Fluorescent Gold Nanoclusters with Interlocked Staples and a Fully Thiolate-Bound Kernel

The structural features that render gold nanoclusters intrinsically fluorescent are currently not well understood. To address this issue, highly fluorescent gold nanoclusters have to be synthesized, and their structures must be determined. We herein report the synthesis of three fluorescent Au-24(SR)(20) nanoclusters (R=C2H4Ph, CH2Ph, or (CH2C6H4Bu)-Bu-t). According to UV/Vis/NIR, differential pulse voltammetry (DPV), and X-ray absorption fine structure (XAFS) analysis, these three nanoclusters adopt similar structures that feature a bi-tetrahedral Au-8 kernel protected by four tetrameric Au-4(SR)(5) motifs. At least two structural features are responsible for the unusual fluorescence of the Au-24(SR)(20) nanoclusters: Two pairs of interlocked Au-4(SR)(5) staples reduce the vibration loss, and the interactions between the kernel and the thiolate motifs enhance electron transfer from the ligand to the kernel moiety through the Au-S bonds, thereby enhancing the fluorescence. This work provides some clarification of the structure-fluorescence relationship of such clusters.