Impurity Induced Molecular Reorientation in p-Terphenyl

Abstract

Molecular reorientation processes of protonated and perdeuterated tetracene guests in p-terphenyl crystals are examined using high-resolution fluorescence and fluorescence excitation spectroscopy. Two of the four sites undergo this process and their phonon sidebands observed in the excitation spectra exhibit an exceptionally long and well resolved progression of a low-frequency local phonon mode superimposed on a broad background. The local phonon identified as a guest librational mode is shown to induce the molecular reorientation processes at an angle of §21° about the L-axis of tetracene in the excited singlet state.