The vibrationally resolved absorption spectra and exciton dynamics in α-phase and β-phase zinc phthalocyanine (ZnPc) aggregates are theoretically calculated using a non-Markovian stochastic Schrödinger equation. The model Hamiltonian applied in the spectral and dynamic simulations involves many different types of interactions including the nearest-neighbor and long-range excitonic couplings, all parametrized by the first-principles calculations. Although the similar characteristic peaks arise in the absorption spectra of the α- and β-phase ZnPc aggregates, the relative intensities of the two absorption peaks in the Q-band region exhibit the opposite behaviors with the aggregation length. The results indicate that the aggregation lengths and long-range excitation energy transfer have remarkable influences on the relative intensities of the two absorption peaks by affecting the relative energy alignment between delocalized Frenkel excitonic (FE) and charge transfer (CT) states for both phases. In order to identify the spectral features of the two phases, the analytical formulas are derived to establish the quantitative relationships between the microstructures and the electronic properties. For the photoinduced dynamics processes from the Q-band region, the simulations reveal that the photo excitation can directly give rise to the mixed states with FE and CT natures, but it is rather difficult to generate the free carriers due to the absence of enough energy. In addition, it is found that the existence of CT states plays an important role in the coherence regeneration when the charge transfer process happens much faster than vibration-induced decoherence process.

Vibrationally resolved absorption spectra and exciton dynamics in α-phase and β-phase zinc phthalocyanine aggregates

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