Irradiation of solutions of naphthalene and triphenylsulphonium trifluoromethanesulphonate initiates an electron transfer reaction which gives 1- and 2-phenylnaphthalenes, 2- and 4-phenylthiobiphenyls, and diphenyl sulphide. The phenylnaphthalenes are formed by an in-cage reaction between phenyl radical and naphthalene radical cation, whereas diphenyl sulphide is an escape product. A second cage process, oxidation of diphenylsulphide by naphthalene radical cation, generates diphenylsulphinyl radical cation; reaction of this intermediate with phenyl radical gives the phenylthiobiphenyl isomers. However, irradiation of anthracene and triphenylsulphonium triflate yields only phenylated anthracenes and diphenylsulphide, because anthracene radical cation cannot oxidize diphenylsulphide. © 1989.