Supramolecular Photocatalyst for the Reduction of Au(III) to Au(I) and High-Turnover Generation of Gold Nanocrystals

International audienceWe report a photocatalyst composed of a diphenylanthracene core appended with two lipophilic thioether side-chains that binds gold(III) chloride. Upon excitation using visible light, the AuIII ions are smoothly reduced to AuI which, in the presence of water, lead to the formation of crystalline gold nanoparticles of 20?50 nm diameter that are devoid of sulfur-containing capping agents. Ultrafast transient absorption spectroscopy shows that the anthracene excited state is quenched with a rate k = 3.5 ? 1010 s?1, assigned to intramolecular energy transfer to the bound gold ions, which then oxidizes the solvent to produce an intermediate low-valency gold(I) species. In the absence of water, the latter is stable and can be used as a homogeneous AuI catalyst. When employed in a biphasic reactor, the photocatalyst shows average turnover numbers of 150 atoms of AuIII reduced to Au0 per molecule of photocatalyst