Heteroleptic Ionic Copper(I) Complexes Based on Pyrazolo[1,5-a][1,10]phenanthrolines: Synthesis, Structure, and Photoluminescence

Heteroleptic copper(I) tetrafluoroborate complexes with pyrazolo[1,5-a][1,10]phenanthrolines (Lⁿ, n = 1–3) and bis[(2-diphenylphosphino)phenyl] ether (POP) were synthesized and structurally characterized. The coordination compounds with the general formula [CuLⁿ(POP)]BF₄·Solv (n = 1, Solv = 0.5MeCN, complex I; n = 2, Solv = 0.5CH₂Cl₂, complex II; n = 3, Solv = 1.25Et₂O, complex III·Et₂O) were prepared by the reaction of CuBF₄ with Lⁿ and POP in organic solvents (MeCN/CH₂Cl₂/Et₂O) at 1 : 1 : 1 molar ratio. Compound III·Et₂O gradually loses solvate molecules to be converted to the complex [CuL³(POP)]BF₄ (III). According to single-crystal X-ray diffraction data, the complexes (I, II, III·Et₂O) are ionic; in complex cation [CuLn(POP)]⁺ the coordination environment of the copper atom is a distorted tetrahedron with CuN₂P₂ chromophore. The photoluminescence properties of the obtained complexes (I–III) were studied in the solid state and in solution. In the absorption spectra of the complexes, a charge transfer band is observed at 380–385 nm; excitation in this range gives rise to two emission bands at 480 and 650 nm in solution. In the solid state, the complexes show photoluminescence only in the red range (λ_max = 600–610 nm) with microsecond lifetimes. It was found that complexes I and III with a more perfect tetrahedral environment have quantum yields an order of magnitude higher than the quantum yield observed for complex II.