Countercation Size-Dependent Conformational Transition and Luminescence Modulation of Cu ₅ Clusters

Precise regulation of metal cluster structures and luminescent properties is critical for the advancement of their practical applications. Copper clusters have garnered extensive attention due to their abundant, inexpensive, and excellent luminescent properties. However, their strong metallophilic interactions often restrict emissions to the red region, making it challenging to controllably tune their emission range─especially toward high-energy bands. In this work, we propose a counterion-induced strategy to modulate the structure and luminescence properties of copper clusters. By adjusting the size of counter cations, we induced varying degrees of distortion in Cu5 anionic cluster structures and directed their crystallization into distinct assembly patterns, successfully obtaining four cluster-based luminescent materials. Theoretical calculations reveal that under the steric effects of counter cations, the four Cu5 clusters exhibit different molecular configurations and intercluster interaction strengths, enabling broad-range emission wavelength modulation (546 → 687 nm). Notably, Cu5-Pr-a and Cu5-Et demonstrate unconventional high-energy emissions. This study provides a novel approach and experimental reference for the precise control of metal cluster structures and luminescent properties.