Photosensitization of Quadricyclene Isomerization by Electron Acceptors. A Short-Circuit Nonradiative Decay Mechanism for Electron Donor-Acceptor Quenching in Polar Media

Article abstract of DOI:10.1021/j100212a001

Quantum efficiences are reported for valence isomerization of quadricyclene to norbornadiene induced on quenching the excited singlet state of electron acceptor sensitizers.The notable feature is the large reduction in yield of isomerization in a polar solvent (acetonitrile) compared with reported data for similar photolysis in nonpolar media.A comparison of isomerization yields and flash photolysis results based on the mode of sensitization (i.e., singlet quenching vs. triplet quenching vs. excitation of ground-state charge-transfer complexes) leads to a distinction among exciplex, contact ion pair, and solvent-separated ion-pair intermediates which are potentially involved in electron donor-acceptor quenching.