ELECTROCHEMICAL INVESTIGATION OF MODIFIED PHOTOSYNTHETIC PIGMENTS

Bacteriochlorophyll a (BChla), bacteriopheophytin a (BPhea), and pheop hytin a (Phea) derivatives with a modified substituent pattern of the macrocyclic system were investigated by means of cyclic voltammetry. T he more electron-withdrawing beta-substituents shifted the redox poten tials toward more negative values; the reduction being much more affec ted than the oxidation. Substituents at C-13(2) or C-17 have only a mi nor influence on the redox potentials, with the exception of the stron gly electron-withdrawing fluoro group at position C-13(2). The trianio ns of the Phea derivatives were observed for the first time, providing information of the energy of the LUMO + 1.