Photocatalytic hydrogen production by means of Pt/brookite TiO2 sensitized with dithienosilole-based organic dyes

The production of H2 from sunlight and water is playing an increasingly important role in the production of clean fuels from sustainable and abundant energy sources. In this process, commonly referred as artificial photosynthesis, the role of the sensitizer, is critical for optimizing the harvesting of visible light and triggering the reduction reaction at the catalytic active site. Organometallic sensitizers have mainly been studied so far, however, thanks to recent advances and lower manufacturing costs, metal-free organic sensitizers have recently received increasing importance. On the basis of recent studies, concerning organic molecules applied on photoactivated H2 production, appeared that those dyes well performing in DSSC are in most cases suitable for hydrogen production. For this reason, we selected a family of organic dyes having a dithienosilole core which are known to lead to high efficiencies in DSSC (10%, 7%) as starting point to synthesize three new dyes (OB1-3) to study the influence of structural changes in the photoactivated H2 evolution process. More in detail, the efficiency of some new organic D-?-A dyes in the H2 production process has been investigated using the commercially available benchmark TiO2 (P25) and the best performing dye was also used to sensitize a catalyst based on a different TiO2 crystalline form, namely brookite/Pt. The aim of this work is to understand the possible correlation between structure and activity of such dyes, in particular the effect of introducing alkyl chains on the scaffold in order to affect several properties such as solubility, aggregation, shielding and wettability of the semiconductor and also the changes induced by the use of a different crystalline form of TiO2.