Anomalous pressure dependence of the electronic properties of molecular crystals explained by changes in intermolecular electronic coupling

Optimization of the electronic properties of crystalline organic semiconductors is important for the evolution of organic optoelectronic devices. One method of tuning the electronic properties is by applying external pressure to semiconducting molecular crystals. A recent dispersion-inclusive density functional theory (DFT)investigation regarding the effect of pressure up to 20 GPa on herringbone polycyclic aromatic hydrocarbons (PAHs)has revealed anomalous pressure dependence of the electronic properties of six systems [J. Phys. Chem. C 122, 23828 (2018)]. Here, we use intermolecular electronic coupling values (H_ab), calculated by fragment orbital DFT (FO-DFT)to elucidate the pressure dependence of the electronic properties. We show that discontinuities in the pressure dependence of the band structures are correlated with pressure-dependent discontinuities in the electronic couplings of certain molecular dimers. H_ab is shown to be a useful descriptor for gaining insight into the pressure dependence of the electronic properties of crystalline organic semiconductors.