Photoluminescence properties of TADF-emitting three-coordinate silver(i) halide complexes with diphosphine ligands: a comparison study with copper(i) complexes

Abstract

Synthesis and X-ray structures of silver(I) bromide complexes with diphosphine ligands L_Me, L_Et, and L_iPr are described, where L_Me = 1,2-bis[bis(2-methylphenyl)phosphino]benzene, L_Et = 1,2-bis[bis(2-ethylphenyl)phosphino]benzene, and L_iPr = 1,2-bis[bis(2-isopropylphenyl)phosphino]benzene. Crystals of complex [(L_Me)AgBr]₂ (1), prepared from L_Me and AgBr, showed a tetrahedral bimetallic structure. L_Et and L_iPr, with bulkier substituents than those of L_Me, reacted with AgBr to give crystalline three-coordinate complexes (L_Et)AgBr (2) and (L_iPr)AgBr (3). Nuclear magnetic resonance (NMR) studies demonstrated that 1 dissociates in solution to yield a monomeric three-coordinate complex (L_Me)AgBr. Luminescence studies showed that complexes 1–3 exhibit efficient blue thermally activated delayed fluorescence (TADF) in both solid state and solution. Density functional theory (DFT)/Time-dependent (TD)-DFT calculations revealed that the electronic transition responsible for TADF corresponds to (σ + Br) → π*. The photophysical properties of silver complexes 1–3 are discussed in detail and compared to those of the copper complex (L_Me)CuBr.