A new class of deep blue emitting four-coordinate NHC-Cu(I) complexes bearing nonconjugated triazolyl-imidazolylidene-type ligand: Synthesis, photophysical properties and theoretical investigations

Abstract

In the present study, a series of the four-coordinate N-hetercycle carbene (NHC) copper (I) complexes [Cu(MethyIm-Meth-benzTriazole)(POP)]PF6 (P1), [Cu(BenzyIm-Meth-benzTriazole)(POP)]PF6 (P2), and [Cu(BenzyBenzoIm-Meth-benzTriazole)(Xantphos)]PF6 (P3), MethyIm-Meth-benzTriazole = 1-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-3-methyl-1H-imidazolylidene, BenzyIm-Meth-benzTriazole = 1-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-3-phenyl-1H-imidazolylidene, BenzyBenIm-Meth-benzTriazole = 3-benzyl-1-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1H-benzo[d]imidazolylidene, POP = bis[(2-diphenylphosphino)phenyl]ether, have been synthesized and characterized. The molecular structure of P2 has been established by single-crystal X-ray diffraction study. The addition of the methylene spacer into the NHC ligand effectively breaks the π-conjugation of the ligand, resulting in a larger HOMO-LUMO energy gap. In the solid state, P1–P3 exhibit deep blue emission in the range of 452–466 nm with the excited-state lifetimes (τ) of 14.9–16.2 μs and the emission quantum yields (Φ) of 8.50–11.9 % at room temperature. Additionally, the photophysical properties are explained by using density functional theory (DFT) and time dependent DFT.