Molecular-scaffold evolution in luminescent copper nanoclusters: Coordination structures and excited-state chemistry

Luminescent copper nanoclusters have developed into a diverse family of molecular emitters, but the relationships among ligand structure, cluster architecture, excited-state behavior, and functional performance remain difficult to generalize across different systems. This review examines these relationships with ligand engineering as its central theme. We classify 31 parent ligands and 49 recently reported ligand elaborations into N-, P-, S-, and mixed-donor families, and examine the effects of donor identity, denticity, chelate geometry, steric environment, conformational rigidity, and peripheral functionalization on Cu-ligand coordination and cluster assembly. Representative coordination motifs and cluster architectures are analyzed in relation to ligand composition and conformation, heterometallic substitution, Cu···Cu interactions, nuclearity, core topology, and structural stabilization. LMCT, LMMCT, MMLCT, and cluster-centered excited states are compared in terms of their orbital characteristics and dependence on ligand environment, Cu···Cu distance, and cluster structure. These relationships are further examined across the reported 427–766 nm emission range, including TADF, circularly polarized luminescence, and near-infrared emission. Ligand-mediated stabilization under chemical, thermal, irradiation, and operational conditions is assessed, followed by representative applications in biomedical imaging, cross-reactive sensing, and X-ray scintillation. Finally, unresolved challenges in nuclearity control, excited-state assignment, stability benchmarking, aqueous-compatible stabilization, and materials translation are discussed. These comparisons clarify the relationships among ligand structure, cluster architecture, excited-state behavior, stability, and functional performance, while identifying current limitations in the rational design of luminescent Cu nanoclusters.