Hypercarbon-Centered Gold(I)-Copper(I) Clusters Exhibiting a Dissolution/Crystallization-Induced Photoluminochromism

Chemical molecules may show very different properties in the solid state and in solution, which is mainly caused by the difference in structure between different physical states. Well-defined metal cluster molecules are ideal models for the investigation of the dynamic dissolution/crystallization process, as they usually exhibit photoluminescence (PL) that is sensitive to reversible changes in coordination geometry and multi-electron structure. Here we report the dissolution/crystallization-induced photoluminochromism (PLC) of carbon-centered Au^I ₆Cu^I ₂ clusters bearing pyridylphosphine or pyridyl N-heterocyclic carbene (NHC) ligands. These clusters, with an octahedral structure doubly capped with copper(I), exhibit greenish-yellow emission in the solid state. Remarkably, the PL of the NHC-protected clusters in solution changes only slightly, whereas the phosphine-protected clusters exhibit red PL accompanied by a large bathochromic shift (>100 nm), a reversible process upon dissolution equilibration. X-ray absorption spectroscopy and theoretical calculations suggest that the octahedral CAu^I ₆ structure in the crystal is twisted into a triangular prismatic structure in solution. This remarkable ligand effect on the dissolution/crystallization-induced PLC would provide advanced design guidance for stimuli-responsive chromic materials.