Dynamics of charge separation in the excited-state chemistry of protochlorophyllide

In this study the excited-state dynamics of protochlorophyllide a (PChlide), the substrate of the enzyme protochlorophyllide oxidoreductase, was examined by means of time-resolved absorption anisotropy and magic-angle measurements. The solvent polarity dependent anisotropy data provide strong evidence for the existence of an excited-state with charge-transfer character. A solvent dependency is also observed in the magic-angle kinetics. In a nonpolar environment wave packet oscillations are monitored while they are quenched in a polar solvent. These results show that the excited-state relaxations of PChlide are determined by the nature of the solvent environment. The implications of these findings are discussed with respect to the enzyme catalysed reaction.