Excited State Characterization and Energy Transfer in Hyperbranched Polytruxenes and Polytruxene-block-Polythiophene Multiblock Copolymers

Abstract

A comprehensive investigation of the excited state characteristics of two hyperbranched truxene polymers (one end-terminated with poly(3-hexylth- iophene) blocks, P3HT) and a bistruxene model compound has been undertaken aiming to rationalize its inherent photophysical properties, including the energy transfer processes between the truxene (donor) and P3HT (acceptor) moieties. The study comprises qualitative absorption, emission, and triplet-singlet difference spectra, together with quantitative measurements of quantum yields (fluorescence, intersystem crossing, internal conversion and singlet oxygen formation) and fluorescence decay times. From the time-resolved data in solvents of different viscosity and as a function of temperature, it was established that with the P3HT- terminated hyperbranched polytruxene, the excited state deactivation mainly results from energy transfer and that conformational relaxation is absent in these systems, which gives further support for the rigidity of these polymers both in the ground and excited state. An energy transfer efficiency of 91% was obtained at room temperature. From a qualitative analysis of the data, it was also seen that radiationless processes (particularly the S1∼∼→S0 internal conversion channel) mainly contribute to the excited state deactivation of the hyperbranched polytruxenes, a behavior that is in contrast to what was observed for the bistruxene model compound. Spectral and fluorescence time-resolved data in thin films was also obtained and compared with the solution data.