In search of stable visible light absorbing photocatalysts: gold nanoclusters

Photochemical reactions are beginning to play an important role in the synthesis of complex organic molecules. The impetus to employ light initiated photoreactions as a synthetic tool derives from the fact that these reactions require no reagents except light. The abundance of sunlight has prompted the chemists to search for the visible light absorbing sensitizers (catalysts) to initiate the desired reactions. Our goal in this context is to develop stable and readily available catalysts that would function under sunlight. In this manuscript, we present the results of our experiments with gold nanoclusters (AuNCs) as a visible light absorbing catalysts. AuNCs absorb and emit in the visible region, soluble in water and transfers electron to suitable acceptors. Employing a series of acceptors we found that excited AuNC can transfer one electron to any acceptor whose reduction potential is above −1.1 eV. In the excited state, AuNC does not accept electrons. Also, it did not serve as an energy transfer sensitizer even with molecular oxygen. We are optimistic that AuNP and AuNC could be developed into a stable and water-soluble visible light absorbing photocatalysts to perform useful photoreactions. Graphical Abstract SYNOPSIS In the context of visible light photocatalysis gold nanoclusters upon light, absorption was found to transfer electron to acceptors whose reduction potential is above −1.1 eV. AuNC has limited value as electron transfer sensitizers in photochemical reactions.