Electronic States and Photoprocesses in Bichromophore Systems

We present the results of quantumchemical investigation of energy transfer in organic molecules and systems and the inferences drawn. The Förster theory has been subjected to a critical analysis in order that the energy transfer could be described in the context of the current theory of nonradiative transitions and the incorrectness of the basic premises of the Förster theory has been demonstrated. A new variant of the mechanism of electronic energy transfer on the basis of the theory of electron transitions and of the quantum mechanics of molecules has been suggested. It is shown that the interaction of the molecules of the donor and acceptor perturbs the electronic states of isolated molecules even before the excitation of the donor molecule. A characteristic feature of the manifestation of intermolecular interaction is the spatial delocalization of the wave functions of the electronic states of interacting molecules, leading to the possibility of occurrence of conventional photophysical processes with participation of the electronic states of various molecules of the bimolecular system. In experimental investigations, the result of the intermolecular nonradiative transition is recorded as evidence of the spatial transfer of the energy of electronic excitation from the donor molecule to the acceptor molecule.