TIME-RESOLVED SPECTRAL INVESTIGATION OF BACTERIOCHLOROPHYLL A AND ITSTRANSMETALATED DERIVATIVES [ZN]-BACTERIOCHLOROPHYLL A AND [PD]-BACTERIOCHLOROPHYLL A

The lowest excited singlet (S-1) and tripler (T-1) states of bacterioc hlorophyll a (BChl) and its central metal derivatives [Zn]- and [Pd]- BChl were investigated by femtosecond lime-resolved absorption and flu orescence spectroscopy. In contrast to previously reported dynamic sol vation effects on the picosecond time scale for BChl, no short kinetic components were observed for BChl and [Zn]-BChl provided that photoch emical transformations of the pigments caused by multiple excitation a re avoided. The S-1 lifetimes of 2.6 ns, 2.1 ns, and 65 ps for BChl, [ Zn]-BChl and [Pd]-BChl, respectively, are dominated by intersystem cro ssing (ISC) to the triplet state T-1. The respective tripler quantum y ields amount to 76%, 85%, and >99%. The data support that [Pd]-BChl is a highly efficient photosensitizer for photodynamic tumor therapy.