Coherence and Efficient Energy Transfer in Molecular Wires: Insights from Surface Hopping Simulations

Abstract

Understanding the dynamics of electronic energy transfer through a molecular wire is essential to understand the working of natural processes like photosynthesis. We investigate simpler 2 and 3‐site model Hamiltonians in this work to understand the importance of coherence to efficient energy transfer. We compare the results of surface hopping simulation with that of numerically exact results and rate theories. Different parameters are analyzed, motivated by a photosynthetic molecular wire – the FMO complex. A comparison of results from different theories shows that coherence can play an important role towards efficient energy transfer for certain parameters. When these coherences are important, even small couplings (of the order of 5 cm−1) in the Hamiltonian can significantly affect rates. Surface hopping simulations capture all the results correctly qualitatively. Rate theories, on the other hand, can differ significantly from numerically exact results when coherences become important. The results of this work should provide design guidelines for efficient energy transfer in molecular wires.

Tunability in 3-Site Electronic Excitation Transfer Dynamics: Insights into the Role of Perturbative Coupling

“…It is this anomalous pronounced dependence of the population dynamics on some values of the perturbative coupling between sites 1 and 3 which has been noticed in ref . We have managed to derive simple analytical expressions for the population dynamics of the 3-site system which explains this anomalous behavior and provide a range for the variation in time scales of the dynamics.…”

“…A recent numerical study has reported an unusually high variation in the uphill dynamics following a minor change in the intersite coupling between site-1 and site-3. 15 The authors attempted to explain this behavior by considering variances in the crossings of diabatic electronic potential energy surfaces corresponding to each site. However, a comprehensive quantitative description of this anomalous behavior is missing, and this will be the main motivation for our work.…”

“…Depending on the relative positioning of the energy levels, two possible configurations of the effective 3-site system are of significant interestuphill and downhill configurations. , The configuration with initial excitation localized at a particular site is deemed downhill when the intersite transitions, as determined by the energy landscape, proceed from higher energy levels to lower ones along all paths; otherwise, it is characterized as an uphill configuration, as shown in Figure . A recent numerical study has reported an unusually high variation in the uphill dynamics following a minor change in the intersite coupling between site-1 and site-3 . The authors attempted to explain this behavior by considering variances in the crossings of diabatic electronic potential energy surfaces corresponding to each site.…”