Ln Induced Thermally Activated Delayed Fluorescence of Chiral Heterometallic Clusters LnAg.

A series of TADF-active compounds: 0D chiral Ln-Ag(I) clusters L-/D-LnAg-0D (Ln=Eu/Gd) and 2D chiral Ln-Ag(I) cluster-based frameworks L-/D-LnAg-2D (Ln=Gd) has been synthesized. Atomic-level structural analysis showed that the chiral Ag(I) cluster units {AgS} in L-/D-LnAg-0D and L-/D-LnAg-2D exhibited similar configurations, linked by varying numbers of [Ln(HO)] (x=6 for 0D, x=3 for 2D) to form the final target compounds. Temperature-dependent emission spectra and decay lifetimes measurement demonstrated the presence of TADF in L-LnAg-0D (Ln=Eu/Gd) and L-GdAg-2D. Experimentally, the remarkable TADF properties primarily originated from {AgS} moieties in these compounds. Notably, {AgS} in L-EuAg-0D and L-GdAg-2D displayed higher promote fluorescence rate and shorter TADF decay times than L-GdAg-0D. Combined with theoretical calculations, it was determined that the TADF behaviors of {AgS} cluster units were induced by 4 f perturbation of Ln ions. Specially, while maintaining ΔE(S-T) small enough, it can significantly increase k(S→S) and reduce TADF decay time by adjusting the type or number of Ln ions, thus achieving the purpose of improving TADF for cluster-based luminescent materials.