Synthesis, Structure, and Characterization of Emissive Neutral Dinuclear CuI Complexes with a Tetraphosphane Bridging Ligand.

A series of new dinuclear copper complexes with a tetraphosphane bridging ligand, [{(pz₄B)Cu}₂(µ-tpbz)] ( 1), [{(pz₂BH₂)Cu}₂(µ-tpbz)] ( 2), and [{(tz₂BH₂)Cu}₂(µ-tpbz)] ( 3) [tpbz = 1,2,4,5-tetrakis(diphenylphosphanyl)benzene, pz₄B = tetrakis(pyrazol-1-yl)borate, pz₂BH₂ = bis(pyrazol-1-yl)borohydrate, and tz₂BH₂ = bis(1,2,4-triazol-1-yl)borohydrate], have been synthesized and structurally characterized. The Cu^I atoms in these complexes are four-coordinate and adopt a tetrahedral coordination geometry. In each complex, the copper centers are bridged by a tpbz ligand and each Cu^I is further terminally chelated by a borate diimine anion. The central phenylene ring and the phosphine atoms of the tpbz ligand are essentially planar. The two Cu^I atoms in each molecule are located above and below the (P₂C₆H₂P₂) mean plane, respectively, leading to a chair-like conformation for the [Cu](P₂C₆H₂P₂)[Cu] fragment. The distances between the Cu^I atoms in each complex are about 8.7 Å. In the solid state, these complexes are emissive and exhibit yellow-orange photoluminescence [emission peaks, λ_max = 580 nm ( 1), 569 nm ( 2), 540 nm ( 3)] with lifetimes of 7.4-20.5 µs and quantum yields Φ = 0.07-0.45 at room temperature. Theoretical and experimental results indicate that these complexes have the lowest singlet (S₁) state and the lowest triplet (T₁) state with very close energy levels, and display thermally activated delayed fluorescence (TADF) at ambient temperature. [ABSTRACT FROM AUTHOR]