Synthesis and Mechanochromic Response of a Large Sterically Hindered Alkynyl-Protected Au₂₂ Nanocluster

A large sterically hindered alkynyl-protected neutral gold nanocluster [Au22L14] (1) (L = 2,4,6-tri(isopropyl)-phenylacetylene) has been prepared by self-assembly under reduction condition. Single-crystal X-ray diffraction reveals that the molecular structure contains a polyhedral Au-18 kernel, which is made of two hexagonal bipyramids and two triangular pyramids with Au atoms as vertices. Four staple-like RC equivalent to C-Au-C equivalent to CR (R = 2,4,6-tri(isopropyl)-phenyl) motifs are located around the Au-18 core, which further built an entire Au-22 core structure of cluster 1. The Au-22 core is stabilized by 14 acetylide ligands with 42 bulky isopropyl groups. It has been observed that the solid-state Au-22 nanocluster is emissive in the near-infrared region with an intensive emission centered at 967 nm, and computational studies indicate that the phosphorescent emission is ascribed to the metal cluster-centered transition, phenylacetylide-centered IL, and LMCT state from phenylacetylide to metal centers. Large Stokes' shifts with a long range of emissive lifetime indicate that the emission likely originates from a triplet-state parentage. Interestingly, under the stimuli of mechanical force, 1 exhibits a significant luminescent blue-shift response.