Unraveling the quantum state mixing of excitonic and vibronic excitations in the dynamics of molecular aggregates

We report on dissipative exciton dynamics calculations performed with the hierarchy equations of motion method for a molecular heterodimer coupled to a multi-mode Brownian oscillator bath. Coherent oscillations in the population dynamics after initial excitation of the highest exciton state are analysed in terms of a Fourier spectrum and compared to the exciton-vibronic structure of the dimer eigen-states obtained by means of direct diagonalization. The signatures of Coulomb coupling induced quantum state mixing between elementary excitonic and vibronic excitations are systematically discussed for various Coulomb coupling strengths and Huang-Rhys factors.