Studies of the Interaction of Excited Chloranil with Acrylonitrile, Methyl Methacrylate, and Styrene by Means of Laser Photolysis

The behavior of electronically excited chloranil interacting with the titled vinyl compounds and solvents has been studied by means of the nanosecond laser photolysis technique. Semiquinone radicals and/or chloranil anions have been detected as transients except in the system containing styrene. Careful observation and analysis of the kinetic behavior of the transient absorptions reveal that these transients are brought about by the interaction of excited triplet state of chloranil with vinyl monomers and/or solvents. The logarithms of the quenching rate constants and rate constants of the formation of transients are linearly related to the ionization potentials of the vinyl monomers and solvents used. The mechanisms of the triplet quenching and transient formation can reasonably be interpreted by taking the relaxed triplet-state complex with a charge-transfer character into account as the precursor leading to the production of semiquinone radicals, chloranil anions, and other intermediate compounds.