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,Au_(18)Ag_(26)(R1COO)_(12)(R_(2)C≡C)_(24)(μ_(4)-O)_(2)(μ_(3)-O)_(2)(Au_(18_Ag_(26),where R_(1)=CH_(3-),Ph-,CHOPh-or CF3Ph-;R_(2)=Phor 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 1.6μs at ambient temperature.Meanwhile,Au18Ag26 shows outstanding stability against oxygen quenching and ambient conditions.Atomic level analysis reveals the strongπ⋯πand C-H⋯πinteractions from the aromatic alkynyl ligands and the enhancement of metal-oxygen-metal interactions by centrally coordinated O^(2−).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 O^(2−)-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.