PICOSECOND ABSORPTION SPECTROSCOPY OF CHLOROPHYLL A DIHYDRATE

Abstract— The solution of chlorophyll a in hexane with more than 70% of chlorophyll molecules in the form of the dihydrate (CHl‐a.2H2O)n is investigated at room temperature by picosecond absorption technique. The transient difference spectra and the kinetic dependences of the absorption changes are measured for several excitation and probe wavelengths. Creation of a new state with blue‐shifted absorption band is observed in the system after excitation. A model of the behaviour of the system after excitation is proposed and checked by comparison of the computer‐simulated spectral and time dependences with the experimental data. According to the model, about 30% of excited molecules are in the state with the 0.046 eV shift of the absorption band in comparison with the ground state absorption. The lifetime of this state has 170‐ps component. The rest of the excited molecules are in the first excited state with the decay time component of 37 ps.