An estimate of the inter-system crossing time in light-emitting polymers

The reported enhanced singlet-exciton yields in light-emitting polymers over the statistical limit of 25% has attracted wide experimental and theoretical attention. Most theoretical estimates of the singlet-exciton yield depend crucially on estimates of the inter-system crossing rates induced by spin-orbit coupling. In this paper we use the experimentally determined phosphorescent life-time and energy of the lowest-lying triplet state, as well as calculated values of Huang-Rhys factors to estimate the spin-orbit matrix element and inter-system crossing time between the lowest-lying singlet and triplet states.