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 Au18 kernel, which is made of two hexagonal bipyramids and two triangular pyramids with Au atoms as vertices. Four staple-like RC≡C–Au–C≡CR (R = 2,4,6-tri(isopropyl)-phenyl) motifs are located around the Au18 core, which further built an entire Au22 core structure of cluster 1. The Au22 core is stabilized by 14 acetylide ligands with 42 bulky isopropyl groups. It has been observed that the solid-state Au22 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.