@article{guha_danilov_berkowitz_oluwajire_grace_2023, title={Consequences of Humidity Cycling on the Moisture Absorption Characteristics of Epoxy Resins with Different Network Architectures}, volume={1}, ISSN={["2637-6105"]}, url={https://doi.org/10.1021/acsapm.2c01570}, DOI={10.1021/acsapm.2c01570}, abstractNote={Absorbed moisture is a perpetual contributor to the steady loss of performance for in-service epoxy-based polymer materials. On the atomistic scale, the state of individual water molecules in a crosslinked epoxy is dependent on the strength of the secondary bonding interactions they engage in and their local physical environment. However, these chemical and physical variables can be tailored on the macroscopic scale through changes in the experimental curing schedule. In this study, crosslinked epoxy matrices with different network architectures were cured by varying the stoichiometric mixing ratios of the epoxy: hardener combination. The samples were subsequently subjected to fluctuating humidity conditions which comprises repeating cycles of high (∼95% RH) and ambient humidity. Both infrared (IR) spectroscopy and dielectric readings were successful in establishing a strong correlation between moisture absorption, network morphology, and dielectric properties. An anomalous behavior observed during the spectral peak analysis helped us understand how absorption history can redistribute the concentrations of water species at the same moisture concentrations. The results from this study elucidate how the phenomenon of absorption itself can act as a damage initiation event, and they also indicate that the spatial quantification of the different water species across a sample can allow us to map damage sites, nanopores, and areas with an overall higher void content.}, journal={ACS APPLIED POLYMER MATERIALS}, author={Guha, Rishabh D. and Danilov, Evgeny O. and Berkowitz, Katherine and Oluwajire, Oluwatimilehin and Grace, Landon R.}, year={2023}, month={Jan} }
 @article{wang_sadeghi_velayati_paul_hetzler_danilov_ligler_wei_2023, title={Low-rate smartphone videoscopy for microsecond luminescence lifetime imaging with machine learning}, volume={2}, ISSN={["2752-6542"]}, url={https://doi.org/10.1093/pnasnexus/pgad313}, DOI={10.1093/pnasnexus/pgad313}, abstractNote={Abstract Time-resolved techniques have been widely used in time-gated and luminescence lifetime imaging. However, traditional time-resolved systems require expensive lab equipment such as high-speed excitation sources and detectors or complicated mechanical choppers to achieve high repetition rates. Here, we present a cost-effective and miniaturized smartphone lifetime imaging system integrated with a pulsed ultraviolet (UV) light-emitting diode (LED) for 2D luminescence lifetime imaging using a videoscopy-based virtual chopper (V-chopper) mechanism combined with machine learning. The V-chopper method generates a series of time-delayed images between excitation pulses and smartphone gating so that the luminescence lifetime can be measured at each pixel using a relatively low acquisition frame rate (e.g. 30 frames per second [fps]) without the need for excitation synchronization. Europium (Eu) complex dyes with different luminescent lifetimes ranging from microseconds to seconds were used to demonstrate and evaluate the principle of V-chopper on a 3D-printed smartphone microscopy platform. A convolutional neural network (CNN) model was developed to automatically distinguish the gated images in different decay cycles with an accuracy of >99.5%. The current smartphone V-chopper system can detect lifetime down to ∼75 µs utilizing the default phase shift between the smartphone video rate and excitation pulses and in principle can detect much shorter lifetimes by accurately programming the time delay. This V-chopper methodology has eliminated the need for the expensive and complicated instruments used in traditional time-resolved detection and can greatly expand the applications of time-resolved lifetime technologies.}, number={10}, journal={PNAS NEXUS}, author={Wang, Yan and Sadeghi, Sina and Velayati, Alireza and Paul, Rajesh and Hetzler, Zach and Danilov, Evgeny and Ligler, Frances S. and Wei, Qingshan}, editor={Reis, RuiEditor}, year={2023}, month={Sep} }
 @article{guha_danilov_berkowitz_oluwajire_grace_2023, title={Suppressing Hydrogen Evolution in Aqueous Lithium-Ion Batteries with Double-Site Hydrogen Bonding}, volume={5}, ISSN={["2637-6105"]}, DOI={10.1021/acsapm.2c01570400}, number={1}, journal={ACS APPLIED POLYMER MATERIALS}, author={Guha, Rishabh D. and Danilov, Evgeny O. and Berkowitz, Katherine and Oluwajire, Oluwatimilehin and Grace, Landon R.}, year={2023}, month={Jan}, pages={400–411} }
 @article{chen_pedersen_dow_fayad_hauke_rosko_danilov_blakemore_dechert-schmitt_knauber_et al._2022, title={A Unified Approach to Decarboxylative Halogenation of (Hetero)aryl Carboxylic Acids}, volume={144}, ISSN={["1520-5126"]}, url={https://doi.org/10.1021/jacs.2c02392}, DOI={10.1021/jacs.2c02392}, abstractNote={Aryl halides are a fundamental motif in synthetic chemistry, playing a critical role in metal-mediated cross-coupling reactions and serving as important scaffolds in drug discovery. Although thermal decarboxylative functionalization of aryl carboxylic acids has been extensively explored, the scope of existing halodecarboxylation methods remains limited, and there currently exists no unified strategy that provides access to any type of aryl halide from an aryl carboxylic acid precursor. Herein, we report a general catalytic method for direct decarboxylative halogenation of (hetero)aryl carboxylic acids via ligand-to-metal charge transfer. This strategy accommodates an exceptionally broad scope of substrates. We leverage an aryl radical intermediate toward divergent functionalization pathways: (1) atom transfer to access bromo- or iodo(hetero)arenes or (2) radical capture by copper and subsequent reductive elimination to generate chloro- or fluoro(hetero)arenes. The proposed ligand-to-metal charge transfer mechanism is supported through an array of spectroscopic studies.}, number={18}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, publisher={American Chemical Society (ACS)}, author={Chen, Tiffany Q. and Pedersen, P. Scott and Dow, Nathan W. and Fayad, Remi and Hauke, Cory E. and Rosko, Michael C. and Danilov, Evgeny O. and Blakemore, David C. and Dechert-Schmitt, Anne-Marie and Knauber, Thomas and et al.}, year={2022}, month={May}, pages={8296–8305} }
 @article{nunn_milikisiyants_danilov_torelli_dei cas_zaitsev_shenderova_smirnov_shames_2022, title={Electron irradiation-induced paramagnetic and fluorescent defects in type Ib high pressure-high temperature microcrystalline diamonds and their evolution upon annealing}, volume={132}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/5.0103313}, DOI={10.1063/5.0103313}, abstractNote={Defects introduced to synthetic type Ib diamond micrometer-size particles by electron-beam irradiation were studied by electron paramagnetic resonance and photoluminescence (PL) spectroscopy as a function of e-beam fluence and post-irradiation thermal annealing. Increasing electron-beam fluence causes a substantial reduction of the substitutional nitrogen (P1) content, accompanied by progressively higher concentrations of paramagnetic negatively charged vacancies (V−) and triplet interstitials (R1/R2). Annealing results in a drastic decrease in the V− and R1/R2 content and an increase in the negatively charged nitrogen-vacancies (NV− or W15). Analysis of PL spectra allows for identification of color centers in the irradiated diamond samples and following their evolution after annealing. These data facilitate understanding of different factors contributing to the formation of color centers in diamond and promote efforts toward controlled engineering of optical centers in fluorescent diamond particles.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Nunn, Nicholas and Milikisiyants, Sergey and Danilov, Evgeny O. and Torelli, Marco D. and Dei Cas, Laura and Zaitsev, Alexander and Shenderova, Olga and Smirnov, Alex I. and Shames, Alexander I.}, year={2022}, month={Aug} }
 @article{ware_wright_mao_han_guffie_danilov_rech_you_luo_gautam_2021, title={Aggregation Controlled Charge Generation in Fullerene Based Bulk Heterojunction Polymer Solar Cells: Effect of Additive}, volume={13}, ISSN={["2073-4360"]}, url={https://doi.org/10.3390/polym13010115}, DOI={10.3390/polym13010115}, abstractNote={Optimization of charge generation in polymer blends is crucial for the fabrication of highly efficient polymer solar cells. While the impacts of the polymer chemical structure, energy alignment, and interface on charge generation have been well studied, not much is known about the impact of polymer aggregation on charge generation. Here, we studied the impact of aggregation on charge generation using transient absorption spectroscopy, neutron scattering, and atomic force microscopy. Our measurements indicate that the 1,8-diiodooctane additive can change the aggregation behavior of poly(benzodithiophene-alt-dithienyl difluorobenzotriazole (PBnDT-FTAZ) and phenyl-C61-butyric acid methyl ester (PCBM)polymer blends and impact the charge generation process. Our observations show that the charge generation can be optimized by tuning the aggregation in polymer blends, which can be beneficial for the design of highly efficient fullerene-based organic photovoltaic devices.}, number={1}, journal={POLYMERS}, author={Ware, Washat and Wright, Tia and Mao, Yimin and Han, Shubo and Guffie, Jessa and Danilov, Evgeny O. and Rech, Jeromy and You, Wei and Luo, Zhiping and Gautam, Bhoj}, year={2021}, month={Jan} }
 @article{kim_danilov_yoon_el-shafei_freeman_2021, title={Characterization of the photophysics of a mixed system of red disperse dyes using experimental and theoretical methods}, volume={184}, ISSN={["1873-3743"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85090416933&partnerID=MN8TOARS}, DOI={10.1016/j.dyepig.2020.108745}, abstractNote={While many disperse dyes have been studied in a variety of scientific fields, from textiles to biochemistry, most studies have been conducted on individual dyes having specific chromogens. However, bearing in mind that dyes are often used in combinations, in order to produce target colors for outdoor environments, an understanding of the photophysics of mixed system of dyes is important. As an extension of our previous work pertaining to scarlet and blue disperse dyes developed for use in outdoor applications, we investigated the photophysics of two commercial colorants and their various components (azo and anthraquinone red disperse dyes) to help account for their photostability when used in combinations. In this regard, experimental and modeling studies were performed to get insight into excited-state properties following light absorption. Transient absorption spectroscopy (TAS) showed that the dye mixtures dissipated excited-state energy much faster than the main component (an anthraquinone disperse red dye), which emphasized the benefit of multiple components in a commercial dye. The reduced excited-state lifetime clearly showed that the presence of additional dyes can play an important role in the photophysics and improving photostability.}, journal={DYES AND PIGMENTS}, author={Kim, Bo Hyung and Danilov, Evgeny and Yoon, Seog Joon and El-Shafei, Ahmed and Freeman, Harold}, year={2021}, month={Jan} }
 @article{zhang_cao_huang_danilov_chung_sun_yang_2021, title={Gamma-Ray Detection Using Bi-Poor Cs2AgBiBr6 Double Perovskite Single Crystals}, volume={9}, ISSN={["2195-1071"]}, url={https://doi.org/10.1002/adom.202001575}, DOI={10.1002/adom.202001575}, abstractNote={Lead halide perovskites have recently attracted intensive attention as competitive alternative candidates of legacy compound materials CdTe, CdZnTe, and TlBr for high sensitivity energy‐resolving gamma‐ray detection at room temperature. However, the use of lead in these lead halide perovskites, which is necessary for increasing the stopping power of gamma radiation, poses a serious environmental concern due to the high toxicity of lead. In this regard, environmental‐friendly perovskite‐based gamma‐ray detector materials with key energy‐resolving capabilities are highly desired. Here, the gamma energy‐resolving performance of a new class of all‐inorganic and lead‐free Cs2AgBiBr6 double perovskite single crystals (SCs) is reported. Two types of Cs2AgBiBr6 SCs, prepared by Bi‐normal and Bi‐poor precursor solutions, respectively, have been grown. Their mobilities and response to gamma radiation are presented. Density of trap states in Bi‐poor Cs2AgBiBr6 SCs (2.65 × 109 cm−3) is one order of magnitude lower than that in Bi‐normal Cs2AgBiBr6 SCs (3.85 × 1010 cm−3). Using laser‐induced photocurrent measurements, the obtained mobility–lifetime (μ–τ) product in Bi‐poor Cs2AgBiBr6 SCs is 1.47 × 10−3 cm2 V−1, indicating their great potentials for gamma‐ray detection. Further, the fabricated detector based on Bi‐poor Cs2AgBiBr6 SC shows response to 59.5 keV gamma‐ray with an energy resolution of 13.91%.}, number={8}, journal={ADVANCED OPTICAL MATERIALS}, publisher={Wiley}, author={Zhang, Zheng and Cao, Da and Huang, Zhengjie and Danilov, Evgeny O. and Chung, Ching-Chang and Sun, Dali and Yang, Ge}, year={2021}, month={Apr} }
 @article{ware_wright_davita_danilov_gautam_2021, title={Impact of Dimensionality on Optoelectronic Properties of Hybrid Perovskites}, volume={2021}, ISBN={1687-529X}, DOI={10.1155/2021/8822703}, abstractNote={Organometal halides are promising materials for photovoltaic applications, offering tunable electronic levels, excellent charge transport, and simplicity of thin-film device fabrication. Two-dimensional (2D) perovskites have emerged as promising candidates over three-dimensional (3D) ones due to their interesting optical and electrical properties. However, maximizing the power conversion efficiency is a critical issue to improve the performance of these solar cells. In this work, we studied the photophysics of a two-dimensional (2D) perovskite (CH3NH3)2Pb(SCN)2I2 thin film using steady-state and time-resolved absorption and emission spectroscopy and compared it with the three-dimensional (3D) counterpart CH3NH3PbI3. We observed a higher bandgap and faster charge recombination in (CH3NH3)2Pb(SCN)2I2 compared to CH3NH3PbI3. This work provides an improved understanding of fundamental photophysical processes in perovskite structures and provides the guideline for the design, synthesis, and fabrication of solar cells.}, journal={INTERNATIONAL JOURNAL OF PHOTOENERGY}, author={Ware, Washat and Wright, Tia and Davita, Antony and Danilov, Evgeny and Gautam, Bhoj}, year={2021} }
 @article{karimi_tabei_fayad_saber_danilov_jones_castellano_gabbai_2021, title={Photodriven Elimination of Chlorine From Germanium and Platinum in a Dinuclear Pt-II -> Ge-IV Complex}, volume={9}, ISSN={["1521-3773"]}, url={https://doi.org/10.1002/anie.202107485}, DOI={10.1002/anie.202107485}, abstractNote={Searching for a connection between the two-electron redox behavior of group 14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o-(Ph 2 P)C 6 H 4 ) 2 Ge IV Cl 2 ]Pt II Cl 2 and [(o-(Ph 2 P)C 6 H 4 ) 2 ClGe III ]Pt III Cl 3 , two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o-(Ph 2 P)C 6 H 4 ) 2 ClGe III ]Pt I Cl with quantum yields of 1.7% and 3.2% for the Ge IV -Pt II and Ge III -Pt II isomers, respectively.  Conversion of the Ge IV -Pt II into the platinum germyl complex is a rare example of a light induced transition metal-main group element bond forming process.  Finally, transient absorption spectroscopy studies carried out on the Ge III -Pt III isomer point to a ligand arene-Cl • charge-transfer complex as an intermediate.}, journal={ANGEWANDTE CHEMIE-INTERNATIONAL EDITION}, publisher={Wiley}, author={Karimi, Mohammadjavad and Tabei, Elham S. and Fayad, Remi and Saber, Mohamed R. and Danilov, Evgeny O. and Jones, Cameron and Castellano, Felix N. and Gabbai, Francois P.}, year={2021}, month={Sep} }
 @article{fayad_engl_danilov_hauke_reiser_castellano_2020, title={Correction to “Direct Evidence of Visible Light-Induced Homolysis in Chlorobis(2,9-dimethyl-1,10-phenanthroline)copper(II)”}, volume={11}, url={https://doi.org/10.1021/acs.jpclett.0c02010}, DOI={10.1021/acs.jpclett.0c02010}, abstractNote={RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to “Direct Evidence of Visible Light-Induced Homolysis in Chlorobis(2,9-dimethyl-1,10-phenanthroline)copper(II)”Remi FayadRemi FayadMore by Remi Fayad, Sebastian EnglSebastian EnglMore by Sebastian Engl, Evgeny O. DanilovEvgeny O. DanilovMore by Evgeny O. Danilovhttp://orcid.org/0000-0002-5551-3749, Cory E. HaukeCory E. HaukeMore by Cory E. Haukehttp://orcid.org/0000-0001-8822-0961, Oliver Reiser*Oliver ReiserMore by Oliver Reiserhttp://orcid.org/0000-0003-1430-573X, and Felix N. Castellano*Felix N. CastellanoMore by Felix N. Castellanohttp://orcid.org/0000-0001-7546-8618Cite this: J. Phys. Chem. Lett. 2020, 11, 14, 5749Publication Date (Web):July 7, 2020Publication History Published online7 July 2020Published inissue 16 July 2020https://doi.org/10.1021/acs.jpclett.0c02010Copyright © 2020 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views630Altmetric-Citations2LEARN 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 PDF (442 KB) Get e-Alerts Get e-Alerts}, number={14}, journal={The Journal of Physical Chemistry Letters}, publisher={American Chemical Society (ACS)}, author={Fayad, Remi and Engl, Sebastian and Danilov, Evgeny O. and Hauke, Cory E. and Reiser, Oliver and Castellano, Felix N.}, year={2020}, month={Jul}, pages={5749–5749} }
 @article{yi_peng_xu_seyitliyev_ho_danilov_kim_reynolds_amassian_gundogdu_et al._2020, title={Critical Role of Polymer Aggregation and Miscibility in Nonfullerene-Based Organic Photovoltaics}, volume={10}, ISSN={["1614-6840"]}, url={http://dx.doi.org/10.1002/aenm.201902430}, DOI={10.1002/aenm.201902430}, abstractNote={Understanding the correlation between polymer aggregation, miscibility, and device performance is important to establish a set of chemistry design rules for donor polymers with nonfullerene acceptors (NFAs). Employing a donor polymer with strong temperature‐dependent aggregation, namely PffBT4T‐2OD [poly[(5,6‐difluoro‐2,1,3‐benzothiadiazol‐4,7‐diyl)‐alt‐(3,3″′‐di(2‐octyldodecyl)‐2,2′;5′,2″;5″,2″′‐quaterthiophen‐5,5‐diyl)], also known as PCE‐11 as a base polymer, five copolymer derivatives having a different thiophene linker composition are blended with the common NFA O‐IDTBR to investigate their photovoltaic performance. While the donor polymers have similar optoelectronic properties, it is found that the device power conversion efficiency changes drastically from 1.8% to 8.7% as a function of thiophene content in the donor polymer. Results of structural characterization show that polymer aggregation and miscibility with O‐IDTBR are a strong function of the chemical composition, leading to different donor–acceptor blend morphology. Polymers having a strong tendency to aggregate are found to undergo fast aggregation prior to liquid–liquid phase separation and have a higher miscibility with NFA. These properties result in smaller mixed donor–acceptor domains, stronger PL quenching, and more efficient exciton dissociation in the resulting cells. This work indicates the importance of both polymer aggregation and donor–acceptor interaction on the formation of bulk heterojunctions in polymer:NFA blends.}, number={8}, journal={ADVANCED ENERGY MATERIALS}, author={Yi, Xueping and Peng, Zhengxing and Xu, Bing and Seyitliyev, Dovletgeldi and Ho, Carr Hoi Yi and Danilov, Evgeny O. and Kim, Taesoo and Reynolds, John R. and Amassian, Aram and Gundogdu, Kenan and et al.}, year={2020}, month={Feb} }
 @article{fayad_engl_danilov_hauke_reiser_castellano_2020, title={Direct Evidence of Visible Light-Induced Homolysis in Chlorobis(2,9-dimethyl-1,10-phenanthroline)copper(II)}, volume={11}, ISSN={1948-7185 1948-7185}, url={http://dx.doi.org/10.1021/acs.jpclett.0c01601}, DOI={10.1021/acs.jpclett.0c01601}, abstractNote={Developments in the field of photoredox catalysis that leveraged the long-lived excited states of Ir(III) and Ru(II) photosensitizers to enable radical coupling processes, paved the way for explorations of synthetic transformations that would otherwise remain unrealized. While first row transition metal photocatalysts have not been as extensively investigated, valuable synthetic transformations covering broad scopes of olefin functionalization have been recently reported featuring photoactivated chlorobis(phenanthroline) Cu(II) complexes. In the current study, the photochemical processes underpinning the catalytic activity of [Cu(dmp)2Cl]Cl (dmp = 2,9-dimethyl-1,10-phenanthroline) were investigated. The combined results from static spectroscopic investigations and conventional photochemistry, ultrafast transient absorption, and electron paramagnetic resonance (EPR) spin trapping experiments, strongly support blue light (ex = 427 or 470 nm) induced Cu-Cl homolytic bond cleavage in [Cu(dmp)2Cl]+ occurring in less than 100 femtoseconds. Based on electronic structure calculations, this bond breaking photochemistry corresponds to the Cl → Cu(II) ligand-to-metal charge transfer (LMCT) transition, unmasking a Cu(I) species [Cu(dmp)2]+ and a Cl• atom, thereby serving as a departure point for both Cu(I)- or Cu(II)-based photoredox transformations. No net photochemistry was observed through direct excitation of the ligand-field transitions in the red (ex = 785 or 800 nm), and all combined experiments indicated no evidence of Cu-Cl bond cleavage under these conditions. The underlying visible light-induced homolysis (VLIH) of a metal-ligand bond yielding a one electron reduced photosensitizer and a radical species, may form the basis for novel photoredox transformations based on first row transition metal complexes.}, number={13}, journal={The Journal of Physical Chemistry Letters}, publisher={American Chemical Society (ACS)}, author={Fayad, Remi and Engl, Sebastian and Danilov, Evgeny O. and Hauke, Cory E. and Reiser, Oliver and Castellano, Felix N.}, year={2020}, month={Jun}, pages={5345–5349} }
 @article{torelli_nunn_jones_vedelaar_padamati_schirhagl_hamers_shames_danilov_zaitsev_et al._2020, title={High Temperature Treatment of Diamond Particles Toward Enhancement of Their Quantum Properties}, volume={8}, ISSN={["2296-424X"]}, DOI={10.3389/fphy.2020.00205}, abstractNote={Fluorescence of the negatively charged nitrogen-vacancy (NV−) center of diamond is sensitive to external electromagnetic fields, lattice strain, and temperature due to the unique triplet configuration of its spin states. Their use in particulate diamond allows for the possibility of localized sensing and magnetic-contrast-based differential imaging in complex environments with high fluorescent background. However, current methods of NV− production in diamond particles are accompanied by the formation of a large number of parasitic defects and lattice distortions resulting in deterioration of the NV− performance. Therefore, there are significant efforts to improve the quantum properties of diamond particles to advance the field. Recently it was shown that rapid thermal annealing (RTA) at temperatures much exceeding the standard temperatures used for NV− production can efficiently eliminate parasitic paramagnetic impurities and, as a result, by an order of magnitude improve the degree of hyperpolarization of 13C via polarization transfer from optically polarized NV− centers in micron-sized particles. Here, we demonstrate that RTA also improves the maximum achievable magnetic modulation of NV− fluorescence in micron-sized diamond by about 4x over conventionally produced diamond particles endowed with NV−. This advancement can continue to bridge the pathway toward developing nano-sized diamond with improved qualities for quantum sensing and imaging.}, journal={FRONTIERS IN PHYSICS}, author={Torelli, Marco D. and Nunn, Nicholas A. and Jones, Zachary R. and Vedelaar, Thea and Padamati, Sandeep Kumar and Schirhagl, Romana and Hamers, Robert J. and Shames, Alexander I. and Danilov, Evgeny O. and Zaitsev, Alexander and et al.}, year={2020}, month={Jun} }
 @article{favale_hauke_danilov_yarnell_castellano_2020, title={Ligand-triplet migration in iridium(iii) cyclometalates featuring π-conjugated isocyanide ligands}, volume={49}, ISSN={1477-9226 1477-9234}, url={http://dx.doi.org/10.1039/D0DT02100H}, DOI={10.1039/d0dt02100h}, abstractNote={The manipulation of the triplet excited state manifold leads to large differences in the photophysical properties within a given class of metal-organic chromophores. By the appropriate choice of ancillary ligand, large changes can be made both to the order and nature of the lowest excited states and therefore to the resulting photophysical properties. Herein, a series of four bis-2-phenylpyridine (ppy) cyclometalated Ir(iii) compounds bearing two arylisocyanide ligands were synthesized and photophysically characterized to understand the effects of using ancillary ligands featuring systematic changes in π-conjugation. By varying the arylisocyanide ligands, the photoluminescence quantum yield ranged from 5% to 49% and the excited state lifetime ranged between 24 μs and 2 ms. These variations in photophysical response are consistent with lowering the triplet ligand-centered (3LC) state of the arylisocyanide ligand as the π system was extended, confirmed by 77 K photoluminescence emission spectra and ultrafast transient absorption experiments. The latter analysis gleaned detailed insight into the importance of the interplay of the 3LC state of the phenylpyridine and arylisocyanide ligands in these polychromophic Ir(iii) molecules.}, number={29}, journal={Dalton Transactions}, publisher={Royal Society of Chemistry (RSC)}, author={Favale, Joseph M. and Hauke, Cory E. and Danilov, Evgeny O. and Yarnell, James E. and Castellano, Felix N.}, year={2020}, pages={9995–10002} }
 @article{zhang_chung_huang_vetter_seyitliyev_sun_gundogdu_castellano_danilov_yang_2020, title={Towards radiation detection using Cs2AgBiBr6 double perovskite single crystals}, volume={269}, ISSN={0167-577X}, url={http://dx.doi.org/10.1016/j.matlet.2020.127667}, DOI={10.1016/j.matlet.2020.127667}, abstractNote={In this work, we studied the optical- and electrical- properties of emerging Cs2AgBiBr6 double perovskite single crystals and demonstrated their potential for detecting ionizing radiation. We prepared Cs2AgBiBr6 double perovskite single crystals from a saturated aqueous solution. Low-temperature photoluminescence (PL) was employed to determine the bandgap energies of Cs2AgBiBr6, which are 2.00 eV (indirect) and 2.26 eV (direct) respectively. Using the space charge limited current method, we estimated the density of trap states and mobility of charge carriers as 1.44 × 1010 cm−3 and 7.02 cm2/V-s respectively. A lower bound value of the mobility-lifetime (μ-τ) product of 2.48 × 10−3 cm2/V was determined using 450 nm laser excitation, which was sufficient for ensuring a long drift distance of charge carriers for several radiation detector applications. Furthermore, we tested the direct response of Cs2AgBiBr6 single crystals to X-ray radiation. Our Cs2AgBiBr6 single crystal device with gold electrodes deposited on the two parallel surfaces exhibited excellent linear response to low energy X-rays.}, journal={Materials Letters}, publisher={Elsevier BV}, author={Zhang, Zheng and Chung, Ching-Chang and Huang, Zhengjie and Vetter, Eric and Seyitliyev, Dovletgeldi and Sun, Dali and Gundogdu, Kenan and Castellano, Felix N. and Danilov, Evgeny O. and Yang, Ge}, year={2020}, month={Jun}, pages={127667} }
 @article{awwad_bui_danilov_castellano_2020, title={Visible-Light-Initiated Free-Radical Polymerization by Homomolecular Triplet-Triplet Annihilation}, volume={6}, ISSN={2451-9294}, url={http://dx.doi.org/10.1016/j.chempr.2020.08.019}, DOI={10.1016/j.chempr.2020.08.019}, abstractNote={Polymerization reactions initiated by ultraviolet light are ubiquitous in scores of industrial applications but would markedly benefit from visible-light activation to overcome stability, energy consumption, light penetration, and sample geometry limitations. The current work leverages visible-light-driven homomolecular triplet-triplet annihilation (TTA) in zinc(II) meso-tetraphenylporphyrin (ZnTPP) to initiate facile free-radical polymerization in trimethylolpropane triacrylate (TMPTA) and methyl acrylate (MA) monomers through ultrafast electron transfer quenching. Selective Q-band (S1) excitation of ZnTPP in the green or yellow sensitizes TTA occurring between two 3ZnTPP∗ energized chromophores, ultimately generating the highly reducing S2 excited state on one ZnTPP molecule (Ered = −2.13 V versus saturated calomel electrode, SCE). Subsequently, this S2 state engages in electron transfer with TMPTA or MA, thereby initiating the radical polymerization process. Bimolecular electron transfer was confirmed through optically gated fluorescence upconversion. FT-IR and EPR spin-trapping experiments verified visible-light-initiated polymerization leading to the formation of well-defined macro- and microscopic objects.}, number={11}, journal={Chem}, publisher={Elsevier BV}, author={Awwad, Nancy and Bui, Anh Thy and Danilov, Evgeny O. and Castellano, Felix N.}, year={2020}, month={Nov}, pages={3071–3085} }
 @article{karki_paul_rajan_belfore_poudel_rockett_danilov_castellano_arehart_marsillac_2019, title={Analysis of Recombination Mechanisms in RbF-Treated CIGS Solar Cells}, volume={9}, ISSN={["2156-3403"]}, url={https://doi.org/10.1109/JPHOTOV.2018.2877596}, DOI={10.1109/JPHOTOV.2018.2877596}, abstractNote={In this paper, we studied the effect of rubidium fluoride (RbF) post-deposition treatment (PDT) on the properties of Cu(In,Ga)Se<sub>2</sub> (CIGS) solar cells. Specifically, the recombination mechanisms were analyzed by a series of characterizations including thermal and optical defect spectroscopies, temperature dependent current density–voltage measurements, and time resolved photoluminescence. It was found that the main effect of RbF PDT on the solar cell was an increase of the open circuit-voltage, <inline-formula><tex-math notation="LaTeX">$V_{{\text{oc}}}$</tex-math></inline-formula>, by 30 mV due to a decrease of the values of the diode quality factor and reverse saturation current. Recombination mechanisms were identified as being in the CIGS space charge region, likely at the grain boundaries and near the CIGS surface. Breakdown of contributions to the <inline-formula><tex-math notation="LaTeX">$V_{{\text{oc}}}$</tex-math></inline-formula> increase showed that part of it is due to an increase of the majority carrier concentration (16 mV) and another to the increase in the minority carrier lifetime (1 mV). The latest is mostly due to a reduction in the E<sub>V</sub>+0.99 eV deep-level trap density. An additional CIGS surface modification (contributing 13 mV), observed by the secondary ion mass spectrometry, is essential to explain the full change in <inline-formula><tex-math notation="LaTeX">$V_{{\text{oc}}}$</tex-math></inline-formula>.}, number={1}, journal={IEEE JOURNAL OF PHOTOVOLTAICS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Karki, Shankar and Paul, Pran and Rajan, Grace and Belfore, Benjamin and Poudel, Deewakar and Rockett, Angus and Danilov, Evgeny and Castellano, Felix and Arehart, Aaron and Marsillac, Sylvain}, year={2019}, month={Jan}, pages={313–318} }
 @article{karki_paul_deitz_poudel_rajan_belfore_danilov_castellano_grassman_arehart_et al._2019, title={Degradation Mechanism in Cu(In,Ga)Se-2 Material and Solar Cells Due to Moisture and Heat Treatment of the Absorber Layer}, volume={9}, ISSN={["2156-3381"]}, url={https://doi.org/10.1109/JPHOTOV.2019.2912707}, DOI={10.1109/JPHOTOV.2019.2912707}, abstractNote={The impact of moisture and heat treatment on the microstructural, chemical, and electrical properties of Cu(In,Ga)Se<sub>2</sub> films and their collective effect on the solar cell device performance was studied. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy measurements show that water exposure causes surface modification and alters the alkali metal distribution, while no composition or structural effect was observed. Deep level transient and optical spectroscopies revealed that the trap densities (<italic>N<sub>T</sub></italic>) for both the <italic>E<sub>V</sub></italic> + 0.65 eV and <italic>E<sub>V</sub></italic> + 0.98 eV traps increase after water exposure, while the majority carrier concentration (<italic>N<sub>A</sub></italic>) decreases. Time-resolved photoluminescence (PL) and steady-state PL measurements indicated the presence of static, not dynamic, quenching. Reduction of open-circuit voltage (<italic>V</italic><sub>OC</sub>) and fill factor (FF) was observed for the devices but was not associated with a change of recombination mechanism, which remains in the absorber space charge region. A small increase in series resistance and shunt conductance accounts for most of the FF change, while the modification in both <italic>N<sub>A</sub></italic> and <italic>N<sub>T</sub></italic> yield most of the change in <italic>V</italic><sub>OC</sub>. A gradient of majority carrier concentration, related to the alkali profile, also yields a small voltage-dependent current collection after moisture and heat treatment.}, number={4}, journal={IEEE JOURNAL OF PHOTOVOLTAICS}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Karki, Shankar and Paul, Pran and Deitz, Julia I. and Poudel, Deewakar and Rajan, Grace and Belfore, Benjamin and Danilov, Evgeny O. and Castellano, Felix N. and Grassman, Tyler J. and Arehart, Aaron and et al.}, year={2019}, month={Jul}, pages={1138–1143} }
 @article{lennox_danilov_dempsey_2019, title={Delayed photoacidity produced through the triplet-triplet annihilation of a neutral pyranine derivative}, volume={21}, ISSN={["1463-9084"]}, DOI={10.1039/c9cp02929j}, abstractNote={A novel pyranine derivative, EtHPTA-OH, was synthesized via the substitution of the anionic sulfonate groups with neutral diethylsulfonamide groups. The photophysical and photochemical properties of EtHPTA-OH were studied using photoluminescence quenching and transient absorption spectroscopy. The singlet state of EtHPTA-OH was found to be highly photoacidic (pKa* = 8.74 in acetonitrile). A series of aniline and pyridine bases were used to investigate excited-state proton transfer (ESPT) from singlet EtHPTA-OH, and rate constants for singlet quenching via ESPT were determined (kq = 5.18 × 109 to 1.05 × 1010 M-1 s-1). EtHPTA-OH was also found to exhibit a long-lived triplet state which reacts through a triplet-triplet annihilation (TTA) process to reform singlet EtHPTA-OH on timescales of up to 80 μs. Detection of ESPT photoproducts on timescales comparable to that of TTA singlet regeneration provides strong evidence for photoacidic behavior stemming from the regenerated singlet EtHPTA-OH.}, number={29}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, author={Lennox, J. Christian and Danilov, Evgeny O. and Dempsey, Jillian L.}, year={2019}, month={Aug}, pages={16353–16358} }
 @article{shaikh_chakraborty_alatis_cai_danilov_morris_2019, title={Light harvesting and energy transfer in a porphyrin-based metal organic framework}, volume={216}, ISSN={["1364-5498"]}, url={https://doi.org/10.1039/C8FD00194D}, DOI={10.1039/c8fd00194d}, abstractNote={We present the synthesis and photophysical characterization of a water stable PCN-223(freebase) metal organic framework (MOF) constructed from meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP). The photophysical properties of the synthesized crystalline material were studied using a wide range of steady-state and time-resolved spectroscopic techniques. Quenching experiments performed on TCPP and PCN-223 demonstrated that the extent and the rate of quenching in the MOF is significantly higher than the monomeric ligand. Based on these results, we propose that upon photo-excitation, the singlet excitation energy migrates across neutral TCPP linkers until it is quenched by a N-protonated TCPP linker. The N-protonated linkers act as trap states that deactivate the excited state to the ground state. Variable temperature measurements aided in understanding the mechanism of singlet-singlet energy transfer in the PCN-223 MOF. The rate of energy transfer and the total exciton hopping distance in PCN-223 were calculated in order to quantify the energy transfer characteristics of PCN-223. Nanosecond transient absorption spectroscopy was used to study the triplet excited state photophysics in both the free ligand and PCN-223 MOF. Furthermore, femtosecond transient absorption spectroscopy was employed to get a better understanding of the photophysical processes taking place in the ligand and MOF on ultrafast timescales. Efficient energy transfer (Förster radius = 54.5 Å) accompanied with long distance exciton hopping (173 Å) was obtained for the PCN-223 MOF.}, journal={FARADAY DISCUSSIONS}, publisher={Royal Society of Chemistry (RSC)}, author={Shaikh, Shaunak M. and Chakraborty, Arnab and Alatis, James and Cai, Meng and Danilov, Evgeny and Morris, Amanda J.}, year={2019}, month={Jul}, pages={174–190} }
 @article{hany_yang_zhou_sun_gundogdu_seyitliyev_danilov_castellano_sun_vetter_et al._2019, title={Low temperature cathodoluminescence study of Fe-doped β-Ga2O3}, volume={257}, ISSN={0167-577X}, url={http://dx.doi.org/10.1016/j.matlet.2019.126744}, DOI={10.1016/j.matlet.2019.126744}, abstractNote={Optical and electrical properties along the b-axis of Fe-doped β-Ga2O3 were studied using low temperature cathodoluminescence (CL) spectroscopy, optical absorption spectroscopy and current-voltage (IV) measurements. The optical absorption spectroscopy showed an absorption edge without near edge shoulder and the corresponding optical bandgap was calculated to be 4.45 eV using direct band gap treatment. The temperature dependent CL measurements exhibited a strong blue to ultraviolet (UV) band composed of multiple low intensity peaks in the blue range, a main blue peak, a main UV peak, and a weak UV band from the as-grown Fe-doped β-Ga2O3. After a controlled annealing in air, the emissions changed to a red to near infrared (R-NIR) band with two sharp peaks and an UV band that is resolved at room temperature to three UV broad peaks. The R-NIR sharp peaks from the air-annealed sample were ascribed to incorporation of nitrogen during air annealing.}, journal={Materials Letters}, publisher={Elsevier BV}, author={Hany, Ibrahim and Yang, Ge and Zhou, Chuanzhen Elaine and Sun, Cheng and Gundogdu, Kenan and Seyitliyev, Dovletgeldi and Danilov, Evgeny O. and Castellano, Felix N. and Sun, Dali and Vetter, Eric and et al.}, year={2019}, month={Dec}, pages={126744} }
 @article{favale_danilov_yarnell_castellano_2019, title={Photophysical Processes in Rhenium(I) Diiminetricarbonyl Arylisocyanides Featuring Three Interacting Triplet Excited States}, volume={58}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/acs.inorgchem.9b01155}, DOI={10.1021/acs.inorgchem.9b01155}, abstractNote={We present a series of four transition-metal complexes based on the rhenium(I) tricarbonyl 1,10-phenanthroline (phen) template, with a lone ancillary arylisocyanide (CNAr) ligand to yield metal-organic chromophores of the generic molecular formula [Re(phen)(CO)3(CNAr)]+ [CNAr = 2,6-diisopropylphenyl isocyanide (1), 4-phenyl-2,6-diisopropylphenyl isocyanide (2), 4-phenylethynyl-2,6-diisopropylphenyl isocyanide (3), and 4-biphenyl-2,6-diisopropylphenyl isocyanide (4)]. This particular series features varied degrees of π-conjugation length in the CNAr moiety, resulting in significant modulation in the resultant photophysical properties. All molecules possess long-lived [8-700 μs at room temperature (RT)], strongly blue-green photoluminescent and highly energetic excited states (λmax,em = 500-518 nm; Φ = 14-64%). Each of these chromophores has been photophysically investigated using static and dynamic spectroscopic techniques, the latter probed from ultrafast to supra-nanosecond time scales using transient absorption and photoluminescence (PL). Time-resolved PL intensity decays recorded as a function of the temperature were consistent with the presence of at least two emissive states lying closely spaced in energy with a third nonemissive state lying much higher in energy and likely ligand-field in character. The combined experimental evidence, along with the aid of electronic structure calculations (density functional theory and time-dependent density functional theory performed at the M06/Def2-SVP/SDD level), illustrates that the CNAr ligand is actively engaged in manipulating the excited-state decay in three of these molecules (2-4), wherein the triplet metal-to-ligand charge-transfer (3MLCT) state along with two distinct triplet ligand-centered (3LC) excited-state configurations (phen and CNAr) conspire to produce the resultant photophysical properties. Because the π conjugation within the CNAr ligand was extended, an interesting shift in the dominant photophysical processes was observed. When the CNAr conjugation length is short, as in 1, the phenanthroline 3LC state dominates, resulting in a configurationally mixed triplet excited state of both LC and MLCT character. With more extended π conjugation in the CNAr subunit (2-4), the initially generated 3LC(phen)/3MLCT excited state ultimately migrates to the CNAr 3LC state on the order of tens of picoseconds. Molecules 3 and 4 in this series also feature unique examples of inorganic excimer formation, as evidenced by dynamic self-quenching in the corresponding PL intensity decays accompanied by the observation of a short-lived low-energy emission feature.}, number={13}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Favale, Joseph M., Jr. and Danilov, Evgeny O. and Yarnell, James E. and Castellano, Felix N.}, year={2019}, month={Jun}, pages={8750–8762} }
 @article{younts_danilov_gundogdu_gautam_2018, title={Charge generation dynamics in polymer nonfullerene solar cells with low energy loss}, volume={8}, ISSN={["1947-7988"]}, DOI={10.1117/1.JPE.8.032209}, abstractNote={Abstract. Polymer nonfullerene solar cells are emerging as an alternative of polymer fullerene solar cells. However, maximizing the short-circuit density and open-circuit voltage is a critical issue in these solar cells. Here, using ultrafast spectroscopy, we measured exciton relaxation and charge separation dynamics in polymer nonfullerene blend with low driving force. Our study indicates high polaron yield despite the energy loss of as low as 0.59 eV. This suggests that the small driving force has minimum detrimental effect in realizing high performance in polymer nonfullerene solar cells.}, number={3}, journal={JOURNAL OF PHOTONICS FOR ENERGY}, author={Younts, Robert and Danilov, Evgeny and Gundogdu, Kenan and Gautam, Bhoj}, year={2018} }
 @article{taliaferro_danilov_castellano_2018, title={Ultrafast Dynamics of the Metal-to-Ligand Charge Transfer Excited States of Ir(III) Proteo and Deutero Dihydrides}, volume={122}, ISSN={1089-5639 1520-5215}, url={http://dx.doi.org/10.1021/acs.jpca.8b02266}, DOI={10.1021/acs.jpca.8b02266}, abstractNote={For decades, transition metal hydrides have been at the forefront of numerous photocatalytic reactions leveraging either photoacid or photohydride generation. Of upmost importance is the nature of the M-H bond itself, which is typically the major site of photochemical reactivity, particularly in Ir(III) hydrides featuring metal-to-ligand charge transfer (MLCT) excited states. As a departure point for understanding the fundamental spectroscopy and photophysics of the MLCT excited states of Ir(III) diimine hydrides, cis-[Ir(bpy)2H2]+ (bpy = 2,2'-bipyridine) and its deuterated analogue cis-[Ir(bpy)2D2]+ were prepared and investigated. The robust nature of these molecules enabled detailed solution-based photophysical studies using ultrafast transient absorption and infrared spectroscopy, executed without the generation of permanent photoproducts. Static Fourier transform infrared and Raman spectra (λex = 785 nm) of these two molecules revealed weak but measurable Ir-H and Ir-D stretching vibrations centered at 2120 and 1510 cm-1, respectively. Short-lived (τ = 25 ps) MLCT excited states were observed for both cis-[Ir(bpy)2H2]+ and cis-[Ir(bpy)2D2]+ following femtosecond pulsed laser excitation at 480 nm in visible and near-IR transient absorption experiments. A similar time constant was measured for the in-phase and out-of-phase Ir-H stretching modes of the triplet excited state between 1900 and 2200 cm-1 using transient IR spectroscopy. The Ir-D stretching modes in the MLCT excited state were masked by bpy-localized vibrations rendering quantitative evaluation of these modes difficult. The time-resolved infrared data were consistent with density functional theory calculated mid-IR difference spectra in both of these molecules, yielding quantitative matches to the measured IR difference spectra. The information presented here provides valuable insight for understanding the primary photophysical events and transient absorption and IR spectroscopic signatures likely to be encountered throughout metal hydride photochemistry.}, number={18}, journal={The Journal of Physical Chemistry A}, publisher={American Chemical Society (ACS)}, author={Taliaferro, Chelsea M. and Danilov, Evgeny O. and Castellano, Felix N.}, year={2018}, month={Apr}, pages={4430–4436} }
 @article{shames_smirnov_milikisiyants_danilov_nunn_mcguire_torelli_shenderova_2017, title={Fluence-Dependent Evolution of Paramagnetic Triplet Centers in e-Beam Irradiated Microcrystalline lb Type HPHT Diamond}, volume={121}, ISSN={["1932-7447"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85031327261&partnerID=MN8TOARS}, DOI={10.1021/acs.jpcc.7b06514}, abstractNote={Paramagnetic triplet centers produced by e-beam irradiation of synthetic microcrystalline Ib-type high-pressure high-temperature (HPHT) diamonds were studied by continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy at X-band (9.4 GHz), pulsed EPR at X- and Q-bands (34 GHz), and fluorescence spectroscopies as a function of radiation fluences up to 5 × 1019 e–/cm2. EPR spectra of mostly “forbidden” Δms = 2 electronic spin transitions observed at g ≈ 4 (i.e., so-called half-field EPR spectra) reveal the presence of the main W15 triplet defects associated with the fluorescent negatively charged nitrogen-vacancy (NV–) centers as well as additional triplet spin centers identified as W16, W17, W18, and W33 that appear upon increasing the e-beam fluence. Consequent annealing at 1,400 °C significantly reduces the content of W17, W18, and W33 but not W15 and W16 defects. The efficacy of NV– center fabrication as a function of fluence dependent e-beam irradiation is also reported.}, number={40}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Shames, Alexander I. and Smirnov, Alex I. and Milikisiyants, Sergey and Danilov, Evgeny O. and Nunn, Nicholas and McGuire, Gary and Torelli, Marco D. and Shenderova, Olga}, year={2017}, month={Oct}, pages={22335–22346} }
 @article{anand_sampat_danilov_peng_rupich_chabal_gartstein_malko_2016, title={Broadband transient absorption study of photoexcitations in lead halide perovskites: Towards a multiband picture}, volume={93}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.93.161205}, abstractNote={Ultrafast transient pump-probe measurements of thin ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbI}}_{3}$ perovskite films over a wide spectral range from 350 to 800 nm reveal a family of photoinduced bleach (PB) and absorption (PA) features unequivocally pointing to the fundamentally multiband character of the underlying electronic structure. Excitation pump-energy dependent kinetics of three long-lived PB peaks at 1.65, 2.55, and 3.15 eV along with a broad PA band shows the involvement of band-edge thermalized carriers in all transitions and at least four, possibly more, electronic bands. The evolution of the transient signatures is described in terms of the redistribution of the conserved oscillator strength of the whole system. The multiband perspective opens up different directions for understanding and controlling photoexcitations in hybrid perovskites.}, number={16}, journal={PHYSICAL REVIEW B}, author={Anand, Benoy and Sampat, Siddharth and Danilov, Evgeny O. and Peng, Weina and Rupich, Sara M. and Chabal, Yves J. and Gartstein, Yuri N. and Malko, Anton V.}, year={2016}, month={Apr} }
 @article{gautam_younts_li_yan_danilov_klump_constantinou_so_you_ade_et al._2016, title={Charge photogeneration in organic photovoltaics: Role of hot versus cold charge-transfer excitons}, volume={6}, DOI={10.1002/aenm.201670002}, abstractNote={In article number 1501032, Kenan Gundogdu and co-workers present hot and cold exciton charge separation at the polymer/fullerene interface. On the left of the image high energy photons create excitons with excess energy. On the right of the image low energy photons create solely low energy charge transfer excitons. Both types separate into free charges effectively.}, number={1}, journal={Advanced Energy Materials}, author={Gautam, B. R. and Younts, R. and Li, W. T. and Yan, L. and Danilov, Evgeny and Klump, E. and Constantinou, I. and So, Franky and You, W. and Ade, Harald and et al.}, year={2016} }
 @article{gautam_lee_younts_lee_danilov_kim_gundogdu_2015, title={Charge Generation Dynamics in Efficient All-Polymer Solar Cells: Influence of Polymer Packing and Morphology}, volume={7}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.5b08531}, abstractNote={All-polymer solar cells exhibit rapid progress in power conversion efficiency (PCE) from 2 to 7.7% over the past few years. While this improvement is primarily attributed to efficient charge transport and balanced mobility between the carriers, not much is known about the charge generation dynamics in these systems. Here we measured exciton relaxation and charge separation dynamics using ultrafast spectroscopy in polymer/polymer blends with different molecular packing and morphology. These measurements indicate that preferential face-on configuration with intermixed nanomorphology increases the charge generation efficiency. In fact, there is a direct quantitative correlation between the free charge population in the ultrafast time scales and the external quantum efficiency, suggesting not only the transport but also charge generation is key for the design of high performance all polymer solar cells.}, number={50}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Gautam, Bhoj R. and Lee, Changyeon and Younts, Robert and Lee, Wonho and Danilov, Evgeny and Kim, Bumjoon J. and Gundogdu, Kenan}, year={2015}, month={Dec}, pages={27586–27591} }
 @article{gautam_barrette_mai_yan_zhang_danilov_you_ade_gundogdu_2015, title={Direct Optical Observation of Stimulated Emission from Hot Charge Transfer Excitons in Bulk Heterojunction Polymer Solar Cells}, volume={119}, ISSN={["1932-7447"]}, DOI={10.1021/acs.jpcc.5b06557}, abstractNote={Charge transfer excitons (CTEs) play an important role in semiconducting polymer-based optoelectronic applications. In organic photovoltaics, they are an intermediate step between tightly bound excitons and free charges. Although CT state energies at the interface of bulk heterojunction organic solar cells have been reported using quantum chemical calculations and by sensitive external quantum efficiency (EQE) measurements, direct optical observation of CT states was limited to relaxed, low energy, CT levels. Here we used polarization anisotropy transient absorption experiments to measure emission from high-energy CT levels. These experimental methods provide means to study high energy CT state dynamics in BHJs with controlled molecular orientations and complement theoretical calculations of interfacial CT state energies.}, number={34}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Gautam, Bhoj R. and Barrette, Andy and Mai, Cong and Yan, Liang and Zhang, Qianqian and Danilov, Eygeny and You, Wei and Ade, Harald and Gundogdu, Kenan}, year={2015}, month={Aug}, pages={19697–19702} }
 @article{mosca_khnayzer_lazorski_danilov_castellano_anzenbacher_2015, title={Sensing of 2,4,6-Trinitrotoluene (TNT) and 2,4-Dinitrotoluene (2,4-DNT) in the Solid State with Photoluminescent Ru-II and Ir-III Complexes}, volume={21}, ISSN={["1521-3765"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84929926404&partnerID=MN8TOARS}, DOI={10.1002/chem.201405717}, abstractNote={A series of metal-organic chromophores containing Ru(II) or Ir(III) were studied for the luminometric detection of nitroaromatic compounds, including trinitrotoluene (TNT). These complexes display long-lived, intense photoluminescence in the visible region and are demonstrated to serve as luminescent sensors for nitroaromatics. The solution-based behavior of these photoluminescent molecules has been studied in detail in order to identify the mechanism responsible for metal-to-ligand charge-transfer (MLCT) excited state quenching upon addition of TNT and 2,4-dinitrotoluene (2,4-DNT). A combination of static and dynamic spectroscopic measurements unequivocally confirmed that the quenching was due to a photoinduced electron transfer (PET) process. Ultrafast transient absorption experiments confirmed the formation of the TNT radical anion product following excited state electron transfer from these metal complexes. Reported for the first time, photoluminescence quenching realized through ink-jet printing and solid-state titrations was used for the solid-state detection of TNT; achieving a limit-of-quantitation (LOQ) as low as 5.6 ng cm(-2). The combined effect of a long-lived excited state and an energetically favorable driving force for the PET process makes the Ru(II) and Ir(III) MLCT complexes discussed here particularly appealing for the detection of nitroaromatic volatiles and related high-energy compounds.}, number={10}, journal={CHEMISTRY-A EUROPEAN JOURNAL}, author={Mosca, Lorenzo and Khnayzer, Rony S. and Lazorski, Megan S. and Danilov, Evgeny O. and Castellano, Felix N. and Anzenbacher, Pavel, Jr.}, year={2015}, month={Mar}, pages={4056–4064} }
 @article{garakyaraghi_danilov_mccusker_castellano_2015, title={Transient Absorption Dynamics of Sterically Congested Cu(I) MLCT Excited States}, volume={119}, ISSN={["1089-5639"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84926435446&partnerID=MN8TOARS}, DOI={10.1021/acs.jpca.5b00901}, abstractNote={Subpicosecond through supra-nanosecond transient absorption dynamics of the homoleptic Cu(I) metal-to-ligand charge transfer (MLCT) photosensitizers including the benchmark [Cu(dmp)2](+) (dmp =2,9-dimethyl-1,10-phenanthroline) chromophore, as well as [Cu(dsbp)2](+) (dsbp =2,9-di(sec-butyl)-1,10-phenanthroline and [Cu(dsbtmp)2](+) (dsbtmp =2,9-di(sec-butyl)-3,4,7,8-tetramethyl-1,10-phenanthroline) were investigated in dichloromethane and tetrahydrofuran solutions. Visible and near-IR spectroelectrochemical measurements of the singly reduced [Cu(dsbp)2](+) and [Cu(dsbtmp)2](+) species were determined in tetrahydrofuran, allowing for the identification of redox-specific phenanthroline-based radical anion spectroscopic signatures prevalent in the respective transient absorption experiments. This study utilized four different excitation wavelengths (418, 470, 500, and 530 nm) to elucidate dynamics on ultrafast times scales spanning probe wavelengths ranging from the UV to the near-IR (350 to 1450 nm). With the current time resolution of ∼150 fs, initial excited state decay in all three compounds was found to be independent of excitation wavelength. Not surprisingly, there was little to no observed influence of solvent in the initial stages of excited state decay in any of these molecules including [Cu(dmp)2](+), consistent with results from previous investigators. The combined experimental data revealed two ranges of time constants observed on short time scales in all three MLCT chromophores and both components lengthen as a function of structure in the following manner: [Cu(dsbtmp)2](+) < [Cu(dsbp)2](+) < [Cu(dmp)2](+). The molecule with the most inhibited potential for distortion, [Cu(dsbtmp)2](+), possessed the fastest ultrafast dynamics as well as the longest excited state lifetimes in both solvents. These results are consistent with a small degree of excited state distortion, rapid intersystem crossing, and weak vibronic coupling to the ground state. The concomitant systematic variation in both initial time constants, assigned to pseudo-Jahn-Teller distortion and intersystem crossing, suggest that both processes are intimately coupled in all molecules in the series. The variability in these time scales illustrate that strongly impeded structural distortion in Cu(I) MLCT excited state enables more rapid surface crossings in the initial deactivation dynamics.}, number={13}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, author={Garakyaraghi, Sofia and Danilov, Evgeny O. and McCusker, Catherine E. and Castellano, Felix N.}, year={2015}, month={Apr}, pages={3181–3193} }