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

Primary stages of the photochemical reactions of electron donor-accept or complexes formed by aromatic amine donors (diphenylamine, diphenylb enzylamine, dibenzylaniline, p dibenzyltoluidine, and triphenylamine) and halogen-containing acceptors are considered., a series of experime ntal results is explained in terms of the concept that an excited stat e of complexes resulted from mixing two components: a charge-transfer state and a local excitation of the donor. Using chemically similar am ines 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 i nitial stages and can determine the composition of end products under conditions of mixing of the states. The broadening of the absorption s pectra of the electron donor-acceptor complexes based on aromatic amin es 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 p otential'' with respect to the acceptor coordinated to both the aromat ic ring (a pi, sigma complex) and the nitrogen atom (a n, sigma* comp lex).