Donor-Acceptor Organic Photosensitizers with Aggregation-Induced ON-OFF Photocatalytic Hydrogen Evolution

The efficient conversion of solar energy into chemical fuels represents one of the most promising strategies to address the increasing global demand for sustainable energy. Among the different approaches, photocatalytic systems based on organic photosensitizers have attracted considerable attention due to their low cost, structural versatility, and metal-free nature. Upon visible-light absorption, these photosensitizers generate excited states that can drive photocatalytic reactions and promote chemical transformations. The aim of this thesis is the design and synthesis of a small library of donor-acceptor (D-A) organic chromophores featuring different combinations of electron-donating and electron-withdrawing moieties, to be employed as visible-light photosensitizers. By varying the donor (triphenylamine or carbazole) and acceptor (pyridinium or anilinium) units, the electronic interactions between the molecules can be modulated, allowing the tuning of their absorption properties, excited state and intramolecular charge transfer characteristics. Understanding these structure-property relationships is essential for the development of efficient photosensitizers. Organic dyes are known to undergo non-radiative decay through intramolecular motions upon photoexcitation, limiting the use of absorbed energy for photocatalysis. It has been already shown that the aggregated state prevents these unwanted pathways, redirecting the excited states towards photocatalytic activity. Based on this behaviour, the photocatalytic activity of the synthesized photosensitizers was evaluated through hydrogen evolution experiments both in solution and in aggregated state in order to evaluate the influence of aggregation on their photocatalytic performance and explore their ON-OFF switching behaviour.