The structure of the charge transfer complex in olefin quenching of benzophenone phosphorescence

The phosphorescence lifetimes of ω-alkenyl esters of p-benzophenone-carboxylic acid have been measured in dilute solution in degassed acetic acid solution. The lifetimes were extrapolated to infinite dilution. Intramolecular quenching was not very significant in benzophenone-4-CO₂(CH₂)_nCHCH₂ for n = 1, 2 or 4. For n = 9 the phosphorescence lifetime was found to be 2 μs compared to 70 μs for n = 1, 2. These results are interpreted to mean that the quenching complex has a specific geometric requirement with the CHCH₂ group approaching within a van der Waals distance of the ketone carbonyl group.