Sulfone-functionalized Stable Molecular Single Crystals for Photocatalytic Hydrogen Evolution

Highly crystalline, hydrophilic and visible-light responsible molecular semiconductor materials are promising photocatalysts for water splitting to produce green hydrogen. However, hydrophobic nature, instability, high cost and the tedious synthesis process of most of the reported organic photocatalysts limit their photocatalytic activity and hinder their scalable applications. Herein, we report stable and easy-to-synthesize sulfone-functionalized molecular single crystals (FSOCA) as efficient hydrophilic photocatalyst for hydrogen evolution reaction. Its structure was determined by 3D electron diffraction technique with atomic resolution. The introduction of the sulfone groups favors the decrease of exciton binding energy, resulting in better exciton separation ability. FSOCA is highly hydrophilic in nature enabling it to efficiently drive sacrificial hydrogen evolution (760 µmol h−1; 76 mmol g−1 h−1). Interestingly, FSOCA remains stable in photocatalytic process for at least 400 hours showing negligible structure change, has and can cumulatively produce 179.2 mmol (about 4 L) of hydrogen. Employing transient spectroscopy, we find that the highly coplanar structure greatly enhances the transport of charge carriers to hole scavengers. In-situ Fourier transform infrared spectroscopy and DFT calculation shows that hydrogen bonding between sacrificial agent (ascorbic acid) with sulfone group is energetically favorable for the adsorption of ascorbic acid on FSOCA, thereby significantly improving the oxidation reaction kinetics and the photocatalytic performance. This work provides a scalable, efficient and low-cost strategy to synthesize highly active and stable organic photocatalysts, which can potentially be applicable in scalable photocatalysis.