Softening of Electron‐Acoustic Phonon Coupling via Core Symmetry Breaking in Metal Nanoclusters

ABSTRACT The core‐skeleton braced low‐frequency acoustic responses, linked to mechanical vibrations, are vital for the reactivity and functionality of a few‐nanometer metal nanoclusters (NCs). Yet, how core‐structure‐dependent acoustic vibrations impact and enhance the luminescence of metal NCs is not fully understood. Using a programmable total‐structure approach, we studied a series of Au 25 NCs, focusing on core symmetry manipulation by altering the shape, stacking patterns, and composition of the icosahedral Au 13 core to disrupt its spherical distribution. Our results show that breaking core symmetry softens electron‐acoustic phonon coupling, thereby enhancing luminescence in NCs. As the Au 13 core deviates from a spherical shape, the frequency and intensity of the radial breathing acoustic mode decrease, and in sequential lower‐frequency quadrupolar and torsional acoustic modes play a reduced role in non‐radiative relaxation. Of note, the core symmetry breaking also redistributes optical phonons, shifting the balance toward non‐radiative dominance. We emphasize that vibrational quenching of electrons in the luminescent state significantly limits NC emission, although electron loss and transfer at higher energies also remain important. These findings offer novel strategies for enhancing luminescence through structural regulation and inspire further exploration of total‐structure suppression and engineering to optimize NC optical performance.