Novel organic sensitizers for photoanode water splitting in dye-sensitized photoelectrochemical cells

Dye-sensitized photoelectrochemical cells (DS-PECs) for water-splitting are receiving increasing attention as a novel technology for visible light-induced solar fuels production. The water oxidation reaction, occurring at the photoanode (PA), represents the key rate-determining step in water splitting, therefore the assembly of efficient and stable photoanodes is an essential part of DS-PECs. Beside the semiconductor (SC) oxide and the water oxidation catalyst (WOC), the role of the dye is crucial for optimizing the harvesting of visible light and triggering the oxidation reaction at the catalytic active site. Most of the dyes tested to date in PA-DS-PEC for water splitting show a narrow absorption spectrum (?max<450 nm) and poor stability. Therefore, the design of dye molecules with a broad optical response, appropriate energy levels, and good stability is urgently needed. In this study, three novel metal-free organic dyes (1a-c), based on a quinoxaline central core, have been investigated as possible anode sensitizers. Compounds 1a-c contains three slightly different donor moieties in order to modulate their HOMO energy level and use them in combination with the chosen WOC: Ru(bda)(pyP)2 (pyP =pyridin-4-methyl phosphonic acid). All the compounds have been successfully obtained through a simple and general synthetic method leading to good overall yields. Preliminary studies, such as absorption and emission spectra and cyclic voltammetry, have been also carried out in order to evaluate their photoelectrochemical properties. All three compounds show promising energy levels, especially dye 1c, for possible application in PA-DS-PEC.