SINGLET AND TRIPLET REACTIVITY IN THE PHOTOINDUCED ELECTRON-TRANSFER FROM AROMATIC-AMINES TO CHLOROBENZENES

The electron transfer quenching from the excited singlet state of several aromatic amines and 9-methylcarbazole to chlorobenzenes and chlorobiphenyls was studied by fluorescence quenching in methanolic solutions. The triplet quenching of N,N-dimethylaniline and 9-methylcarbazole was measured by laser flash photolysis. It was found that the singlet rate constants do not follow the same free-energy correlation as the triplet state. The reactivity of the excited singlet is lower than that of the triplet for a given overall free-energy change. It is proposed that this effect is due to a contribution from an inner-sphere reorganization to the intrinsic energy barrier, which would be higher in the case of the singlet reaction.