QUENCHING OF THE TRIPLET STATE OF BENZIL BY RARE EARTH CHELATES.

Quenching of the triplet state of benzil by rare earth-tris dipivaloylmethane chelates was studied in degassed cyclohexane solutions at 18 C. A spectrophotofluorometer was used for all measurements of phosphorescence intensity. Compounds were chosen such that quenching by electronic energy transfer was not expected. Stern-Volmer graphs were constructed for the observed quenching, and the slopes from these graphs were used to calculate quenching rate constants of the order 10,000,000/M sec. The magnitude of these constants indicates that the quenching is not diffusionally controlled, and that the quenching is the result of enhanced spin-orbit coupling in the presence of the chelate. (Author)