Journal of Physical Chemistry B, Vol.102, No.42, 8336-8342, 1998
Time-resolved spectral investigation of bacteriochlorophyll a and its transmetalated derivatives [Zn]-bacteriochlorophyll a and [Pd]-bacteriochlorophyll a
The lowest excited singlet (S-1) and tripler (T-1) states of bacteriochlorophyll a (BChl) and its central metal derivatives [Zn]- and [Pd]- BChl were investigated by femtosecond lime-resolved absorption and fluorescence spectroscopy. In contrast to previously reported dynamic solvation effects on the picosecond time scale for BChl, no short kinetic components were observed for BChl and [Zn]-BChl provided that photochemical transformations of the pigments caused by multiple excitation are 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 crossing (ISC) to the triplet state T-1. The respective tripler quantum yields amount to 76%, 85%, and >99%. The data support that [Pd]-BChl is a highly efficient photosensitizer for photodynamic tumor therapy.
Keywords:PHOTOSYNTHETIC REACTION CENTERS, RHODOBACTER-SPHAEROIDES R26;STATE ENERGY-TRANSFER, RADIATIONLESS TRANSITIONS, PHOTODYNAMICTHERAPY, CHARGE SEPARATION, ABSORPTION, METALLOPORPHYRIN;CHLOROPHYLL, PORPHYRINS