Silver(i)–iodine cluster with efficient thermally activated delayed fluorescence and suppressed concentration quenching

Abstract

Reports on highly efficient silver(I)-based thermally activated delayed fluorescence (TADF) materials are scarce due to challenges in molecular design, although these materials show great potential for photoluminescent and electroluminescent applications. Herein, a silver(I)–iodine cluster, namely Ag₂I₂(dppb-Ac)₂, is synthesized by employing a donor–acceptor (D–A) type bisphosphine ligand. Due to the introduction of electron-donating iodine ligands, Ag₂I₂(dppb-Ac)₂ exhibits an emissive singlet state characterized by (metal + iodine)-to-ligand charge transfer and intra-ligand charge transfer transitions, as well as a small singlet–triplet energy gap. Additionally, its non-planar, highly distorted D–A structure efficiently separates adjacent molecules in aggregated state. As a result, Ag₂I₂(dppb-Ac)₂ exhibits efficient TADF and suppressed luminescence concentration quenching in thin films. For instance, the 10 wt%-doped PMMA film and neat film of Ag₂I₂(dppb-Ac)₂ display bright bluish-green and green emission, peaking at 506 and 532 nm, with photoluminescence quantum yields (PLQYs) of 70% and 52%, and lifetimes of 18.9 and 7.9 μs, respectively. The high PLQYs and efficiently suppressed emission concentration quenching of Ag₂I₂(dppb-Ac)₂ in films are outstanding among reported Ag(I)-based TADF emitters.