Mechanochemical Construction of 0D Cu(I)-Based Luminescent Superclusters through Dynamic Ligand Fusion: Toward Eco-Friendly Stimuli-Switchable Optical Materials

Zero-dimensional (0D) Cu(I)-based organic-inorganic metal halides (OIMHs) show promise for optoelectronics but face challenges in eco-friendly synthesis and stability. We present a solvent-free mechanochemical strategy to construct luminescent multinuclear clusters via a dynamic ligand fusion. Starting from the preorganized dinuclear complex (BPBI)2Cu2Br4 (BPBI = 1-benzyl-3-(2-pyridinylmethyl)-1H-benzoimidazol-3-ium), the in situ formation of cationic [6,5,5,6]-fused heterotetracyclic ligands is driven by the Cu(I)-mediated C-N coupling between imidazole carbene and pyridine groups under alkali-driven mechanochemical conditions (t-BuONa). This process is supposed to involve a N-heterocyclic carbene-copper intermediate that directs the assembly toward the 0D organic-inorganic multinuclear cluster (BBIIP)4Cu4Br8 (BBIIP = 6-benzyl-6H-benzo[4',5']imidazo[2',1':2,3]-imidazo[1,5-a]pyridin-11-ium), where the planar π-conjugated BBIIP+ cationic coordinate with the [Cu4Br8]4- cluster to strengthen Cu···Cu interactions and stabilize the lattice. Crystallographic and DFT analyses demonstrate that the cluster's rigid architecture contributes to its photophysical performance: a photoluminescence quantum yield of 93%, lifetime of 6.01 μs, and thermal stability up to 300 °C. Furthermore, the ligand-cation interactions enable stimuli-responsive dual-mode emissions, with reversible spectral shifts and intensity modulation upon thermal and solvent stimuli, a behavior rarely reported in Cu(I) halides. By integrating the solvent-free synthesis, cluster-based structural design, and stimuli-responsive behavior, this work provides a viable approach to multifunctional optical materials, as exemplified in anticounterfeiting and adaptive optoelectronic applications.