Photocatalysis with Aggregated Donor-Acceptor Organic Dyes

The development of systems for sustainable energy production through the conversion of sunlight into solar fuels is gaining a lot of interest in chemical research. Inspired by molecular photosensitizers that are able to absorb light and generate excited states exploitable to promote chemical reactions, the challenge and the opportunity is to create a photocatalytic system where organic dyes are used as photosensitizers, chosen because of low-cost production, tunable properties and the absence of metals. The aim of this thesis is to prepare donor-acceptor organic dyes exploitable as visible-light photosensitizers thanks to their ability of intramolecular charge transfer resulting in red-shifted light absorption. The dyes are made of a donor and acceptor unit linked by different π-bridges. The linkers between the two moieties were changed to study how the increase of conjugation and efficiency of charge transfer would influence the photophysical properties and the photocatalytic activity. The dyes in solution relax from the excited state through intermolecular motion. Whereas, the aggregate state prevents such non-radiative decay and the photophysical properties change. For this reason, the synthesized dyes were tested both as solution and aggregates to compare their photocatalytic H2 evolution in presence of ascorbic acid as sacrificial agent and Pt nanoparticles as catalytic centres.