Novel Thermochromism Relating to Supramolecular Cuprophilic Interaction: Design, Synthesis, and Luminescence of Copper(I) Pyrazolate Trimer and Polymer

Solvothermal reactions of 4-(pyrid-4′-yl)-3,5-dimethylpyrazole (HPpz) with CuBr in two mixed solvents, NH3·H2O/EtOH and NH3·H2O/MeCN, afforded respectively a copper(Ι) trimer, [Cu(Ppz)]3 (1), and a polymer, {[Cu(Ppz)]3[CuCN]3} (2), both containing the [Cu(Ppz)]3 entity as a building block. The products were found to be photoluminescent and, more interestingly, when cooled from room temperature to 10 K, they showed a blue shift followed by a red shift (hereafter shortened to a red-after-blue shift) of emission.