Evidence for temperature-independent triplet diffusion in a ladder-type conjugated polymer

We study the temperature dependence of triplet formation and decay by considering the phosphorescence dynamics in a prototypical conjugated polymer matrix. The dynamics of triplet formation as a function of temperature are unraveled by applying an electric field during optical singlet generation and recording the phosphorescence quenching. The diffusivity of triplet excitons in conjugated polymers is shown to be independent of temperature up to 200 K. We propose a diffusion model that describes the relaxation dynamics of triplet excitons at all times through triplet-triplet annihilation and spin orbit coupling at static heavy atom sites.