Cu(I) Halide Complexes with Benzo[b]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[b]thiophene units, along with three corresponding mononuclear copper(I) halide complexes─CuX(L1) [where L1 = ((phenylphosphanediyl)bis(benzo[b]thiophene-2,3-diyl))bis(diphenylphosphane), and X = I (1), Br (2), Cl (3)]─were successfully synthesized. Their structures and photophysical properties were systematically characterized. At room temperature (297 K), complexes 1-3 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 1 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 1 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.