Size- and Shape-Dependent Photoexcitation Electron Transfer in Metal Nanoclusters

There are some unresolved fundamental issues for metal nanoclusters; for instance, the close-packed structure transformation from face-centered cubic (fcc) to hexagonal close-packed (hcp) has not yet been reported, and photoexcitation electron transfer is not well understood. Herein, we realized for the first time the fcc-to-hcp structure transformation and revealed the size- and shape-dependent photoexcitation electron transfer for metal nanoclusters. Specifically, a thermally induced ligand exchange method was developed, and a rod-shaped hcp Au42(SCH2Ph)32 (HSCH2Ph: benzyl mercaptan) with the largest aspect ratio was synthesized from fcc Au28(SPh-tBu)20 (HSPh-tBu: p-tert-butylphenol) and structurally resolved, which shows a sharp absorption at 815 nm and dual emission that is well interpreted by time-dependent density functional theory (TD-DFT) calculations. The structure transformation pathway was proposed, and a novel, rod-shaped hcp Au58(SR)40 with larger aspect ratio was predicted. Interestingly, it is found that the kernel-based middle-to-both ends sp ← sp photoexcitation electron transfer can be extended to other rod-like (one-dimensional) gold nanoclusters, and the major photoexcitation turns to the kernel-based sp ← sp transition from the staple-to-kernel sp ← d transition when the spherical gold nanocluster size is increased to Au42 and the Au(6sp) composition increases with increasing size for structure-similar nanoclusters. These findings deepen our understanding of metal nanocluster photoexcitation electron transfer and provide guidance for future nanocluster property tuning aimed at practical applications.