Lattice Modulation on Singlet-Triplet Splitting of Silver Cluster Boosting Near-Unity Photoluminescence Quantum Yield

Developing thermally activated delayed fluorescence (TADF)-active silver clusters with near-unity quantum efficiency is of practical importance in cutting-edge optoelectronic devices, but remains a tremendous challenge due to the difficulty of de novo synthesis and uncertainty of properties. Herein, we demonstrate a lattice modulation on parent TADF- active silver cluster, achieving TADF-driven photoluminescence quantum yield (PLQY) from 12 % to near-unity. Systematic experimental and calculated results reveal that the lattice modulation effectively lowers the singlet-triplet splitting (ΔE_ST) from 718 to 549 cm^-1, thereby facilitating thermally activated reverse intersystem crossing: T₅→S₅, leading to extremely efficient TADF by surpassing both phosphorescence and non-radiative decay, thus boosting the near-unity PLQY. Such high PLQY is extremely rare in the TADF-active silver clusters and even in the whole noble-metal clusters. This research showcases an unparalleled example of lattice modulation to realize near unity PLQY of TADF-active silver clusters.