Molecular crystals based on conjugated aromatic molecules have attracted a lot of interest, since their combined electrical and optical properties enable them many technical applicatins. The optical features and the anisotropic electron mobility strongly depend on the crystalline structure of such materials, which itself is determined by the inter-and intramolecular interactions. We investigate those interactions by performing full potential linearized augmented plane wave (FP-LAPW) band structure calculcations accompanied by X-ray [powder diffraction experiments imder hydrpstatoc [ressure up to 50 κbar. In this work we focus on the compounds anthracene and para-terphenyl and report their internal geometry, electronic structure and optical spectra as a functionof pressure.