Pressure-induced phosphorescence enhancement and piezochromism of a carbazole-based cyclic trinuclear Cu(i) complex

Abstract

Interest in piezochromic luminescence has increased in recent decades, even though it is mostly limited to pure organic compounds and fluorescence. In this work, a Cu3Pz3(Cu3, Pz: pyrazolate) cyclic trinuclear complex (CTC) with two different crystalline polymorphs, namely1aand1b, was synthesized. The CTC consists of two functional moieties: carbazole (Cz) chromophore andCu3units. In crystals of1a, discreteCz-Cu3-Cu3-Czstacking was found, showing abnormal pressure-induced phosphorescence enhancement (PIPE), which was 12 times stronger at 2.23 GPa compared to under ambient conditions. This novel observation is ascribed to cooperation between heavy-atom effects (i.e., from Cu atoms) and metal-ligand charge-transfer promotion. The infinite π-π stacking ofCzmotifs was observed in1band it exhibited good piezochromism as the pressure increased. This work demonstrates a new concept in the design of piezochromic materials to achieve PIPEviacombining organic chromophores and metal-organic phosphorescence emitters.