High‐Nuclear Organometallic Copper(I)–Alkynide Clusters: Thermochromic Near‐Infrared Luminescence and Solution Stability

<jats:title>Abstract</jats:title><jats:p>Cu(CF<jats:sub>3</jats:sub>COO)<jats:sub>2</jats:sub> reacts with <jats:italic>tert</jats:italic>‐butylacetylene (<jats:italic>t</jats:italic>BuC≡CH) in methanol in the presence of metallic copper powder to give two air‐stable clusters, [Cu<jats:sup>I</jats:sup><jats:sub>15</jats:sub>(<jats:italic>t</jats:italic>BuC≡C)<jats:sub>10</jats:sub>(CF<jats:sub>3</jats:sub>COO)<jats:sub>5</jats:sub>]⋅<jats:italic>t</jats:italic>BuC≡CH (<jats:bold>1</jats:bold>) and [Cu<jats:sup>I</jats:sup><jats:sub>16</jats:sub>(<jats:italic>t</jats:italic>BuC≡C)<jats:sub>12</jats:sub>(CF<jats:sub>3</jats:sub>COO)<jats:sub>4</jats:sub>(CH<jats:sub>3</jats:sub>OH)<jats:sub>2</jats:sub>] (<jats:bold>2</jats:bold>). The assembly process involves in situ comproportionation reaction between Cu<jats:sup>2+</jats:sup> and Cu<jats:sup>0</jats:sup> and the formation of two different clusters is controlled by reactants concentration. The clusters consist of Cu<jats:sub>15</jats:sub> and Cu<jats:sub>16</jats:sub> cores co‐stabilized by strong by σ‐ and π‐bonded <jats:italic>tert</jats:italic>‐butylethynide and CF<jats:sub>3</jats:sub>COO<jats:sup>−</jats:sup> (together with methanol molecule in <jats:bold>2</jats:bold>). Their stabilities in solution were confirmed using electrospray ionization mass spectrometry in which the cluster core remains intact for <jats:bold>1</jats:bold> in chloroform and acetone, and for <jats:bold>2</jats:bold> in acetonitrile. Strong thermochromic luminescence in the near infrared (NIR) region was observed in the solid‐state. Of particular interest, the emission maximum of <jats:bold>1</jats:bold> is red‐shifted from 710 nm at 298 K to 793 nm at 93 K, along with a 17‐fold fluorescence enhancement. In contrast, <jats:bold>2</jats:bold> exhibits red shift from 298 to 123 K followed by blue shift from 123 to 93 K. The emission wavelength was correlated with the structural parameters using variable‐temperature X‐ray single‐crystal analyses. The rich cuprophilic interaction plays a significant role in the formation of <jats:sup>3</jats:sup>LMCT (<jats:italic>t</jats:italic>BuC≡C→Cu<jats:sub>x</jats:sub>) excited state mixed with cluster‐centered (<jats:sup>3</jats:sup>CC) characters, which can be considerably influenced by temperature, leading to thermochromic luminescence. The present work provides 1) a new synthetic protocol for the high‐nuclear Cu<jats:sup>I</jats:sup>–alkynyl clusters; 2) a comprehensive insight into the mechanism of thermochromic luminescence; 3) unusual emissive materials with the characters of NIR and thermochromic luminescence simultaneously.</jats:p>