Naphthalene Photocatalysed Decomposition of Chlorobenzenes in Exciplex Forming Systems

The photophysical behaviour of N,N-diethyl-2-( 1 -naphthyl)ethylamine I, N-benzyl-N-ethyl-2-(1naphthy1)ethylamine VI and N-ethyl-2(1 -naphthyl) -N(2,4,6-trichlorobenzyI)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 111, 3,5d ic h loro-N,N-d iet hyl benzylamine IV and 2,4,6 tric h loro N,Nd iet hyl benzylamine V has also been studied. The photodechlorination quantum yields have been determined for the systems I + trichlorobenzene, 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.