Modelling ultrafast exciton transfer in fluorene-based organic semiconductors

Abstract

We present a theoretical study of exciton dynamics in solutions and films of fluorene-based molecules, complemented by experimental work carried out by our colleagues at the University of St Andrews. We start by introducing the importance and relevance of such a study, and the methods we use to model ultra-fast (picoand sub-picosecond) exciton photo-physics in these systems. We then demonstrate that exciton transfer in solution of some branched star-shaped oligofluorene-based molecules arises from molecular geometry relaxation, and, at a slower time-scale, from F¨orster hopping between the arms. Straight oligofluorenes do not exhibit ultra-fast exciton transfer in solution. Finally, we introduce improvements to the standard line-dipole theory which we use to build a microscopic model for ultra-fast exciton dynamics in polyfluorene films. Our results show very good agreement with experiments and enable us to gain fundamental insight into the exciton transfer processes in these materials.