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

Synthesis and X-ray structures of silver(I) bromide complexes with diphosphine ligands LMe, LEt, and LiPr are described, where LMe = 1,2-bis[bis(2-methylphenyl)phosphino]benzene, LEt = 1,2-bis[bis(2-ethylphenyl)phosphino]benzene, and LiPr = 1,2-bis[bis(2-isopropylphenyl)phosphino]benzene. Crystals of complex [(LMe)AgBr]2 (1), prepared from LMe and AgBr, showed a tetrahedral bimetallic structure. LEt and LiPr, with bulkier substituents than those of LMe, reacted with AgBr to give crystalline three-coordinate complexes (LEt)AgBr (2) and (LiPr)AgBr (3). Nuclear magnetic resonance (NMR) studies demonstrated that 1 dissociates in solution to yield a monomeric three-coordinate complex (LMe)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 (LMe)CuBr.