Crystal structure of oligoacenes under high pressure.

We report crystal structures of anthracene, tetracene, and pentacene under pressure. Energy dispersive x-ray diffraction experiments up to 9 GPa were performed. Quasiharmonic lattice dynamics calculations are compared to the experimental results and show excellent agreement. The results are discussed with particular emphasis on the pressure dependence of the unit cell dimensions and the rearrangement of the molecules. The high pressure data also allow an analysis of the equation of state of these substances as a function of molecular length. We report the bulk modulus of tetracene and pentacene B0=9.0 and 9.6 GPa, respectively and its pressure derivative B0=7.9 and 6.4, respectively. We find that the unit-cell volume and bulk modulus at ambient pressure follow a linear relationship with the molecular length.