Atomically precise Au ₂₄ (SR) ₂₀ nanoclusters with multiemission

Atomically precise metal nanoclusters (NCs) offer distinct platforms for exquisite control over photophysics, yet their complex photoluminescence (PL) mechanisms remain elusive. Here, we investigate a correlated series of Au ₂₄ (SR) ₂₀ with the same core but different R groups, revealing a unified triple-emission mechanism modulated by the R groups. By integrating cryogenic PL, femtosecond transient absorption and time-resolved electron paramagnetic resonance, we provide the first direct experimental “fingerprint” of short-lived excited triplet state (T ₁ ) of ∼350-nanosecond lifetime at room temperature, resolving the exciton relaxation cascade from the initial singlet state (S ₁ ) to a distorted singlet state with charge-transfer character to a T ₁ . These states contribute to multiemission (600 to 1400 nanometers, visible to near-infrared). Crucially, the R group symmetry of the 3,5-dimethylbenzylthiolate ligand-induced locking increases the kinetic barrier for structural distortion. This rigidity inhibits S ₁ rotational relaxation and decelerates intersystem crossing, yielding enhanced solution fluorescence. This study proposes a paradigm for designing efficient, multiemissive NCs by manipulating the excited-state dynamics and spin character.