| Abstract
| - The triplet energy accepting properties of bridged hydroxy and methyl derivatives of acetophenone oximewere examined. Sandros and Agmon−Levine−Balzani (ALB) models were used to deduce the oxime tripletenergies,, and the reorganizational intrinsic barriers, ΔG#(0), associated with the reaction. It is found forthe first time that these compounds exhibit different degrees of nonvertical energy transfer (NVET) behavior,depending on their chemical structure. These structural properties have been investigated at both the AM1and the B3LYP/6-31+G(d) levels of theory. The flexibility of the ground-state molecule and the structuralchanges occurring during the S0 → T1 sensitized transition seem to play crucial roles. It appears that twoimportant rearrangements are involved, namely, rotation about the C−N double bond and a π system flatteningassociated with a torsion about the formal C−C single bond. To relate the NVET character to these structuralchanges, the energy variations associated with these latter were evaluated and successfully related to ΔG#(0).Moreover, the role of the thermal activation of the molecular coordinates is evidenced through the calculationsof the ground and triplet potential energy surfaces (PESs) at DFT and CIS levels. A simple model, based onthe Sandros equation, was derived to include the influence of such torsional modes on the energy-transferbehavior. Finally, the experimental quenching data were fitted to this model, leading to the conclusion that,although both C−N double bond and C−C single bond torsions occur during the sensitization, the thermalactivation of C−C single bond torsion plays the major role in the NVET character of oxime derivatives.
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