Identification of a Highly Luminescent Au22(SG)18 Nanocluster

The luminescence property of thiolated gold nanoclusters (Au NCs) is thought to involve the Au(I)-thiolate motifs on the NC surface; however, this hypothesis remains largely unexplored because of the lack of precise molecular composition and structural information of highly luminescent Au NCs. Here we report a new red-emitting thiolated Au NC, which has a precise molecular formula of Au-22(SR)(18) and exhibits intense luminescence. Interestingly, this new Au-22(SR)(18) species shows distinctively different absorption and emission features from the previously reported Au-22(SR)(16), Au-22(SR)(17), and Au-25(SR)(18). In stark contrast, Au-22(SR)(18) luminesces intensely at similar to 665 nm with a high quantum yield of similar to 8%, while the other three Au NCs show very weak luminescence. Our results indicate that the luminescence of Au-22(SR)(18) originates from the long Au(I)-thiolate motifs on the NC surface via the aggregation-induced emission pathway. Structure prediction by density functional theory suggests that Au-22(SR)(18) has two RS-[Au-SR](3) and two RS-[Au-SR](4) motifs, interlocked and capping on a prolate Au-8 core. This predicted structure is further verified experimentally by Au L-3-edge X-ray absorption fine structure analysis.