Ln³⁺ Induced Thermally Activated Delayed Fluorescence of Chiral Heterometallic Clusters Ln₂Ag₂₈

Abstract

A series of TADF‐active compounds: 0D chiral Ln‐Ag(I) clusters L‐/D‐Ln2Ag28‐0D (Ln = Eu/Gd) and 2D chiral Ln‐Ag(I) cluster‐based frameworks L‐/D‐Ln2Ag28‐2D (Ln = Gd) has been synthesized. Atomic‐level structural analysis showed that the chiral Ag(I) cluster units {Ag14S12} in L‐/D‐Ln2Ag28‐0D and L‐/D‐Ln2Ag28‐2D exhibited similar configurations, linked by varying numbers of [Ln(H2O)x]3+ (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‐Ln2Ag28‐0D (Ln = Eu/Gd) and L‐Gd2Ag28‐2D. Experimentally, the remarkable TADF properties primarily originated from {Ag14S12} moieties in these compounds. Notably, {Ag14S12} in L‐Eu2Ag28‐0D and L‐Gd2Ag28‐2D displayed higher promote fluorescence rate and shorter TADF decay times than L‐Gd2Ag28‐0D. Combined with theoretical calculations, it was determined that the TADF behaviors of {Ag14S12} cluster units were induced by 4f perturbation of Ln3+ ions. Specially, while maintaining ΔE(S1‐T1) small enough, it can significantly increase k(S1→S0) and reduce TADF decay time by adjusting the type or number of Ln3+ ions, thus achieving the purpose of improving TADF for cluster‐based luminescent materials.