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

Abstract 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.