Naphthalene photocatalysed decomposition of chlorobenzenes in exciplex forming systems

Abstract

The photophysical behaviour of N,N-diethyl-2-(1-naphthyl)ethylamine I, N-benzyl-N-ethyl-2-(1-naphthyl)ethylamine VI and N-ethyl-2-(1-naphthyl)-N-(2,4,6-trichlorobenzyl)ethylamine VII, molecules that are able to form intramolecular exciplexes, has been examined in ethyl acetate. Compounds I and VI are fluorescent, but VII is non fluorescent and decomposes with formation of hydrogen chloride. The behaviour of the intermolecular exciplexes formed by naphthalene N and the bifunctional quenchers N,N-diethylbenzylamine II,4-chloro-N,N-diethylbenzylamine III, 3,5-dichloro-N,N-diethylbenzylamine IV and 2,4,6-trichloro-N,N-diethylbenzylamine V has also been studied.

The photodechlorination quantum yields have been determined for the systems I+ trichloro-benzene, N+V and VII and compared with that of the system N+ triethylamine + trichlorobenzene. The production of hydrogen chloride in these reactions is explained by an electron transfer model in which the naphthalene behaves as a photocatalyst. Evidence is given for the quenching of exciplexes formed by naphthalene and an amine, by the electron acceptor trichlorobenzene, occurring from the acceptor (naphthalene) side of the exciplex.