@article{marshburn_ashley_curtin_sultana_liu_vinueza_ison_jakubikova_2021, title={Are all charge-transfer parameters created equally? A study of functional dependence and excited-state charge-transfer quantification across two dye families}, volume={8}, ISSN={["1463-9084"]}, url={https://doi.org/10.1039/D1CP03383B}, DOI={10.1039/d1cp03383b}, abstractNote={Small molecule organic dyes have many potential uses in medicine, textiles, forensics, and light-harvesting technology. Being able to computationally predict the spectroscopic properties of these dyes could greatly expedite screening efforts, saving time and materials. Time-dependent density functional theory (TD-DFT) has been shown to be a good tool for this in many instances, but characterizing electronic excitations with charge-transfer (CT) character has historically been challenging and can be highly sensitive to the chosen exchange-correlation functional. Here we present a combined experimental and computational study of the excited-state electronic structure of twenty organic dyes obtained from the Max Weaver Dye Library at NCSU. Results of UV-vis spectra calculations on these dyes with six different exchange-correlation functionals, BP86, B3LYP, PBE0, M06, BH and HLYP, and CAM-B3LYP, were compared against their measured UV-vis spectra. It was found that hybrid functionals with modest amounts (20-30%) of included Hartree-Fock exchange are the most effective at matching the experimentally determined λmax. The interplay between the observed error, the functional chosen, and the degree of CT was analyzed by quantifying the CT character of λmax using four orbital and density-based metrics, Λ, Δr, SC and DCT, as well as the change in the dipole moment, Δμ. The results showed that the relationship between CT character and the functional dependence of error is not straightforward, with the observed behavior being dependent both on how CT was quantified and the functional groups present in the molecules themselves. It is concluded that this may be a result of the examined excitations having intermediate CT character. Ultimately it was found that the nature of the molecular "family" influenced how a given functional behaved as a function of CT character, with only two of the examined CT quantification methods, Δr and DCT, showing consistent behavior between the different molecular families. This suggests that further work needs to be done to ensure that currently used CT quantification methods show the same general trends across large sets of multiple dye families.}, journal={PHYSICAL CHEMISTRY CHEMICAL PHYSICS}, publisher={Royal Society of Chemistry (RSC)}, author={Marshburn, Richard Drew and Ashley, Daniel C. and Curtin, Gregory M. and Sultana, Nadia and Liu, Chang and Vinueza, Nelson R. and Ison, Elon A. and Jakubikova, Elena}, year={2021}, month={Aug} }
 @article{braley_ashley_kulesa_jakubikova_smith_2021, title={Electrode-adsorption activates trans-[Cr(cyclam)Cl-2](+) for electrocatalytic nitrate reduction (vol 56, pg 603, 2020)}, volume={57}, ISSN={["1364-548X"]}, DOI={10.1039/d1cc90148f}, abstractNote={Correction for 'Electrode-adsorption activates trans-[Cr(cyclam)Cl2]+ for electrocatalytic nitrate reduction' by Sarah E. Braley et al., Chem. Commun., 2020, 56, 603-606, DOI: 10.1039/C9CC08550E.}, number={35}, journal={CHEMICAL COMMUNICATIONS}, author={Braley, Sarah E. and Ashley, Daniel C. and Kulesa, Krista M. and Jakubikova, Elena and Smith, Jeremy M.}, year={2021}, month={May}, pages={4332–4332} }
 @article{kwon_ashley_jakubikova_2021, title={Halogenation affects driving forces, reorganization energies and "rocking" motions in strained [Fe(tpy)(2)](2+) complexes}, volume={9}, ISSN={["1477-9234"]}, DOI={10.1039/d1dt02314d}, abstractNote={Controlling the energetics of spin crossover (SCO) in Fe(II)-polypyridine complexes is critical for designing new multifunctional materials or tuning the excited-state lifetimes of iron-based photosensitizers. It is well established that the Fe-N "breathing" mode is important for intersystem crossing from the singlet to the quintet state, but this does not preclude other, less obvious, structural distortions from affecting SCO. Previous work has shown that halogenation at the 6 and 6'' positions of tpy (tpy = 2,2';6',2''-terpyridine) in [Fe(tpy)2]2+ dramatically increased the lifetime of the excited MLCT state and also had a large impact on the ground state spin-state energetics. To gain insight into the origins of these effects, we used density functional theory calculations to explore how halogenation impacts spin-state energetics and molecular structure in this system. Based on previous work we focused on the ligand "rocking" motion associated with SCO in [Fe(tpy)2]2+ by constructing one-dimensional potential energy surfaces (PESs) along the tpy rocking angle for various spin states. It was found that halogenation has a clear and predictable impact on ligand rocking and spin-state energetics. The rocking is correlated to numerous other geometrical distortions, all of which likely affect the reorganization energies for spin-state changes. We have quantified trends in reorganization energy and also driving force for various spin-state changes and used them to interpret the experimentally measured excited-state lifetimes.}, journal={DALTON TRANSACTIONS}, author={Kwon, Hyuk-Yong and Ashley, Daniel C. and Jakubikova, Elena}, year={2021}, month={Sep} }
 @article{braley_ashley_jakubikova_smith_2020, title={Electrode-adsorption activates trans-[Cr(cyclam)Cl-2](+) for electrocatalytic nitrate reduction}, volume={56}, ISSN={["1364-548X"]}, DOI={10.1039/c9cc08550e}, abstractNote={The mercury working electrode promotes electrocatalytic nitrate reduction by trans-Cr(cyclam)Cl2+.}, number={4}, journal={CHEMICAL COMMUNICATIONS}, author={Braley, Sarah E. and Ashley, Daniel C. and Jakubikova, Elena and Smith, Jeremy M.}, year={2020}, month={Jan}, pages={603–606} }
 @article{ashley_mukherjee_jakubikova_2019, title={Designing air-stable cyclometalated Fe(II) complexes: stabilization via electrostatic effects}, volume={48}, ISSN={["1477-9234"]}, DOI={10.1039/c8dt04402c}, abstractNote={Substitution of EWGs onto the cyclometelated iron complexes electrostatically stabilizes the Fe(ii) center while still preserving the increased ligand field strength.}, number={2}, journal={Dalton Transactions}, author={Ashley, D.C. and Mukherjee, S. and Jakubikova, E.}, year={2019}, pages={374–378} }
 @article{xu_kwon_ashley_chen_jakubikova_smith_2019, title={Intramolecular Hydrogen Bonding Facilitates Electrocatalytic Reduction of Nitrite in Aqueous Solutions}, volume={58}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.9b01274}, abstractNote={This work reports a combined experimental and computational mechanistic investigation into the electrocatalytic reduction of nitrite to ammonia by a cobalt macrocycle in an aqueous solution. In the presence of a nitrite substrate, the Co(III) precatalyst, [Co(DIM)(NO2)2]+ (DIM = 2,3-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,3-diene), is formed in situ. Cyclic voltammetry and density functional theory (DFT) calculations show that this complex is reduced by two electrons, the first of which is coupled with nitrite ligand loss, to provide the active catalyst. Experimental observations suggest that the key N-O bond cleavage step is facilitated by intramolecular proton transfer from an amine group of the macrocycle to a nitro ligand, as supported by modeling several potential reaction pathways with DFT. These results provide insights into how the combination of a redox active ligand and first-row transition metal can facilitate the multiproton/electron process of nitrite reduction.}, number={14}, journal={INORGANIC CHEMISTRY}, author={Xu, Song and Kwon, Hyuk-Yong and Ashley, Daniel C. and Chen, Chun-Hsing and Jakubikova, Elena and Smith, Jeremy M.}, year={2019}, month={Jul}, pages={9443–9451} }
 @article{ashley_jakubikova_2019, title={Predicting the electrochemical behavior of Fe(II) complexes from ligand orbital energies}, volume={376}, ISSN={["1010-6030"]}, DOI={10.1016/j.jphotochem.2019.01.026}, abstractNote={Abstract An attractive strategy for harvesting solar energy is to use dye-sensitized solar cells employing earth-abundant Fe(II) chromophores. These dyes need to meet several criteria to be effective for this purpose, including air stability, and an ability to be regenerated by common electrolytes. Both of these properties are related to the Fe(III/II) reduction potentials. Here we show how the Fe(III/II) reduction potentials of Fe(II) complexes can be estimated from a single experimental Fe(III/II) reduction potential and computationally cheap calculations on single isolated ligands. This method requires refinement, but could prove highly useful for large-scale computational screening and design of Fe(II) dyes.}, journal={JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY}, author={Ashley, Daniel C. and Jakubikova, Elena}, year={2019}, month={May}, pages={7–11} }
 @article{xu_ashley_kwon_ware_chen_losovyj_gao_jakubikova_smith_2018, title={A flexible, redox-active macrocycle enables the electrocatalytic reduction of nitrate to ammonia by a cobalt complex}, volume={9}, ISSN={["2041-6539"]}, DOI={10.1039/c8sc00721g}, abstractNote={Mechanistic investigations into electrocatalytic nitrate reduction by a cobalt complex reveal the critical role played by the flexible, redox-active ligand.}, number={22}, journal={CHEMICAL SCIENCE}, author={Xu, Song and Ashley, Daniel C. and Kwon, Hyuk-Yong and Ware, Gabrielle R. and Chen, Chun-Hsing and Losovyj, Yaroslav and Gao, Xinfeng and Jakubikova, Elena and Smith, Jeremy M.}, year={2018}, month={Jun}, pages={4950–4958} }
 @article{castillo_espinosa-duran_dobscha_ashley_debnath_hirsch_schrecke_baik_ortoleva_raghavachari_et al._2018, title={Amphiphile self-assembly dynamics at the solution-solid interface reveal asymmetry in head/tail desorption}, volume={54}, ISSN={["1364-548X"]}, DOI={10.1039/c8cc04465a}, abstractNote={Asymmetric dynamics in fundamental adsorption and desorption steps drive self-assembly at solution/solid interface.}, number={72}, journal={CHEMICAL COMMUNICATIONS}, author={Castillo, Henry D. and Espinosa-Duran, John M. and Dobscha, James R. and Ashley, Daniel C. and Debnath, Sibali and Hirsch, Brandon E. and Schrecke, Samantha R. and Baik, Mu-Hyun and Ortoleva, Peter J. and Raghavachari, Krishnan and et al.}, year={2018}, month={Sep}, pages={10076–10079} }
 @article{ashley_jakubikova_2018, title={Ray-Dutt and Bailar Twists in Fe(II)-Tris(2,2'-bipyridine): Spin States, Sterics, and Fe-N Bond Strengths}, volume={57}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.8b00560}, abstractNote={Twisting motions in six-coordinate trischelate transition-metal complexes have long been recognized as a potential reaction coordinate for nondissociative racemization by changing the coordination geometry from octahedral to trigonal prismatic in the transition state. These pathways have been previously established as the Bailar twist (conversion to D3 h symmetry) and the Ray-Dutt twist (conversion to C2 v symmetry). Twisting motions have been shown to be associated with changes in spin state and are therefore of relevance not only to thermal isomerization pathways but also to spin-crossover (SCO) and intersystem crossing mechanisms. In this work, density functional theory and complete active space self-consistent field calculations are used to probe the structural and energetic features of idealized Bailar and Ray-Dutt twisting mechanisms for a model Fe(II) polypyridine complex, [Fe(bpy)3]2+ (bpy = 2,2'-bipyridine). We find that the energies of the D3 h and C2 v trigonal prismatic structures are strongly dependent on spin state, with thermally accessible species only being possible on the quintet surface, enforcing the necessary relationship between SCO and torsional motion. The Ray-Dutt twist on the quintet surface is calculated to proceed with a low barrier, and is likely the preferable twisting mechanism for this complex. We additionally identify a new distorted Bailar twist of C3 h geometry, which is considerably lower in energy than the idealized D3 h structure due to a combination of both steric and electronic factors. The computational analysis presented herein offers insight into how Fe-N bond strength, interligand steric repulsion, and ligand flexibility can be exploited to influence the rates of different twisting mechanisms and the critical motions involved.}, number={9}, journal={INORGANIC CHEMISTRY}, author={Ashley, Daniel C. and Jakubikova, Elena}, year={2018}, month={May}, pages={5585–5596} }
 @article{ashley_jakubikova_2018, title={Tuning the Redox Potentials and Ligand Field Strength of Fe(II) Polypyridines: The Dual pi-Donor and pi-Acceptor Character of Bipyridine}, volume={57}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.8b01002}, abstractNote={The quintet-singlet energy difference (Δ EQ/S) in Fe(II) polypyridine complexes is often interpreted in terms of metal-ligand π interactions. DFT calculations on a series of substituted [Fe(bpy)3]2+ (bpy = 2,2'-bipyridine) complexes show the disparate magnitudes of substituent effects on tuning Δ EQ/S and reduction potentials ( E°). In this series, E° spans a much larger range than Δ EQ/S (2.07 vs 0.29 eV). While small changes in Δ EQ/S are controlled by metal-ligand π interactions, large changes in E° arise from modification of the electrostatic environment around the Fe center. Molecular orbital analysis reveals that, contrary to the typical description of bpy as a π-acceptor, bpy is better described as acting as both a π-donor and π-acceptor in [Fe(bpy)3]2+ complexes, even when it is substituted with highly electron withdrawing substituents. Overall, substituent modification is a useful strategy for fine-tuning the ligand field strength but not for significant reordering of the spin-state manifold, despite the large effect on metal-ligand electrostatic interactions.}, number={16}, journal={INORGANIC CHEMISTRY}, author={Ashley, Daniel C. and Jakubikova, Elena}, year={2018}, month={Aug}, pages={9907–9917} }
 @misc{ashley_jakubikova_2017, title={Ironing out the photochemical and spin-crossover behavior of Fe(II) coordination compounds with computational chemistry}, volume={337}, ISSN={["1873-3840"]}, DOI={10.1016/j.ccr.2017.02.005}, abstractNote={Effective strategies for designing Fe(II) coordination complexes with specifically tailored spin-state energetics can lead to advances in many areas of inorganic and materials chemistry. These include, but are not limited to, rational development of novel spin crossover complexes, efficient chromophores for photosensitization of dye-sensitized solar cells, and multifunctional materials. As the spin-state ordering of transition metal complexes is strongly rooted in their electronic structures, computational chemistry has naturally played an important role in assisting experimental work in this area. Unfortunately, despite many advances, accurate determination of the spin-state energetics of Fe(II) complexes still poses a remarkable challenge for virtually all applicable forms of electronic structure theory due to being controlled by a delicate balancing between correlation and exchange effects. This review focuses on some of the more notable successes and failures of modern electronic structure theory in properly describing these systems in the absence of solid-state effects. The strengths and weaknesses of using traditional wavefunction based methods and density functional theory are considered, and illustrative examples are provided to demonstrate that the modern computational chemist should make use of experimental data whenever possible and expect to utilize a combination of methods to obtain the best results. The review closes by briefly surveying some of the many interesting combined computational and experimental studies of Fe(II) chemistry that have lead to greater fundamental insight and practical understanding of this challenging class of systems.}, journal={COORDINATION CHEMISTRY REVIEWS}, author={Ashley, Daniel C. and Jakubikova, Elena}, year={2017}, month={Apr}, pages={97–111} }