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

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 (ψTET) and rate constant (kTET) of TET in these systems were obtained. It was shown that the value of kTET was dependent not only on the solvent viscosity (η) but also on the dielectric constant (κ) of the solvents, and ψTET and kTET increased with increasing κ, contrary to the Dexter prediction. An increase in kTET with increasing κ may be caused by the contribution of the dipole–dipole interaction (by the Forster 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).