High pressure study of the intramolecular vibrational modes in sexithiophene single crystals

We report on the effects of a high hydrostatic pressure on the intra-molecu lar modes of a sexithiophene (T6) single crystal. Raman experiments were pe rformed at low temperature up to a pressure of 80 kbar. We find that interm olecular interaction gives rise to a sizeable redistribution of the intensi ties of the strongest intra-molecular Raman lines. These changes are due to a slight deformation occurring in the terminal rings of the sexithiophene molecule. The frequencies of the bending modes involving sulfur atoms are t he most affected by pressure. A Davydov doublet and a mixed inter/intra-mol ecular mode are observed. These results confirm the role played by the sulf ur atoms in modulating the electronic overlap between chains. (C) 2001 Else vier Science B.V. All rights reserved.