Photochemical Reactions of Aromatic Compounds. XLII. Photosensitized Reactions of Some Selected Diarylcyclobutanes by Aromatic Nitriles and Chloranil. Implications of Charge-Transfer Contributions on Exciplex Reactivities

Article abstract of DOI:10.1246/bcsj.59.1133

Photosensitized reactions of cis- and trans-1,2-diphenylcyclobutane and cis-transoid-cis-cyclobuta<1,2-a:4,3-a'>diindene by 1-cyanonaphthalene, 9,10-dicyanoanthracene, 1,4-dicyanonaphthalene, and chloranil, which mainly give the ring-splitting product (styrene or indene), have been investigated to explore steric and electronic requirements of the reactions associated with charge-transfer and excitation-resonance contributions of exciplex intermediates.The reaction efficies increase with an increase in the electron-accepting power of the sensitizers irrespective of the spin states.The formation of 1-phenyltetralin in the photosensitized reactions of the diphenylcyclobutanes occurs from the polar singlet exciplex with the dicyanoarenes but not at all from the less polar exciplex with 1-cyanonaphthalene nor from the triplet chloranil exciplex of high charge-transfer nature.Exciplex reactivities are discussed in terms of roles of charge-transfer contributions in exciplex decay channels as well as in terms of configurational and conformational effects on orbital interactions in the cyclobutanes.