Shedding Light on Benzo[d]pyrrolo[2,1-b]thiazole-3-carbonitrile Sensitizer-Based TiO₂ Photocatalysts for Enhanced Hydrogen Generation

In this work, we study a series of benzo[d]pyrrolo[2,1-b]thiazole-3-carbonitrile (BP) derivatives, which act as sensitizers for photocatalytic hydrogen generation applications. The metal-free BP organic sensitizers 1-(tert-butylamino)-2-(3,4,5-trimethoxy-phenyl)benzo[d]pyrrolo[2,1-b]thiazole-3-carbonitrile, 2-(2-bromo-phenyl)-1-(tributyl-amino)benzo[d]pyrrolo[2,1-b]thiazole-3-carbonitrile, and 2-(2-bromophenyl)-1-(cyclohexyl-amino)benzo[d]pyrrolo[2,1-b]thiazole-3-carbonitrile, termed BP-1, BP-2, and BP-3, respectively, act as light-harvesting units when loaded onto n-type semiconductors. In this study, we paired these sensitizers with the n-type semiconductor platinized TiO2 to create the materials TiO2-BP-1, TiO2-BP-2, and TiO2-BP-3. TiO2-BP-1 showed superior hydrogen generation efficiency compared to TiO2-BP-2, TiO2-BP-3, and pristine platinized TiO2. The electron transfer dynamics that take place between the dyes and TiO2 were studied using photoemission spectroscopy. The light-harvesting capacity, theoretical highest occupied molecular orbital and lowest unoccupied molecular orbital levels, and redox potential behavior of the sensitizers were evaluated by completing systematic photophysical, electrochemical, and computational studies. For TiO2-BP-1, a significant hydrogen generation rate of 3.32 mmol g-1 h(-1), with an apparent quantum yield (AQY) of 8.5% and a turnover number (TON) of 3344, was obtained at 420 nm, thus indicating the excellent light-harvesting capability of the BP-1 sensitizer. The increased photocatalytic activity of the devices when under simulated sunlight shows that BP derivatives have the potential to be useful photosensitizers in sustainable hydrogen generation applications.