Molecular Engineering of Robust Starburst-Based Organic Photosensitizers for Highly Efficient Photocatalytic Hydrogen Generation from Water

Six donor-donor-π-acceptor (D-D-π-A) triphenylamine-based starburst organic dyes with different electron-donating moieties and thiophene-based π-linkers were synthesized and characterized. Their photophysical and electrochemical properties, together with their photocatalytic hydrogen evolution performance as photosensitizers (PSs), were investigated. Distinctive and prolonged hydrogen evolution performances of these PSs under visible-light irradiation from water in their platinized TiO₂ composites were demonstrated: a turnover number (TON) of up to 24900 (252 h) with 1560 μmol (37.6 mL) hydrogen produced, an initial turnover frequency (TOF_i) of 1130 h^-1, initial activity (Activityi) of 705 mmol g^-1 h^-1, and initial apparent quantum yield (AQY_i) of 12.1%. To the best of our knowledge, according to the TOF and TON values, the designed PS system is one of the most efficient and robust photocatalytic H₂ generation systems adopting a TiO₂-anchoring molecular PS in the literature. The results showed that the starburst triarylamine donor moiety with phenothiazine functionality and the alkyl chain on the thiophene π-linker could boost the performance and longevity of the photocatalytic system, providing a powerful strategy for the development of starburst-based highly efficient and robust D-D-π-A organic photosensitizers in the future.