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Unit cells of inorganic crystals are composed of few atoms and do not carry a separate identity. Crystals made of molecules are distinct in this regard, since features of isolated molecules often dominate, and periodic interactions are weak. Transport of excitation and charge in such systems can occur in both coherent and hopping regimes, depending on intermolecular interactions and temperature. Generally, periodic organic matter raises important questions about disorder, spatial extent of coherence, and the relative importance of local and periodic properties.
Modelling excitation and charge transport in Molecular Crystals with surface hopping techniques creates additional questions regarding the choice of representation (local or delocalized), treatment of quantum (de-)coherence, and model size to represent fluctuations and disorder. We contributed to development of methods suitable for such simulations.
L. J. Wang, O. V. Prezhdo, D. Beljonne, “Mixed quantum-classical dynamics for charge transport in organics”, Phys. Chem. Chem. Phys., 17, 12395-12406 (2015).
L.-J. Wang, O. V. Prezhdo, “A simple solution to the trivial crossing problem in surface hopping”, J. Phys. Chem. Lett., 5, 713 (2014).
Molecular Crystals exhibit an interesting phenomenon called singlet fission, in which an excitation of a singlet state by a photon generates two triplet states, thereby doubling the number of charge carriers generated per absorbed photon. A similar process called multiple exciton generation occurs in quantum dots. Singlet fission competes with energy relaxation and charge transfer, necessitating careful design of Molecular Crystals to maximize the yield.
L. J. Wang, Y. Olivier, O. V. Prezhdo, D. Beljonne, “Maximizing singlet fission by intermolecular packing”, J. Phys. Chem. Lett., 5, 3345-3353 (2014).
A. V. Akimov, O. V. Prezhdo “Non-adiabatic dynamics of charge transfer and singlet fission at the pentacene/C60 interface”, J. Am. Chem. Soc., 136, 1599 (2014).
Molecular systems can be made periodic on a ring or via absorption onto intrinsically periodic systems, such as carbon nanotubes. The use of templates provides another tool to control properties of periodic molecular assemblies, as demonstrated by our simulations.
S. Mondal, U. Chowdhury, S. Dey, M. Habib, C. Mora-Perez, T. Frauenheim, R. Sarkar, S. Pal, O. V. Prezhdo, “Controlling Charge Carrier Dynamics in Porphyrin Nanorings by Optically Active Templates”, J. Phys. Chem. Lett., 14, 11384-11392 (2023).
R. Sarkar, M. Habib, S. M. Kovaleko, S. Pal, O. V. Prezhdo, “Mixed Metals Slow Down Nonradiative Recombination in Saddle-Shaped Porphyrin Nanorings: A Time-Domain Atomistic Simulation”, J. Phys. Chem. C, 125, 16620-16628 (2021).
R. Sarkar, M. Habib, S. Pal, O. V. Prezhdo, “Ultrafast, asymmetric charge transfer and slow charge recombination in porphyrin/CNT composites demonstrated by time-domain atomistic simulation”, Nanoscale, 10, 12683-12694 (2018).
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