Factors affecting adiabaticity in bimolecular photoinduced electron transfer reaction between anthracene derivatives and organic donors

A study of the dynamics of the photoinduced electron transfer reaction between anthracene derivatives and aromatics or aliphatic amines as donors in acetonitrile is reported. It is observed that the different accepters behave similarly towards aromatics ('pi' donors). In contrast, when aliphatic amines ('n' donors) are used the accepters exhibit different plateau values for the electron transfer rate constant k(et) in the exergonic region. From the fact that the orbitals involved are not the same for the two types of donors, this difference is tentatively ascribed to the role of the electronic coupling matrix element H-el in the framework of non-adiabatic theory. Moreover, due to the necessary mutual orientation of the reactants before the reaction can occur, the possibility of a rate saturation is investigated, since the same limiting value of k(et)(max) is observed for'pi' and 'n' donors.