A computational study of organic molecular crystals for photocatalytic water splitting

Organic crystalline materials are potential candidates for photocatalytic overall water splitting (OWS). Although organic crystals have been heavily investigated for application in organic electronics, such as organic light-emitting diodes (OLEDs) and solar cells, there have been comparatively fewer studies into OWS in these materials. A major challenge is the large number of electronic and structural criteria that must be met for a material to make a viable OWS photocatalyst. Optical absorption, reduction and oxidation potentials and charge-transport properties are among the key considerations, and these are influenced both by molecular structure and the solid-state packing arrangement, making computational modelling challenging. Here, we investigate a series of known organic electronic materials using periodic density functional theory (DFT) and compare their calculated electronic properties of optical absorption and reduction and oxidation potentials with literature experimental data. We also perform a series of gas-phase molecular calculations, which show a good agreement with both the literature data and periodic DFT calculations for the optoelectronic properties of the systems studied, showing that gas-phase molecular calculations can be used to screen organic crystals for OWS at a reduced computational cost.