Orientation effects in triplet–triplet energy transfer from benzophenone to phenanthrene by photoselection studies

Abstract

The method of photoselection has been used to measure the degrees of polarisation for benzophenone and phenanthrene phosphorescence in poly(methyl methacrylate)(PMMA) at room temperature and 77 K. These measurements are compared with the degrees of polarisation of benzophenone phosphorescence and sensitised phenanthrene phosphorescence obtained upon selective excitation of benzophenone in a mixture of benzophenone and phenanthrene in PMMA. The studies indicate that if an orientation effect exists for triplet–triplet energy transfer it is a slowermoving function than the square of the sine of the angle between the CO axis of benzophenone and the normal to the molecular plane of phenanthrene. The results of photoselection and magnetophotoselection studies are compared with studies of intramolecular energy transfer between chromophores of known molecular orientation.