Thermally Activated Delayed Fluorescence in Ag₁₉ Nanocluster from Hybrid Locally Excited and Charge-Transfer States

Atomically precise nanoclusters exhibiting thermally activated delayed fluorescence (TADF) remain underdeveloped for both mechanistic and optoelectrical applications. Herein, we report the synthesis of [Ag19(SAdm)10(DPPM)4(NO3)2]3+ (Ag19), a nanocluster coprotected by bis(diphenylphosphino)methane (DPPM) and 1-adamantanethiol (HS-Adm) ligands. The Ag19 crystal displays TADF properties with an absolute photoluminescence quantum yield (PLQY) of ∼55.7% and a decay time of 199.73 μs at room temperature. Time-dependent density functional theory calculations reveal hybrid locally excited and charge-transfer states in Ag19 and the TADF process occurs via reverse intersystem crossing from the triplet T2 to singlet S1 excited state, with a calculated triplet-singlet energy gap of 0.03 eV. This study provides important insight into the fundamental principles underlying the TADF mechanism of atomically precise silver nanoclusters.