Exciton-Vibration Dynamics in J-Aggregates of a Perylene Bisimide from Real-Time Path Integral Calculations

We use the modular path integral (MPI) and the small matrix path integral (SMatPI) methods to obtain numerically exact, fully quantum mechanical results for the excitation energy-transfer (EET) dynamics of perylene bisimide (PBI) J-aggregates containing 2, 3, 5, or 25 PBI-1 molecular units at zero and room temperature. Our calculations are based on a parameterized Frenkel exciton Hamiltonian and treat explicitly 28 intramolecular vibrations in each molecule that have been found to have nonzero Huang-Rhys factors. We find that the vibrational modes cause significant changes to the dynamics, smearing electronic recurrence peaks and introducing a substantial temperature dependence to the time evolution of the electronic populations. We also identify a high-frequency vibronic mode which is primarily responsible for additional oscillatory features that exhibit variable temperature sensitivity dependent on aggregate length. These results provide a quantitative picture and useful insights into the complex interplay of exciton-vibration interactions in the EET dynamics of PBI aggregates.