Cu(I) Halide Complexes with Benzo[ <i>b</i> ]thiophenyl Triphosphine for Highly Emissive TADF-OLEDs

Highly luminescent Cu(I) halide complexes employing rigid aryl and heteroaryl tridentate phosphine ligands have received considerable research interest; however, related systems based on rigid aromatic fused-heterocyclic triphosphine ligands remain unreported to date. Moreover, achieving simultaneously high quantum efficiency and short decay lifetimes continues to be a significant challenge. In this work, a rigid triphosphine ligand incorporating benzo[<i>b</i>]thiophene units, along with three corresponding mononuclear copper(I) halide complexes─CuX(<b>L1</b>) [where <b>L1</b> = ((phenylphosphanediyl)bis(benzo[<i>b</i>]thiophene-2,3-diyl))bis(diphenylphosphane), and X = I (<b>1</b>), Br (<b>2</b>), Cl (<b>3</b>)]─were successfully synthesized. Their structures and photophysical properties were systematically characterized. At room temperature (297 K), complexes <b>1</b>-<b>3</b> in the solid state display intense yellow-green to yellow-orange delayed fluorescence (λ_em = 557-586 nm, τ = 3.5-6.9 μs, Φ = 0.18-0.58). The incorporation of an additional fused benzene ring into the thiophene moiety significantly enhances the photoluminescence quantum yield (PLQY) and allows precise tuning of the emission color. Notably, complex <b>1</b> achieves a high PLQY of 0.58 alongside a relatively short decay lifetime of 6.9 μs. Vacuum-deposited organic light-emitting devices (OLEDs) utilizing complex <b>1</b> as the emitter demonstrated high-purity yellow electroluminescence, reaching a maximum external quantum efficiency (EQE) of 11.77% and a current efficiency of 27.79 cd A^-1.