Benzil/triethylamine: a photo-reducing system for Cu²⁺

Abstract: We have investigated the photo-induced reduction of Cu²⁺–Cu⁰ using benzil/triethylamine mixtures. The formation of elemental Cu is indicated by the appearance of its characteristic plasmon absorption peaks at 515 nm and 620 nm. Importantly, the nature of the counterion of the Cu²⁺ salt affects the reduction process. In the presence of Cl⁻, the reduction proceeds faster than with SO₄ ^2-. Photo-induced electron transfer between excited benzil and triethylamine leads to the benzil radical anion, which acts as the reducing agent for Cu²⁺ and generates Cu⁰. Graphical abstract: [Figure not available: see fulltext.].