Dynamics of interaction between a 1,9-biradical and lanthanide ions

Abstract

The lifetime of the triplet 1,9-biradical derived from 2,10-diphenylcyclodecanone was studied in the presence of lanthanide(III) ions (Ln/sup 3 +/) in methanol solvent. The biradical lifetime is greatly decreased in the presence of several of the Ln/sup 3 +/ ions. Bimolecular rate constants k/sub e/ for the Ln/sup 3 +/-induced biradical decay range from 0 to 2.8 x 10/sup 8/ M/sup -1/ s/sup -1/. The Ln/sup 3 +/ effect is not due to chemical reaction, since no new products are observed and the product ratio is minimally perturbed. It is proposed that k/sub e/ represents spin exchange between biradical and Ln/sup 3 +/. As a model for dipolar electronic relaxation by Ln/sup 3 +/, a possible alternative mechanism for Ln/sup 3 +/-induced biradical decay, proton T/sub 1/ relaxation times for sodium dodecyl sulfate micelles were measured in the presence of Ln/sup 3 +/ ions. The pattern of Ln/sup 3 +/-induced nuclear relaxation enhancements as a function of Ln/sup 3 +/ was significantly different from the pattern of k/sub e/ vs Ln/sup 3 +/. On the other hand, the known theory of spin exchange accounts qualitatively for the dependence of k/sub e/ on Ln/sup 3 +/. The evidence thus suggests spinmore » exchange as the dominant mechanism.« less