Femtosecond spectroscopy study of electronically excited states of Chlorophyll a molecules in ethanol

A femtosecond transient absorption technique is used to investigate the vibrational frequencies of the first electronically excited state of Chlorophyll a. From the quantum beats analysis, we obtain vibrational frequencies within 98–791 cm−1. Based on these frequencies, we calculate the absorption and fluorescence spectra using the displaced–distorted harmonic potential surface model. The ratio of the absorption intensities of the first and second excited states yields ∼7.5. We perform various excitations to obtain anisotropy profiles and find that they vary between −0.005 ± 0.005 and 0.41 ± 0.015. To understand the kinetics appearing in the profiles, we propose a microscopic model.