Synthesis and characterization of phosphorescent two-coordinate copper(i) complexes bearing diamidocarbene ligands

The photophysical properties of four, two-coordinate, linear diamidocarbene copper(i) complexes, [(DAC)₂Cu][BF₄] (1), (DAC)CuOSiPh₃ (2), (DAC)CuC₆F₅ (3) and (DAC)Cu(2,4,6-Me₃C₆H₂) (4) (DAC = 1,3-bis(2,4,6-trimethylphenyl)-5,5-dimethyl-4,6-diketopyrimidinyl-2-ylidene) have been investigated. Complex 1 shows a high photoluminescence quantum efficiency (ΦPL) in both the solid state (ΦPL = 0.85) and in CH₂Cl₂ solution (ΦPL = 0.65). The emission band of 1, both as a crystalline solid and in solution, is narrow (fwhm = 2300 cm⁻¹) relative to the emission bands of 2 (fwhm = 2900 cm⁻¹) and 3 (fwhm = 3700 cm⁻¹). Complexes 2 and 3 are each brightly luminescent in the solid state (ΦPL = 0.62 and 0.18, respectively), but markedly less so in CH₂Cl₂ solution (ΦPL = 0.03 and <0.01, respectively). Complex 4 is not emissive in either the solid state or in solution. Phosphorescence of 1 in CH₂Cl₂ solution shows negligible quenching by oxygen in CH₂Cl₂ solution. This insensitivity to quenching is attributed to the excited state redox potential being insufficient for electron transfer to oxygen.