Vibrationally Resolved Absorption Spectra and Exciton Dynamics in Zinc Phthalocyanine Aggregates: Effects of Aggregation Lengths and Remote Exciton Transfer.

The vibrationally resolved absorption spectra and exciton dynamics in the α-zinc phthalocyanine aggregates are theoretically investigated by using a non-Markovian stochastic Schrodinger equation. The model Hamiltonian adopted for spectral and dynamic simulations explicitly includes the couplings for both nearest-neighbor and remote exciton transfer, and it is parametrized from first-principles calculations. The results indicate that aggregation lengths and remote exciton transfer significantly influence the relative energy alignment between delocalized Frenkel exciton (FE) and charge transfer (CT) states, which in turn strongly affects the relative intensities of the two absorption peaks in the Q-band region. Analytical formulas are derived to establish quantitative structure-spectra relationships in aggregates, and they offer simple patterns to extract electronic-state properties directly from absorption spectra. The dynamics simulations reveal that the light absorption can directly generate mixed states with both FE and CT features, but it is hard for the photoexcitation from the Q-band region to generate free carriers due to the high energies of charge-separated states.