Tuning interchain and intrachain interactions in polyfluorene copolymers

Abstract

We study how intermolecular interactions, conformational changes, and polarization effects control the nature of the electronic excitations in conjugated polymer blends. Quantum-chemical calculations and high-pressure photoluminescence experiments are used to assess these effects in polyfluorene-based donor--acceptor systems. The redshift of charge-transfer--like excitations usually observed under pressure is found to arise primarily from the reduced interchain distance; the corresponding shift of bulk excitons is equally sensitive to the interchain spacing and planarization alterations. Intermolecular charge-transfer states are shown to have shorter radiative lifetimes and higher oscillator strengths at high pressure. In contrast, intramolecular bulk excitons build up interchain charge-transfer character and lose oscillator strength and radiative efficiency with increasing pressure.