2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/86570The 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.Submitted to Physical Review BChemical Physicstext