Impact of molecular subunit engineering for viologen-based systems toward efficient photocatalytic hydrogen generation

The increasing global demand for clean energy and the environmental concerns associated with fossil fuels have intensified interest in sustainable hydrogen production technologies. Photocatalytic hydrogen evolution, a process mimicking natural photosynthesis, offers a promising pathway for generating hydrogen using solar energy. To address these challenges, viologen-derived organic molecules have emerged as effective catalysts due to their strong electron-accepting properties, stable radical cation formation, and enhanced charge carrier separation. In this study, two viologen-based photocatalysts, TPCBP-A and TPCBP-B, containing allyl (-CH<inf>2</inf>CH CH<inf>2</inf>) and butyl (-(CH<inf>2</inf>)<inf>4</inf>-) functional groups, respectively, were synthesized and characterized to investigate the effect of structural modification on photocatalytic hydrogen evolution performance. Comparative analysis revealed that TPCBP-A exhibited superior hydrogen production efficiency (38.77 mmol g⁻¹), attributed to the conjugated allyl group’s role in enhancing π-conjugation, narrowing the energy gap, and improving visible-light absorption. These findings highlight the potential of functionalized viologens in designing efficient, visible-light-responsive photocatalysts for sustainable hydrogen generation.