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 4 f 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.

Keywords: Chiral; Cluster; Lanthanide; Thermally Activated Delayed Fluorescence.