Solvent dependence of triplet energy transfer from triplet benzophenone to naphthols and methoxynaphthalenes

Abstract

Solvent effects on triplet–triplet energy transfer (TET) from triplet benzophenone (³BP*) to naphthol (NpOH) competing with hydrogen atom abstraction (HA) of ³BP* from NpOH and methoxynaphthalene (NpOMe) without HA have been studied in fluid media by 355 nm laser flash photolysis at 295 K. The efficiency (ψ_TET) and rate constant (k_TET) of TET in these systems were obtained. It was shown that the value of k_TET was dependent not only on the solvent viscosity (η) but also on the dielectric constant (κ) of the solvents, and ψ_TET and k_TET increased with increasing κ, contrary to the Dexter prediction. An increase in k_TET with increasing κ may be caused by the contribution of the dipole–dipole interaction (by the Förster theory) due to perturbation of the ¹(π, π*) state to the lowest triplet state ³(n, π*) of benzophenone, in addition to the electron-exchange mechanism (by the Dexter theory).