Ligand-Isomerization Strategy Achieves Exceptional Wide-Range Zero-Thermal-Quenching Phosphorescence in Copper–Iodide Cluster–Organic Frameworks

Copper(I)-halide cluster materials have attracted considerable research interest for advanced optoelectronic applications, owing to their exceptional photophysical characteristics. Nevertheless, their luminescent performance is significantly undermined by thermal quenching (TQ) effects, which fundamentally limits their viability in cutting-edge applications. Herein, we present a molecular strategy that dramatically enhances the antithermal quenching (anti-TQ) performance of copper(I)–iodide cluster-based luminescent materials. Through isomeric ligand engineering using ortho- and para-substituted bis(imidazole) benzene ligands, two distinct cluster-based coordination polymers ( CP1 and CP2 ) exhibiting cluster-centered phosphorescence were synthesized. Remarkably, CP2 demonstrates zero-thermal-quenching (ZTQ) behavior, maintaining nearly constant emission intensity even up to 500 K, while CP1 shows conventional TQ with 72% intensity loss at 500 K. Structural and photophysical analyses reveal that the exceptional thermal stability of CP2 originates from its rigid crystalline architecture featuring a confined cluster core structure and ordered π–π stacking networks, which effectively suppress nonradiative decay. As a result, the potential applications of these molecular-based materials have been explored in light-emitting diode technology and anticounterfeiting, showing excellent prospects for practical implementation. This work provides fundamental insights into structure–property relationships in cluster-based emitters and establishes a new design paradigm for anti-TQ luminescent materials.