Crystallization-Induced Coordination Diversity of Cu(I)-Pyridine Halide Complexes Resulting in Optical Tunability

Copper(I) derivatives have emerged as a versatile class of luminescent and photoactive materials, combining earth abundance, structural adaptability, and rich excited-state dynamics that enable their application in luminescent devices, photocatalysis, and sensing technologies. Herein, we report a family of copper(I) pyridine halide complexes supported by a 4-(<i>N,N</i>-dimethylamino)pyridine (DMAP) ligand, featuring crystallization-induced diversity of coordination motifs. The variation of halides and stoichiometry of [Cu(NCMe)₄]BF₄/CuX X = Cl, Br, I precursors enabled the selective isolation of a series of cationic/neutral mono- and multinuclear hybrid species, namely, [(DMAP)₂Cu]BF₄, [(DMAP)CuCl], [(DMAP)₄Cu₂(μ₂-X)]BF₄ X = Cl, Br, [(DMAP)₄Cu₄(μ₂-Br)₂(μ₃-Br)₂][(DMAP)₂Cu]₂(BF₄)₂, and [(DMAP)₂Cu₂(μ₂-I)₂]₂[(DMAP)₂Cu]₃(BF₄)₃. Single-crystal X-ray diffraction revealed that the bridging mode of halides is decisive in governing packing topology, nuclearity, and structural arrangement of metal/cluster centers. Photophysical studies demonstrated tunable solid-state phosphorescence spanning from sky blue (478 nm) to deep red (640 nm), with quantum yields and radiative rates reaching 0.41 and 7.3 × 10⁴ s^-1, respectively. Advanced photophysical studies combined with DFT/TD-DFT calculations facilitated the untangling of structural characteristics responsible for control over photophysical properties such as triplet formation and its (non)radiative decay or the nature of luminescent excited states, defining multiple structure-property relationships. These results establish an effective strategy to unlock new coordination motifs in copper(I) halide chemistry and to achieve broadband optical tunability in earth-abundant photoactive materials by means of crystallization tools.