi.org/10.1063/5.0050667}, DOI={10.1063/5.0050667}, abstractNote={This review focuses on molecular ensemble junctions in which the individual molecules of a monolayer each span two electrodes. This geometry favors quantum mechanical tunneling as the dominant mechanism of charge transport, which translates perturbances on the scale of bond lengths into nonlinear electrical responses. The ability to affect these responses at low voltages and with a variety of inputs, such as de/protonation, photon absorption, isomerization, oxidation/reduction, etc., creates the possibility to fabricate molecule-scale electronic devices that augment; extend; and, in some cases, outperform conventional semiconductor-based electronics. Moreover, these molecular devices, in part, fabricate themselves by defining single-nanometer features with atomic precision via self-assembly. Although these junctions share many properties with single-molecule junctions, they also possess unique properties that present a different set of problems and exhibit unique properties. The primary trade-off of ensemble junctions is complexity for functionality; disordered molecular ensembles are significantly more difficult to model, particularly atomistically, but they are static and can be incorporated into integrated circuits. Progress toward useful functionality has accelerated in recent years, concomitant with deeper scientific insight into the mediation of charge transport by ensembles of molecules and experimental platforms that enable empirical studies to control for defects and artifacts. This review separates junctions by the trade-offs, complexity, and sensitivity of their constituents; the bottom electrode to which the ensembles are anchored and the nature of the anchoring chemistry both chemically and with respect to electronic coupling; the molecular layer and the relationship among electronic structure, mechanism of charge transport, and electrical output; and the top electrode that realizes an individual junction by defining its geometry and a second molecule–electrode interface. Due to growing interest in and accessibility of this interdisciplinary field, there is now sufficient variety in each of these parts to be able to treat them separately. When viewed this way, clear structure–function relationships emerge that can serve as design rules for extracting useful functionality.}, number={2}, journal={Chemical Physics Reviews}, publisher={AIP Publishing}, author={Liu, Yuru and Qiu, Xinkai and Soni, Saurabh and Chiechi, Ryan C.}, year={2021}, month={Jun}, pages={021303} }
 @article{ye_liu_qiu_stäter_qiu_liu_yang_hildner_koster_chiechi_2021, title={Controlling n-Type Molecular Doping via Regiochemistry and Polarity of Pendant Groups on Low Band Gap Donor–Acceptor Copolymers}, volume={54}, url={https://doi.org/10.1021/acs.macromol.1c00317}, DOI={10.1021/acs.macromol.1c00317}, abstractNote={We demonstrate the impact of the type and position of pendant groups on the n-doping of low-band gap donor–acceptor (D–A) copolymers. Polar glycol ether groups simultaneously increase the electron affinities of D–A copolymers and improve the host/dopant miscibility compared to nonpolar alkyl groups, improving the doping efficiency by a factor of over 40. The bulk mobility of the doped films increases with the fraction of polar groups, leading to a best conductivity of 0.08 S cm–1 and power factor (PF) of 0.24 μW m–1 K–2 in the doped copolymer with the polar pendant groups on both the D and A moieties. We used spatially resolved absorption spectroscopy to relate commensurate morphological changes to the dispersion of dopants and to the relative local doping efficiency, demonstrating a direct relationship between the morphology of the polymer phase, the solvation of the molecular dopant, and the electrical properties of doped films. Our work offers fundamental new insights into the influence of the physical properties of pendant chains on the molecular doping process, which should be generalizable to any molecularly doped polymer films.}, number={8}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Ye, Gang and Liu, Jian and Qiu, Xinkai and Stäter, Sebastian and Qiu, Li and Liu, Yuru and Yang, Xuwen and Hildner, Richard and Koster, L. Jan Anton and Chiechi, Ryan C.}, year={2021}, month={Apr}, pages={3886–3896} }
 @article{dong_liu_qiu_chiechi_koster_portale_2021, title={Engineering the Thermoelectrical Properties of PEDOT:PSS by Alkali Metal Ion Effect}, volume={7}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85107031169&partnerID=MN8TOARS}, DOI={10.1016/j.eng.2021.02.011}, abstractNote={Engineering the electrical properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) holds great potential for various applications such as sensors, thermoelectric (TE) generators, and hole transport layers in solar cells. Various strategies have been applied to achieve optimal electrical properties, including base solution post-treatments. However, the working mechanism and the exact details of the structural transformations induced by base post-treatments are still unclear. In this work, we present a comparative study on the post-treatment effects of using three common and green alkali base solutions: namely LiOH, NaOH, and KOH. The structural modifications induced in the film by the base post-treatments are studied by techniques including atomic force microscopy, grazing-incidence wide-angle X-ray scattering, ultraviolet–visible–near-infrared spectroscopy, and attenuated total reflectance Fourier-transform infrared spectroscopy. Base-induced structural modifications are responsible for an improvement in the TE power factor of the films, which depends on the basic solution used. The results are explained on the basis of the different affinity between the alkali cations and the PSS chains, which determines PEDOT dedoping. The results presented here shed light on the structural reorganization occurring in PEDOT:PSS when exposed to high-pH solutions and may serve as inspiration to create future pH-/ion-responsive devices for various applications.}, number={5}, journal={Engineering}, author={Dong, J. and Liu, J. and Qiu, X. and Chiechi, R. and Koster, L.J.A. and Portale, G.}, year={2021}, pages={647–654} }
 @article{torabi_qiu_lópez-ortiz_loznik_herrmann_kermanpur_ashrafi_chiechi_2021, title={Fullerenes Enhance Self-Assembly and Electron Injection of Photosystem I in Biophotovoltaic Devices}, volume={9}, url={https://doi.org/10.1021/acs.langmuir.1c01542}, DOI={10.1021/acs.langmuir.1c01542}, abstractNote={This paper describes the fabrication of microfluidic devices with a focus on controlling the orientation of photosystem I (PSI) complexes, which directly affects the performance of biophotovoltaic devices by maximizing the efficiency of the extraction of electron/hole pairs from the complexes. The surface chemistry of the electrode on which the complexes assemble plays a critical role in their orientation. We compared the degree of orientation on self-assembled monolayers of phenyl-C61-butyric acid and a custom peptide on nanostructured gold electrodes. Biophotovoltaic devices fabricated with the C61 fulleroid exhibit significantly improved performance and reproducibility compared to those utilizing the peptide, yielding a 1.6-fold increase in efficiency. In addition, the C61-based devices were more stable under continuous illumination. Our findings show that fulleroids, which are well-known acceptor materials in organic photovoltaic devices, facilitate the extraction of electrons from PSI complexes without sacrificing control over the orientation of the complexes, highlighting this combination of traditional organic semiconductors with biomolecules as a viable approach to coopting natural photosynthetic systems for use in solar cells.}, number={39}, journal={Langmuir}, publisher={American Chemical Society (ACS)}, author={Torabi, Nahid and Qiu, Xinkai and López-Ortiz, Manuel and Loznik, Mark and Herrmann, Andreas and Kermanpur, Ahmad and Ashrafi, Ali and Chiechi, Ryan C.}, year={2021}, month={Oct}, pages={11465–11473} }
 @article{zhang_doremaele_ye_stevens_song_chiechi_burgt_2021, title={High performance ambipolar organic mixed ionic-electronic conductor for adaptive logic circuits and neuromorphic electronics}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85126188528&partnerID=MN8TOARS}, DOI={10.26434/chemrxiv-2021-46v82}, abstractNote={Organic mixed ionic-electronic conductors (OMIECs) are central to bioelectronic applications such as biosensors, health monitoring devices and neural interfaces, and have facilitated efficient next-generation brain-inspired computing and biohybrid systems. Most OMIECs are hole-conducting (p-type) materials, while complimentary logic circuits and various biosensors require electron-conducting (n-type) materials too. Here we show an ambipolar mixed ionic-electronic polymer that achieves high on/off ratios with high ambient p- and n- type stability. We highlight the versatility of the material by demonstrating its use as a neuromorphic memory element, an adaptable ambipolar complementary logic inverter, and a neurotransmitter sensor. The ambipolar operation of this material allows for straightforward monolithic fabrication and integration, and opens a route towards more sophisticated complex logic and adaptive circuits.}, journal={ChemRxiv}, author={Zhang, Y. and Doremaele, E.R.W. and Ye, G. and Stevens, T. and Song, J. and Chiechi, R.C. and Burgt, Y.}, year={2021} }
 @article{qiu_rousseva_ye_hummelen_chiechi_2021, title={In Operando Modulation of Rectification in Molecular Tunneling Junctions Comprising Reconfigurable Molecular Self‐Assemblies}, volume={33}, url={https://doi.org/10.1002/adma.202006109}, DOI={10.1002/adma.202006109}, abstractNote={The reconfiguration of molecular tunneling junctions during operation via the self‐assembly of bilayers of glycol ethers is described. Well‐established functional groups are used to modulate the magnitude and direction of rectification in assembled tunneling junctions by exposing them to solutions containing different glycol ethers. Variable‐temperature measurements confirm that rectification occurs by the expected bias‐dependent tunneling–hopping mechanism for these functional groups and that glycol ethers, besides being an unusually efficient tunneling medium, behave similarly to alkanes. Memory bits are fabricated from crossbar junctions prepared by injecting eutectic Ga–In (EGaIn) into microfluidic channels. The states of two 8‐bit registers were set by trains of droplets such that they are able to perform logical AND operations on bit strings encoded into chemical packets that alter the composition of the crossbar junctions through self‐assembly to effect memristor‐like properties. This proof‐of‐concept work demonstrates the potential for fieldable devices based on molecular tunneling junctions comprising self‐assembled monolayers and bilayers.}, number={4}, journal={Advanced Materials}, author={Qiu, Xinkai and Rousseva, Sylvia and Ye, Gang and Hummelen, Jan C. and Chiechi, Ryan C.}, year={2021}, month={Jan} }
 @article{liu_van der zee_villava_ye_kahmann_kamperman_dong_qiu_portale_loi_et al._2021, title={Molecular Doping Directed by a Neutral Radical}, volume={13}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85110186428&partnerID=MN8TOARS}, DOI={10.1021/acsami.1c03411}, abstractNote={Molecular doping makes possible tunable electronic properties of organic semiconductors, yet a lack of control of the doping process narrows its scope for advancing organic electronics. Here, we demonstrate that the molecular doping process can be improved by introducing a neutral radical molecule, namely nitroxyl radical (2,2,6,6-teramethylpiperidin-i-yl) oxyl (TEMPO). Fullerene derivatives are used as the host and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazoles (DMBI-H) as the n-type dopant. TEMPO can abstract a hydrogen atom from DMBI-H and transform the latter into a much stronger reducing agent DMBI•, which efficiently dopes the fullerene derivative to yield an electrical conductivity of 4.4 S cm–1. However, without TEMPO, the fullerene derivative is only weakly doped likely by a hydride transfer following by an inefficient electron transfer. This work unambiguously identifies the doping pathway in fullerene derivative/DMBI-H systems in the presence of TEMPO as the transfer of a hydrogen atom accompanied by electron transfer. In the absence of TEMPO, the doping process inevitably leads to the formation of less symmetrical hydrogenated fullerene derivative anions or radicals, which adversely affect the molecular packing. By adding TEMPO we can exclude the formation of such species and, thus, improve charge transport. In addition, a lower temperature is sufficient to meet an efficient doping process in the presence of TEMPO. Thereby, we provide an extra control of the doping process, enabling enhanced thermoelectric performance at a low processing temperature.}, number={25}, journal={ACS Applied Materials and Interfaces}, author={Liu, J. and Van Der Zee, B. and Villava, D.R. and Ye, G. and Kahmann, S. and Kamperman, M. and Dong, J. and Qiu, L. and Portale, G. and Loi, M.A. and et al.}, year={2021}, pages={29858–29865} }
 @article{liu_ye_potgieser_koopmans_sami_nugraha_villalva_sun_dong_yang_et al._2020, title={Amphipathic Side Chain of a Conjugated Polymer Optimizes Dopant Location toward Efficient N‐Type Organic Thermoelectrics}, volume={33}, ISSN={0935-9648 1521-4095}, url={http://dx.doi.org/10.1002/adma.202006694}, DOI={10.1002/adma.202006694}, abstractNote={There is no molecular strategy for selectively increasing the Seebeck coefficient without reducing the electrical conductivity for organic thermoelectrics. Here, it is reported that the use of amphipathic side chains in an n‐type donor–acceptor copolymer can selectively increase the Seebeck coefficient and thus increase the power factor by a factor of ≈5. The amphipathic side chain contains an alkyl chain segment as a spacer between the polymer backbone and an ethylene glycol type chain segment. The use of this alkyl spacer does not only reduce the energetic disorder in the conjugated polymer film but can also properly control the dopant sites away from the backbone, which minimizes the adverse influence of counterions. As confirmed by kinetic Monte Carlo simulations with the host–dopant distance as the only variable, a reduced Coulombic interaction resulting from a larger host–dopant distance contributes to a higher Seebeck coefficient for a given electrical conductivity. Finally, an optimized power factor of 18 µW m–1 K–2 is achieved in the doped polymer film. This work provides a facile molecular strategy for selectively improving the Seebeck coefficient and opens up a new route for optimizing the dopant location toward realizing better n‐type polymeric thermoelectrics.}, number={4}, journal={Advanced Materials}, publisher={Wiley}, author={Liu, Jian and Ye, Gang and Potgieser, Hinderikus G. O. and Koopmans, Marten and Sami, Selim and Nugraha, Mohamad Insan and Villalva, Diego Rosas and Sun, Hengda and Dong, Jingjin and Yang, Xuwen and et al.}, year={2020}, month={Dec}, pages={2006694} }
 @article{kumar_soni_danowski_beek_feringa_rudolf_chiechi_2020, title={Correlating the Influence of Disulfides in Monolayers across Photoelectron Spectroscopy Wettability and Tunneling Charge-Transport}, volume={142}, url={https://doi.org/10.1021/jacs.0c06508}, DOI={10.1021/jacs.0c06508}, abstractNote={Despite their ubiquity, self-assembled monolayers (SAMs) of thiols on coinage metals are difficult to study and are still not completely understood, particularly with respect to the nature of thiol–metal bonding. Recent advances in molecular electronics have highlighted this deficiency due to the sensitivity of tunneling charge-transport to the subtle differences in the overall composition of SAMs and the chemistry of their attachment to surfaces. These advances have also challenged assumptions about the spontaneous formation of covalent thiol–metal bonds. This paper describes a series of experiments that correlate changes in the physical properties of SAMs to photoelectron spectroscopy to unambiguously assign binding energies of noncovalent interactions to physisorbed disulfides. These disulfides can be converted to covalent metal–thiolate bonds by exposure to free thiols, leading to the remarkable observation of the total loss and recovery of length-dependent tunneling charge-transport. The identification and assignment of physisorbed disulfides solve a long-standing mystery and reveal new, dynamic properties in SAMs of thiols.}, number={35}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Kumar, Sumit and Soni, Saurabh and Danowski, Wojciech and Beek, Carlijn L. F. and Feringa, Ben L. and Rudolf, Petra and Chiechi, Ryan C.}, year={2020}, month={Sep}, pages={15075–15083} }
 @article{gu_zhang_zhao_ai_zheng_chiechi_li_shi_zhang_2020, title={Engineering Colloidal Lithography and Nanoskiving to Fabricate Rows of Opposing Crescent Nanogaps}, volume={8}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85081250622&partnerID=MN8TOARS}, DOI={10.1002/adom.202000006}, abstractNote={A scalable fabrication route combining colloidal lithography and nanoskiving is reported for generating free‐standing asymmetric metal nanostructures of crescent‐shaped gold nanowires and rows of opposing crescents with and without nanogaps. Strong localized surface plasmon resonances and propagating surface plasmon polaritons are excited at the sharp tips of the crescent and in the sub‐10 nm nanogaps. High‐order resonance modes are excited due to the coupling between the resonances in the tips and gaps. The Raman signals are greatly enhanced due to the strong electric fields. In addition, the optical responses and electric field distributions can be controlled by the polarization of the incident light. The strong electric field enhancement coupled with facile, scalable fabrication make crescent‐shaped nanostructures promising in nonlinear optics, optical trapping, and surface‐enhanced spectroscopy.}, number={10}, journal={Advanced Optical Materials}, author={Gu, P. and Zhang, W. and Zhao, Z. and Ai, B. and Zheng, T. and Chiechi, R.C. and Li, C. and Shi, Z. and Zhang, G.}, year={2020} }
 @article{liu_ornago_carlotti_ai_abbassi_soni_asyuda_zharnikov_zant_chiechi_2020, title={Intermolecular Effects on Tunneling through Acenes in Large-Area and Single-Molecule Junctions}, volume={124}, url={https://doi.org/10.1021/acs.jpcc.0c05781}, DOI={10.1021/acs.jpcc.0c05781}, abstractNote={This paper describes the conductance of single-molecules and self-assembled monolayers comprising an oligophenyleneethynylene core, functionalized with acenes of increasing length that extend conjugation perpendicular to the path of tunneling electrons. In the Mechanically Controlled Break Junction (MCBJ) experiment, multiple conductance plateaus were identified. The high conductance plateau, which we attribute to the single molecule conformation, shows an increase of conductance as a function of acene length, in good agreement with theoretical predictions. The lower plateau is attributed to multiple molecules bridging the junctions with intermolecular interactions playing a role. In junctions comprising a self-assembled monolayer with eutectic Ga–In top-contacts (EGaIn), the pentacene derivative exhibits unusually low conductance, which we ascribe to the inability of these molecules to pack in a monolayer without introducing significant intermolecular contacts. This hypothesis is supported by the MCBJ data and theoretical calculations showing suppressed conductance through the PC films. These results highlight the role of intermolecular effects and junction geometries in the observed fluctuations of conductance values between single-molecule and ensemble junctions, and the importance of studying molecules in both platforms.}, number={41}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Liu, Yuru and Ornago, Luca and Carlotti, Marco and Ai, Yong and Abbassi, Maria El and Soni, Saurabh and Asyuda, Andika and Zharnikov, Michael and Zant, Herre S. J. and Chiechi, Ryan C.}, year={2020}, month={Oct}, pages={22776–22783} }
 @article{qiu_chiechi_2020, title={Large-Area Molecular Junctions: Synthesizing Integrated Circuits for Next-Generation Nonvolatile Memory}, volume={2}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85089355866&partnerID=MN8TOARS}, DOI={10.1016/j.trechm.2020.07.006}, abstractNote={The development of high-speed, nonvolatile memory devices with low power consumption remains a significant challenge for next-generation computing. A recent study reported molecular switches operating at low voltages in large-area junctions by coupling supramolecular structural changes and counterion migration to bias-dependent redox, culminating in proof-of-concept memory comprising self-assembled monolayers.}, number={10}, journal={Trends in Chemistry}, author={Qiu, X. and Chiechi, R.C.}, year={2020}, pages={869–872} }
 @article{liu_van der zee_alessandri_sami_dong_nugraha_barker_rousseva_qiu_qiu_et al._2020, title={N-type organic thermoelectrics: demonstration of ZT > 0.3}, volume={11}, ISSN={2041-1723}, url={http://dx.doi.org/10.1038/s41467-020-19537-8}, DOI={10.1038/s41467-020-19537-8}, abstractNote={The 'phonon-glass electron-crystal' concept has triggered most of the progress that has been achieved in inorganic thermoelectrics in the past two decades. Organic thermoelectric materials, unlike their inorganic counterparts, exhibit molecular diversity, flexible mechanical properties and easy fabrication, and are mostly 'phonon glasses'. However, the thermoelectric performances of these organic materials are largely limited by low molecular order and they are therefore far from being 'electron crystals'. Here, we report a molecularly n-doped fullerene derivative with meticulous design of the side chain that approaches an organic 'PGEC' thermoelectric material. This thermoelectric material exhibits an excellent electrical conductivity of >10 S cm-1 and an ultralow thermal conductivity of <0.1 Wm-1K-1, leading to the best figure of merit ZT = 0.34 (at 120 °C) among all reported single-host n-type organic thermoelectric materials. The key factor to achieving the record performance is to use 'arm-shaped' double-triethylene-glycol-type side chains, which not only offer excellent doping efficiency (~60%) but also induce a disorder-to-order transition upon thermal annealing. This study illustrates the vast potential of organic semiconductors as thermoelectric materials.}, number={1}, journal={Nature Communications}, publisher={Springer Science and Business Media LLC}, author={Liu, Jian and van der Zee, Bas and Alessandri, Riccardo and Sami, Selim and Dong, Jingjin and Nugraha, Mohamad I. and Barker, Alex J. and Rousseva, Sylvia and Qiu, Li and Qiu, Xinkai and et al.}, year={2020}, month={Nov}, pages={5694} }
 @article{ye_liu_liu_qiu_koster_chiechi_2020, title={Protonic acid doping of low band-gap conjugated polyions}, volume={4}, url={https://doi.org/10.1039/D0QM00278J}, DOI={10.1039/D0QM00278J}, abstractNote={This paper describes the design and synthesis of a series of conjugated polyions (CPIZ-T, CPIZ-TT and CPIZ-TT-DEG) that incorporate a formal positive charge into their conjugated backbones, balanced by anionic pendant groups with increasing electron-donating ability. The energy levels and the bandgap of these conjugated polyions were determined by using optical absorption spectroscopy and cyclic voltammetry (CV) and were easily modulated by varying the electron donating group. The energies of the occupied states increase with increasing electron-donating ability, while the energies of the unoccupied states are almost unchanged due to the presence of tritylium ions in the conjugated backbone. All conjugated polyions exhibit pristine semiconducting properties in weak protonic acids, but with sufficiently strong acids, the polymers exhibit spontaneous spin unpairing and convert to a metallic state. The required strength of the acids varies with the electron-donating ability, with higher HOMO levels leading to more facile proton acid doping and higher electrical conductivities. The mechanism of protonic acid doping of conjugated polyions involves a spinless doping process (dehydration) followed by a spontaneous spin unpairing leading to the formation of polarons. While protonic acid doping occurs in polyaniline, conjugated polyions offer synthetic tunability and selective processing into insulating, semiconducting and metallic states simply by controlling acidity.}, number={12}, journal={Materials Chemistry Frontiers}, author={Ye, Gang and Liu, Yuru and Liu, Jian and Qiu, Xinkai and Koster, L. Jan Anton and Chiechi, Ryan C.}, year={2020}, pages={3585–3593} }
 @article{lu_ye_punj_chiechi_orrit_2020, title={Quantum Yield Limits for the Detection of Single-Molecule Fluorescence Enhancement by a Gold Nanorod}, volume={7}, url={https://doi.org/10.1021/acsphotonics.0c00803}, DOI={10.1021/acsphotonics.0c00803}, abstractNote={Fluorescence-based single-molecule optical detection techniques are widely chosen over other methods, owing to the ease of background screening and better signal-to-noise throughput. Nonetheless, t...}, number={9}, journal={ACS Photonics}, publisher={American Chemical Society (ACS)}, author={Lu, Xuxing and Ye, Gang and Punj, Deep and Chiechi, Ryan C. and Orrit, Michel}, year={2020}, month={Sep}, pages={2498–2505} }
 @article{mukhopadhyay_karuppannan_guo_fereiro_bergren_mukundan_qiu_castañeda ocampo_chen_chiechi_et al._2020, title={Solid-State Protein Junctions: Cross-Laboratory Study Shows Preservation of Mechanism at Varying Electronic Coupling}, volume={23}, ISSN={2589-0042}, url={http://dx.doi.org/10.1016/j.isci.2020.101099}, DOI={10.1016/j.isci.2020.101099}, abstractNote={Successful integration of proteins in solid-state electronics requires contacting them in a non-invasive fashion, with a solid conducting surface for immobilization as one such contact. The contacts can affect and even dominate the measured electronic transport. Often substrates, substrate treatments, protein immobilization, and device geometries differ between laboratories. Thus the question arises how far results from different laboratories and platforms are comparable and how to distinguish genuine protein electronic transport properties from platform-induced ones. We report a systematic comparison of electronic transport measurements between different laboratories, using all commonly used large-area schemes to contact a set of three proteins of largely different types. Altogether we study eight different combinations of molecular junction configurations, designed so that Ageoof junctions varies from 105 to 10-3 μm2. Although for the same protein, measured with similar device geometry, results compare reasonably well, there are significant differences in current densities (an intensive variable) between different device geometries. Likely, these originate in the critical contact-protein coupling (∼contact resistance), in addition to the actual number of proteins involved, because the effective junction contact area depends on the nanometric roughness of the electrodes and at times, even the proteins may increase this roughness. On the positive side, our results show that understanding what controls the coupling can make the coupling a design knob. In terms of extensive variables, such as temperature, our comparison unanimously shows the transport to be independent of temperature for all studied configurations and proteins. Our study places coupling and lack of temperature activation as key aspects to be considered in both modeling and practice of protein electronic transport experiments.}, number={5}, journal={iScience}, publisher={Elsevier BV}, author={Mukhopadhyay, Sabyasachi and Karuppannan, Senthil Kumar and Guo, Cunlan and Fereiro, Jerry A. and Bergren, Adam and Mukundan, Vineetha and Qiu, Xinkai and Castañeda Ocampo, Olga E. and Chen, Xiaoping and Chiechi, Ryan C. and et al.}, year={2020}, month={May}, pages={101099} }
 @article{qiu_rousseva_ye_hummelen_chiechi_2020, title={Stochastic Computing via in Operando Modulation of Rectification in Molecular Tunneling Junctions}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85098907555&partnerID=MN8TOARS}, DOI={10.26434/chemrxiv.12839714.v1}, abstractNote={This paper describes the reconfiguration of molecular tunneling junctions during operation via the self-assembly of bilayers of glycol ethers. We use well-established functional groups to modulate the magnitude and direction of rectification in assembled tunneling junctions by exposing them to solutions containing different glycol ethers. Variable-temperature measurements establish that rectification occurs by a bias-dependent tunneling-hopping mechanism and that glycol ethers, beside being an unusually efficient tunneling medium, behave identically to alkanes. We fabricated memory bits from crossbar junctions prepared by injecting eutectic Ga-In into microfluidic channels. Two 8-bit registers were able to perform logical AND operations on bit strings encoded into chemical packets as microfluidic droplets that alter the composition of the crossbar junctions through self-assembly to effect memristor-like properties. This proof of concept work demonstrates the potential for fieldable molecular-electronic devices based on tunneling junctions of self-assembled monolayers and bilayers.}, journal={ChemRxiv}, author={Qiu, X. and Rousseva, S. and Ye, G. and Hummelen, J.C. and Chiechi, R.C.}, year={2020} }
 @article{ye_liu_abdu-aguye_loi_chiechi_2020, title={Synthesis, Optical and Electrochemical Properties of High-Quality Cross-Conjugated Aromatic Polyketones}, volume={5}, url={https://doi.org/10.1021/acsomega.0c00223}, DOI={10.1021/acsomega.0c00223}, abstractNote={This paper describes the synthesis and characterization of three new aromatic polyketones with repeating units based on 2,2′-(2,5-dihexyl-1,4-phenylene) dithiophene (PTK), 2,2′-(9,9-dihexyl-9H-fluorene-2,7-diyl)dithiophene (PFTK), and 4,7-bis(3-hexylthiophen-2-yl)benzo[c][1,2,5]thiadiazole (PBTK). These polymers were obtained with a one-pot Suzuki–Miyaura cross-coupling-promoted homopolymerization to afford high-quality, defect-free polymers. Experimental and theoretical studies were applied to investigate their optical and electrical properties. The cross-conjugated nature of aromatic polyketones imparts excellent thermal stability. Exposure to acid converts the cross-conjugation to linear-conjugation, enabling the dynamic tuning of optoelectronic properties.}, number={9}, journal={ACS Omega}, publisher={American Chemical Society (ACS)}, author={Ye, Gang and Liu, Yuru and Abdu-Aguye, Mustapha and Loi, Maria A. and Chiechi, Ryan C.}, year={2020}, month={Mar}, pages={4689–4696} }
 @article{qiu_ivasyshyn_qiu_enache_dong_rousseva_portale_stöhr_hummelen_chiechi_2020, title={Thiol-free self-assembled oligoethylene glycols enable robust air-stable molecular electronics}, volume={19}, url={https://doi.org/10.1038/s41563-019-0587-x}, DOI={10.1038/s41563-019-0587-x}, abstractNote={Self-assembled monolayers (SAMs) are widely used to engineer the surface properties of metals. The relatively simple and versatile chemistry of metal–thiolate bonds makes thiolate SAMs the preferred option in a range of applications, yet fragility and a tendency to oxidize in air limit their long-term use. Here, we report the formation of thiol-free self-assembled mono- and bilayers of glycol ethers, which bind to the surface of coinage metals through the spontaneous chemisorption of glycol ether-functionalized fullerenes. As-prepared assemblies are bilayers presenting fullerene cages at both the substrate and ambient interface. Subsequent exposure to functionalized glycol ethers displaces the topmost layer of glycol ether-functionalized fullerenes, and the resulting assemblies expose functional groups to the ambient interface. These layers exhibit the key properties of thiolate SAMs, yet they are stable to ambient conditions for several weeks, as shown by the performance of tunnelling junctions formed from SAMs of alkyl-functionalized glycol ethers. Glycol ether-functionalized spiropyrans incorporated into mixed monolayers lead to reversible, light-driven conductance switching. Self-assemblies of glycol ethers are drop-in replacements for thiolate SAMs that retain all of their useful properties while avoiding the drawbacks of metal–thiolate bonds. Chemisorbed molecules combining glycol-ether moieties and fullerenes are shown to form uniform and air-stable self-assembled bilayers on coinage metals, and are amenable to versatile functionalization by in-place exchange of the top layer.}, number={3}, journal={Nature Materials}, author={Qiu, Xinkai and Ivasyshyn, Viktor and Qiu, Li and Enache, Mihaela and Dong, Jingjin and Rousseva, Sylvia and Portale, Giuseppe and Stöhr, Meike and Hummelen, Jan C. and Chiechi, Ryan C.}, year={2020}, month={Mar}, pages={330–337} }
 @article{soni_ye_zheng_zhang_asyuda_zharnikov_hong_chiechi_2020, title={Understanding the Role of Parallel Pathways via In‐Situ Switching of Quantum Interference in Molecular Tunneling Junctions}, volume={132}, url={https://doi.org/10.1002/ange.202005047}, DOI={10.1002/ange.202005047}, abstractNote={Abstract This study describes the modulation of tunneling probabilities in molecular junctions by switching one of two parallel intramolecular pathways. A linearly conjugated molecular wire provides a rigid framework that allows a second, cross‐conjugated pathway to be effectively switched on and off by protonation, affecting the total conductance of the junction. This approach works because a traversing electron interacts with the entire quantum‐mechanical circuit simultaneously; Kirchhoff's rules do not apply. We confirm this concept by comparing the conductances of a series of compounds with single or parallel pathways in large‐area junctions using EGaIn contacts and single‐molecule break junctions using gold contacts. We affect switching selectively in one of two parallel pathways by converting a cross‐conjugated carbonyl carbon into a trivalent carbocation, which replaces destructive quantum interference with a symmetrical resonance, causing an increase in transmission in the bias window.}, number={34}, journal={Angewandte Chemie}, publisher={Wiley}, author={Soni, Saurabh and Ye, Gang and Zheng, Jueting and Zhang, Yanxi and Asyuda, Andika and Zharnikov, Michael and Hong, Wenjing and Chiechi, Ryan C.}, year={2020}, month={Aug}, pages={14414–14418} }
 @article{soni_ye_zheng_zhang_asyuda_zharnikov_hong_chiechi_2020, title={Understanding the Role of Parallel Pathways via In‐Situ Switching of Quantum Interference in Molecular Tunneling Junctions}, volume={59}, url={https://doi.org/10.1002/anie.202005047}, DOI={10.1002/anie.202005047}, abstractNote={Abstract This study describes the modulation of tunneling probabilities in molecular junctions by switching one of two parallel intramolecular pathways. A linearly conjugated molecular wire provides a rigid framework that allows a second, cross‐conjugated pathway to be effectively switched on and off by protonation, affecting the total conductance of the junction. This approach works because a traversing electron interacts with the entire quantum‐mechanical circuit simultaneously; Kirchhoff's rules do not apply. We confirm this concept by comparing the conductances of a series of compounds with single or parallel pathways in large‐area junctions using EGaIn contacts and single‐molecule break junctions using gold contacts. We affect switching selectively in one of two parallel pathways by converting a cross‐conjugated carbonyl carbon into a trivalent carbocation, which replaces destructive quantum interference with a symmetrical resonance, causing an increase in transmission in the bias window.}, number={34}, journal={Angewandte Chemie International Edition}, publisher={Wiley}, author={Soni, Saurabh and Ye, Gang and Zheng, Jueting and Zhang, Yanxi and Asyuda, Andika and Zharnikov, Michael and Hong, Wenjing and Chiechi, Ryan C.}, year={2020}, month={Aug}, pages={14308–14312} }
 @article{doumon_wang_qiu_minnaard_chiechi_koster_2019, title={1,8-diiodooctane acts as a photo-acid in organic solar cells}, volume={9}, ISSN={2045-2322}, url={http://dx.doi.org/10.1038/s41598-019-40948-1}, DOI={10.1038/s41598-019-40948-1}, abstractNote={Abstract The last decade saw myriad new donor polymers, among which benzodithiophene-co-thienothiophene polymers are attractive due to their relatively high power conversion efficiency in bulk heterojunction solar cells. We examine the effect of UV-light on the stability of these polymers. The relationship between the polymer chemical structure and the UV-stability of the cells is explored on the one hand, and on the other hand, the effect of additives on their UV-stability: 1,8-diiodooctane against 1-chloronaphthalene in the cells and 1,8-octanedithiol in solution. For example, PBDTTT-E with 18% efficiency loss is more stable than PBDTTT-ET with 36% loss throughout the exposure. While 1,8-diiodooctane acts as photo-acid and leads to accelerated degradation of the solar cells, 1-chloronaphthalene does not. Acidity is known to be detrimental to the efficiency and stability of organic solar cells. The degradation is initiated upon UV-irradiation by the cleavage of the side chains, resulting in more electron traps and by the formation of iodine, dissolved HI and carbon-centered radicals from 1,8-diiodooctane as revealed by 1 H NMR spectrum. The 1,8-octanedithiol spectra do not show such species. Finally, the mechanisms behind the effect of 1,8-diiodooctane are explained, paving the way for the design of new, efficient as well as stable materials and additives.}, number={1}, journal={Scientific Reports}, publisher={Springer Science and Business Media LLC}, author={Doumon, Nutifafa Y. and Wang, Gongbao and Qiu, Xinkai and Minnaard, Adriaan J. and Chiechi, Ryan C. and Koster, L. Jan Anton}, year={2019}, month={Mar} }
 @article{gu_zhou_zhao_möhwald_li_chiechi_shi_zhang_2019, title={3D zig-zag nanogaps based on nanoskiving for plasmonic nanofocusing}, volume={11}, url={https://doi.org/10.1039/C8NR08946A}, DOI={10.1039/C8NR08946A}, abstractNote={We combine anisotropic wet etching and nanoskiving to create a novel three-dimensional (3D) nanoantenna for plasmonic nanofocusing, vertically aligned zig-zag nanogaps, constituted of nanogaps with defined angles. Instead of conventional lithography, we used the thickness of a self-assembled monolayer (SAM) to define nanogaps with high throughput, and anisotropic etching of Si V-grooves to naturally define ultra-sharp tips. Both nanogaps and sharp tips can synergistically squeeze the electro-magnetic (EM) field and excite 3D nanofocusing, enabling great potential applications in chemical sensing and plasmonic devices. The dependence of the EM field enhancement on structural features is systematically investigated and optimized. We found that the field enhancement and confinement are stronger at the tipped-nanogap compared to what standalone tips or nanogaps produce. The intensity of surface-enhanced Raman spectroscopy (SERS) recorded on the 70.5° tipped-nanogaps is 45 times higher than that recorded with linear nanogaps and 5 times higher than that recorded with tip-only nanowires, which is attributed to the integration of the tip and gap in plasmonic nanostructures. This proposed nanofabrication technique and the resulting structures equipped with a strongly enhanced EM field will promote broad applications for nanophotonics and surface-enhanced spectroscopy.}, number={8}, journal={Nanoscale}, publisher={Royal Society of Chemistry (RSC)}, author={Gu, Panpan and Zhou, Ziwei and Zhao, Zhiyuan and Möhwald, Helmuth and Li, Chunguang and Chiechi, Ryan C. and Shi, Zhan and Zhang, Gang}, year={2019}, pages={3583–3590} }
 @article{kumar_merelli_danowski_rudolf_feringa_chiechi_2019, title={Chemical Locking in Molecular Tunneling Junctions Enables Nonvolatile Memory with Large On–Off Ratios}, volume={31}, url={https://doi.org/10.1002/adma.201807831}, DOI={10.1002/adma.201807831}, abstractNote={This paper describes the reversible chemical locking of sypiropyran switches bound to metallic surfaces to enable the encoding of nonvolatile information. Data are encoded spatially by selectively locking the spiropyran moieties in their merocyanine form using a combination of exposure to acid and UV light. Without exposure to acid, the merocyanine form spontaneously converts back to the spiropyran form. Bits are resolved by defining the regions of the monolayer that are exposed to acid, using a “soft punchcard” fabricated from a silicone elastomer. Information is read by measuring the tunneling charge–transport through the monolayer using eutectic Ga–In top‐contacts. The merocyanine form is more than three orders of magnitude more conductive than the spiropyran form, allowing the differentiation of bits. Photoelectron spectroscopy shows that the monolayers are undamaged by exposure to light, acid, base, and applied bias, enabling proof‐of‐concept devices in which an 8‐bit ASCII encoded six‐character string is written, erased, and rewritten.}, number={15}, journal={Advanced Materials}, author={Kumar, Sumit and Merelli, Michele and Danowski, Wojciech and Rudolf, Petra and Feringa, Ben L. and Chiechi, Ryan C.}, year={2019}, month={Apr} }
 @article{schmitz_qiu_glöß_van leusen_izarova_nadeem_griebel_chiechi_kögerler_monakhov_2019, title={Conductive Self-Assembled Monolayers of Paramagnetic {CoIICo4III} and {Co4IICo2III} Coordination Clusters on Gold Surfaces}, volume={7}, ISSN={2296-2646}, url={http://dx.doi.org/10.3389/fchem.2019.00681}, DOI={10.3389/fchem.2019.00681}, abstractNote={Two polynuclear cobalt(II,III) complexes, [Co5(N3)4(N-n-bda)4(bza·SMe)2] (1) and [Co6(N3)4(N-n-bda)2(bza·SMe)5(MeOH)4]Cl (2), where Hbza·SMe = 4-(methylthio)benzoic acid and N-n-H2bda = N-n-butyldiethanolamine, were synthesized and fully characterized by various techniques. Compound 1 exhibits an unusual, approximately C2-symmetric {CoIICo4III} core of two isosceles Co3 triangles with perpendicularly oriented planes, sharing a central, high-spin CoII ion residing in a distorted tetrahedral coordination environment. This central CoII ion is connected to four outer, octahedrally coordinated low-spin CoIII ions via oxo bridges. Compound 2 comprises a semi-circular {Co4IICo2III} motif of four non-interacting high-spin CoII and two low-spin CoIII centers in octahedral coordination environments. Self-assembled monolayers (SAMs) of 1 and 2 were physisorbed on template-stripped gold surfaces contacted by an eutectic gallium-indium (EGaIn) tip. The acquired current density-voltage (I-V) data revealed that the cobalt-based SAMs are more electrically robust than those of the previously reported dinuclear {CuIILnIII} complexes with Ln = Gd, Tb, Dy, or Y (Schmitz et al., 2018a). In addition, between 170 and 220°C, the neutral, mixed-valence compound 1 undergoes a redox modification, yielding a {Co5}-based coordination cluster (1-A) with five non-interacting, high-spin octahedral CoII centers as indicated by SQUID magnetometry analysis in combination with X-ray photoelectron spectroscopy and infrared spectroscopy. Solvothermal treatment of 1 results in a high-nuclearity coordination cluster, [Co10(N3)2(N-n-bda)6(bza·SMe)6] (3), containing 10 virtually non-interacting high-spin CoII centers.}, journal={Frontiers in Chemistry}, publisher={Frontiers Media SA}, author={Schmitz, Sebastian and Qiu, Xinkai and Glöß, Maria and van Leusen, Jan and Izarova, Natalya V. and Nadeem, Muhammad Arif and Griebel, Jan and Chiechi, Ryan C. and Kögerler, Paul and Monakhov, Kirill Yu.}, year={2019}, month={Nov} }
 @article{ye_doumon_rousseva_liu_abdu-aguye_loi_hummelen_koster_chiechi_2019, title={Conjugated Polyions Enable Organic Photovoltaics Processed from Green Solvents}, volume={2}, url={https://doi.org/10.1021/acsaem.8b02226}, DOI={10.1021/acsaem.8b02226}, abstractNote={This paper describes the design, synthesis, and optical and electronic properties of two conjugated polymers CPIZ-B and CPIZ-T that incorporate closed-shell cations into their conjugated backbones, balanced by anionic pendant groups. The zwitterionic nature of the polymers renders them soluble in and processable from polar, protic solvents to form semiconducting films that are not doped. These unique properties are confirmed by absorption and electron paramagnetic resonance spectroscopy. The energies of the unoccupied states respond to the tritylium moieties in the conjugated backbone, while the occupied states respond to the electron-donating ability of the uncharged, aromatic units in the backbone. Films cast from 80:20 HCOOH/H2O by volume show good electron mobilities, enabling a photovoltaic effect in proof-of-concept, bilayer solar cells.}, number={3}, journal={ACS Applied Energy Materials}, publisher={American Chemical Society (ACS)}, author={Ye, Gang and Doumon, Nutifafa Y. and Rousseva, Sylvia and Liu, Yuru and Abdu-Aguye, Mustapha and Loi, Maria A. and Hummelen, Jan C. and Koster, L. Jan Anton and Chiechi, Ryan C.}, year={2019}, month={Mar}, pages={2197–2204} }
 @article{carlotti_soni_qiu_ai_sauter_zharnikov_chiechi_2019, title={Correction: Systematic experimental study of quantum interference effects in anthraquinoid molecular wires (Nanoscale Advances (2019) DOI: 10.1039/c8na00223a)}, volume={1}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85072048927&partnerID=MN8TOARS}, DOI={10.1039/c9na90018g}, abstractNote={Correction for ‘Systematic experimental study of quantum interference effects in anthraquinoid molecular wires’ by Marco Carlotti et al., Nanoscale Adv., 2019, DOI: 10.1039/c8na00223a.}, number={5}, journal={Nanoscale Advances}, author={Carlotti, M. and Soni, S. and Qiu, X. and Ai, Y. and Sauter, E. and Zharnikov, M. and Chiechi, R.C.}, year={2019}, pages={2040} }
 @article{kumar_soni_danowski_leach_faraji_feringa_rudolf_chiechi_2019, title={Eliminating Fatigue in Surface-Bound Spiropyrans}, volume={123}, url={https://doi.org/10.1021/acs.jpcc.9b05889}, DOI={10.1021/acs.jpcc.9b05889}, abstractNote={This paper describes an experimental approach to eliminating the loss of reversibility that surface-bound spiropyrans exhibit when switched with light. Although such fatigue can be controlled in other contexts, on surfaces, the photochromic compounds are held in close proximity to each other and relatively few molecules modulate the properties of a device, leading to a loss of functionality after only a few switching cycles. The switching process was characterized by photoelectron spectroscopy and differences in tunneling currents in the spiropyran and merocyanine forms using eutectic Ga−In. Self-assembled monolayers comprising only the photochromic compounds degraded rapidly, while mixed monolayers with hexanethiol showed different behaviors depending on the relative humidity. Under dry conditions, no chemical degradation was observed and the switching process was reversible over at least 100 cycles. Under humid conditions, no degradation occurred, but the switching process became irreversible. The absence of degradation observed in mixed monolayers is ascribed to the lack of solvation, which increases the barrier to a key bond rotation past the available thermal energy. These results highlight important differences in the contexts in which photochromic compounds are utilized and demonstrate that they can be leveraged to extract device-relevant functionality from surface-bound switches by suppressing fatigue and irreversibility.}, number={42}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Kumar, Sumit and Soni, Saurabh and Danowski, Wojciech and Leach, Isaac F. and Faraji, Shirin and Feringa, Ben L. and Rudolf, Petra and Chiechi, Ryan C.}, year={2019}, month={Oct}, pages={25908–25914} }
 @article{azevedo_braunschweig_chiechi_diaz fernandez_gildersleeve_godula_hartmann_miura_schmidt_turnbull_et al._2019, title={Glycan interactions on glycocalyx mimetic surfaces: General discussion}, volume={219}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85074444964&partnerID=MN8TOARS}, DOI={10.1039/C9FD90063B}, abstractNote={Adam Braunschweig opened discussion of the paper by Yoshiko Miura: Carbohydrate – carbohydrate interactions are poorly understood, even considered by some to be a myth because they are so weak. I was wondering if your materials could exploit or examine carbohydrate – carbohydrate interactions by using them for separations of carbohydrates, which still remain a major challenge. Yoshiko Miura answered: The multivalent compounds are also applied to the carbohydrate – carbohydrate interaction. First of all, the carbohydrate – carbohydrate interactions are much weaker than sugar – protein interactions. It is still di ffi cult to obtain quantitative binding constants of carbohydrate – carbohydrate interactions. The carbohydrate – carbohydrate interactions are ampli  ed by multivalent glycopolymer compounds and carbohydrate – protein interactions. 1 In my opinion, from the quantitative measurement results, the carbohydrate – carbohydrate interactions are too weak to apply it as a functional material. (The binding constants of the glycopolymer and carbohydrate are in the order of 10 4 M (cid:1) 1 , which are too weak.) However, the continuous  ow system is a useful method to estimate the carbohydrate – carbohydrate interaction. 2 Investigation of the glycopolymer monolith (porous materials) is still its infancy and should be expanded to new areas including carbohydrate – carbohydrate interactions.}, journal={Faraday Discussions}, author={Azevedo, H.S. and Braunschweig, A.B. and Chiechi, R.C. and Diaz Fernandez, Y. and Gildersleeve, J.C. and Godula, K. and Hartmann, L. and Miura, Y. and Schmidt, S. and Turnbull, W.B. and et al.}, year={2019}, pages={183–188} }
 @article{azevedo_braunschweig_chiechi_claridge_cronin_diaz fernandez_feizi_hartmann_huang_miura_et al._2019, title={New directions in surface functionalization and characterization: General discussion}, volume={219}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85074378136&partnerID=MN8TOARS}, DOI={10.1039/C9FD90064K}, abstractNote={Citation for published version (APA): Azevedo, H. S., Braunschweig, A. B., Chiechi, R. C., Claridge, S. A., Cronin, L., Fernandez, Y. D., Feizi, T., Hartmann, L., Huang, M., Miura, Y., Palma, M., Qiu, X., Ravoo, B. J., Schmidt, S., Turnbull, W. B., Werner, C., Zheng, Z., & Zhou, D. (2019). New directions in surface functionalization and characterization: General discussion. Faraday Discussions, 219, 252-261. https://doi.org/10.1039/C9FD90064K}, journal={Faraday Discussions}, author={Azevedo, H.S. and Braunschweig, A.B. and Chiechi, R.C. and Claridge, S.A. and Cronin, L. and Diaz Fernandez, Y. and Feizi, T. and Hartmann, L. and Huang, M. and Miura, Y. and et al.}, year={2019}, pages={252–261} }
 @article{liu_shi_dong_nugraha_qiu_su_chiechi_baran_portale_guo_et al._2019, title={Overcoming Coulomb Interaction Improves Free-Charge Generation and Thermoelectric Properties for n-Doped Conjugated Polymers}, volume={4}, url={https://doi.org/10.1021/acsenergylett.9b00977}, DOI={10.1021/acsenergylett.9b00977}, abstractNote={Molecular doping of organic semiconductors creates Coulombically bound charge and counterion pairs through a charge-transfer process. However, their Coulomb interactions and strategies to mitigate their effects have been rarely addressed. Here, we report that the number of free charges and thermoelectric properties are greatly enhanced by overcoming the Coulomb interaction in an n-doped conjugated polymer. Poly(2,2′-bithiazolothienyl-4,4′,10,10′-tetracarboxydiimide) (PDTzTI) and the benchmark N2200 are n-doped by tetrakis (dimethylamino) ethylene (TDAE) for thermoelectrics. Doped PDTzTI exhibits ∼10 times higher free-charge density and 500 times higher conductivity than doped N2200, leading to a power factor of 7.6 μW m–1 K–2 and ZT of 0.01 at room temperature. Compared to N2200, PDTzTI features a better molecular ordering and two-dimensional charge delocalization, which help overcome the Coulomb interaction in the doped state. Consequently, free charges are more easily generated from charge–counterion pa...}, number={7}, journal={ACS Energy Letters}, publisher={American Chemical Society (ACS)}, author={Liu, Jian and Shi, Yongqiang and Dong, Jingjin and Nugraha, Mohamad I. and Qiu, Xinkai and Su, Mengyao and Chiechi, Ryan C. and Baran, Derya and Portale, Giuseppe and Guo, Xugang and et al.}, year={2019}, month={Jul}, pages={1556–1564} }
 @article{braunschweig_byrne_chiechi_diaz fernandez_gildersleeve_godula_hartmann_mahon_miura_nelson_et al._2019, title={Preparation of multivalent glycan micro- and nano-arrays: General discussion}, volume={219}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85074378831&partnerID=MN8TOARS}, DOI={10.1039/C9FD90062D}, abstractNote={Adam Braunschweig opened the discussion of the paper by Je ff rey Gilder-sleeve: In your contribution to this Discussion, you have shown that the avidity between protein and glycan is sensitively dependent upon glycan – glycan spacing, linker composition, linker length, etc . As a result, di ff erent microarrays produce di ff erent results for speci  city and avidity towards a particular lectin. Given this inherent complexity, is there a “ true value ” for avidity that re  ects most accurately how this recognition may be occurring in biology? Je ff Gildersleeve answered: This is an interesting consideration. A glycan determinant can be present in varying contexts in biology. The avidity will depend on the structure of the determinant as well as the presentation. For example, a lectin might have four binding sites. In some settings, the lectin might only be able to engage two binding sites. In other settings, the lectin might bind glycans using all four of its binding sties. These could both be biologically relevant, but the avidities could be quite di ff erent. So, there are likely many “ true values ” for avidity for each glycan determinant. When connecting apparent K d values measured on a glycan microarray to biological systems, I think of it as potential – “ in the right context, this lectin could bind with an apparent K d value of X to this glycan ” . It has the potential to bind, but it will depend on other factors, such as the nature of the carrier chain and the spacing and orientation of the glycans. Daniel Valles asked: Since there has been much discussion about the varying binding constants}, journal={Faraday Discussions}, author={Braunschweig, A. and Byrne, J.P. and Chiechi, R. and Diaz Fernandez, Y. and Gildersleeve, J. and Godula, K. and Hartmann, L. and Mahon, C. and Miura, Y. and Nelson, A. and et al.}, year={2019}, pages={128–137} }
 @article{pütt_qiu_kozłowski_gildenast_linnenberg_zahn_chiechi_monakhov_2019, title={Self-assembled monolayers of polyoxovanadates with phthalocyaninato lanthanide moieties on gold surfaces}, volume={55}, url={https://doi.org/10.1039/C9CC06852J}, DOI={10.1039/C9CC06852J}, abstractNote={The two first representatives of phthalocyaninato (Pc) lanthanide-ligated polyoxovanadate cages {[V12O32(Cl)](LnPc)n}n-5 (n = 1 or 2, Ln = Yb3+) were synthesised and fully characterised. These magnetic complexes form two-dimensional self-assembled monolayers exhibiting electrical conductivity on gold substrate surfaces, as assessed by using an EGaIn tip.}, number={90}, journal={Chemical Communications}, publisher={Royal Society of Chemistry (RSC)}, author={Pütt, Ricarda and Qiu, Xinkai and Kozłowski, Piotr and Gildenast, Hans and Linnenberg, Oliver and Zahn, Stefan and Chiechi, Ryan C. and Monakhov, Kirill Yu.}, year={2019}, pages={13554–13557} }
 @article{ivasyshyn_smit_chiechi_2019, title={Synthesis of a Hominal Bis(difluoromethyl) Fragment}, volume={4}, url={https://doi.org/10.1021/acsomega.9b02131}, DOI={10.1021/acsomega.9b02131}, abstractNote={This paper describes the synthesis of a discrete unit of hominal bis(gem-CF2). The controlled introduction of fluorine atoms is a powerful synthetic tool to introduce dipole moments with minimal impact to sterics. Poly(vinylidene difluoride) is a striking example of the influence of fluorine atoms, which impart ferroelectric behavior from the alignment of the dipole moments of CF2 units; however, it is prepared via direct polymerization of vinylidene difluoride. Thus, a different synthetic pathway is required to produce synthons containing discrete numbers of CF2 groups in a hominal relation to each other. We found out that, in the case of short chains, the consecutive deoxofluorination of sequentially introduced keto groups is inefficient, as it requires harsh conditions and decreasing yields at each step. To solve this problem, we combined the selective desulfurative fluorination of dithiolanes with pyridinium fluoride and the deoxofluorination of keto groups with morpholinosulfur trifluoride. This strategy is highly reproducible and scalable, allowing the synthesis of the hominal bis(gem-CF2) fragment as a shelf-stable tosylate, which can be used to install discrete chains of hominal bis(gem-CF2) on a variety of synthons and monomers.}, number={9}, journal={ACS Omega}, publisher={American Chemical Society (ACS)}, author={Ivasyshyn, Viktor and Smit, Hans and Chiechi, Ryan C.}, year={2019}, month={Aug}, pages={14140–14150} }
 @article{ivasyshyn_smit_chiechi_2019, title={Synthesis of a Hominal Bis(difluoromethyl) Fragments}, volume={3}, url={https://doi.org/10.26434/chemrxiv.7813460.v1}, DOI={10.26434/chemrxiv.7813460.v1}, abstractNote={This paper describes the synthesis of discrete units of hominal bis(gem-CF2). The controlled introduction of fluorine atoms is a powerful synthetic tool to introduce dipole moments with minimal impact to sterics. Polyvinylidene fluoride (PVDF) is a striking example of the influence of fluorine atoms, which impart ferroelectric behavior from the alignment of the dipole moments of CF2 units, however, it is prepared via direct polymerization of vinylidene difluoride. Thus, a different synthetic pathway is required to produce synthons containing discrete numbers of CF2 groups in a hominal relation to each other. We found out that, in the case of short chains, the consecutive deoxofluorination of sequentially-introduced keto groups is very inefficient, as it requires harsh conditions and sharply decreasing yields at each step. To solve this problem, we combined the selective desulfurative fluorination of dithiolanes with pyridinium fluoride and the deoxofluorination of keto groups with morpholinosulfur trifluoride. This strategy is highly reproducible and scalable, allowing the synthesis of the hominal bis(gem-CF2) fragment as a shelf-stable tosylate, which can be used to install discrete chains of hominal bis(gem-CF2) on a variety of synthons and monomers.}, journal={ChemRxiv}, publisher={American Chemical Society (ACS)}, author={Ivasyshyn, Viktor Viktor and Smit, Hans and Chiechi, Ryan}, year={2019}, month={Mar} }
 @article{carlotti_soni_qiu_sauter_zharnikov_chiechi_2019, title={Systematic experimental study of quantum interference effects in anthraquinoid molecular wires}, volume={1}, url={https://doi.org/10.1039/C8NA00223A}, DOI={10.1039/C8NA00223A}, abstractNote={In order to translate molecular properties in molecular-electronic devices, it is necessary to create design principles that can be used to achieve better structure–function control oriented toward device fabrication. In molecular tunneling junctions, cross-conjugation tends to give rise to destructive quantum interference effects that can be tuned by changing the electronic properties of the molecules. We performed a systematic study of the tunneling charge-transport properties of a series of compounds characterized by an identical cross-conjugated anthraquinoid molecular skeleton but bearing different substituents at the 9 and 10 positions that affect the energies and localization of their frontier orbitals. We compared the experimental results across three different experimental platforms in both single-molecule and large-area junctions and found a general agreement. Combined with theoretical models, these results separate the intrinsic properties of the molecules from platform-specific effects. This work is a step towards explicit synthetic control over tunneling charge transport targeted at specific functionality in (proto-)devices.}, number={5}, journal={Nanoscale Advances}, publisher={Royal Society of Chemistry (RSC)}, author={Carlotti, Marco and Soni, Saurabh and Qiu, Xinkai and Sauter, Eric and Zharnikov, Michael and Chiechi, Ryan C.}, year={2019}, pages={2018–2028} }
 @article{liu_maity_roosloot_qiu_qiu_chiechi_hummelen_hauff_koster_2019, title={The Effect of Electrostatic Interaction on n‐Type Doping Efficiency of Fullerene Derivatives}, volume={5}, ISSN={2199-160X 2199-160X}, url={http://dx.doi.org/10.1002/aelm.201800959}, DOI={10.1002/aelm.201800959}, abstractNote={The molecular doping of organic semiconductors represents a key strategy for advancing organic electronic applications. However, the n‐doping of organic materials is usually less efficient than p‐doping and strategies toward the design of more efficient n‐doping still remain less explored. In this contribution, the impact of electrostatic interaction is explored on the doping efficiency of fullerene derivatives. [6,6]‐Phenyl‐C61‐butyric acid methyl ester (PCBM) and a [60]fulleropyrrolidine with a more polarizable triethylene glycol type side chain (PTEG‐1) are employed for a comparative study. It is found that the doping efficiency of lightly doped PCBM layers is limited to a few percent, while doped PTEG‐1 films exhibit very high doping efficiency approaching 100%. The enhanced n‐doping of PTEG‐1 compared with that of PCBM is further substantiated by Raman and Fourier transform infrared spectroscopic studies. The activation energy for charge generation in doped PTEG‐1 is much smaller than that of doped PCBM, which confirms a higher probability for dissociation of charge transfer complexes in the former compared to the latter. The enhanced molecular n‐doping for PTEG‐1 is attributed to the electrostatic interaction between the charge transfer complex and the polar environment offered by the triethylene glycol diether side chain.}, number={11}, journal={Advanced Electronic Materials}, publisher={Wiley}, author={Liu, Jian and Maity, Sudeshna and Roosloot, Nathan and Qiu, Xinkai and Qiu, Li and Chiechi, Ryan C. and Hummelen, Jan C. and Hauff, Elizabeth and Koster, L. Jan Anton}, year={2019}, month={Feb}, pages={1800959} }
 @article{zhang_ye_soni_qiu_krijger_jonkman_carlotti_sauter_zharnikov_chiechi_2018, title={Controlling destructive quantum interference in tunneling junctions comprising self-assembled monolayers via bond topology and functional groups}, volume={9}, url={https://doi.org/10.1039/C8SC00165K}, DOI={10.1039/C8SC00165K}, abstractNote={Three different benzodithiophene derivatives were designed to isolate the effects of bond topology from that of functional groups in quantum interference to examine the role of the quinone functionality separate from cross-conjugation.}, number={19}, journal={Chemical Science}, publisher={Royal Society of Chemistry (RSC)}, author={Zhang, Yanxi and Ye, Gang and Soni, Saurabh and Qiu, Xinkai and Krijger, Theodorus L. and Jonkman, Harry T. and Carlotti, Marco and Sauter, Eric and Zharnikov, Michael and Chiechi, Ryan C.}, year={2018}, pages={4414–4423} }
 @article{ozcelik_pereira-cameselle_weber_paszkiewicz_carlotti_paintner_zhang_lin_zhang_barth_et al._2018, title={Device-Compatible Chiroptical Surfaces through Self-Assembly of Enantiopure Allenes}, volume={34}, url={https://doi.org/10.1021/acs.langmuir.8b00305}, DOI={10.1021/acs.langmuir.8b00305}, abstractNote={Chiroptical methods have been proven to be superior compared to their achiral counterparts for the structural elucidation of many compounds. To expand the use of chiroptical systems to everyday applications, the development of functional materials exhibiting intense chiroptical responses is essential. Particularly, tailored and robust interfaces compatible with standard device operation conditions are required. Herein, we present the design and synthesis of chiral allenes and their use for the functionalization of gold surfaces. The self-assembly results in a monolayer-thin room-temperature-stable upstanding chiral architecture as ascertained by ellipsometry, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure. Moreover, these nanostructures anchored to device-compatible substrates feature intense chiroptical second harmonic generation. Both straightforward preparation of the device-compatible interfaces along with their chiroptical nature provide major prospects for everyday applications.}, note={PMID: 29551068}, number={15}, journal={Langmuir}, author={Ozcelik, A. and Pereira-Cameselle, R. and Weber, A. and Paszkiewicz, M. and Carlotti, M. and Paintner, T. and Zhang, L. and Lin, T. and Zhang, Y.-Q. and Barth, J. V. and et al.}, year={2018}, pages={4548–4553} }
 @article{qihui_zhiyuan_ziwei_gang_c._rijn patrick_2018, title={Directing Mesenchymal Stem Cells with Gold Nanowire Arrays}, volume={5}, url={https://onlinelibrary.wiley.com/doi/abs/10.1002/admi.201800334}, DOI={10.1002/admi.201800334}, abstractNote={Controlling cell organization is still a major bottleneck in biointerface engineering when the material dimensions decrease to the nanoscale. Here, Au nanowire‐patterned array platforms with multiscale design from the macroscale to the nanoscale are developed for studying human bone marrow–derived mesenchymal stem cell (hBM‐MSC) response. When the angle of the Au nanowires on glass is increased from 0° to 90°, hBM‐MSC arrangement exhibits a transition from a unidirectional distribution induced by a vector response to a bimodal polarization pattern. The degree of cell vector response and elongation decreases with increasing nanowire angles from 0° to 90°. Further, it is demonstrated that the specific cell adhesion and organization are dependent on the surface micro/nanotopography, which is greatly enhanced by introducing stem cell‐material affinity differences. An ideal model and new insights into a deeper understanding of cell–nano‐biointerface interactions are provided.}, number={14}, journal={Advanced Materials Interfaces}, author={Qihui, Zhou and Zhiyuan, Zhao and Ziwei, Zhou and Gang, Zhang and C., Chiechi Ryan and Rijn Patrick}, year={2018}, pages={1800334} }
 @article{oomen_zhang_chiechi_verpoorte_mathwig_2018, title={Electrochemical sensing with single nanoskived gold nanowires bisecting a microchannel}, volume={18}, url={https://doi.org/10.1039/C8LC00787J}, DOI={10.1039/C8LC00787J}, abstractNote={We suspended a single nanoskived gold nanowire in a microfluidic channel. In this preliminary report, a 200 nm-diameter nanowire was used as an electrode to perform hydrodynamic voltammetry in the center of solution flow. Suspended nanowires exhibit superior current response due to highly efficient mass transport in the area of fastest flow.}, number={19}, journal={Lab on a Chip}, publisher={Royal Society of Chemistry (RSC)}, author={Oomen, Pieter E. and Zhang, Yanxi and Chiechi, Ryan C. and Verpoorte, Elisabeth and Mathwig, Klaus}, year={2018}, pages={2913–2916} }
 @article{schmitz_kovalchuk_martín-rodríguez_leusen_izarova_bourone_ai_ruiz_chiechi_kögerler_et al._2018, title={Element-Selective Molecular Charge Transport Characteristics of Binuclear Copper(II)-Lanthanide(III) Complexes}, volume={57}, url={https://doi.org/10.1021/acs.inorgchem.8b01279}, DOI={10.1021/acs.inorgchem.8b01279}, abstractNote={A series of isostructural dinuclear 3d-4f complexes, isolated as [CuLn(L·SMe)2(OOCMe)2(NO3)]· xMeOH (Ln = Gd 1, Tb 2, Dy 3, and Y 4; x = 0.75-1) and comprising one acetate and two thioether-Schiff base (L·SMe-) bridging ligands based on 4-(methylthio)aniline and 2-hydroxy-3-methoxybenzaldehyde (HL·SMe = C15H15NO2S), was synthesized and fully characterized. The magnetic properties of the charge-neutral {CuLn} complexes are dominated by ferromagnetic CuII-LnIII exchange interactions. Large-area electron transport studies reveal that the average conductivity of robust, self-assembled {CuLn} monolayers on a gold substrate is significantly lower than that of common alkanethiolates. Theoretical calculations of transmission spectra of individual complexes 1 and 4 embedded between two metallic electrodes show that the molecular current-voltage ( I- V) characteristics are strongly influenced by electron transport through the Cu centers and thus fully independent of the lanthanide ion, in excellent agreement with the experimental I- V data for 1-4. The β-polarized transmission indicated by calculations of 1 and 4 points out their potential as spin filters. In addition, the reactivity of the title compound 1 with CuII in a square-pyramidal coordination environment toward methanolate and azide was examined, resulting in the formation of a linear trinuclear complex, [Cu2Na(L·SMe)4]NO3·3MeOH (5), characterized by antiferromagnetic exchange interactions between the two copper ions.}, number={15}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Schmitz, Sebastian and Kovalchuk, Andrew and Martín-Rodríguez, Alejandro and Leusen, Jan and Izarova, Natalya V. and Bourone, Svenja D. M. and Ai, Yong and Ruiz, Eliseo and Chiechi, Ryan C. and Kögerler, Paul and et al.}, year={2018}, month={Aug}, pages={9274–9285} }
 @article{liu_qiu_alessandri_qiu_portale_dong_talsma_ye_sengrian_souza_et al._2018, chapter={1704630}, title={Enhancing Molecular n-Type Doping of Donor–Acceptor Copolymers by Tailoring Side Chains}, volume={30}, url={http://dx.doi.org/10.1002/adma.201704630}, DOI={10.1002/adma.201704630}, abstractNote={In this contribution, for the first time, the molecular n‐doping of a donor–acceptor (D–A) copolymer achieving 200‐fold enhancement of electrical conductivity by rationally tailoring the side chains without changing its D–A backbone is successfully improved. Instead of the traditional alkyl side chains for poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl](NDI)‐alt‐5,5′‐(2,2′‐bithiophene)} (N2200), polar triethylene glycol type side chains is utilized and a high electrical conductivity of 0.17 S cm−1 after doping with (4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine is achieved, which is the highest reported value for n‐type D–A copolymers. Coarse‐grained molecular dynamics simulations indicate that the polar side chains can significantly reduce the clustering of dopant molecules and favor the dispersion of the dopant in the host matrix as compared to the traditional alkyl side chains. Accordingly, intimate contact between the host and dopant molecules in the NDI‐based copolymer with polar side chains facilitates molecular doping with increased doping efficiency and electrical conductivity. For the first time, a heterogeneous thermoelectric transport model for such a material is proposed, that is the percolation of charge carriers from conducting ordered regions through poorly conductive disordered regions, which provides pointers for further increase in the themoelectric properties of n‐type D–A copolymers.}, number={7}, journal={Advanced Materials}, author={Liu, Jian and Qiu, Li and Alessandri, Riccardo and Qiu, Xinkai and Portale, Giuseppe and Dong, JingJin and Talsma, Wytse and Ye, Gang and Sengrian, Aprizal Akbar and Souza, Paulo C. T. and et al.}, year={2018}, pages={1704630} }
 @article{shao_cui_duim_qiu_dong_brink_portale_chiechi_zhang_hou_et al._2018, title={Enhancing the Performance of the Half Tin and Half Lead Perovskite Solar Cells by Suppression of the Bulk and Interfacial Charge Recombination}, volume={30}, url={https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201803703}, DOI={10.1002/adma.201803703}, abstractNote={In this article it is investigated how the hole extraction layer (HEL) influence the charge recombination and performance in half tin and half lead (FASn0.5Pb0.5I3) based solar cells (HPSCs). FASn0.5Pb0.5I3 film grown on PEDOT:PSS displays a large number of pin‐holes and open grain boundaries, resulting in a high defect density and shunts in the perovskite film causing significant bulk and interfacial charge recombination in the HPSCs. By contrast, FASn0.5Pb0.5I3 films grown on PCP‐Na, an anionic conjugated polymer, show compact and pin‐hole free morphology over a large area, which effectively eliminates the shunts and trap states. Moreover, PCP‐Na is characterized by a higher work function, which determines a favorable energy alignment at the anode interface, enhancing the charge extraction. Consequently, both the interfacial and bulk charge recombination in devices using PCP‐Na HEL are considerably reduced giving rise to an overall improvement of all the device parameters. The HPSCs fabricated with this HEL display power conversion efficiency up to 16.27%, which is 40% higher than the efficiency of the control devices using PEDOT:PSS HEL (11.60%). Furthermore, PCP‐Na as HEL offers superior performance in larger area devices compared to PEDOT:PSS.}, number={35}, journal={Advanced Materials}, author={Shao, Shuyan and Cui, Yong and Duim, Herman and Qiu, Xinkai and Dong, JingJin and Brink, Gert H. and Portale, Giuseppe and Chiechi, Ryan C. and Zhang, Shaoqing and Hou, Jianhui and et al.}, year={2018}, pages={1803703} }
 @article{ai_kovalchuk_qiu_zhang_kumar_wang_kühnel_nørgaard_chiechi_2018, title={In-Place Modulation of Rectification in Tunneling Junctions Comprising Self-Assembled Monolayers}, volume={18}, url={https://doi.org/10.1021/acs.nanolett.8b03042}, DOI={10.1021/acs.nanolett.8b03042}, abstractNote={This paper describes tunneling junctions comprising self-assembled monolayers that can be converted between resistor and diode functionality in-place. The rectification ratio is affected by the hydration of densely packed carboxylic acid groups at the interface between the top-contact and the monolayer. We studied this process by treatment with water and a water scavenger using three different top-contacts, eutectic Ga–In (EGaIn), conducting-probe atomic force microscopy (CP-AFM), and reduced graphene oxide (rGO), demonstrating that the phenomena is molecular in nature and is not platform-speciffc. We propose a mechanism in which the tunneling junctions convert to diode behavior through the lowering of the LUMO, which is suffcient to bring it close to resonance at positive bias, potentially assisted by a Stark shift. This shift in energy is supported by calculations and a change in polarization observed by X-ray photoelectron spectroscopy and Kelvin probe measurements. We demonstrate light-driven modulation using spiropyran as a photoacid, suggesting that any chemical process that is coupled to the release of small molecules that can tightly bind carboxylic acid groups can be used as an external stimulus to modulate rectification. The ability to convert a tunneling junction reversibly between a diode and a resistor via an effect that is intrinsic to the molecules in the junction extends the possible applications of Molecular Electronics to reconfigurable circuits and other new functionalities that do not have direct analogs in conventional semiconductor devices.}, number={12}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Ai, Yong and Kovalchuk, Andrii and Qiu, Xinkai and Zhang, Yanxi and Kumar, Sumit and Wang, Xintai and Kühnel, Martin and Nørgaard, Kasper and Chiechi, Ryan C.}, year={2018}, month={Dec}, pages={7552–7559} }
 @article{liu_ye_zee_dong_qiu_liu_portale_chiechi_koster_2018, title={N-Type Organic Thermoelectrics of Donor-Acceptor Copolymers: Improved Power Factor by Molecular Tailoring of the Density of States}, volume={30}, ISSN={0935-9648}, url={http://dx.doi.org/10.1002/adma.201804290}, DOI={10.1002/adma.201804290}, abstractNote={It is demonstrated that the n‐type thermoelectric performance of donor–acceptor (D–A) copolymers can be enhanced by a factor of >1000 by tailoring the density of states (DOS). The DOS distribution is tailored by embedding sp2‐nitrogen atoms into the donor moiety of the D–A backbone. Consequently, an electrical conductivity of 1.8 S cm−1 and a power factor of 4.5 µW m−1 K−2 are achieved. Interestingly, an unusual sign switching (from negative to positive) of the Seebeck coefficient of the unmodified D–A copolymer at moderately high dopant loading is observed. A direct measurement of the DOS shows that the DOS distributions become less broad upon modifying the backbone in both pristine and doped states. Additionally, doping‐induced charge transfer complexes (CTC) states, which are energetically located below the neutral band, are observed in DOS of the doped unmodified D–A copolymer. It is proposed that charge transport through these CTC states is responsible for the positive Seebeck coefficients in this n‐doped system. This is supported by numerical simulation and temperature dependence of Seebeck coefficient. The work provides a unique insight into the fundamental understanding of molecular doping and sheds light on designing efficient n‐type OTE materials from a perspective of tailoring the DOS.}, number={44}, journal={Advanced Materials}, publisher={Wiley}, author={Liu, Jian and Ye, Gang and Zee, Bas van der and Dong, Jingjin and Qiu, Xinkai and Liu, Yuru and Portale, Giuseppe and Chiechi, Ryan C. and Koster, L. Jan Anton}, year={2018}, month={Sep}, pages={1804290} }
 @article{jia_famili_carlotti_liu_wang_grace_feng_wang_zhao_ding_et al._2018, title={Quantum interference mediated vertical molecular tunneling transistors}, volume={4}, ISSN={2375-2548}, url={http://dx.doi.org/10.1126/sciadv.aat8237}, DOI={10.1126/sciadv.aat8237}, abstractNote={We report graphene/self-assembly monolayer vertical molecular transistors operating in the quantum tunneling regime. Molecular transistors operating in the quantum tunneling regime represent potential electronic building blocks for future integrated circuits. However, due to their complex fabrication processes and poor stability, traditional molecular transistors can only operate stably at cryogenic temperatures. Here, through a combined experimental and theoretical investigation, we demonstrate a new design of vertical molecular tunneling transistors, with stable switching operations up to room temperature, formed from cross-plane graphene/self-assembled monolayer (SAM)/gold heterostructures. We show that vertical molecular junctions formed from pseudo-p-bis((4-(acetylthio)phenyl)ethynyl)-p-[2,2]cyclophane (PCP) SAMs exhibit destructive quantum interference (QI) effects, which are absent in 1,4-bis(((4-acetylthio)phenyl)ethynyl)benzene (OPE3) SAMs. Consequently, the zero-bias differential conductance of the former is only about 2% of the latter, resulting in an enhanced on-off current ratio for (PCP) SAMs. Field-effect control is achieved using an ionic liquid gate, whose strong vertical electric field penetrates through the graphene layer and tunes the energy levels of the SAMs. The resulting on-off current ratio achieved in PCP SAMs can reach up to ~330, about one order of magnitude higher than that of OPE3 SAMs. The demonstration of molecular junctions with combined QI effect and gate tunability represents a critical step toward functional devices in future molecular-scale electronics.}, number={10}, journal={Science Advances}, publisher={American Association for the Advancement of Science (AAAS)}, author={Jia, Chuancheng and Famili, Marjan and Carlotti, Marco and Liu, Yuan and Wang, Peiqi and Grace, Iain M. and Feng, Ziying and Wang, Yiliu and Zhao, Zipeng and Ding, Mengning and et al.}, year={2018}, month={Oct} }
 @article{qiu_ocampo_vries_putten_loznik_herrmann_chiechi_2018, title={Self-Regenerating Soft Biophotovoltaic Devices}, volume={10}, url={https://doi.org/10.1021/acsami.8b11115}, DOI={10.1021/acsami.8b11115}, abstractNote={This paper describes the fabrication of soft, stretchable biophotovoltaic devices that generate photocurrent from photosystem I (PSI) complexes that are self-assembled onto Au electrodes with a preferred orientation. Charge is collected by the direct injection of electrons into the Au electrode and the transport of holes through a redox couple to liquid eutectic gallium–indium (EGaIn) electrodes that are confined to microfluidic pseudochannels by arrays of posts. The pseudochannels are defined in a single fabrication step that leverages the non-Newtonian rheology of EGaIn. This strategy is extended to the fabrication of reticulated electrodes that are inherently stretchable. A simple shadow evaporation technique is used to increase the surface area of the Au electrodes by a factor of approximately 106 compared to planar electrodes. The power conversion efficiency of the biophotovoltaic devices decreases over time, presumably as the PSI complexes denature and/or detach from the Au electrodes. However, by circulating a solution of active PSI complexes the devices self-regenerate by mass action/self-assembly. These devices leverage simple fabrication techniques to produce complex function and prove that photovoltaic devices comprising PSI can retain the ability to regenerate, one of the most important functions of photosynthetic organisms.}, number={43}, journal={ACS Applied Materials & Interfaces}, publisher={American Chemical Society (ACS)}, author={Qiu, Xinkai and Ocampo, Olga Castañeda and Vries, Hendrik W. and Putten, Maikel and Loznik, Mark and Herrmann, Andreas and Chiechi, Ryan C.}, year={2018}, month={Oct}, pages={37625–37633} }
 @article{liu_qiu_portale_torabi_stuart_qiu_koopmans_chiechi_hummelen_koster_2018, title={Side-chain effects on N-type organic thermoelectrics: A case study of fullerene derivatives}, volume={52}, url={http://www.sciencedirect.com/science/article/pii/S2211285518305445}, DOI={https://doi.org/10.1016/j.nanoen.2018.07.056}, abstractNote={In this contribution, the two key parameters, the polarity and side chain length have been changed to study their effects on n-type organic thermoelectrics of a series of fullerene derivatives. Fullerene derivatives bearing either an alkyl side chain or ethylene glycol (EG) side chains of different lengths are used as the host molecules for molecular doping. It is found that the polar EG side chains can enable better miscibility with the polar dopant than the alkyl side chain, which leads to more than 5-fold enhancement of doping efficiency. Beyond the doping efficiency, another crucial parameter of molecular doping, the molecular order, is readily acquired by simultaneous control of the polarity and the length of the side chain. A polar side chain with an appropriate chain length can contribute to increasing Seebeck coefficients of doped fullerene derivatives more effectively than an alkyl side chain, likely due to the resultant good miscibility and high molecular order. As a result, an optimized power factor of 23.1 μW m-1 K-2 is achieved in the fullerene derivative with a tetraethylene glycol side chain. This represents one of the best n-type organic thermoelectrics. Additionally, EG side chains can improve the air stability of n-doped fullerene derivatives films as compared to an alkyl side chain. Our work sheds light on the design of side-chains in efficient n-type small molecules thermoelectric materials and contributes to the understanding of their thermoelectric properties.}, journal={Nano Energy}, author={Liu, Jian and Qiu, Li and Portale, Giuseppe and Torabi, Solmaz and Stuart, Marc C.A. and Qiu, Xinkai and Koopmans, Marten and Chiechi, Ryan C. and Hummelen, Jan C. and Koster, L. Jan Anton}, year={2018}, pages={183–191} }
 @article{liu_qiu_portale_torabi_stuart_qiu_koopmans_chiechi_hummelen_anton koster_2018, title={Side-chain effects on N-type organic thermoelectrics: A case study of fullerene derivatives}, volume={52}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85050674048&partnerID=MN8TOARS}, DOI={10.1016/j.nanoen.2018.07.056}, abstractNote={In this contribution, the two key parameters, the polarity and side chain length have been changed to study their effects on n-type organic thermoelectrics of a series of fullerene derivatives. Fullerene derivatives bearing either an alkyl side chain or ethylene glycol (EG) side chains of different lengths are used as the host molecules for molecular doping. It is found that the polar EG side chains can enable better miscibility with the polar dopant than the alkyl side chain, which leads to more than 5-fold enhancement of doping efficiency. Beyond the doping efficiency, another crucial parameter of molecular doping, the molecular order, is readily acquired by simultaneous control of the polarity and the length of the side chain. A polar side chain with an appropriate chain length can contribute to increasing Seebeck coefficients of doped fullerene derivatives more effectively than an alkyl side chain, likely due to the resultant good miscibility and high molecular order. As a result, an optimized power factor of 23.1 μW m-1 K-2 is achieved in the fullerene derivative with a tetraethylene glycol side chain. This represents one of the best n-type organic thermoelectrics. Additionally, EG side chains can improve the air stability of n-doped fullerene derivatives films as compared to an alkyl side chain. Our work sheds light on the design of side-chains in efficient n-type small molecules thermoelectric materials and contributes to the understanding of their thermoelectric properties.}, journal={Nano Energy}, author={Liu, J. and Qiu, L. and Portale, G. and Torabi, S. and Stuart, M.C.A. and Qiu, X. and Koopmans, M. and Chiechi, R.C. and Hummelen, J.C. and Anton Koster, L.J.}, year={2018}, pages={183–191} }
 @article{douvogianni_qiu_qiu_jahani_kooistra_hummelen_chiechi_2018, title={Soft non-Damaging Contacts formed from Eutectic Ga-In for the Accurate Determination of Dielectric Constants of Organic Materials}, volume={0}, url={https://doi.org/10.1021/acs.chemmater.8b02212}, DOI={10.1021/acs.chemmater.8b02212}, abstractNote={A method for accurately measuring the relative dielectric constant (εr) of thin films of soft, organic materials is described. The effects of the bombardment of these materials with hot Al atoms, the most commonly used top electrode, are mitigated by using electrodes fabricated from eutectic gallium–indium (EGaIn). The geometry of the electrode is defined by injection into microchannels to form stable structures that are nondamaging and that conform to the topology of the organic thin film. The εr of a series of references and new organic materials, polymers, and fullerene derivatives was derived from impedance spectroscopy measurements for both Al and EGaIn electrodes showing the specific limitations of Al with soft, organic materials and overcoming them with EGaIn to determine their dielectric properties and provide realistic values of εr.}, number={ja}, journal={Chemistry of Materials}, publisher={American Chemical Society (ACS)}, author={Douvogianni, Evgenia and Qiu, Xinkai and Qiu, Li and Jahani, Fatemeh and Kooistra, Floris B. and Hummelen, Jan C. and Chiechi, Ryan C.}, year={2018}, month={Aug}, pages={null} }
 @article{zhang_soni_krijger_gordiichuk_qiu_ye_jonkman_herrmann_zojer_zojer_et al._2018, title={Tunneling Probability Increases with Distance in Junctions Comprising Self-Assembled Monolayers of Oligothiophenes}, volume={140}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/jacs.8b09793}, DOI={10.1021/jacs.8b09793}, abstractNote={Molecular tunneling junctions should enable the tailoring of charge-transport at the quantum level through synthetic chemistry but are hindered by the dominance of the electrodes. We show that the frontier orbitals of molecules can be decoupled from the electrodes, preserving their relative energies in self-assembled monolayers even when a top-contact is applied. This decoupling leads to the remarkable observation of tunneling probabilities that increase with distance in a series of oligothiophenes, which we explain using a two-barrier tunneling model. This model is generalizable to any conjugated oligomers for which the frontier orbital gap can be determined and predicts that the molecular orbitals that dominate tunneling charge-transport can be positioned via molecular design rather than by domination of Fermi-level pinning arising from strong hybridization. The ability to preserve the electronic structure of molecules in tunneling junctions facilitates the application of well-established synthetic design rules to tailor the properties of molecular-electronic devices.}, number={44}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Zhang, Yanxi and Soni, Saurabh and Krijger, Theodorus L. and Gordiichuk, Pavlo and Qiu, Xinkai and Ye, Gang and Jonkman, Harry T. and Herrmann, Andreas and Zojer, Karin and Zojer, Egbert and et al.}, year={2018}, month={Oct}, pages={15048–15055} }
 @article{carlotti_soni_kumar_ai_sauter_zharnikov_chiechi_2018, title={Two-Terminal Molecular Memory via Reversible Switching of Quantum Interference Features in Tunneling Junctions}, volume={0}, url={https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201807879}, DOI={10.1002/anie.201807879}, abstractNote={Abstract Large‐area molecular tunneling junctions comprising self‐assembled monolayers of redox‐active molecules are described that exhibit two‐terminal bias switching. The as‐prepared monolayers undergo partial charge transfer to the underlying metal substrate (Au, Pt, or Ag), which converts their cores from a quinoid to a hydroquinoid form. The resulting rearomatization converts the bond topology from a cross‐conjugated to a linearly conjugated π system. The cross‐conjugated form correlates to the appearance of an interference feature in the transmission spectrum that vanishes for the linearly conjugated form. Owing to the presence of electron‐withdrawing nitrile groups, the reduction potential and the interference feature lie close to the work function and Fermi level of the metallic substrate. We exploited the relationship between conjugation patterns and quantum interference to create nonvolatile memory in proto‐devices using eutectic Ga–In as the top contact.}, number={ja}, journal={Angewandte Chemie International Edition}, author={Carlotti, Marco and Soni, Saurabh and Kumar, Sumit and Ai, Yong and Sauter, Eric and Zharnikov, Michael and Chiechi, Ryan C.}, year={2018}, month={Sep} }
 @article{carlotti_soni_kumar_ai_sauter_zharnikov_chiechi_2018, title={Two‐Terminal Molecular Memory through Reversible Switching of Quantum Interference Features in Tunneling Junctions}, url={https://doi.org/10.1002/ange.201807879}, DOI={10.1002/ange.201807879}, abstractNote={This paper describes large-area molecular tunneling junctions comprising self-assembled monolayers of redox-active molecules that exhibit two-terminal bias switching. The as-prepared monolayers undergo partial charge-transfer to the underlying metal substrate (Au, Pt or Ag) that converts their cores from a quinoid to hydroquinoid form. The resulting rearomatization converts the bond topology from a cross-conjugated to linearly-conjugated π system. The cross-conjugated form correlates to appearance of an interference feature in the transmission spectrum that vanishes in the linear-conjugated form. Due to the presence of electron-withdrawing 1 10.1002/anie.201807879 A cc ep te d M an us cr ip t Angewandte Chemie International Edition This article is protected by copyright. All rights reserved. nitrile groups, the reduction potential and the interference feature lie close the work function and Fermi level of the metallic substrate. The relationship between conjugation patterns and quantum interference is well-studied. We exploit this relationship to create non-volatile memory in proto-devices using eutectic Ga-In as the top-contact. The underlying switching mechanism reorders bond topology without changing connectivity or altering the tunneling distance or thickness of the monolayer. These results are a proof-of-concept for switching quantum interference features on and off via in operando redox chemistry.}, journal={Angewandte Chemie}, author={Carlotti, Marco and Soni, Saurabh and Kumar, Sumit and Ai, Yong and Sauter, Eric and Zharnikov, Michael and Chiechi, Ryan C.}, year={2018}, month={Nov} }
 @article{qiu_liu_alessandri_qiu_koopmans_havenith_marrink_chiechi_koster_hummelen_2017, title={Enhancing doping efficiency by improving host-dopant miscibility for fullerene-based n-type thermoelectrics}, volume={5}, url={https://doi.org/10.1039/C7TA06609K}, DOI={10.1039/C7TA06609K}, abstractNote={This paper describes a promising n-type doping system with high performance for thermoelectric applications. By introducing the polar triethylene glycol (TEG) side chain onto both fullerene host (PTEG-1) and dopant (TEG-DMBI) materials, the TEG-DMBI doped PTEG-1 films obtained through solution processing provide a better miscibility compared with films doped with commercially available N-DMBI (bearing a dimethylamino group instead of TEG), as determined by phase imaging AFM (atomic force microscopy) measurements and coarse-grain molecular dynamics simulations, leading to high doping efficiency up to 18% at 20 mol% doping concentration and thus high carrier density and mobility, which are critical to the electrical conductivity. Therefore a record power factor of 19.1 μW m−1 K−2 is obtained with an electrical conductivity of 1.81 S cm−1, one of the highest values reported for solution processable fullerene derivatives as n-type organic materials for thermoelectric applications to date.}, number={40}, journal={J. Mater. Chem. A}, publisher={Royal Society of Chemistry (RSC)}, author={Qiu, Li and Liu, Jian and Alessandri, Riccardo and Qiu, Xinkai and Koopmans, Marten and Havenith, Remco W. A. and Marrink, Siewert J. and Chiechi, Ryan C. and Koster, L. Jan Anton and Hummelen, Jan C.}, year={2017}, pages={21234–21241} }
 @article{zhou_doumon_abdu-aguye_bartesaghi_loi_koster_chiechi_hummelen_2017, title={High-quality conjugated polymers via one-pot Suzuki–Miyaura homopolymerization}, volume={7}, url={https://doi.org/10.1039/C7RA03539J}, DOI={10.1039/C7RA03539J}, abstractNote={This paper describes a one-pot Suzuki–Miyaura homopolymerization that involves in situ borylation/cross coupling of dibrominated donor–acceptor conjugated macromonomers, in contrast to the standard Stille copolymerization of thienosilole and isoindigo monomers. Reaction kinetics investigation reveals that bis(pinacolato)diboron promotes an efficient polymerization. The homopolymer showed blue-shifted absorption compared to the Stille copolymer, which is rationalized by quantum chemical calculations of a series of oligomers containing various donor–acceptor configurations. The calculations suggest that the homopolymerization of asymmetrical macromonomers likely introduced both acceptor–acceptor and donor–donor segments into the backbone. The acceptor–acceptor segment is found to contribute mostly to the blue-shift of maximum absorption wavelength. Furthermore, detailed analysis of MALDI-TOF (matrix-assisted laser-desorption ionization-time of flight) spectra of these two polymers indicated that while the homopolymer is well defined, the Stille copolymer is end-capped mostly with the thienosilole moieties and/or methyl groups, implicating that destannylation and methyl transfer are the most-likely chain-termination pathways that limit high molecular weight. This is in sharp contrast to the homopolymerization, where chain-terminators are required to control the molecular weight for obtaining soluble material. The photovoltaic performances of bulk-heterojunction solar cells based on these polymers are compared.}, number={44}, journal={RSC Advances}, publisher={Royal Society of Chemistry (RSC)}, author={Zhou, Difei and Doumon, Nutifafa Y. and Abdu-Aguye, Mustapha and Bartesaghi, Davide and Loi, Maria A. and Koster, L. Jan Anton and Chiechi, Ryan C. and Hummelen, Jan C.}, year={2017}, pages={27762–27769} }
 @article{zhang_qiu_gordiichuk_soni_krijger_herrmann_chiechi_2017, title={Mechanically and Electrically Robust Self-Assembled Monolayers for Large-Area Tunneling Junctions}, volume={121}, url={https://doi.org/10.1021/acs.jpcc.7b03853}, DOI={10.1021/acs.jpcc.7b03853}, abstractNote={This paper examines the relationship between mechanical deformation and the electronic properties of self-assembled monolayers (SAMs) of the oligothiophene 4-([2,2′:5′,2″:5″,2‴-quaterthiophen]-5-yl)butane-1-thiol (T4C4) in tunneling junctions using conductive probe atomic force microscopy (CP-AFM) and eutectic Ga–In (EGaIn). We compared shifts in conductivity, transition voltages of T4C4 with increasing AFM tip loading force to alkanethiolates. While these shifts result from an increasing tilt angle from penetration of the SAM by the AFM tip for the latter, we ascribe them to distortions of the π system present in T4C4, which is more mechanically robust than alkanethiolates of comparable length; SAMs comprising T4C4 shows about five times higher Young’s modulus than alkanethiolates. Density functional theory calculations confirm that mechanical deformations shift the barrier height due to changes in the frontier orbitals caused by small rearrangements to the conformation of the quaterthiophene moiety. The mechanical robustness of T4C4 manifests as an increased tolerance to high bias in large-area EGaIn junctions suggesting that electrostatic pressure plays a significant role in the shorting of molecular junctions at high bias.}, number={27}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Zhang, Yanxi and Qiu, Xinkai and Gordiichuk, Pavlo and Soni, Saurabh and Krijger, Theodorus L. and Herrmann, Andreas and Chiechi, Ryan C.}, year={2017}, month={Jul}, pages={14920–14928} }
 @article{gordiichuk_pesce_ocampo_marcozzi_wetzelaer_paul_loznik_gloukhikh_richter_chiechi_et al._2017, title={Orientation and Incorporation of Photosystem I in Bioelectronics Devices Enabled by Phage Display}, volume={1}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85011072101&partnerID=MN8TOARS}, DOI={10.1002/advs.201600393}, abstractNote={Interfacing proteins with electrode surfaces is important for the field of bioelectronics. Here, a general concept based on phage display is presented to evolve small peptide binders for immobilizing and orienting large protein complexes on semiconducting substrates. Employing this method, photosystem I is incorporated into solid‐state biophotovoltaic cells.}, number={5}, journal={Advanced Science}, publisher={Wiley-Blackwell}, author={Gordiichuk, Pavlo and Pesce, Diego and Ocampo, Olga E. Castañeda and Marcozzi, Alessio and Wetzelaer, Gert-Jan A. H. and Paul, Avishek and Loznik, Mark and Gloukhikh, Ekaterina and Richter, Shachar and Chiechi, Ryan C. and et al.}, year={2017}, month={Jan}, pages={1600393} }
 @article{qiu_zhang_krijger_qiu_hof_hummelen_chiechi_2017, title={Rectification of current responds to incorporation of fullerenes into mixed-monolayers of alkanethiolates in tunneling junctions}, volume={8}, url={https://doi.org/10.1039/C6SC04799H}, DOI={10.1039/c6sc04799h}, abstractNote={This paper describes the rectification of current through molecular junctions comprising self-assembled monolayers of decanethiolate through the incorporation of C60 fullerene moieties in junctions using eutectic Ga–In (EGaIn) and Au conducting probe AFM top-contacts.}, number={3}, journal={Chem. Sci.}, publisher={Royal Society of Chemistry (RSC)}, author={Qiu, Li and Zhang, Yanxi and Krijger, Theodorus L. and Qiu, Xinkai and Hof, Patrick and Hummelen, Jan C. and Chiechi, Ryan C.}, year={2017}, pages={2365–2372} }
 @article{doumon_wang_chiechi_koster_2017, title={Relating polymer chemical structure to the stability of polymer:fullerene solar cells}, volume={5}, url={https://doi.org/10.1039/C7TC01455D}, DOI={10.1039/C7TC01455D}, abstractNote={The design of novel polymers has brought more attention to bulk heterojunction polymer:fullerene solar cells in the past decade. A typical example is the synthesis, through chemical structure engineering, of the benzodithiophene-co-thieno[3,4-b]thiophene (BDT-TT) polymers leading to power conversion efficiency of over 10%. In this work, we study the stability for a set of PBDT-TT polymers. We conduct a systematic UV-degradation study on the solar cells. Most importantly, the paper shows clearly the effect of polymer chemical structure on the UV-degradation pathway of the solar cells. We find that based on the polymer chemical structure, solar cells of polymers with alkoxy side chains are more stable (<20% loss in PCE) than those with alkylthienyl side chains (∼48% loss in PCE) over the period of study. These findings pave the way for new materials that yield efficient as well as stable organic solar cells.}, number={26}, journal={Journal of Materials Chemistry C}, publisher={Royal Society of Chemistry (RSC)}, author={Doumon, Nutifafa Y. and Wang, G. and Chiechi, Ryan C. and Koster, L. Jan Anton}, year={2017}, pages={6611–6619} }
 @article{kalkman_zhang_monachino_mathwig_kamminga_pourhossein_oomen_stratmann_zhao_oijen_et al._2016, title={Bisecting Microfluidic Channels with Metallic Nanowires Fabricated by Nanoskiving.}, volume={2}, url={http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&id=26836373&retmode=ref&cmd=prlinks}, DOI={10.1021/acsnano.5b07996}, abstractNote={This paper describes the fabrication of millimeter-long gold nanowires that bisect the center of microfluidic channels. We fabricated the nanowires by nanoskiving and then suspended them over a trench in a glass structure. The channel was sealed by bonding it to a complementary poly(dimethylsiloxane) structure. The resulting structures place the nanowires in the region of highest flow, as opposed to the walls, where it approaches zero, and expose their entire surface area to fluid. We demonstrate active functionality, by constructing a hot-wire anemometer to measure flow through determining the change in resistance of the nanowire as a function of heat dissipation at low voltage (<5 V). Further, passive functionality is demonstrated by visualizing individual, fluorescently labeled DNA molecules attached to the wires. We measure rates of flow and show that, compared to surface-bound DNA strands, elongation saturates at lower rates of flow and background fluorescence from nonspecific binding is reduced.}, number={2}, journal={ACS Nano}, author={Kalkman, Gerard A and Zhang, Yanxi and Monachino, Enrico and Mathwig, Klaus and Kamminga, Machteld E and Pourhossein, Parisa and Oomen, Pieter E and Stratmann, Sarah A and Zhao, Zhiyuan and Oijen, Antoine M and et al.}, year={2016}, month={Feb}, pages={2852–2859} }
 @article{bartesaghi_ye_chiechi_koster_2016, title={Compatibility of PTB7 and [70]PCBM as a Key Factor for the Stability of PTB7:[70]PCBM Solar Cells}, volume={4}, url={http://onlinelibrary.wiley.com/doi/10.1002/aenm.201502338/full}, DOI={10.1002/aenm.201502338}, abstractNote={The rapid degradation of organic photovoltaic (OPV) devices compared to conventional inorganic solar cells is one of the critical issues that have to be solved in order to make OPV a competitive commercial technology. The understanding of the fundamental mechanisms that reduce the power conversion efficiency (PCE) over time is beneficial for the design of new materials with enhanced stability. This paper focuses on bulk heterojunction organic solar cells based on thieno [3,4‐b] thiophene‐alt‐benzodithiophene (PTB7) mixed with [6,6]‐phenyl‐C71‐butyric acid methyl esther ([70]PCBM). In spite of being promising in terms of PCE, devices based on this blend are unstable and have a short lifetime. When exposed to light in inert atmosphere, the PCE drops by 15% in less than 1 h and by 35% in 8 h; this degradation is induced by the ultraviolet (UV) part of the spectrum. This paper analyzes the effect induced by UV light on the transport of charges in PTB7:[70]PCBM. Contrary to expectations, the electron transport shows evidence of trapping, while the transport of holes appears unaffected. Furthermore, it is proven that the loss of PCE is due to a reaction between PTB7 and [70]PCBM, while the intrinsic instability of the polymer plays a marginal role.}, number={13}, journal={Advanced Energy Materials}, author={Bartesaghi, Davide and Ye, Gang and Chiechi, Ryan C and Koster, L Jan Anton}, year={2016}, month={Apr} }
 @article{carlotti_kovalchuk_wächter_qiu_zharnikov_chiechi_2016, title={Conformation-driven quantum interference effects mediated by through-space conjugation in self-assembled monolayers.}, volume={7}, url={http://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&id=27996036&retmode=ref&cmd=prlinks}, DOI={10.1038/ncomms13904}, abstractNote={Tunnelling currents through tunnelling junctions comprising molecules with cross-conjugation are markedly lower than for their linearly conjugated analogues. This effect has been shown experimentally and theoretically to arise from destructive quantum interference, which is understood to be an intrinsic, electronic property of molecules. Here we show experimental evidence of conformation-driven interference effects by examining through-space conjugation in which π-conjugated fragments are arranged face-on or edge-on in sufficiently close proximity to interact through space. Observing these effects in the latter requires trapping molecules in a non-equilibrium conformation closely resembling the X-ray crystal structure, which we accomplish using self-assembled monolayers to construct bottom-up, large-area tunnelling junctions. In contrast, interference effects are completely absent in zero-bias simulations on the equilibrium, gas-phase conformation, establishing through-space conjugation as both of fundamental interest and as a potential tool for tuning tunnelling charge-transport in large-area, solid-state molecular-electronic devices.}, journal={Nature communications}, publisher={Springer Nature}, author={Carlotti, Marco and Kovalchuk, Andrii and Wächter, Tobias and Qiu, Xinkai and Zharnikov, Michael and Chiechi, Ryan C.}, year={2016}, month={Dec}, pages={13904} }
 @article{kovalchuk_egger_abu-husein_zojer_terfort_chiechi_2016, title={Correction: Dipole-induced asymmetric conduction in tunneling junctions comprising self-assembled monolayers}, volume={6}, DOI={10.1039/c6ra90069k}, abstractNote={Correction for ‘Dipole-induced asymmetric conduction in tunneling junctions comprising self-assembled monolayers’ by Andrii Kovalchuk et al., RSC Adv., 2016, 6, 69479–69483.}, number={80}, journal={RSC Adv.}, publisher={Royal Society of Chemistry (RSC)}, author={Kovalchuk, Andrii and Egger, David A. and Abu-Husein, Tarek and Zojer, Egbert and Terfort, Andreas and Chiechi, Ryan C.}, year={2016}, pages={76110–76112} }
 @article{kovalchuk_egger_abu-husein_zojer_terfort_chiechi_2016, title={Dipole-induced asymmetric conduction in tunneling junctions comprising self-assembled monolayers}, volume={6}, url={http://pubs.rsc.org/en/content/articlehtml/2016/ra/c6ra10471a}, DOI={10.1039/C6RA10471A}, abstractNote={This paper describes the observation of asymmetric conductance in the form of differing ratios of current density (J) as a function of voltage (|V|) in tunneling junctions comprising self-assembled monolayers on gold using eutectic Ga–In as a top contact. Monolayers comprising compounds with nearly identical physical and electronic properties show opposite directions of this asymmetry. We tested the statistical significance of the effect and ascribed it to the collective action of embedded dipoles arising from pyrimidyl groups that are arranged parallel or antiparallel to the transport direction. We ascribe the effect to the bias-induced (de)localization of the frontier states that mitigate transport.}, number={73}, journal={Rsc Advances}, publisher={The Royal Society of Chemistry}, author={Kovalchuk, Andrii and Egger, David A. and Abu-Husein, Tarek and Zojer, Egbert and Terfort, Andreas and Chiechi, Ryan C.}, year={2016}, month={Jul}, pages={69479–69483} }
 @inproceedings{oomen_zhang_chiechi_verpoorte_mathwig_2016, title={Electrochemical sensing with a suspended Single nanowire}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85014147041&partnerID=MN8TOARS}, booktitle={20th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2016}, author={Oomen, P.E. and Zhang, Y. and Chiechi, R.C. and Verpoorte, E. and Mathwig, K.}, year={2016}, pages={102–103} }
 @article{zhou_zhao_yu_ai_möhwald_chiechi_yang_zhang_2016, title={From 1D to 3D: Tunable Sub-10 nm Gaps in Large Area Devices.}, volume={2}, url={http://doi.wiley.com/10.1002/adma.201505929}, DOI={10.1002/adma.201505929}, abstractNote={Tunable sub-10 nm 1D nanogaps are fabricated based on nanoskiving. The electric field in different sized nanogaps is investigated theoretically and experimentally, yielding nonmonotonic dependence and an optimized gap-width (5 nm). 2D nanogap arrays are fabricated to pack denser gaps combining surface patterning techniques. Innovatively, 3D multistory nanogaps are built via a stacking procedure, processing higher integration, and much improved electric field.}, number={15}, journal={Advanced materials (Deerfield Beach, Fla.)}, author={Zhou, Ziwei and Zhao, Zhiyuan and Yu, Ye and Ai, Bin and Möhwald, Helmuth and Chiechi, Ryan C and Yang, Joel K W and Zhang, Gang}, year={2016}, month={Feb}, pages={n/a-n/a} }
 @article{kumar_herpt_gengler_feringa_rudolf_chiechi_2016, title={Mixed Monolayers of Spiropyrans Maximize Tunneling Conductance Switching by Photoisomerization at the Molecule–Electrode Interface in EGaIn Junctions}, volume={138}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84989237413&partnerID=MN8TOARS}, DOI={10.1021/jacs.6b06806}, abstractNote={This paper describes the photoinduced switching of conductance in tunneling junctions comprising self-assembled monolayers of a spiropyran moiety using eutectic Ga–In top contacts. Despite separation of the spiropyran unit from the electrode by a long alkyl ester chain, we observe an increase in the current density J of a factor of 35 at 1 V when the closed form is irradiated with UV light to induce the ring-opening reaction, one of the highest switching ratios reported for junctions incorporating self-assembled monolayers. The magnitude of switching of hexanethiol mixed monolayers was higher than that of pure spiropyran monolayers. The first switching event recovers 100% of the initial value of J and in the mixed-monolayers subsequent dampening is not the result of degradation of the monolayer. The observation of increased conductivity is supported by zero-bias DFT calculations showing a change in the localization of the density of states near the Fermi level as well as by simulated transmission spectra revealing positive resonances that broaden and shift toward the Fermi level in the open form.}, number={38}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Kumar, Sumit and Herpt, Jochem T. and Gengler, Régis Y. N. and Feringa, Ben L. and Rudolf, Petra and Chiechi, Ryan C.}, year={2016}, month={Sep}, pages={12519–12526} }
 @article{pourhossein_vijayaraghavan_meskers_chiechi_2016, title={Optical modulation of nano-gap tunnelling junctions comprising self-assembled monolayers of hemicyanine dyes.}, volume={7}, url={http://www.nature.com/doifinder/10.1038/ncomms11749}, DOI={10.1038/ncomms11749}, abstractNote={Light-driven conductance switching in molecular tunnelling junctions that relies on photoisomerization is constrained by the limitations of kinetic traps and either by the sterics of rearranging atoms in a densely packed monolayer or the small absorbance of individual molecules. Here we demonstrate light-driven conductance gating; devices comprising monolayers of hemicyanine dyes trapped between two metallic nanowires exhibit higher conductance under irradiation than in the dark. The modulation of the tunnelling current occurs faster than the timescale of the measurement (∼1 min). We propose a mechanism in which a fraction of molecules enters an excited state that brings the conjugated portion of the monolayer into resonance with the electrodes. This mechanism is supported by calculations showing the delocalization of molecular orbitals near the Fermi energy in the excited and cationic states, but not the ground state and a reasonable change in conductance with respect to the effective barrier width.}, journal={Nature communications}, publisher={Nature Publishing Group}, author={Pourhossein, Parisa and Vijayaraghavan, Ratheesh K and Meskers, Stefan C J and Chiechi, Ryan C}, year={2016}, pages={11749} }
 @article{carlotti_degen_zhang_chiechi_2016, title={Pronounced Environmental Effects on Injection Currents in EGaIn Tunneling Junctions Comprising Self-Assembled Monolayers}, volume={120}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84987943621&partnerID=MN8TOARS}, DOI={10.1021/acs.jpcc.6b07089}, abstractNote={Large-area tunneling junctions using eutectic Ga–In (EGaIn) as a top contact have proven to be a robust, reproducible, and technologically relevant platform for molecular electronics. Thus far, the majority of studies have focused on saturated molecules with backbones consisting mainly of alkanes in which the frontier orbitals are either highly localized or energetically inaccessible. We show that self-assembled monolayers of wire-like oligophenyleneethynylenes (OPEs), which are fully conjugated, only exhibit length-dependent tunneling behavior in a low-O2 environment. We attribute this unexpected behavior to the sensitivity of injection current on environment. We conclude that, contrary to previous reports, the self-limiting layer of Ga2O3 strongly influences transport properties and that the effect is related to the wetting behavior of the electrode. This result sheds light on the nature of the electrode–molecule interface and suggests that adhesive forces play a significant role in tunneling charge-transport in large-area molecular junctions.}, number={36}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Carlotti, Marco and Degen, Maarten and Zhang, Yanxi and Chiechi, Ryan C.}, year={2016}, month={Sep}, pages={20437–20445} }
 @article{zhao_zhou_zhang_chiechi_2016, title={Transfer and control of the orientation of 3D nanostructures fabricated by nanoskiving}, volume={1}, url={http://pubs.rsc.org/en/content/articlehtml/2016/nh/c6nh00099a}, DOI={10.1039/C6NH00099A}, abstractNote={This communication describes the transfer and stacking of slabs of epoxy containing nanostructures fabricated by nanoskiving. Removal of the sacrificial layer and epoxy matrices produces 3D nanostructures via control over the position and alignment of each sequential layer. The process uses mild etchants and transfers the nanoskived features without wrinkling or damage. We demonstrate the utility of this method of transfer with aligned and intersecting nanowires and arrays of nano-holes and crescents.}, number={6}, journal={Nanoscale Horizons}, publisher={The Royal Society of Chemistry}, author={Zhao, Zhiyuan and Zhou, Ziwei and Zhang, Gang and Chiechi, Ryan C.}, year={2016}, pages={473–479} }
 @article{kovalchuk_abu-husein_fracasso_egger_zojer_zharnikov_terfort_chiechi_2016, title={Transition voltages respond to synthetic reorientation of embedded dipoles in self-assembled monolayers}, volume={7}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84951035828&partnerID=MN8TOARS}, DOI={10.1039/c5sc03097h}, abstractNote={Transition voltages respond to the collective action of dipole moments embedded in self-assembled monolayers.}, number={1}, journal={Chem. Sci.}, publisher={Royal Society of Chemistry (RSC)}, author={Kovalchuk, Andrii and Abu-Husein, Tarek and Fracasso, Davide and Egger, David A. and Zojer, Egbert and Zharnikov, Michael and Terfort, Andreas and Chiechi, Ryan C.}, year={2016}, pages={781–787} }
 @article{voortman_bartesaghi_koster_chiechi_2015, title={Cross-Conjugated n-Dopable Aromatic Polyketone}, volume={48}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84944081108&partnerID=MN8TOARS}, DOI={10.1021/acs.macromol.5b01387}, abstractNote={This paper describes the synthesis and characterization of a high molecular weight cross-conjugated polyketone synthesized via scalable Friedel–Crafts chemistry. Cross-conjugated polyketones are precursors to conjugated polyions; they become orders of magnitude more conductive after a two-electron reduction and demonstrate reversible spinless doping upon protonation with acids. Cross-conjugated polyketones are a new polymer platform that possess the same optoelectronic tunability as conventional polymers but with excellent thermal and oxidative stability. We constructed a proof-of-concept organic light-emitting diode device and demonstrate that a cross-conjugated polyketone can be successfully used as an n-dopable semiconducting material.}, number={19}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Voortman, Thomas P. and Bartesaghi, Davide and Koster, L. Jan Anton and Chiechi, Ryan C.}, year={2015}, month={Oct}, pages={7007–7014} }
 @article{castañeda ocampo_gordiichuk_catarci_gautier_herrmann_chiechi_2015, title={Mechanism of Orientation-Dependent Asymmetric Charge Transport in Tunneling Junctions Comprising Photosystem I.}, volume={137}, url={http://pubs.acs.org/doi/10.1021/jacs.5b01241}, DOI={10.1021/jacs.5b01241}, abstractNote={Recently, photoactive proteins have gained a lot of attention due to their incorporation into bioinspired (photo)electrochemical and solar cells. This paper describes the measurement of the asymmetry of current transport of self-assembled monolayers (SAMs) of the entire photosystem I (PSI) protein complex (not the isolated reaction center, RCI), on two different “director SAMs” supported by ultraflat Au substrates. The director SAMs induce the preferential orientation of PSI, which manifest as asymmetry in tunneling charge-transport. We measured the oriented SAMs of PSI using eutectic Ga–In (EGaIn), a large-area technique, and conducting probe atomic force microscopy (CP-AFM), a single-complex technique, and determined that the transport properties are comparable. By varying the temperatures at which the measurements were performed, we found that there is no measurable dependence of the current on temperature from ±0.1 to ±1.0 V bias, and thus, we suggest tunneling as the mechanism for transport; there are no thermally activated (e.g., hopping) processes. Therefore, it is likely that relaxation in the electron transport chain is not responsible for the asymmetry in the conductance of SAMs of PSI complexes in these junctions, which we ascribe instead to the presence of a large, net dipole moment present in PSI.}, number={26}, journal={Journal of the American Chemical Society}, author={Castañeda Ocampo, Olga E and Gordiichuk, Pavlo and Catarci, Stefano and Gautier, Daniel A and Herrmann, Andreas and Chiechi, Ryan C}, year={2015}, month={Jul}, pages={8419–8427} }
 @article{torabi_jahani_van severen_kanimozhi_patil_havenith_chiechi_lutsen_vanderzande_cleij_et al._2015, title={Strategy for Enhancing the Dielectric Constant of Organic Semiconductors Without Sacrificing Charge Carrier Mobility and Solubility}, volume={25}, url={http://onlinelibrary.wiley.com/doi/10.1002/adfm.201402244/full}, DOI={10.1002/adfm.201402244}, abstractNote={Current organic semiconductors for organic photovoltaics (OPV) have relative dielectric constants (relative permittivities, ε r) in the range of 2–4. As a consequence, Coulombically bound electron‐hole pairs (excitons) are produced upon absorption of light, giving rise to limited power conversion efficiencies. We introduce a strategy to enhance ε r of well‐known donors and acceptors without breaking conjugation, degrading charge carrier mobility or altering the transport gap. The ability of ethylene glycol (EG) repeating units to rapidly reorient their dipoles with the charge redistributions in the environment was proven via density functional theory (DFT) calculations. Fullerene derivatives functionalized with triethylene glycol side chains were studied for the enhancement of ε r together with poly(p‐phenylene vinylene) and diketopyrrolopyrrole based polymers functionalized with similar side chains. The polymers showed a doubling of ε r with respect to their reference polymers in identical backbone. Fullerene derivatives presented enhancements up to 6 compared with phenyl‐C61‐butyric acid methyl ester (PCBM) as the reference. Importantly, the applied modifications did not affect the mobility of electrons and holes and provided excellent solubility in common organic solvents.}, number={1}, journal={Advanced Functional Materials}, author={Torabi, Solmaz and Jahani, Fatemeh and Van Severen, Ineke and Kanimozhi, Catherine and Patil, Satish and Havenith, Remco W A and Chiechi, Ryan C and Lutsen, Laurence and Vanderzande, Dirk J M and Cleij, Thomas J and et al.}, year={2015}, month={Jan}, pages={150–157} }
 @article{abu-husein_schuster_egger_kind_santowski_wiesner_chiechi_zojer_terfort_zharnikov_2015, title={The Effects of Embedded Dipoles in Aromatic Self-Assembled Monolayers}, volume={25}, url={http://onlinelibrary.wiley.com/doi/10.1002/adfm.201500899/full}, DOI={10.1002/adfm.201500899}, abstractNote={Using a representative model system, here electronic and structural properties of aromatic self‐assembled monolayers (SAMs) are described that contain an embedded, dipolar group. As polar unit, pyrimidine is used, with its orientation in the molecular backbone and, consequently, the direction of the embedded dipole moment being varied. The electronic and structural properties of these embedded‐dipole SAMs are thoroughly analyzed using a number of complementary characterization techniques combined with quantum‐mechanical modeling. It is shown that such mid‐chain‐substituted monolayers are highly interesting from both fundamental and application viewpoints, as the dipolar groups are found to induce a potential discontinuity inside the monolayer, electrostatically shifting the core‐level energies in the regions above and below the dipoles relative to one another. These SAMs also allow for tuning the substrate work function in a controlled manner independent of the docking chemistry and, most importantly, without modifying the SAM‐ambient interface.}, number={25}, journal={Advanced Functional Materials}, author={Abu-Husein, Tarek and Schuster, Swen and Egger, David A and Kind, Martin and Santowski, Tobias and Wiesner, Adrian and Chiechi, Ryan C and Zojer, Egbert and Terfort, Andreas and Zharnikov, Michael}, year={2015}, month={Jul}, pages={3943–3957} }
 @article{voortman_chiechi_2015, title={Thin Films Formed from Conjugated Polymers with Ionic, Water-Soluble Backbones.}, volume={2}, url={http://pubs.acs.org/doi/abs/10.1021/acsami.5b00564}, DOI={10.1021/acsami.5b00564}, abstractNote={This paper compares the morphologies of films of conjugated polymers in which the backbone (main chain) and pendant groups are varied between ionic/hydrophilic and aliphatic/hydrophobic. We observe that conjugated polymers in which the pendant groups and backbone are matched, either ionic-ionic or hydrophobic-hydrophobic, form smooth, structured, homogeneous films from water (ionic) or tetrahydrofuran (hydrophobic). Mismatched conjugated polymers, by contrast, form inhomogeneous films with rough topologies. The polymers with ionic backbone chains are conjugated polyions (conjugated polymers with closed-shell charges in the backbone), which are semiconducting materials with tunable bad-gaps, not unlike uncharged conjugated polymers.}, number={51}, journal={Acs Applied Materials & Interfaces}, publisher={American Chemical Society}, author={Voortman, Thomas P and Chiechi, Ryan C}, year={2015}, month={Feb}, pages={150227143007001} }
 @article{zhang_zhao_fracasso_chiechi_2014, title={Bottom-Up Molecular Tunneling Junctions Formed by Self-Assembly}, volume={54}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84903214296&partnerID=MN8TOARS}, DOI={10.1002/ijch.201400033}, abstractNote={This Minireview focuses on bottom-up molecular tunneling junctions - a fundamental component of molecular electronics - that are formed by self-assembly. These junctions are part of devices that, in part, fabricate themselves, and therefore, are particularly dependent on the chemistry of the molecules selected. The discussion covers the history of these junctions as well as recent advances. It is broken into the broad categories of conformal and rigid contacts, which place different constraints on the molecules used to form the junctions. The intention of this Minireview is to give an overview of research efforts in molecular electronics that is targeted at chemists, whose efforts are playing an increasingly important role in molecular electronics.}, number={5-6}, journal={Isr. J. Chem.}, publisher={Wiley-Blackwell}, author={Zhang, Yanxi and Zhao, Zhiyuan and Fracasso, Davide and Chiechi, Ryan C.}, year={2014}, month={May}, pages={513–533} }
 @article{jahani_torabi_chiechi_koster_hummelen_2014, title={Fullerene derivatives with increased dielectric constants}, volume={50}, url={http://dx.doi.org/10.1039/C4CC04366A}, DOI={10.1039/C4CC04366A}, abstractNote={The invention of new organic materials with high dielectric constants is of extreme importance for the development of organic-based devices such as organic solar cells. We report on a synthetic way to increase the dielectric constant of fullerene derivatives. It is demonstrated that introducing triethylene glycol monoethyl ether (teg) side chains into fulleropyrrolidines increases the dielectric constant by ~46 percent without devaluation of optical properties, electron mobility and the energy level of the compound.}, number={73}, journal={Chemical communications (Cambridge, England)}, publisher={Royal Society of Chemistry}, author={Jahani, Fatemeh and Torabi, Solmaz and Chiechi, Ryan C. and Koster, L. Jan Anton and Hummelen, Jan C.}, year={2014}, month={Aug}, pages={10645–10647} }
 @article{fracasso_kumar_rudolf_chiechi_2014, title={Self-assembled monolayers of terminal acetylenes as replacements for thiols in bottom-up tunneling junctions}, volume={4}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84908620423&partnerID=MN8TOARS}, DOI={10.1039/c4ra09880c}, abstractNote={Why use thiols in Molecular Electronics? They stink, oxidize readily, poison catalysts, and often require nontrivial protection/deprotection chemistry. In this communication we demonstrate the fabrication of tunneling junctions formed by contact of self-assembled monolayers (SAMs) of terminal alkynes onto silver and gold substrates. The SAMs form spontaneously upon exposure of the substrates to ethanolic solutions of the alkynes. Characterization by vibrational spectroscopy, XPS, and contact angles shows that the packing of the SAMs is nearly identical to those formed from equivalent thiols. Electrical characterization of the junctions revealed virtually no differences between SAMs on gold and silver, yielding βAu = 1.17 ± 0.04nC−1, J0 = (2.836 ± 0.001) × 103 A cm−2 for Au, and βAg = 1.23 ± 0.09nC−1, J0 = (4.722 ± 0.002) × 103 A cm−2 for Ag. These values are in excellent agreement with junctions formed from alkanethiols of the same lengths as the alkynes, suggesting that there is no functional difference between thiols and alkynes as anchoring groups for SAMs. Yet alkynes are synthetically versatile, do not poison catalysts, are not odorous, and do not spontaneously oxidize, which are all attractive features for use in Molecular Electronics.}, number={99}, journal={RSC Adv.}, publisher={Royal Society of Chemistry (RSC)}, author={Fracasso, Davide and Kumar, Sumit and Rudolf, Petra and Chiechi, Ryan C.}, year={2014}, month={Oct}, pages={56026–56030} }
 @article{voortman_gier_havenith_chiechi_2014, title={Stabilizing cations in the backbones of conjugated polymers}, volume={2}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84898068147&partnerID=MN8TOARS}, DOI={10.1039/c3tc32204a}, abstractNote={We synthesized a cross-conjugated polymer containing ketones in the backbone and converted it to a linearly conjugated, cationic polyarylmethine via a process we call “spinless doping” to create a new class of materials, conjugated polyions. This process involves activating the ketones with a Lewis acid and converting them to trivalent cations via the nucleophilic addition of electron-rich aryl moieties. Spinless doping lowers the optical band gap from 3.26 to 1.55 eV while leaving the intrinsic semiconductor properties of the polymer intact. Electrochemical reduction (traditional doping) further decreases the predicted gap to 1.18 eV and introduces radicals to form positive polarons; here, n-doping produces a p-doped polymer in its metallic state. Treatment with a nucleophile (NaOMe) converts the cationic polymer to a neutral, non-conjugated state, allowing the band gap to be tuned chemically, post-polymerization. The synthesis of these materials is carried out entirely without the use of Sn or Pd and relies on scalable Friedel–Crafts chemistry.}, number={17}, journal={J. Mater. Chem. C}, publisher={Royal Society of Chemistry (RSC)}, author={Voortman, Thomas P. and Gier, Hilde D. and Havenith, Remco W. A. and Chiechi, Ryan C.}, year={2014}, pages={3407} }
 @inproceedings{torabi_jahani bahnamiri_van severen_patil_havenith_chiechi_lutsen_vanderzande_cleij_hummelen_et al._2014, title={Strategy for enhancing the electric permittivity of organic semiconductors}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85085846145&partnerID=MN8TOARS}, DOI={10.1364/e2.2014.jw6a.31}, abstractNote={We present a strategy to increase the electric permittivity (ϵr) of organic semiconductors with unchanged charge carrier mobility or transport gap. An increase in the efficiency of OPV is expected through enhancement of ϵr}, booktitle={Optics for Solar Energy, OSE 2014}, author={Torabi, S. and Jahani Bahnamiri, F. and Van Severen, I. and Patil, S. and Havenith, R.W.A. and Chiechi, R.C. and Lutsen, L. and Vanderzande, D. and Cleij, T.J. and Hummelen, J.C. and et al.}, year={2014} }
 @inproceedings{torabi_jahani bahnamiri_van severen_patil_havenith_chiechi_lutsen_vanderzande_cleij_hummelen_et al._2014, title={Strategy for enhancing the electric permittivity of organic semiconductors}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85118317270&partnerID=MN8TOARS}, booktitle={Solid-State and Organic Lighting, SOLED 2014}, author={Torabi, S. and Jahani Bahnamiri, F. and Van Severen, I. and Patil, S. and Havenith, R.W.A. and Chiechi, R.C. and Lutsen, L. and Vanderzande, D. and Cleij, T.J. and Hummelen, J.C. and et al.}, year={2014} }
 @article{pourhossein_chiechi_2013, title={Fabricating Nanogaps by Nanoskiving}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84901730347&partnerID=MN8TOARS}, DOI={10.3791/50406}, abstractNote={There are several methods of fabricating nanogaps with controlled spacings, but the precise control over the sub-nanometer spacing between two electrodes-and generating them in practical quantities-is still challenging. The preparation of nanogap electrodes using nanoskiving, which is a form of edge lithography, is a fast, simple and powerful technique. This method is an entirely mechanical process which does not include any photo- or electron-beam lithographic steps and does not require any special equipment or infrastructure such as clean rooms. Nanoskiving is used to fabricate electrically addressable nanogaps with control over all three dimensions; the smallest dimension of these structures is defined by the thickness of the sacrificial layer (Al or Ag) or self-assembled monolayers. These wires can be manually positioned by transporting them on drops of water and are directly electrically-addressable; no further lithography is required to connect them to an electrometer.}, number={75}, journal={JoVE}, publisher={MyJove Corporation}, author={Pourhossein, Parisa and Chiechi, Ryan C.}, year={2013} }
 @article{fracasso_muglali_rohwerder_terfort_chiechi_2013, title={Influence of an Atom in EGaIn/Ga 2 O 3 Tunneling Junctions Comprising Self-Assembled Monolayers}, volume={117}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84878352585&partnerID=MN8TOARS}, DOI={10.1021/jp401703p}, abstractNote={We compared the electrical properties of self-assembled monolayers (SAMs) formed on template-stripped Au from two homologous series of five different oligo(phenylene)s bearing alkane thiol tails. The terminal phenyl ring is substituted by a 4-pyridyl ring in one series, thus the two differ only by the substitution of C–H for N. We formed tunneling junctions using the liquid metal eutectic Ga–In (EGaIn) as a nondamaging, conformal top contact that is insensitive to functional groups and measured the current-density, J, tunneling decay constants, β, and transition voltages, Vtrans. Conductance measurements alone did not sufficiently differentiate the two series of molecules. The length dependences of the two series of SAMs produced values of β of 0.44 and 0.42 A–1 for pyridyl- and phenyl-terminated SAMs, respectively, which lie between the expected values for alkanethiolates and oligo(phenylene)s. The values of Vtrans were ∼0.3 V larger for the phenyl-terminated SAMs than for the pyridyl-terminated SAMs. A ...}, number={21}, journal={J. Phys. Chem. C}, publisher={American Chemical Society (ACS)}, author={Fracasso, Davide and Muglali, Mutlu Iskender and Rohwerder, Michael and Terfort, Andreas and Chiechi, Ryan C.}, year={2013}, month={May}, pages={11367–11376} }
 @article{chiechi_havenith_hummelen_koster_loi_2013, title={Modern plastic solar cells: materials, mechanisms and modeling}, volume={16}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84883180390&partnerID=MN8TOARS}, DOI={10.1016/j.mattod.2013.07.003}, abstractNote={We provide a short review of modern 'plastic' solar cells, a broad topic that spans materials science, physics, and chemistry. The aim of this review is to provide a primer for non-experts or researchers in related fields who are curious about this rapidly growing field of interdisciplinary research. We introduce the basic concepts of plastic solar cells and design rules for maximizing their efficiency, including modern quantum chemical calculations that can aide in the design of new materials. We discuss the history of the materials and modern trends in polymeric donor materials and fullerene acceptors, and provide demonstrative data from hybrid polymer/quantum dot devices.}, number={7-8}, journal={Materials Today}, publisher={Elsevier BV}, author={Chiechi, Ryan C. and Havenith, Remco W.A. and Hummelen, Jan C. and Koster, L. Jan Anton and Loi, Maria A.}, year={2013}, month={Jul}, pages={281–289} }
 @inproceedings{fracasso_chiechi_2013, title={Quantum interference in EGaIn based tunneling junctions}, volume={8811}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84889049610&partnerID=MN8TOARS}, DOI={10.1117/12.2026174}, abstractNote={In this report we discuss the great potential of Eutectic Gallium Indium (EGaIn) as conformal soft top electrode. EGaIn is a liquid eutectic supporting a skin (∼ 1 nm-thick) of self-limiting oxide Ga2O3 as a non-damaging, conformal top-contact. In the last half of decade EGaIn has been used by several group to form molecular junctions and study charge transport properties in self-assembled monolayer (SAMs). We compared the current density (J) versus applied bias (V) for three different self-assembled monolayers (SAMs) of ethynylthiophenol- functionalized anthracene derivatives with approximately the same thickness and diverse conjugation: linear- conjugation (AC), cross-conjugation (AQ), and broken-conjugation (AH) by using liquid eutectic Ga-In (EGaIn). This skin imparts non-Newtonian rheological properties that distinguish EGaIn from other top-contacts, however it may also have limited the maximum values of J observed for AC. We measure values of J for AH and AQ which are not significantly different (J ≈ 10-1 A/cm2 at V = 0.4 V). For AC, however, J is one (using log-averages) or two (using Gaussian mean) orders of magnitude higher than both AH and AQ. Our results are also in good qualitative agreement with gDFTB calculations on single AC, AQ, and AH molecules transport calculation, based on chemisorbed between Au contacts which predict currents, I, that are two orders of magnitude higher for AC than AH at 0 < |V| < 0.4 V. We ascribe these observations to quantum-interference effects. The agreement between the theoretical predictions on single-molecules and the measurements on SAMs suggest that molecule-molecule interactions do not play a significant role in the transport properties of AC, AQ, and AH.}, booktitle={Physical Chemistry of Interfaces and Nanomaterials XII}, publisher={SPIE-Intl Soc Optical Eng}, author={Fracasso, Davide and Chiechi, Ryan C.}, editor={Banerji, Natalie and Silva, CarlosEditors}, year={2013}, month={Sep}, pages={88110U} }
 @article{mays_pourhossein_savithri_genzer_chiechi_dickey_2013, title={Thiol-containing polymeric embedding materials for nanoskiving}, volume={1}, ISSN={["2050-7534"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84879924924&partnerID=MN8TOARS}, DOI={10.1039/c2tc00030j}, abstractNote={This paper describes the characterization of new embedding resins for nanoskiving (ultramicrotomy) that contain thiols. Nanoskiving is a technique to produce nanoscale structures using an ultramicrotome to section thin films of materials (e.g., gold) embedded in polymer. Epoxies are used typically as embedding resins for microtomy. Epoxies, however, do not adhere well to gold or other smooth metallic structures that are used commonly for nanoskiving. Thiol–ene and thiol–epoxy polymers provide improved adhesion to gold due to the thiol functional group. In addition, the thiol–ene polymers can be prepared within minutes using photopolymerization, which allows for rapid prototyping. Two commercial thiol-containing adhesives were evaluated as resins in addition to several formulations of commercially available monomers. The important physical and mechanical properties for microtomy of these unconventional embedding resins were characterized and the properties were compared to commercial epoxy resins. Gold nanowires were fabricated using nanoskiving of gold films embedded in these unconventional resins. These studies show that a 3 : 4 mixture of thiol (pentaerythritol tetra(3-mercaptopropionate)) and ene (triallyl-1,3,5-triazine-2,4,6-trione) works very well as a resin for nanoskiving and provides improved adhesion and reduced preparation time relative to epoxies.}, number={1}, journal={JOURNAL OF MATERIALS CHEMISTRY C}, publisher={Royal Society of Chemistry (RSC)}, author={Mays, Robin L. and Pourhossein, Parisa and Savithri, Dhanalekshmi and Genzer, Jan and Chiechi, Ryan C. and Dickey, Michael D.}, year={2013}, pages={121–130} }
 @article{pourhossein_chiechi_2012, title={Directly Addressable Sub-3 nm Gold Nanogaps Fabricated by Nanoskiving Using Self-Assembled Monolayers as Templates}, volume={6}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84862883356&partnerID=MN8TOARS}, DOI={10.1021/nn301510x}, abstractNote={This paper describes the fabrication of electrically addressable, high-aspect-ratio (>10000:1) nanowires of gold with square cross sections of 100 nm on each side that are separated by gaps of 1.7-2.2 nm which were defined using self-assembled monolayers (SAMs) as templates. We fabricated these nanowires and nanogaps without a clean room or any photo- or electron-beam lithographic processes by mechanically sectioning sandwich structures of gold separated by a SAM using an ultramicrotome. This process is a form of edge lithography known as Nanoskiving. These wires can be manually positioned by transporting them on drops of water and are directly electrically addressable; no further lithography is required to connect them to an electrometer. Once a block has been prepared for Nanoskiving (which takes less than one day), hundreds of thousands of nanogaps can be generated, on demand, at a rate of about one nanogap per second. After ashing the organic components with oxygen plasma, we measured the width of a free-standing gap formed from a SAM of 16-mercaptodohexanoic acid (2.4 nm in length) of 2.6 ± 0.5 nm by transmission electron microscopy. By fitting current-voltage plots of unashed gaps containing three alkanedithiolates of differing lengths to Simmons’ approximation, we derived a value of β = 0.75 Å(-1) (0.94 n(C)(-1)) at 500 mV. This value is in excellent agreement with literature values determined by a variety of methods, demonstrating that the gap-size can be controlled at resolutions as low as 2.5 Å (i.e., two carbon atoms).}, number={6}, journal={ACS Nano}, publisher={American Chemical Society (ACS)}, author={Pourhossein, Parisa and Chiechi, Ryan C.}, year={2012}, month={Jun}, pages={5566–5573} }
 @article{cademartiri_thuo_nijhuis_reus_tricard_barber_sodhi_brodersen_kim_chiechi_et al._2012, title={Electrical Resistance of Ag TS –S(CH 2 )  n −1  CH 3 //Ga 2 O 3 /EGaIn Tunneling Junctions}, volume={116}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84861503441&partnerID=MN8TOARS}, DOI={10.1021/jp212501s}, abstractNote={Tunneling junctions having the structure AgTS–S(CH2)n−1CH3//Ga2O3/EGaIn allow physical–organic studies of charge transport across self-assembled monolayers (SAMs). In ambient conditions, the surface of the liquid metal electrode (EGaIn, 75.5 wt % Ga, 24.5 wt % In, mp 15.7 °C) oxidizes and adsorbs―like other high-energy surfaces―adventitious contaminants. The interface between the EGaIn and the SAM thus includes a film of metal oxide, and probably also organic material adsorbed on this film; this interface will influence the properties and operation of the junctions. A combination of structural, chemical, and electrical characterizations leads to four conclusions about AgTS–S(CH2)n−1CH3//Ga2O3/EGaIn junctions. (i) The oxide is ∼0.7 nm thick on average, is composed mostly of Ga2O3, and appears to be self-limiting in its growth. (ii) The structure and composition (but not necessarily the contact area) of the junctions are conserved from junction to junction. (iii) The transport of charge through the junction...}, number={20}, journal={J. Phys. Chem. C}, publisher={American Chemical Society (ACS)}, author={Cademartiri, Ludovico and Thuo, Martin M. and Nijhuis, Christian A. and Reus, William F. and Tricard, Simon and Barber, Jabulani R. and Sodhi, Rana N. S. and Brodersen, Peter and Kim, Choongik and Chiechi, Ryan C. and et al.}, year={2012}, month={May}, pages={10848–10860} }
 @article{chiechi_hummelen_2012, title={Polymer Electronics, Quo Vadis?}, volume={1}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84872565167&partnerID=MN8TOARS}, DOI={10.1021/mz3004133}, abstractNote={At the heart of polymer electronics lies more than three decades of research into conjugated polymers. The future of these materials is intimately tied to the development of organic photovoltaic (OPV) devices that can compete with traditional, inorganic devices in efficiency and cost. In addition to functioning as light-harvesting materials, polymers, conjugated or not, are increasingly being used at interfaces in thin-film OPV and other electronic devices, reprising the successes of poly(ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS). The push toward more efficient OPV devices is moving chemists to think beyond band-gaps and toward charge, dielectric properties, and new synthetic methods.}, number={10}, journal={ACS Macro Lett.}, publisher={American Chemical Society (ACS)}, author={Chiechi, Ryan C. and Hummelen, Jan C.}, year={2012}, month={Oct}, pages={1180–1183} }
 @article{fracasso_valkenier_hummelen_solomon_chiechi_2011, title={Evidence for Quantum Interference in SAMs of Arylethynylene Thiolates in Tunneling Junctions with Eutectic Ga–In (EGaIn) Top-Contacts}, volume={133}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79959208402&partnerID=MN8TOARS}, DOI={10.1021/ja202471m}, abstractNote={This paper compares the current density (J) versus applied bias (V) of self-assembled monolayers (SAMs) of three different ethynylthiophenol-functionalized anthracene derivatives of approximately the same thickness with linear-conjugation (AC), cross-conjugation (AQ), and broken-conjugation (AH) using liquid eutectic Ga-In (EGaIn) supporting a native skin (~1 nm thick) of Ga(2)O(3) as a nondamaging, conformal top-contact. This skin imparts non-Newtonian rheological properties that distinguish EGaIn from other top-contacts; however, it may also have limited the maximum values of J observed for AC. The measured values of J for AH and AQ are not significantly different (J ≈ 10(-1)A/cm(2) at V = 0.4 V). For AC, however, J is 1 (using log averages) or 2 (using Gaussian fits) orders of magnitude higher than for AH and AQ. These values are in good qualitative agreement with gDFTB calculations on single AC, AQ, and AH molecules chemisorbed between Au contacts that predict currents, I, that are 2 orders of magnitude higher for AC than for AH at 0 < |V| < 0.4 V. The calculations predict a higher value of I for AQ than for AH; however, the magnitude is highly dependent on the position of the Fermi energy, which cannot be calculated precisely. In this sense, the theoretical predictions and experimental conclusions agree that linearly conjugated AC is significantly more conductive than either cross-conjugated AQ or broken conjugate AH and that AQ and AH cannot necessarily be easily differentiated from each other. These observations are ascribed to quantum interference effects. The agreement between the theoretical predictions on single molecules and the measurements on SAMs suggest that molecule-molecule interactions do not play a significant role in the transport properties of AC, AQ, and AH.}, number={24}, journal={J. Am. Chem. Soc.}, publisher={American Chemical Society (ACS)}, author={Fracasso, Davide and Valkenier, Hennie and Hummelen, Jan C. and Solomon, Gemma C. and Chiechi, Ryan C.}, year={2011}, month={Jun}, pages={9556–9563} }
 @article{valkenier_huisman_hal_leeuw_chiechi_hummelen_2011, title={Formation of High-Quality Self-Assembled Monolayers of Conjugated Dithiols on Gold: Base Matters}, volume={133}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79953872588&partnerID=MN8TOARS}, DOI={10.1021/ja110358t}, abstractNote={This Article reports a systematic study on the formation of self-assembled monolayers (SAMs) of conjugated molecules for molecular electronic (ME) devices. We monitored the deprotection reaction of acetyl protected dithiols of oligophenylene ethynylenes (OPEs) in solution using two different bases and studied the quality of the resulting SAMs on gold. We found that the optimal conditions to reproducibly form dense, high-quality monolayers are 9-15% triethylamine (Et(3)N) in THF. The deprotection base tetrabutylammonium hydroxide (Bu(4)NOH) leads to less dense SAMs and the incorporation of Bu(4)N into the monolayer. Furthermore, our results show the importance of the equilibrium concentrations of (di)thiolate in solution on the quality of the SAM. To demonstrate the relevance of these results for molecular electronics applications, large-area molecular junctions were fabricated using no base, Et(3)N, and Bu(4)NOH. The magnitude of the current-densities in these devices is highly dependent on the base. A value of β=0.15 Å(-1) for the exponential decay of the current-density of OPEs of varying length formed using Et(3)N was obtained.}, number={13}, journal={J. Am. Chem. Soc.}, publisher={American Chemical Society (ACS)}, author={Valkenier, Hennie and Huisman, Everardus H. and Hal, Paul A. and Leeuw, Dago M. and Chiechi, Ryan C. and Hummelen, Jan C.}, year={2011}, month={Apr}, pages={4930–4939} }
 @article{brouwer_alma_valkenier_voortman_hillebrand_chiechi_hummelen_2011, title={Using bis(pinacolato)diboron to improve the quality of regioregular conjugated co-polymers}, volume={21}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78751528660&partnerID=MN8TOARS}, DOI={10.1039/c0jm02359k}, abstractNote={We demonstrate the use of bis(pinacolato)diboron to directly polymerize symmetric, bisbromo, thiophene-based monomers via a Suzuki homo-polymerization to form co-polymers in less steps than the corresponding co-polymerization. We compare this method to the commonly used Stille co-polymerization by preparing four thiophene-based co-polymers using both methods. We use MALDI-TOF mass spectrometry to show that this new method produces high-quality, uniform polymers with narrow distributions of end-groups. By varying the electronegativity of the monomers, we demonstrate rudimentary control over these end-groups, forming either bis-H-, mono-H-mono-Br-, or bis-Br-terminated polymers in order of increasing electronegativity.}, number={5}, journal={J. Mater. Chem.}, publisher={Royal Society of Chemistry (RSC)}, author={Brouwer, Frank and Alma, Jan and Valkenier, Hennie and Voortman, Thomas P. and Hillebrand, Jorrit and Chiechi, Ryan C. and Hummelen, Jan C.}, year={2011}, pages={1582} }
 @article{bell_chiechi_johnson_kimball_matzger_wan_weakley_haley_2010, title={ChemInform Abstract: A Versatile Synthetic Route to Dehydrobenzoannulenes via in situ Generation of Reactive Alkynes.}, volume={32}, DOI={10.1002/chin.200131100}, abstractNote={Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.}, number={31}, journal={ChemInform}, publisher={Wiley-Blackwell}, author={Bell, Michael L. and Chiechi, Ryan C. and Johnson, Charles A. and Kimball, David B. and Matzger, Adam J. and Wan, W. Brad and Weakley, Timothy J. R. and Haley, Michael M.}, year={2010}, month={May}, pages={no-no} }
 @article{wudl_walker_veldman_chiechi_patil_bendikov_2009, title={Antiaromatic Lowering of the HOMO-LUMO Gap}, volume={2009}, DOI={10.1055/s-0028-1087493}, abstractNote={There is increasing interest in materials that absorb and emit light in the far red (near IR) regions of the spectrum. A great deal of the solar radiation that strikes the earth is to the red of the visible and human tissue exhibits greater transparency at wavelengths greater than 700 nm wherein there is reduced absorbance by blood. New materials for medical and energy applications require an expanded design space afforded by new electronic building blocks.}, number={02}, journal={Synfacts}, publisher={Thieme Publishing Group}, author={Wudl, F. and Walker, W. and Veldman, B. and Chiechi, R. and Patil, S. and Bendikov, M.}, year={2009}, month={Jan}, pages={0151–0151} }
 @article{thomas_chiechi_lafratta_webb_lee_wiley_zakin_walt_whitesides_2009, title={Infochemistry and infofuses for the chemical storage and transmission of coded information}, volume={106}, ISSN={0027-8424 1091-6490}, url={http://dx.doi.org/10.1073/pnas.0902476106}, DOI={10.1073/pnas.0902476106}, abstractNote={This article describes a self-powered system that uses chemical reactions—the thermal excitation of alkali metals—to transmit coded alphanumeric information. The transmitter (an “infofuse”) is a strip of the flammable polymer nitrocellulose patterned with alkali metal ions; this pattern encodes the information. The wavelengths of 2 consecutive pulses of light represent each alphanumeric character. While burning, infofuses transmit a sequence of pulses (at 5–20 Hz) of atomic emission that correspond to the sequence of metallic salts (and therefore to the encoded information). This system combines information technology and chemical reactions into a new area—“infochemistry”—that is the first step toward systems that combine sensing and transduction of chemical signals with multicolor transmission of alphanumeric information.}, number={23}, journal={Proceedings of the National Academy of Sciences}, publisher={Proceedings of the National Academy of Sciences}, author={Thomas, S. W. and Chiechi, R. C. and LaFratta, C. N. and Webb, M. R. and Lee, A. and Wiley, B. J. and Zakin, M. R. and Walt, D. R. and Whitesides, G. M.}, year={2009}, month={May}, pages={9147–9150} }
 @inproceedings{weiss_geyer_porter_chiechi_bawendi_whitesides_2009, title={The use of multi-size arrays of colloidal quantum dots to study energy and electron transport in QD junctions}, volume={1121}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77954266278&partnerID=MN8TOARS}, booktitle={Materials Research Society Symposium Proceedings}, author={Weiss, E.A. and Geyer, S.M. and Porter, V.J. and Chiechi, R.C. and Bawendi, M.G. and Whitesides, G.M.}, year={2009}, pages={1–10} }
 @article{chiechi_weiss_dickey_whitesides_2008, title={Eutectic Gallium–Indium (EGaIn): A Moldable Liquid Metal for Electrical Characterization of Self-Assembled Monolayers}, volume={120}, DOI={10.1002/ange.200703642}, abstractNote={Angewandte ChemieVolume 120, Issue 1 p. 148-150 Zuschrift Eutectic Gallium–Indium (EGaIn): A Moldable Liquid Metal for Electrical Characterization of Self-Assembled Monolayers† Ryan C. Chiechi Dr., Ryan C. Chiechi Dr. Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, MA 02138, USA, Fax: (+1) 617-495-9857Search for more papers by this authorEmily A. Weiss Dr., Emily A. Weiss Dr. Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, MA 02138, USA, Fax: (+1) 617-495-9857Search for more papers by this authorMichael D. Dickey Dr., Michael D. Dickey Dr. Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, MA 02138, USA, Fax: (+1) 617-495-9857Search for more papers by this authorGeorge M. Whitesides Prof., George M. Whitesides Prof. [email protected] Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, MA 02138, USA, Fax: (+1) 617-495-9857Search for more papers by this author Ryan C. Chiechi Dr., Ryan C. Chiechi Dr. Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, MA 02138, USA, Fax: (+1) 617-495-9857Search for more papers by this authorEmily A. Weiss Dr., Emily A. Weiss Dr. Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, MA 02138, USA, Fax: (+1) 617-495-9857Search for more papers by this authorMichael D. Dickey Dr., Michael D. Dickey Dr. Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, MA 02138, USA, Fax: (+1) 617-495-9857Search for more papers by this authorGeorge M. Whitesides Prof., George M. Whitesides Prof. [email protected] Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, MA 02138, USA, Fax: (+1) 617-495-9857Search for more papers by this author First published: 13 December 2007 https://doi.org/10.1002/ange.200703642Citations: 125 † We acknowledge funding from NSF CHE-0518055, and the shared facilities supported by the NSF under NSEC (PHY-0117795), and MRSEC (DMR-0213805). E.A.W. thanks the Petroleum Research Fund of the American Chemical Society for a fellowship (PRF 43083-AEF). Read the full textAboutPDF ToolsRequest permissionAdd to favorites ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Graphical Abstract Mikroelektroden aus der Titelverbindung erweisen sich als ideal für die Messung der elektrischen Eigenschaften selbstorganisierter Monoschichten. Im Bild ist gezeigt, wie sich das EGaIn zwischen einer Metallnadel und einer Ag-Oberfläche (nicht erkennbar) teilt. Aus dem Teil oberhalb der weißen Pfeile wird später die EGaIn-Elektrode. Supporting Information Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2001/2008/z703642_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. References 1S. J. French, D. J. Saunders, G. W. Ingle, J. Phys. Chem. 1938, 42, 265. 10.1021/j100897a011 CASWeb of Science®Google Scholar 2D. Zrnic, D. S. Swatik, J. Less-Common Met. 1969, 18, 67. 10.1016/0022-5088(69)90121-0 CASWeb of Science®Google Scholar 3A. D. Pasquier, S. Miller, M. Chhowalla, Solar Energy Mater. Solar Cells 2006, 90, 1828. 10.1016/j.solmat.2005.11.003 CASWeb of Science®Google Scholar 4E. J. Lous, P. W. M. Blom, L. W. Molenkamp, D. M. d. Leeuw, J. Appl. Phys. 1997, 81. 10.1063/1.364990 CASPubMedWeb of Science®Google Scholar 5C. P. Rhodes, J. W. Long, M. S. Doescher, J. J. Fontanella, D. R. Rolison, J. Phys. Chem. B 2004, 108, 13079. 10.1021/jp047671u CASWeb of Science®Google Scholar 6E. A. Weiss, G. K. Kaufman, J. K. Kriebel, Z. Li, R. Schalek, G. M. Whitesides, Langmuir 2007, 23, 9686. 10.1021/la701919r CASPubMedWeb of Science®Google Scholar 7J. Chen, T. Lee, J. Su, W. Wang, M. A. Reed, A. M. Rawlett, M. Kozaki, Y. Yao, R. C. Jagessar, S. M. Dirk, D. W. Price, J. M. Tour, D. S. Grubisha, D. W. Bennett in Molecular Nanoelectronics (Eds.: ), American Scientific Publishers, Valencia, 2003, p. 1. Google Scholar 8T.-W. Kim, G. Wang, H. Lee, T. Lee, Nanotechnology 2007, 18, 315204. 10.1088/0957-4484/18/31/315204 CASWeb of Science®Google Scholar 9J. M. Beebe, J. G. Kushmerick, Appl. Phys. Lett. 2007, 90, 083117. 10.1063/1.2696653 CASWeb of Science®Google Scholar 10F. Milani, C. Grave, V. Ferri, P. Samori, M. A. Rampi, Chem. Phys. Phys. Chem. 2007, 8, 515. 10.1002/cphc.200600672 CASPubMedWeb of Science®Google Scholar 11H. B. Akkerman, P. W. M. Blom, D. M. d. Leeuw, B. d. Boer, Nature 2006, 441, 69. 10.1038/nature04699 CASPubMedWeb of Science®Google Scholar 12C. Schoenenberger, J. Jorritsma, J. A. M. Sondag-Huethorst, L. G. J. Fokkink, J. Phys. Chem. 1995, 99, 3259. 10.1021/j100010a042 CASWeb of Science®Google Scholar 13E. A. Weiss, R. C. Chiechi, G. K. Kaufman, J. K. Kriebel, Z. Li, M. Duati, M. A. Rampi, G. M. Whitesides, J. Am. Chem. Soc. 2007, 129, 4336. 10.1021/ja0677261 CASPubMedWeb of Science®Google Scholar 14M. A. Rampi, G. M. Whitesides, Chem. Phys. 2002, 281, 373. 10.1016/S0301-0104(02)00445-7 CASWeb of Science®Google Scholar 15Hg has been used as a top contact for monolayers of alkanes on Si; these monolayers are formed, however, through the covalent attachment of alkenes to Si rather than the dynamic equilibria that are involved in the formation of SAMs on metals; see: O. Seitz et al., J. Am. Chem. Soc. 2007, 129, 7494. 10.1021/ja071960p CASPubMedWeb of Science®Google Scholar 16M. D. Dickey, R. C. Chiechi, R. J. Larsen, E. A. Weiss, D. A. Weitz, G. M. Whitesides, Adv. Funct. Mater., unpublished results. Google Scholar 17The surface energy of γ-Al2O3 is 560 dynes cm−1: A. Bondi, Chem. Rev. 1953, 52, 417. 10.1021/cr60162a002 CASWeb of Science®Google Scholar 18The origin of the sudden change in the shape of the J–V trace in Figure 2 a between V=±0.05 is probably a switch from the “low-bias regime” (e V≪Φ) to the “intermediate-bias regime” (e V<Φ), whereby Φ is the height of the tunneling barrier imposed by the organic monolayer (within the often-used Simmons model). In the low-bias regime, J depends only linearly on V, but, in the intermediate bias regime, J depends exponentially on V as a result of the so-called “barrier-lowering effect” of the applied bias. We did not acquire data in small enough intervals of V to capture the shape of the J–V response in this region; the transition from low- to intermediate-bias regimes therefore appears as a discontinuity in the plot in Figure 2 a; see: Chen et al. in Molecular Nanoelectronics (Eds.: ), American Scientific Publishers, Valencia, 2003, pp. 1–76. Google Scholar 19E. A. Weiss, R. C. Chiechi, S. M. Geyer, V. J. Porter, D. C. Bell, M. G. Bawendi, G. M. Whitesides, J. Am. Chem. Soc., in press. Google Scholar Citing Literature Volume120, Issue1December 17, 2007Pages 148-150 This is the German version of Angewandte Chemie. Note for articles published since 1962: Do not cite this version alone. Take me to the International Edition version with citable page numbers, DOI, and citation export. We apologize for the inconvenience. ReferencesRelatedInformation}, number={1}, journal={Angew. Chem.}, publisher={Wiley-Blackwell}, author={Chiechi, Ryan C. and Weiss, Emily A. and Dickey, Michael D. and Whitesides, George M.}, year={2008}, month={Jan}, pages={148–150} }
 @article{dickey_chiechi_larsen_weiss_weitz_whitesides_2008, title={Eutectic gallium-indium (EGaIn): A liquid metal alloy for the formation of stable structures in microchannels at room temperature}, volume={18}, ISSN={["1616-301X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-42549111682&partnerID=MN8TOARS}, DOI={10.1002/adfm.200701216}, abstractNote={Abstract}, number={7}, journal={ADVANCED FUNCTIONAL MATERIALS}, publisher={Wiley-Blackwell}, author={Dickey, Michael D. and Chiechi, Ryan C. and Larsen, Ryan J. and Weiss, Emily A. and Weitz, David A. and Whitesides, George M.}, year={2008}, month={Apr}, pages={1097–1104} }
 @article{chiechi_weiss_dickey_whitesides_2008, title={Eutectic gallium-indium (EGaIn): A moldable liquid metal for electrical characterization of self-assembled monolayers}, volume={47}, ISSN={["1521-3773"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-37549043162&partnerID=MN8TOARS}, DOI={10.1002/anie.200703642}, abstractNote={Herein we describe the formation of conformal electrodes from the fluid metal eutectic, Ga–In (which we abbreviate “EGaIn” and pronounce “e-gain”; 75% Ga, 25% In by weight, m.p.= 15.5 8C), and their use in studying charge transport across self-assembled monolayers (SAMs). Although EGaIn is a liquid at room temperature, it does not spontaneously reflow into the shape with the lowest interfacial free energy as do liquids such as Hg and H2O: as a result, it can be formed into metastable, nonspherical structures (e.g., cones, and filaments with diameters 1 mm). This behavior, along with its high electrical conductivity (3.4 4 10 Scm ) and its tendency to make low contact-resistance interfaces with a variety of materials, makes EGaIn useful for forming electrodes for thin-film devices. We discuss the convenience and precision of measurements of current density (J, Acm ) versus applied voltage (V, V) through SAMs of n-alkanethiolates on template-stripped, ultraflat Ag (Ag–SCn Ag–SCnH2n+1, n= 10, 12, 14, 16) using EGaIn. An ideal electrode for physical-organic studies of SAMs would 1) make conformal, but nondamaging, physical contacts, 2) readily form small-area (micrometer diameter) contacts, to minimize the contribution of defects in the SAM to J, 3) form without specialized equipment, and 4) be nontoxic. Point 3 is particularly important: elimination of procedures such as evaporating metals or lithographic patterning would allow a wide range of laboratories—including those without access to clean rooms—to survey relationships between structure and electrical conductivity. There are currently three general techniques for forming top contacts for large-area (i.e., more than a few molecules) electrical measurements on SAMs of organic molecules: 1) The direct deposition of metals such as Au or Ti by using electron-beam or thermal evaporation ensures atomic-level contact, but results in low yields of devices owing to damage to the organic monolayer by reaction with hot metal vapors, and in the formation of metal filaments that short the junctions. 2) The installation of an electrically conducting polymer between the SAM and a metallic top contact inhibits formation of metal filaments, but the instability of SAMs of alkanethiolates to the temperatures required to anneal most electroactive polymers limits the broad application of this approach. 3) The use of Hg allows formation of conformal contacts at room temperature, but Hg is toxic, amalgamates with metals, tends to form junctions that short, is difficult to form into small contacts, and measurements with Hg must be performed under a solvent bath. EGaIn does not flow until it experiences a critical surface stress (0.5 Nm ), at which point it yields (i.e., flows). EGaIn 1) makes conformal, nondamaging contacts at room temperature, 2) can be molded into nonspherical shapes with micrometer-scale (or larger) dimensions, 3) is commercially available, 4) can be deposited with a pipette or syringe without high temperatures or vacuum, 5) has a low vapor pressure, and 6) is nontoxic. The work function of EGaIn (4.1–4.2 eV) is close to that of Hg (4.5 eV), but EGaIn does not alloy with many metals. It is therefore an ideal replacement for Hg, especially in devices that incorporate SAMs (which are generally formed on Au or Ag). Auger spectroscopy on samples of EGaIn in air show that its surface is principally composed of oxides of Ga (see the Supporting Information); gallium oxide is an n-type semiconductor. There is undoubtedly an adsorbed film of water on this surface, as EGaIn has a high surface free energy (ca. 630 dynescm ), as do oxides formed from similar metals. During our measurements, there were no observable changes in the average magnitude or range of J when EGaIn was allowed to sit in air for extended periods before we deposited it on the SAM, or when we performed the measurements using the same drop of EGaIn to form between three and five junctions, or while we flowed dry N2 over the sample: therefore the contribution of the surface oxide to J was probably constant for the duration of the experiments. We formed EGaIn electrodes by suspending a drop of EGaIn from a metal 26s-gauge needle affixed to a 10-mL syringe, bringing the drop into contact with the bare surface of a sacrificial film of Ag using a micromanipulator, and retracting the needle slowly (ca. 50 mms ); the EGaIn adhered to both the needle and the Ag (Figure 1). The drop of EGaIn pinched into to an hour-glass shape until it bifurcated into two structures, one attached to the syringe (a cone approximately 0.05 mL in volume) and one (which was discarded) attached to the Ag. We produced conical tips of EGaIn with diameters ranging from less than 1 mm to 100 mm; the larger the bore of the needle, and the more rapidly we [*] Dr. R. C. Chiechi, Dr. E. A. Weiss, Dr. M. D. Dickey, Prof. G. M. Whitesides Department of Chemistry and Chemical Biology Harvard University 12 Oxford St., Cambridge, MA 02138 (USA) Fax: (+1)617-495-9857 E-mail: gwhitesides@gmwgroup.harvard.edu}, number={1}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, publisher={Wiley-Blackwell}, author={Chiechi, Ryan C. and Weiss, Emily A. and Dickey, Michael D. and Whitesides, George M.}, year={2008}, pages={142–144} }
 @article{dickey_weiss_smythe_chiechi_capasso_whitesides_2008, title={Fabrication of arrays of metal and metal oxide nanotubes by shadow evaporation}, volume={2}, ISSN={["1936-086X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-46849115799&partnerID=MN8TOARS}, DOI={10.1021/nn800036r}, abstractNote={This paper describes a simple technique for fabricating uniform arrays of metal and metal oxide nanotubes with controlled heights and diameters. The technique involves depositing material onto an anodized aluminum oxide (AAO) membrane template using a collimated electron beam evaporation source. The evaporating material enters the porous openings of the AAO membrane and deposits onto the walls of the pores. The membrane is tilted with respect to the column of evaporating material, so the shadows cast by the openings of the pores onto the inside walls of the pores define the geometry of the tubes. Rotation of the membrane during evaporation ensures uniform deposition inside the pores. After evaporation, dissolution of the AAO in base easily removes the template to yield an array of nanotubes connected by a thin backing of the same metal or metal oxide. The diameter of the pores dictates the diameter of the tubes, and the incident angle of evaporation determines the height of the tubes. Tubes up to approximately 1.5 mum in height and 20-200 nm in diameter were fabricated. This method is adaptable to any material that can be vapor-deposited, including indium-tin oxide (ITO), a conductive, transparent material that is useful for many opto-electronic applications. An array of gold nanotubes produced by this technique served as a substrate for surface-enhanced Raman spectroscopy: the Raman signal (per molecule) from a monolayer of benzenethiolate was a factor of approximately 5 x 10(5) greater than that obtained using bulk liquid benzenethiol.}, number={4}, journal={ACS NANO}, publisher={American Chemical Society (ACS)}, author={Dickey, Michael D. and Weiss, Emily A. and Smythe, Elizabeth J. and Chiechi, Ryan C. and Capasso, Federico and Whitesides, George M.}, year={2008}, month={Apr}, pages={800–808} }
 @article{lipomi_chiechi_dickey_whitesides_2008, title={Fabrication of conjugated polymer nanowires by edge lithography}, volume={8}, ISSN={["1530-6984"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-53149142545&partnerID=MN8TOARS}, DOI={10.1021/nl8009318}, abstractNote={This paper describes the fabrication of conjugated polymer nanowires by a three stage process: (i) spin-coating a composite film comprising alternating layers of a conjugated polymer and a sacrificial material, (ii) embedding the film in an epoxy matrix and sectioning it with an ultramicrotome (nanoskiving), and (iii) etching the sacrificial material to reveal nanowires of the conjugated polymer. A free-standing, 100-layer film of two conjugated polymers was spin-coated from orthogonal solvents: poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) from chloroform and poly(benzimidazobenzophenanthroline ladder) (BBL) from methanesulfonic acid. After sectioning the multilayer film, dissolution of the BBL with methanesulfonic acid yielded uniaxially aligned MEH-PPV nanowires with rectangular cross sections, and etching MEH-PPV with an oxygen plasma yielded BBL nanowires. The conductivity of MEH-PPV nanowires changed rapidly and reversibly by >10 (3) upon exposure to I 2 vapor. The result suggests that this technique could be used to fabricate high-surface-area structures of conducting organic nanowires for possible applications in sensing and in other fields where a high surface area in a small volume is desirable.}, number={7}, journal={NANO LETTERS}, publisher={American Chemical Society (ACS)}, author={Lipomi, Darren J. and Chiechi, Ryan C. and Dickey, Michael D. and Whitesides, George M.}, year={2008}, month={Jul}, pages={2100–2105} }
 @article{lipomi_chiechi_reus_whitesides_2008, title={Laterally Ordered Bulk Heterojunction of Conjugated Polymers: Nanoskiving a Jelly Roll}, volume={18}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-55849150529&partnerID=MN8TOARS}, DOI={10.1002/adfm.200800578}, abstractNote={This paper describes the fabrication of a nanostructured heterojunction of two conjugated polymers by a three‐step process: i) spin‐coating a multilayered film of the two polymers, ii) rolling the film into a cylinder (a “jelly roll”) and iii) sectioning the film perpendicular to the axis of the roll with an ultramicrotome (nanoskiving). The conjugated polymers are poly(benzimidazobenzophenanthroline ladder) (BBL, n‐type) and poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene) (MEH‐PPV, p‐type). The procedure produces sections with an interdigitated junction of the two polymers. The spacing between the phases is determined by spin‐coating (∼15 nm to 100 nm) and the thickness of each section is determined by the ultramicrotome (100 to 1000 nm). The minimum width of the MEH‐PPV layers accessible with this technique (∼15 nm) is close to reported exciton diffusion lengths for the polymer. When placed in a junction between two electrodes with asymmetric work functions (tin‐doped indium oxide (ITO) coated with poly(3,4‐ethylenedioxythiophene:poly(styrenesulfonate) (PEDOT:PSS), and eutectic gallium‐indium, EGaIn) the heterostructures exhibit a photovoltaic response under white light, although the efficiency of conversion of optical to electrical energy is low. Selective excitation of BBL with red light confirms that the photovoltaic effect is the result of photoinduced charge transfer between BBL and MEH‐PPV.}, number={21}, journal={Adv. Funct. Mater.}, publisher={Wiley-Blackwell}, author={Lipomi, Darren J. and Chiechi, Ryan C. and Reus, William F. and Whitesides, George M.}, year={2008}, month={Nov}, pages={3469–3477} }
 @article{weiss_chiechi_geyer_porter_bell_bawendi_whitesides_2008, title={Size-Dependent Charge Collection in Junctions Containing Single-Size and Multi-Size Arrays of Colloidal CdSe Quantum Dots}, volume={130}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-38349043778&partnerID=MN8TOARS}, DOI={10.1021/ja076438h}, abstractNote={This paper describes the electrical characteristics of junctions composed of three-dimensional arrays of colloidal CdSe quantum dots (QDs) with tin-doped indium oxide (ITO)/poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) and eutectic Ga-In (EGaIn) electrodes. It focuses on a comparison of junctions containing QDs of one size to those of arrays containing QDs of multiple sizes. This comparison makes it possible to estimate the relative contributions of transport across various interfaces (e.g., between the QDs and between the QDs and the electrodes) to the observed electrical characteristics of the junction and to evaluate the dependence of these contributions on the locations of various sizes of QDs within the junction. The junctions were diodes, and their turn-on voltage depended on the size of the QDs next to the PEDOT:PSS. We describe this dependence using a Marcus model to estimate the barrier for charge transfer induced by the difference in energies between the orbitals of the QDs and the valence band of PEDOT:PSS.}, number={1}, journal={J. Am. Chem. Soc.}, publisher={American Chemical Society (ACS)}, author={Weiss, Emily A. and Chiechi, Ryan C. and Geyer, Scott M. and Porter, Venda J. and Bell, David C. and Bawendi, Moungi G. and Whitesides, George M.}, year={2008}, month={Jan}, pages={74–82} }
 @inproceedings{weiss_chiechi_porter_geyer_bawendi_whitesides_2008, title={The Use of Multi-Size Arrays of Colloidal Quantum Dots to Study Energy and Electron Transport in QD Junctions}, DOI={10.1557/proc-1121-n04-01}, booktitle={Materials Research Society Symposium Proceedings}, publisher={Cambridge University Press (CUP)}, author={Weiss, Emily and Chiechi, Ryan and Porter, Venda and Geyer, Scott and Bawendi, Moungi and Whitesides, George}, year={2008} }
 @article{weiss_porter_chiechi_geyer_bell_bawendi_whitesides_2008, title={The Use of Size-Selective Excitation To Study Photocurrent through Junctions Containing Single-Size and Multi-Size Arrays of Colloidal CdSe Quantum Dots}, volume={130}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-38349070351&partnerID=MN8TOARS}, DOI={10.1021/ja076439+}, abstractNote={This paper describes a study of the generation and flow of photocurrent through junctions containing three-dimensional arrays of colloidal CdSe quantum dots (QDs) of either a single size or multiple sizes. The electrodes were indium tin oxide (ITO) covered with a thin layer of poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) and a eutectic alloy of Ga and In (EGaIn). We measured the current-voltage characteristics of the junctions in the dark and under illumination, with various sources and wavelengths of excitation, and their photocurrent action spectra. Size-selective photoexcitation of the arrays of multiple sizes of QDs helped to determine (i) the location of the interface at which photoinduced separation of charge occurred, (ii) whether the energy absorbed by the QDs was redistributed before separation of charge, and (iii) the dependence of the photovoltage on the locations of various sizes of QDs within the junction. This research is a step toward the use of QDs for harvesting light and for transporting energy and charge in devices-for example, solar cells and photodetectors-that operate at zero bias.}, number={1}, journal={J. Am. Chem. Soc.}, author={Weiss, Emily A. and Porter, Venda J. and Chiechi, Ryan C. and Geyer, Scott M. and Bell, David C. and Bawendi, Moungi G. and Whitesides, George M.}, year={2008}, month={Jan}, pages={83–92} }
 @article{walker_veldman_chiechi_patil_bendikov_wudl_2008, title={Visible and Near-Infrared Absorbing, Low Band Gap Conjugated Oligomers Based on Cyclopentadieneones}, volume={41}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-55649115790&partnerID=MN8TOARS}, DOI={10.1021/ma8004873}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTVisible and Near-Infrared Absorbing, Low Band Gap Conjugated Oligomers Based on CyclopentadieneonesWesley Walker†, Brittnee Veldman‡, Ryan Chiechi†§, Satish Patil†∥, Michael Bendikov⊥, and Fred Wudl*†‡View Author Information Department of Chemistry and Biochemistry, University of California, Los Angeles, 607 Charles E. Young Drive East, Box 951569, Los Angeles, California 90095-1569, and Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106-9510* Corresponding author. E-mail: [email protected]†University of California, Los Angeles.‡University of California, Santa Barbara.§Current address: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford St., Cambridge, MA 02138.∥Current address: Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, India 560012.⊥Current address: Department of Organic Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel.Cite this: Macromolecules 2008, 41, 20, 7278–7280Publication Date (Web):September 25, 2008Publication History Received4 March 2008Revised14 August 2008Published online25 September 2008Published inissue 28 October 2008https://doi.org/10.1021/ma8004873Copyright © 2008 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views2484Altmetric-Citations40LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (152 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Absorption,Conjugated polymers,Electrical conductivity,Monomers,Polymers Get e-Alerts}, number={20}, journal={Macromolecules}, publisher={American Chemical Society (ACS)}, author={Walker, Wesley and Veldman, Brittnee and Chiechi, Ryan and Patil, Satish and Bendikov, Michael and Wudl, Fred}, year={2008}, month={Oct}, pages={7278–7280} }
 @article{yang_cho_chiechi_walker_coates_moses_heeger_wudl_2008, title={Visible−Near Infrared Absorbing Dithienylcyclopentadienone−Thiophene Copolymers for Organic Thin-Film Transistors}, volume={130}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-57549097793&partnerID=MN8TOARS}, DOI={10.1021/ja806784e}, abstractNote={Structural design, synthesis, and characterization of a series of organic semiconductors consisting exclusively of dithienylcyclopentadienone subunits within a polythiophene backbone are described as the first example for organic electronic devices. The donor (thiophene)-alt-acceptor (cyclopentadienone) copolymers exhibit a substantial p-carrier mobility in OFET but an unexpected noncorrelation between absorption and photoconductivity.}, number={49}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Yang, Changduk and Cho, Shinuk and Chiechi, Ryan C. and Walker, Wesley and Coates, Nelson E. and Moses, Daniel and Heeger, Alan J. and Wudl, Fred}, year={2008}, pages={16524–16526} }
 @article{weiss_chiechi_kaufman_kriebel_li_duati_rampi_whitesides_2007, title={Influence of Defects on the Electrical Characteristics of Mercury-Drop Junctions:  Self-Assembled Monolayers of n -Alkanethiolates on Rough and Smooth Silver}, volume={129}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34247127494&partnerID=MN8TOARS}, DOI={10.1021/ja0677261}, abstractNote={This paper compares the structural and electrical characteristics of self-assembled monolayers (SAMs) of n-alkanethiolates, SCn (n = 10, 12, 14), on two types of silver substrates: one used as-deposited (AS-DEP) by an electron-beam evaporator, and one prepared using the method of template-stripping. Atomic force microscopy showed that the template-stripped (TS) silver surfaces were smoother and had larger grains than the AS-DEP surfaces, and reflectance-absorbance infrared spectroscopy showed that SAMs formed on TS substrates were more crystalline than SAMs formed on AS-DEP substrates. The range of current densities, J (A/cm2), measured through mercury-drop junctions incorporating a given SAM on AS-DEP silver was, on average, several orders of magnitude larger than the range of J measured through the same SAM on TS silver, and the AS-DEP junctions failed, on average, 3.5 times more often within five current density-voltage (J-V) scans than did TS junctions (depending on the length of the alkyl chains of the molecules in the SAM). The apparent log-normal distribution of J through the TS junctions suggests that, in these cases, it is the variability in the effective thickness of the insulating layer (the distance the electron travels between electrodes) that results in the uncertainty in J. The parameter describing the decay of current density with the thickness of the insulating layer, beta, was either 0.57 A-1 at V = +0.5 V (calculated using the log-mean of the distribution of values of J) or 0.64 A-1 (calculated using the peak of the distribution of values of J) for the TS junctions; the latter is probably the more accurate. The mechanisms of failure of the junctions, and the degree and sources of uncertainty in current density, are discussed with respect to a variety of defects that occur within Hg-drop junctions incorporating SAMs on silver.}, number={14}, journal={J. Am. Chem. Soc.}, publisher={American Chemical Society (ACS)}, author={Weiss, Emily A. and Chiechi, Ryan C. and Kaufman, George K. and Kriebel, Jennah K. and Li, Zhefeng and Duati, Marco and Rampi, Maria A. and Whitesides, George M.}, year={2007}, month={Apr}, pages={4336–4349} }
 @article{marchioni_chiechi_patil_wudl_chen_shinar_2006, title={Absolute photoluminescence quantum yield enhancement of poly(2-methoxy 5-[2[sup ʹ]-ethylhexyloxy]-p-phenylenevinylene)}, volume={89}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33747121320&partnerID=MN8TOARS}, DOI={10.1063/1.2335365}, abstractNote={A twofold absolute photoluminescence quantum yield (PLQY) enhancement of poly(2-methoxy 5-[2′-ethylhexyloxy]-p-phenylenevinylene) (MEH-PPV) is demonstrated by simple preparation of films where the polymer is blended with the small organic molecule 7,8,10-triphenylfluoranthene (3PF). The photophysical investigation of this particular energy transfer process was carried out using steady state absorption/luminescence spectroscopy and optically detected magnetic resonance techniques. The enhanced PLQY is attributed to direct sensitization of the intrachain emitting state of MEH-PPV by energy transfer from 3PF.}, number={6}, journal={Appl. Phys. Lett.}, publisher={AIP Publishing}, author={Marchioni, F. and Chiechi, R. and Patil, S. and Wudl, F. and Chen, Y. and Shinar, J.}, year={2006}, pages={061101} }
 @article{chiechi_tseng_marchioni_yang_wudl_2006, title={Efficient Blue-Light-Emitting Electroluminescent Devices with a Robust Fluorophore: 7,8,10-Triphenylfluoranthene}, volume={18}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-32244443358&partnerID=MN8TOARS}, DOI={10.1002/adma.200501682}, abstractNote={Silicon semiconductor technology has driven the profusion of information technology into every aspect of modern life. An obvious example of this is the emergence of portable electronic devices, such as cellular phones (mobile phones), personal digital assistants, palmtop computers, etc., that are rapidly becoming essential. These share a common Achilles heel, namely, battery life. The most obvious way to attack this problem is through replacement of the power hungry back-lit liquid-crystal displays (LCDs) that reside in all lightweight devices. It is this impetus that has brought organic light-emitting devices (OLEDs) to the forefront of modern materials science. The ability to mass produce thin, efficient, bright displays from organic polymers and small molecules that can supplant modern LCDs depends almost entirely on the ability to create new materials that can undergo efficient electroluminescence at a variety of wavelengths. This has lead to many publications and patents but to date has failed to produce an efficient, cheap, and robust blue-light emitter. It is, of course, not an easy task to find a small molecule that possesses not only a very large bandgap but also stability to the harsh electrochemical environment of OLEDs and a very large quantum yield in the solid state. One class of molecules in particular, fluorenes—especially spirofluorenes—has received much attention because of the outstanding properties in this area, but lengthy syntheses and low-yielding steps, such as boronic acid/ester formations, are less than ideal for singlelayer/host materials. In an effort to redirect some of the explorations, we have investigated a close cousin of fluorenes—fluoranthenes—for applications as blue-light emitters in OLEDs (Scheme 1). In particular, we have studied 7,8,10triphenylfluoranthene (TPF), a highly luminescent solid-state blue-light-emitting small molecule, which can be obtained in two steps from commercial starting materials. After the elucidation of the structure of fluoranthene at the turn of the 20th century, the chemistry of fluoranthenes evolved rapidly. Studies of the interesting photophysical properties followed, but interest in fluoranthenes faded fast. Of particular note is the synthesis of fluoranthene derivatives by a double Knoevenagel condensation between 2-propanone and acenaphthenequinone, which allows functionalization at the carbon 7 and 10 positions. A subsequent Diels–Alder addition allows further functionalization at the 8 and 9 positions. Finally, starting from bromoacenapthenequinone, the carbon 3 position is open to functionalization. With these synthetic tools in hand, we set about finding a fluoranthene derivative that would not crystallize and would remain highly blue-luminescent in the solid state. The most obvious candidate was a perphenylated derivative, which, due to steric hindrance, would keep the phenyl rings out of plane, thus presenting a ball-like surface to resist crystallization and reduce facial contacts that can lead to excimer quenching and bathochromic shifts in emission. To our surprise, only the 7,8,10-triphenyl derivative (2, Scheme 2) exhibited strong luminescence; the 7,8,9,10-tetraphenyl derivative is essentially non-fluorescent (in the solid state), and the 3,7,8,9-tetraphenyl derivative suffers from a large bathochromic shift in the solid state. The introduction of other functionality (e.g., esters, carboxylic acids, and halides) led to green/yellow emission and/or solubility problems. As with the other derivatives, 7,8,10-triphenylfluoranthene was synthesized via the Knoevenagel/Diels–Alder method (Scheme 2) from acenapthenequinone, diphenylacetone, and phenylacetylene, using only ethanol (EtOH) and (optionally) xylenes for solvents; all are inexpensive and readily available. Purification is uncompliC O M M U N IC A IO N S}, number={3}, journal={Advanced Materials}, publisher={Wiley-Blackwell}, author={Chiechi, R. C. and Tseng, R. J. and Marchioni, F. and Yang, Y. and Wudl, F.}, year={2006}, month={Feb}, pages={325–328} }
 @article{tseng_chiechi_wudl_yang_2006, title={Highly efficient 7,8,10-triphenylfluoranthene-doped blue organic light-emitting diodes for display application}, volume={88}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33644701607&partnerID=MN8TOARS}, DOI={10.1063/1.2167814}, abstractNote={We have demonstrated an organic light-emitting diode based on blue-fluorescent dopant 7,8,10-triphenylfluoranthene in a host of dipyrenylfluorene derivatives. The device shows pure blue emission with a peak wavelength of 456 nm and Commission International de L’Eclairage coordinate at (0.164, 0.188). An electroluminescence efficiency as high as 3.33cd∕A and external quantum efficiency of 2.48% can be achieved. Comparison of the photoluminescence and electroluminescence spectra reveals a nearly identical exciton relaxation and efficient energy transfer from the host to the dopant.}, number={9}, journal={Appl. Phys. Lett.}, publisher={AIP Publishing}, author={Tseng, Ricky J. and Chiechi, Ryan C. and Wudl, Fred and Yang, Yang}, year={2006}, pages={093512} }
 @article{chiechi_sonmez_wudl_2005, title={A Robust Electroactive n-Dopable Aromatic Polyketone}, volume={15}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-15944427112&partnerID=MN8TOARS}, DOI={10.1002/adfm.200400291}, abstractNote={A new n‐dopable polyketone, poly[(5‐(2,5‐dihexyl‐4‐(thiophen‐2‐yl)phenyl)thiophen‐2‐yl)(4‐ketophenyl)methanone] (PTK), is synthesized via Friedel–Crafts acylation. Though insulating in the neutral state, PTK becomes conductive upon electrochemical reduction. The stable, two‐electron, fully reversible reduction is probed spectroelectrochemically and via in‐situ conductivity measurements.}, number={3}, journal={Adv. Funct. Mater.}, publisher={Wiley-Blackwell}, author={Chiechi, R. C. and Sonmez, G. and Wudl, F.}, year={2005}, month={Mar}, pages={427–432} }
 @article{wan_chiechi_weakley_haley_2002, title={ChemInform Abstract: Synthesis and Spectroscopic Studies of Expanded Planar Dehydrotribenzo[n]annulenes Containing One or Two Isolated Alkene Units.}, volume={33}, DOI={10.1002/chin.200217083}, abstractNote={Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.}, number={17}, journal={ChemInform}, publisher={Wiley-Blackwell}, author={Wan, W. Brad and Chiechi, Ryan C. and Weakley, Timothy J. R. and Haley, Michael M.}, year={2002}, month={Apr}, pages={no-no} }
 @article{bell_chiechi_johnson_kimball_matzger_wan_weakley_haley_2001, title={A versatile synthetic route to dehydrobenzoannulenes via in situ generation of reactive alkynes}, volume={57}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035938180&partnerID=MN8TOARS}, DOI={10.1016/s0040-4020(01)00229-0}, abstractNote={This paper outlines the development of a protocol that allows in situ generation of unstable alkynes under Pd-catalyzed cross-coupling conditions. Cu-mediated intramolecular cyclization of the resultant α,ω-polyynes provides dehydrobenzoannulenes as singular species, in very good overall yields, and in a variety of topologies that are inaccessible by traditional routes or previously available in low yield only. In addition, we will discuss the solid-state structure and reactivity of these macrocycles, as well as the ability of the planar dehydrobenzoannulenes to support weak induced ring currents.}, number={17}, journal={Tetrahedron}, publisher={Elsevier BV}, author={Bell, Michael L and Chiechi, Ryan C and Johnson, Charles A and Kimball, David B and Matzger, Adam J and Wan, W Brad and Weakley, Timothy J.R and Haley, Michael M}, year={2001}, month={Apr}, pages={3507–3520} }
 @article{wan_chiechi_weakley_haley_2001, title={Synthesis and Spectroscopic Studies of Expanded Planar Dehydrotribenzo[n]annulenes Containing One or Two Isolated Alkene Units}, volume={2001}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0001951525&partnerID=MN8TOARS}, DOI={10.1002/1099-0690(200109)2001:18<3485::aid-ejoc3485>3.0.co;2-i}, abstractNote={Dehydrobenzoannulene derivatives containing isolated alkene linkages were synthesized by combining an in-situ Pd/Cu-mediated cross-coupling with an intramolecular cyclization strategy. 1H NMR studies of these macrocycles and comparison with related systems verify that highly alkynylated dehydrobenzoannulenes possess weak induced ring currents, indicative of aromatic (4n+2 π-systems) and anti-aromatic (4n π-systems) behavior, in spite of their large size and extensive benzannulation.}, number={18}, journal={Eur. J. Org. Chem.}, publisher={Wiley-Blackwell}, author={Wan, W. Brad and Chiechi, Ryan C. and Weakley, Timothy J. R. and Haley, Michael M.}, year={2001}, month={Sep}, pages={3485–3490} }