Thermally activated delayed fluorescence Au‐Ag‐oxo nanoclusters: From photoluminescence to radioluminescence

Thermally activated delayed fluorescence (TADF) materials have numerous applications in energy conversion and luminescent imaging. However, they are typically achieved as metal-organic complexes or pure organic molecules. Herein, we report the largest Au-Ag-oxo nanoclusters to date, Au18Ag26(R1COO)12(R2C≡C)24(μ4-O)2(μ3-O)2 (Au18Ag26, where R1 = CH3-, Ph-, CHOPh- or CF3Ph-; R2 = Ph- or FPh-). These nanoclusters exhibit exceptional TADF properties, including a small S1-T1 energy gap of 55.5 meV, a high absolute photoluminescence quantum yield of 86.7%, and a microseconds TADF decay time of 1.6 μs at ambient temperature. Meanwhile, Au18Ag26 shows outstanding stability against oxygen quenching and ambient conditions. Atomic level analysis reveals the strong π⋯π and C-H⋯π interactions from the aromatic alkynyl ligands and the enhancement of metal-oxygen-metal interactions by centrally coordinated O2−. Modeling of the electronic structure shows spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital, which promote charge transfer from the ligand shell, predominantly carboxylate ligands, to O2−-embedded metal core. Furthermore, TADF Au-Ag-oxo nanoclusters exhibit promising radioluminescence properties, which we demonstrate for X-ray imaging. Our work paves the way for the design of TADF materials based on large metal nanoclusters for light-emission and radioluminescence applications.