TRIPLET EXCITATION TRANSFER INVOLVING β-IONONE. A KINETIC STUDY BY LASER FLASH PHOTOLYSIS |
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Authors: | S. K. Chattopadhyay,&dagger ,C. V. Kumar,&dagger P. K. Das |
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Affiliation: | Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA |
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Abstract: | Abstract— Employing nanosecond laser flash photolysis, β-ionone (BI) has been examined as an acceptor and as a donor of triplet excitation. In the limit of diffusion-control as well as below it, the rate constants for the quenching of a series of sensitizer triplets by BI are2–3 times smaller than those by 2,4-hexadienal (HD), although the triplet energies (spectroscopic) of the two carbonyl-containing dienes are estimated to be the same (∼55 kcal mol-1). We attribute the difference to a steric effect arising from ground-state geometric distortion and heavy alkyl-substitution in BI. In spite of possible exothermic energy transfer, BI triplet is nearly nonquenchable by azulene and ferrocene; this is explainable by torsional relaxation to an equilibrium geometry at which the vertical energy gap is smaller than 40 kcal mol-1. The singlet oxygen yield from the interaction of BI triplet with oxygen in benzene is estimated to be 0.5, suggesting that spin-exchange and energy-transfer may be involved to the same extent in the oxygen quenching process. |
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