Free Enthalpy Dependence of Free Radical Yield of Photoincuced Electron Transfer in Acetonitrile

Article abstract of DOI:10.1021/j100159a048

The free enthalpy dependence of the free-radical yield Φ_R of the electron-transfer (ET) fluorescence quenching was studied in acetonitrile by using anthracenecarbonitriles as the electron-accepting fluorescer and 1,4-diphenyl-1,3-butadienes as the electron-donating quencher. Φ_R decreases, passes through a minimum, increases with increase of ΔG_f, the free enthalpy change involved in the actual ET process, and then suddenly falls when ΔG_f goes beyond -0.25 eV.Switchover of the quenching mechanism was suggested for the ET fluorescence quenching: The radical pairs are exclusively produced by the full ET in the encounter state bet ween the fluorescer and the quencher when ΔG_f is smaller than -0.4 eV, but in contrast through the partial ET, i.e., the exciplex formation as the primary quenching products when ΔG_f is larger than -0.4 eV.