Hierarchical Confinement of Intramolecular Motion for Highly Emissive Copper Nanoclusters

Excessive nonradiative energy dissipation, arising from active intramolecular rotation and vibration, substantially limits the photoluminescence (PL) efficiency of metal nanoclusters. Although restriction of intramolecular motion (RIM) has been recognized as an effective strategy to enhance PL intensity of nanoclusters, precise regulation of molecular motions at the atomic level remains challenging. Here, a hierarchical, two‐step RIM approach is presented that integrates the restriction of intramolecular rotation and the restriction of intramolecular vibration, resulting in a pronounced enhancement of the PL intensity of Cu 4 nanoclusters. Rational ligand design effectively suppresses the rotational freedom of surface ligands, increasing the solution‐state PL quantum yield (QY) from 1.26% to 2.93%. Subsequent crystallization further rigidifies the Cu 4 framework through the formation of extensive intermolecular noncovalent interactions within the crystal lattice, thereby restricting intramolecular vibrations and enhancing the QY of crystalline Cu 4 clusters to 12.08%—a 12‐fold improvement relative to the initial state. Comprehensive structural and spectroscopic analyses confirm that enhanced supramolecular interactions are responsible for the rigidified packing and the suppression of nonradiative decay pathways. This work establishes a hierarchical confinement strategy to modulate intramolecular motions in nanoclusters, offering a promising approach to the design and fabrication of strongly luminescent cluster‐based nanomaterials.