@article{tichnell_miller_liu_mukherjee_jakubikova_mccusker_2020, title={Influence of Electrolyte Composition on Ultrafast Interfacial Electron Transfer in Fe-Sensitized TiO2-Based Solar Cells}, volume={124}, ISSN={["1932-7455"]}, DOI={10.1021/acs.jpcc.9b09404}, abstractNote={TiO2-based dye-sensitized solar cells employing Fe(2,2′-bipyridine-4,4′-dicarboxylic acid)2(CN)2 (F2CA) have been studied by spectroscopic, electrochemical, photoelectrochemical, time-resolved spec...}, number={3}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Tichnell, Christopher R. and Miller, Jennifer N. and Liu, Chang and Mukherjee, Sriparna and Jakubikova, Elena and McCusker, James K.}, year={2020}, month={Jan}, pages={1794–1811} }
 @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{britz_gawelda_assefa_jamula_yarranton_galler_khakhulin_diez_hardee_doumy_et al._2019, title={Using Ultrafast X-ray Spectroscopy To Address Questions in Ligand-Field Theory: The Excited State Spin and Structure of [Fe(dcpp)(2)](2+)}, volume={58}, ISBN={1520-510X}, DOI={10.1021/acs.inorgchem.9b01063}, abstractNote={We have employed a range of ultrafast X-ray spectroscopies in an effort to characterize the lowest energy excited state of [Fe(dcpp)2]2+ (where dcpp is 2,6-(dicarboxypyridyl)pyridine). This compound exhibits an unusually short excited-state lifetime for a low-spin Fe(II) polypyridyl complex of 270 ps in a room-temperature fluid solution, raising questions as to whether the ligand-field strength of dcpp had pushed this system beyond the 5T2/3T1 crossing point and stabilizing the latter as the lowest energy excited state. Kα and Kβ X-ray emission spectroscopies have been used to unambiguously determine the quintet spin multiplicity of the long-lived excited state, thereby establishing the 5T2 state as the lowest energy excited state of this compound. Geometric changes associated with the photoinduced ligand-field state conversion have also been monitored with extended X-ray absorption fine structure. The data show the typical average Fe-ligand bond length elongation of ∼0.18 Å for a 5T2 state and suggest a high anisotropy of the primary coordination sphere around the metal center in the excited 5T2 state, in stark contrast to the nearly perfect octahedral symmetry that characterizes the low-spin 1A1 ground state structure. This study illustrates how the application of time-resolved X-ray techniques can provide insights into the electronic structures of molecules-in particular, transition metal complexes-that are difficult if not impossible to obtain by other means.}, number={14}, journal={INORGANIC CHEMISTRY}, author={Britz, Alexander and Gawelda, Wojciech and Assefa, Tadesse A. and Jamula, Lindsey L. and Yarranton, Jonathan T. and Galler, Andreas and Khakhulin, Dmitry and Diez, Michael and Hardee, Manuel and Doumy, Gilles and et al.}, year={2019}, pages={9341–9350} }
 @article{mukherjee_liu_jakubikova_2018, title={Comparison of Interfacial Electron Transfer Efficiency in [Fe(ctpy)(2)](2+)-TiO2 and [Fe(cCNC)(2)](2+)-TiO2 Assemblies: Importance of Conformational Sampling}, volume={122}, ISSN={["1089-5639"]}, DOI={10.1021/acs.jpca.7b10932}, abstractNote={Fe(II)-polypyridines have limited applications as chromophores in dye-sensitized solar cells due to the short lifetimes (∼100 fs) of their photoactive metal-to-ligand charge transfer (MLCT) states formed upon photoexcitation. Recently, a 100-fold increase in the MLCT lifetime was observed in a [Fe(CNC)2]2+ complex (CNC = 2,6-bis(3-methylimidazole-1-ylidine)pyridine) which has strong σ-donating N-heterocyclic carbene ligand in comparison to the weaker field parent [Fe(tpy)2]2+ complex (tpy = 2,2':6',2″-terpyridine). This study utilizes density functional theory (DFT), time-dependent DFT, and quantum dynamics simulations to investigate the interfacial electron transfer (IET) in [Fe(cCNC)2]2+ (cCNC = 4'-carboxy-2,6-bis(3-methylimidazole-1-ylidine)pyridine) and [Fe(ctpy)2]2+ (ctpy = 4'-carboxy-2,2':6',2″-terpyridine) sensitized TiO2. Our results suggest that the replacement of tpy by CNC ligand does not significantly speed up the IET kinetics in the [Fe(cCNC)2]2+-TiO2 assembly in comparison to the [Fe(ctpy)2]2+-TiO2 analogue. The high IET efficiency in the [Fe(cCNC)2]2+-TiO2 assemblies is therefore due to longer lifetime of [Fe(cCNC)2]2+ photoactive 3MLCT states rather than faster electron injection kinetics. It was also found that the inclusion of conformational sampling in the computational model is important for proper description of the IET processes in these systems, as the models relying on the use of only fully optimized structures may yield misleading results. The simulations presented in this work also illustrate various pitfalls of utilizing properties such as electronic coupling, number of available acceptor states, and driving force, as well as calculations based on Fermi's golden rule framework, to reach conclusions on the IET efficiency in dye-semiconductor systems.}, number={7}, journal={JOURNAL OF PHYSICAL CHEMISTRY A}, author={Mukherjee, Sriparna and Liu, Chang and Jakubikova, Elena}, year={2018}, month={Feb}, pages={1821–1830} }
 @article{mukherjee_torres_jakubikova_2017, title={HOMO inversion as a strategy for improving the light-absorption properties of Fe(II) chromophores}, volume={8}, ISSN={["2041-6539"]}, DOI={10.1039/c7sc02926h}, abstractNote={Substitution of π-conjugated donor groups onto the polypyridine ligands in Fe(ii) complexes inverts the HOMO character and improves the light-absorption.}, number={12}, journal={CHEMICAL SCIENCE}, author={Mukherjee, Sriparna and Torres, David E. and Jakubikova, Elena}, year={2017}, month={Dec}, pages={8115–8126} }
 @article{frasco_mukherjee_sommer_perry_lambic_abboud_jakubikoya_ison_2016, title={Nondirected C-H Activation of Arenes with Cp*Ir(III) Acetate Complexes: An Experimental and Computational Study}, volume={35}, ISSN={["1520-6041"]}, DOI={10.1021/acs.organomet.6b00308}, abstractNote={Combined experimental and computational studies have revealed factors that influence the nondirected C–H activation in Cp*Ir complexes that contain carboxylate ligands. A two-step acetate-assisted pathway was shown to be operational where the first step involves substrate binding and the second step involves cleavage of the C–H bond of the substrate. A nonlinear Hammett plot was obtained to examine substituted arenes where a strong electronic dependence (ρ = 1.67) was observed for electron-donating groups, whereas no electronic dependence was observed for electron-withdrawing groups. Electron-donating substituents in the para position were shown to have a bigger impact on the C–H bond cleavage step, whereas electron-withdrawing substituents influenced the substrate-binding step. Although cleavage of the C–H bond was predicted to be more facile with arenes that contain substituents in the para position by DFT calculations, the cyclometalations of anisole and benzonitrile were observed experimentally. This ...}, number={15}, journal={ORGANOMETALLICS}, publisher={American Chemical Society (ACS)}, author={Frasco, Daniel A. and Mukherjee, Sriparna and Sommer, Roger D. and Perry, Cody M. and Lambic, Nikola S. and Abboud, Khalil A. and Jakubikoya, Elena and Ison, Elon A.}, year={2016}, month={Aug}, pages={2435–2445} }
 @article{mukherjee_bowman_jakubikova_2015, title={Cyclometalated Fe(II) Complexes as Sensitizers in Dye-Sensitized Solar Cells}, volume={54}, ISSN={["1520-510X"]}, DOI={10.1021/ic502438g}, abstractNote={Dye-sensitized solar cells (DSSCs) often utilize transition metal-based chromophores for light absorption and semiconductor sensitization. Ru(II)-based dyes are among the most commonly used sensitizers in DSSCs. As ruthenium is both expensive and rare, complexes based on cheaper and more abundant iron could serve as a good alternative. In this study, we investigate Fe(II)-bis(terpyridine) and its cyclometalated analogues, in which pyridine ligands are systematically replaced by aryl groups, as potential photosensitizers in DSSCs. We employ density functional theory at the B3LYP/6-31G*,SDD level to obtain the ground state electronic structure of these complexes. Quantum dynamics simulations are utilized to study interfacial electron transfer between the Fe(II) photosensitizers and a titanium dioxide semiconductor. We find that cyclometalation stabilizes the singlet ground state of these complexes by 8-19 kcal/mol but reduces the electron density on the carboxylic acid attached to the aryl ring. The results suggest that cyclometalation provides a feasible route to increasing the efficiency of Fe(II) photosensitizers but that care should be taken in choosing the substitution position for the semiconductor anchoring group.}, number={2}, journal={INORGANIC CHEMISTRY}, author={Mukherjee, Sriparna and Bowman, David N. and Jakubikova, Elena}, year={2015}, month={Jan}, pages={560–569} }
 @article{nance_bowman_mukherjee_kelley_jakubikova_2015, title={Insights into the Spin-State Transitions in [Fe(tpy)2]2+: Importance of the Terpyridine Rocking Motion}, volume={54}, ISSN={0020-1669 1520-510X}, url={http://dx.doi.org/10.1021/acs.inorgchem.5b01747}, DOI={10.1021/acs.inorgchem.5b01747}, abstractNote={Iron(II) polypyridine complexes have the potential for numerous applications on a global scale, such as sensitizers, sensors, and molecular memory. The excited-state properties of these systems, particularly the intersystem crossing (ISC) rates, are sensitive to the choice of ligands and can be significantly altered depending on the coordination environment. We employ density functional theory and Smolyak's sparse grid interpolation algorithm to construct potential energy surfaces (PESs) for the photophysically relevant states ((1)A, (3,5)MC, and (1,3)MLCT) of the [Fe(tpy)2](2+) (tpy = 2,2':6',2"-terpyridine) complex, with the goal of obtaining a deeper understanding of the ground- and excited-state electronic structure of this system. The three dimensions that define our adiabatic PESs consist of equatorial and axial metal-ligand bond length distortions and a terpyridine ligand "rocking angle", which has not previously been investigated. The intersection crossing seams and minimum energy crossing points (MECPs) between surfaces are also determined. Overall, we find that the PESs of all electronic excited states investigated are characterized by low-energy valleys along the tpy rocking-angle coordinate. This results in the presence of large low-energy areas around the MECPs on the intersection seams of different electronic states and indicates that inclusion of this third coordinate is crucial for an adequate description of the PESs and surface crossing seams of the [Fe(tpy)2](2+) complex. Finally, we suggest that tuning the energetics of the tpy ligand rocking motion could provide a way to control the ISC process in this complex.}, number={23}, journal={Inorganic Chemistry}, publisher={American Chemical Society (ACS)}, author={Nance, James and Bowman, David N. and Mukherjee, Sriparna and Kelley, C. T. and Jakubikova, Elena}, year={2015}, month={Nov}, pages={11259–11268} }
 @article{bowman_mukherjee_barnes_jakubikova_2015, title={Linker dependence of interfacial electron transfer rates in Fe(II)-polypyridine sensitized solar cells}, volume={27}, number={13}, journal={Journal of Physics. Condensed Matter}, author={Bowman, D. N. and Mukherjee, S. and Barnes, L. J. and Jakubikova, E.}, year={2015} }
 @article{bowman_bondarev_mukherjee_jakubikova_2015, title={Tuning the Electronic Structure of Fe(II) Polypyridines via Donor Atom and Ligand Scaffold Modifications: A Computational Study}, volume={54}, ISSN={["1520-510X"]}, DOI={10.1021/acs.inorgchem.5b01409}, abstractNote={Fe(II) polypyridines are an important class of pseudo-octahedral metal complexes known for their potential applications in molecular electronic switches, data storage and display devices, sensors, and dye-sensitized solar cells. Fe(II) polypyridines have a d(6) electronic configuration and pseudo-octahedral geometry and can therefore possess either a high-spin (quintet) or a low-spin (singlet) ground state. In this study, we investigate a series of complexes based on [Fe(tpy)2](2+) (tpy = 2,2';6',2″-terpyridine) and [Fe(dcpp)2](2+) (dcpp = 2,6-bis(2-carboxypyridyl)pyridine). The ligand field strength in these complexes is systematically tuned by replacing the central pyridine with five-membered (N-heterocyclic carbene, pyrrole, furan) or six-membered (aryl, thiazine-1,1-dioxide, 4-pyrone) moieties. To determine the impact of ligand substitutions on the relative energies of metal-centered states, the singlet, triplet, and quintet states of the Fe(II) complexes were optimized in water (PCM) using density functional theory at the B3LYP+D2 level with 6-311G* (nonmetals) and SDD (Fe) basis sets. It was found that the dcpp ligand scaffold allows for a more ideal octahedral coordination environment in comparison to the tpy ligand scaffold. The presence of six-membered central rings also allows for a more ideally octahedral coordination environment relative to five-membered central rings, regardless of the ligand scaffold. We find that the ligand field strength in the Fe(II) polypyridines can be tuned by altering the donor atom identity, with C donor atoms providing the strongest ligand field.}, number={17}, journal={INORGANIC CHEMISTRY}, author={Bowman, David N. and Bondarev, Alexey and Mukherjee, Sriparna and Jakubikova, Elena}, year={2015}, month={Sep}, pages={8786–8793} }