Carboranealkynyl-Protected Gold Nanoclusters: Size Conversion and UV/Vis-NIR Optical Properties.

Abstract

Structure evolution has become an effective way to assemble novel monolayer-protected metal nanomolecules. However, evolution with alkynyl-stabilized metal clusters still remains rarely explored. Herein, we present a carboranealkynyl-protected gold nanocluster [Au28 (C4 B10 H11 )12 (tht)8 ]3+ (Au28 , tht=tetrahydrothiophene) possessing an open-shell electronic structure with 13 free electrons, which was isolated by a facile self-reduction method with 9-HC≡C-closo-1,2-C2 B10 H11 as the two-in-one reducing and protecting agent. Notably, Au28 undergoes a complete transformation in methanol into a stable and smaller-sized nanocluster [Au23 (C4 B10 H11 )9 (tht)6 ]2+ (Au23 ) bearing 12 valence electrons and crystal-field-like split superatomic 1D orbitals. The transformation process was systematically monitored with ESI-MS and UV/Vis absorption spectra. Au28 and Au23 both display optical absorption covering the UV/Vis-NIR range and NIR emission, which facilitates their potential application in the biomedical and photocatalytic fields.