Polarized Raman Spectra of a Rubrene Single Crystal

We report for the first time lattice phonon Raman spectra of the organic semiconductor 5,6,11,12-tetraphenyl-tetracene (rubrene). Polarized spectra were recorded for symmetry assignments. A comparison of experimental data with quasi harmonic lattice dynamics calculations, performed starting from the experimental X-ray structures, is given. It is shown that the experimental data can only be explained by invoking an efficient coupling between lattice vibrations and low energy intramolecular modes. Calculations also show that the experimental crystal structure corresponds to a stable thermodynamical minimum, whose temperature dependence reproduces well the experimental thermal expansion of the crystal.