Fluorescence and excited state absorption in modified pigments of bacterial photosynthesis a comparative study of metal-substituted bacteriochlorophylls a

Abstract A series of transmetalated bacteriochlorophylls, where the central magnesium has been replaced by Pd, Ni, Zn, Cd, Cu, have been investigated by linear and non-linear laser spectroscopic methods. A strong dependence of the fluorescence on the central metal was obtained. Differences in fluorescence lifetimes and quantum yields are caused mainly by different efficiencies of intersystem crossing. Strong excited state absorptions were found, in particular, the Pd-compound has a strong transient absorption in the 550–670 nm range. The results are of interest with respect to a possible oxygen-free sensitizing action of Pd-BPhe a for photodynamic tumor therapy.