Anomalous Fluorescence of Terrylene in Neon Matrix

Fluorescence and fluorescence excitation spectra of terrylene deposited in Ne and Ar matrixes at 7 K have been studied. The (0,0) fluorescence band of terrylene in Ne matrixes is shifted by 330 cm-1 to low energy with respect to the (0,0) fluorescence excitation band observed at 18990 cm-1. Furthermore, the vibronic structures of both spectra are different. In contrary to this observation, the fluorescence and fluorescence excitation spectra of terrylene in Ar matrixes have a common origin at 18312 cm-1 and demonstrate mirror symmetry. Semiempirical AM1 calculations combined with the analysis of the vibronic structure of the spectra suggest that terrylene molecules in the excited S1 state are subject to relaxation. This relaxation is possible in soft Ne but it is frozen in rigid Ar matrix.