PRIMARY STAGES OF PHOTOCHEMICAL-REACTIONS IN COMPLEXES BASED ON AROMATIC-AMINES - A REVIEW

Primary stages of the photochemical reactions of electron donor-acceptor complexes formed by aromatic amine donors (diphenylamine, diphenylbenzylamine, dibenzylaniline, p dibenzyltoluidine, and triphenylamine) and halogen-containing acceptors are considered., a series of experimental results is explained in terms of the concept that an excited state of complexes resulted from mixing two components: a charge-transfer state and a local excitation of the donor. Using chemically similar amines as an example (namely, diphenylamine and diphenylbenzylamine), it was demonstrated that minor variations in the relative arrangement of energy levels of these components change radically the mechanism of initial stages and can determine the composition of end products under conditions of mixing of the states. The broadening of the absorption spectra of the electron donor-acceptor complexes based on aromatic amines and the change in the direction of photochemical processes in going from liquid media to polymeric matrices were explained by ''freezing in'' amine conformation isomers, which differ in the angle of rotation between the aromatic-ring plane and the orbital of the lone electron pair of the nitrogen atom (twist angles) and, hence, in ''ionization potential'' with respect to the acceptor coordinated to both the aromatic ring (a pi, sigma* complex) and the nitrogen atom (a n, sigma* complex).