DYNAMICS OF INTERACTION BETWEEN A 1,9-BIRADICAL AND LANTHANIDE IONS

Article abstract of DOI:10.1021/j100324a009

The lifetime of triplet 1,9-biradical derived from 2,10-diphenylcyclodecanone was studied in the presence of lanthanide(III) ions (Ln(3+)) in methanol solvent.The biradical lifetime is greatly decreased in the presence of several of the Ln(3+) ions.Bimolecular rate constants k_e for the Ln(3+)-induced biradical decay range from 0 to 2.8 * 1E8 M^-1 s^-1.The Ln(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_e represents spin exchange between biradical and Ln(3+).As a model for dipolar electronic relaxation by Ln(3+), a possible alternative mechanism for Ln(3+)-induced biradical decay, proton T₁ relaxation times for sodium dodecyl sulfate micelles were measured in the presence of Ln(3+) ions.The pattern of Ln(3+)-induced nuclear relaxation enhancements as a function of Ln(3+) was significantly different from the pattern of k_e vs Ln(3+).On the other hand, the known theory of spin exchange accounts qualitatively for the dependence of k_e on Ln(3+).The evidence thus suggests spin exchange as the dominant mechanism.