Quenching of triplet benzophenone by methyl and methoxy benzenes: are triplet exciplexes involved?

The quenching of triplet benzophenone by methyl and methoxy substituted benzenes in acetonitrile was investigated. For both series of donors the quenching rate constants are considerably higher than expected from the Rehm-Weller relationship, which could be explained by a mechanism involving a (triplet) exciplex intermediate. Two corresponding models from the literature were chosen for simulating the experimental data. The results are in accord with the exciplex proposal. For a given driving force the quenching rate constants differ substantially for the two kinds of donor employed. Together with the free ion yields, obtained by transient photoconductivity measurements, this confirms the important role of the chemical structure of the donors which determines the stability of the exciplexes. (C) 1997 Elsevier Science S.A.