SymCorrel2021 | Excitation transport in molecular aggregates with thermal motion (Ritesh Pant)

One of the promising features of molecular aggregates is the transport of exciton energy over the long distance due to the Coulomb coupling [1]. In our work [2] we explore to what extent thermal motion of entire monomers can guide or enhance the excitation transport. The motion induces changes of aggregate geometry and hence modifies exciton states. Under certain conditions, excitation energy can thus be transported by the aggregate adiabatically, following a certain exciton eigenstate. We show that transport through motion can yield higher transport efficiencies in the presence of on-site energy disorder than the static counterpart for two simple models of molecular motion: (i) longitudinal vibrations along the aggregation direction (ii) torsional motion of planar monomers in a plane orthogonal to the aggregation direction. The parameters and potential shapes used are relevant to dye-molecule aggregates. We employ a quantum-classical method, in which molecules move through simplified classical molecular dynamics, while the excitation transport is treated quantum mechanically using Schroedinger’s equation [3]. For both models we find parameter regimes in which the motion enhances excitation transport, however these are more realistic for the torsional scenario, due to the limited motional range in a typical Morse type inter-molecular potential. We finally show that the transport enhancement can be linked to adiabatic quantum dynamics, for this we set an adiabaticity measure in [4]. This transport enhancement through adiabatic motion appears a useful resource to combat exciton trapping by disorder. In the next step of this exploration, we include the effect of intramolecular vibrations and extend the quantum dynamics calculation for excitation transport to an open-quantum-system technique, a non-Markovian quantum state diffusion [5], which is an efficient method to study the effect of non-Markovian environment on excitation transport. [1] A. T. Haedler, K. Kreger, A. Issac, B. Wittmann, M. Kivala, N. Hammer, J. Ko ̈hler, H.-W. Schmidt and R. Hildner, Nature, 2015, 523, 196. [2] R. Pant and S. Wu ̈ster, Physical Chemistry Chemical Physics 22, 21169 (2020). [3] J. C. Tully, The Journal of Chemical Physics, 1990, 93, 1061–1071. [4] R. Pant and S. Wu ̈ster, 2020, https://arxiv.org/abs/2007.10707. [5] D. Suess, A. Eisfeld and W. Strunz, Physical Review Letters, 2014, 113, 150403.



This contributed talk is part of the International Symposium on Correlated Electrons 2021, hosted and supported by MCQST on the MeetAnyway platform.