Designing bithiazole-based conjugated polymers as alternatives to benzothiadiazoles for photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution on bithiazole (Tz)-based conjugated polymers was demonstrated for the first time, establishing Tz as a new building block beyond conventional benzothiadiazole (BT) systems. Two Tz-based donor-acceptor polymers were synthesized: one consisting of fluorene and Tz units (PFOTz), and the other incorporating a thiophene π-spacer between Tz units (PFOTzT). The use of thiophene-incorporating PFOTzT leads to a more ordered nanostructure within the resulting nanoparticles, promoting stronger interchain interactions and red-shifted absorption. Photocatalytic nanoparticles were prepared via mini-emulsion and nanoprecipitation methods with various surfactants. The hydrogen evolution reaction (HER) performance was evaluated under visible-light irradiation using ascorbic acid as the sacrificial electron donor. Both Tz-based polymers showed HER activity, but PFOTzT exhibited significantly higher HER activity. Time-resolved photoluminescence and transient absorption spectroscopy revealed that its superior performance arises from efficient exciton dissociation and suppressed charge recombination, resulting in prolonged carrier lifetimes. These results establish Tz as an alternative to BT in the design of high-performance organic photocatalysts and underscore the crucial impact of nanoscale morphology and interfacial engineering on photocatalytic efficiency.