Theoretical analysis of internal conversion pathways and vibrational relaxation process of chlorophyll-a in ethyl ether solvent

The internal conversion (IC) pathways and times between S3 and S1 states are investigated by simulating the fluorescence depletion spectrum (FDS) of chlorophyll-a (Chl-a) in ethyl ether solvent using the perturbative density matrix method and the transient linear susceptibility theory. The calculated internal conversion (IC) times from S2 to S1 states and from S3 to S1 states are 110 and 143 fs, respectively, and vibrational relaxation rate constant is 8.5 ps−1 for the Chl-a in ethyl ether at room temperature. The theoretical calculation shows that sequential process, S3 → S2 → S1, is a main pathway for the IC process.