Luminescence\nThermochromism of a Noncluster Copper\nIodide Complex

Hybrid copper(I) halide materials are currently attracting\nsignificant\nattention due to their exceptional luminescence properties, offering\ngreat potential for the development of multifunctional emissive materials\nwith, in addition, eco-friendly features. A binuclear copper iodide\ncomplex, based on the [Cu<sub>2</sub>I<sub>2</sub>L<sub>4</sub>] motif\nwith phosphite derivatives as ligands, has been synthesized and structurally\ncharacterized. Photophysical investigations indicate that this complex\ndisplays luminescence thermochromic properties, which are characterized\nby a temperature-dependent change in the relative intensity of two\nemission bands. The high-contrast luminescence thermochromism, with\nan important color variation from purple to cyan, is ascribed to the\nthermal equilibrium of two different excited states. While thermochromism\nis relatively known for multimetallic complexes, the perfectly controlled\nthermochromism of the studied compound is unprecedented for a binuclear\ncomplex. From theoretical investigations, this original feature is\ndue to the coordination of phosphite ligands, which induces a specific\nenergy layout of the complex, presenting vacant orbitals of varying\nnature. This single-component, dual-emissive binuclear complex, displaying\nrelevant sensitivity temperature response, presents great potential\nfor luminescence ratiometric thermometry applications. This study\nunderlines the relevance of the ligand engineering strategy in developing\noriginal, emissive, and sustainable copper-based materials.