Excited-state processes in protochlorophyllide a – a femtosecond time-resolved absorption study

The excited-state dynamics of protochlorophyllide a, a porphyrine like compound and precursor of the chlorophyll biosynthesis, was studied by femtosecond absorption spectroscopy. Three kinetic components with time constants of 4, 27 and 200 ps are found to be involved in the excited-state decay. According to similar kinetic processes observed in the ultrafast dynamics of prophyrins, the 4-ps component is attributed to vibrational relaxation leading to thermal equilibrium in the lowest excited singlet state. The 27- and 200-ps processes are suggested to correspond with the decay via a second decay channel into the electronic ground state.