Absorption, excitation, and emission spectroscopy of terrylene in p-terphenyl: Bulk measurements and single molecule studies

Abstract

This paper reports spectroscopic investigations of the chromophore terrylene embedded in a matrix of crystalline p-terphenyl. While this system is particularly well suited for single molecule spectroscopy, little is known about the guest site configuration of terrylene. To shed some light on this issue, we employed absorption and fluorescence spectroscopy and compared the experimental data to the results of theoretical calculations. Based on this comparison we suggest a substitution scheme which is in agreement with all the spectroscopic evidence. The dispersed fluorescence spectra of single molecules in the wings of the inhomogeneous distribution deviate significantly from the bulk spectra. This observation is discussed in terms of a host-induced change of the structure and a possible C13 isotopic substitution of the chromophores. Finally we investigated the dynamic host–guest interactions via the temperature-dependent shift and broadening of single molecule excitation lines and found these processes dominated by coupling to characteristic pseudolocal phonon modes of the host, although chromophores in the wings of the inhomogeneous distribution exhibit additional contributions which we attribute to thermal matrix expansion.