Small matrix path integral study of excitation energy transfer with distance-dependent electronic coupling

We use the small matrix path integral (SMatPI) methodology to examine the impact of electronic coupling strength variation on the population dynamics of model molecular aggregates containing up to five monomers in a single-file arrangement. The excited electronic state of each molecular unit interacts with the intramolecular vibrational modes, while the skeletal vibrations of the aggregate modulate the electronic coupling. The interaction between exciton states and intramolecular vibrations is treated using the iterative SMatPI algorithm, while the skeletal vibrations are included either through an augmented system Hamiltonian or through the ensemble-averaged classical path (EACP) approximation. We compare results obtained using an exponential coupling function of monomer separation, which describes short-distance interactions, and an inverse cubic model, relevant to dipolar interactions at larger monomer separations. We find that the variation of electronic coupling gives rise to behaviors that differ in significant ways from those observed when the coupling is held fixed, generally quenching oscillatory components of exciton populations. These findings supplement the insights derived from earlier work with fixed electronic couplings.