Yields of excited states in the pulse radiolysis of solutions of substituted anthracenes

A series of substituted anthracenes covering the complete range of photochemical fluorescence and triplet quantum yields, φF and φT, have been examined in cyclohexane, benzene and dioxan solutions by pulse radiolysis. Extinction coefficients have been determined for triplet-triplet absorptions by means of Land's method and these have been used to obtain G-values for triplet states. Values for G(fluorescence) and hence G(total singlet) relative to a standard have also been measured. G(triplet) is independent of φT for cyclohexane solutions, but is dependent on φT for benzene and dioxan. G(fluorescence) is approximately proportional to φF, which implies constancy of G(total singlet) for a given solvent. The mechanistic implications of these findings are discussed.