Dynamics of ground and excited state chlorophyll a molecules in pyridine solution probed by femtosecond transient absorption spectroscopy

Femtosecond pump–probe spectroscopy was used to investigate the ground and excited state dynamics of chlorophyll a (Chl a) in pyridine following excitation by a 100 fs optical pulse. The transient absorption spectrum and kinetics reveal spectral evolution on two ultrafast time scales: ∼100 fs and ∼3 ps. We attribute these dynamics to ground-state transient hole-burning and solvation dynamics. Transient absorption anisotropy at early times (∼500 fs) was measured for Chl a in pyridine and shows a pronounced wavelength dependence, where anisotropy varies between 0 and 0.5. Strong contribution from excited state absorption is the origin of the variation.