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Three four-coordinated N-heterocyclic carbene (NHC) copper(I) complexes, [Cu(NaphIm-Py)(POP)]PF 6 ( 1 ), [Cu(AnthrIm-Py)(POP)]PF 6 ( 2 ), and [Cu(PhBenIm- c -Py)(POP)]PF 6 ( 3 ) (NaphIm-Py = 3-(naphthalen-2-ylmethyl-1-(pyridin-2-yl)-1 H -imidazolylidene, AnthrIm-Py = 3-(anthracen-9-ylmethyl)-1-(pyridin-2-yl)-1 H -imidazolylidene, PhBenIm- c -Py = 3-benzyl-1-(pyridin-2-ylmethyl)-1 H -benzo[ d ]imidazolylidene, POP = bis[2-diphenylphosphino]-phenyl)ether) have been synthesized and characterized. The effect of varying carbene ligands with different substituents on the structural aspects and photophysical properties of the complexes is systematically investigated. The lowest absorption bands of 1 at about 350 nm are assigned as metal-to-ligand charge transfer (MLCT) character with some contribution from ligand-to-ligand charge transfer (LLCT) character, while the π-π* transition of the anthryl group are responsible for the lowest absorption band of 2 . For 3 , no MLCT absorption band are observed in lower energy region. The emission wavelengths of all NHC-Cu(I) complexes are in the range of 520–550 nm with the phosphorescent origin in the solid state. 1 and 2 with naphthyl and anthryl groups show the lower photoluminescence efficiency due to the strong π-π stacking interactions, whereas 3 exhibit good photoluminescence properties companying with the higher quantum yields and long excited-state lifetimes. Density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations were employed to rationalize the photophysical properties of the NHC-Cu(I) complexes. [ABSTRACT FROM AUTHOR]

• Four-coordinate N-heterocyclic carbene (NHC) Cu(I) complexes with thiazole/benzoxazole moiety are synthesized and characterized. • The photophysical properties of the resulting complexes is investigated. • Complexes show blue-green emission in 517–551 nm region with the phosphorescent origin. • The differences of the photophysical properties were rationalized by DFT and TDDFT calculations. Here, we report a series of the four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes with imidazolylidene and POP ligands, [Cu(BenzThiazolyl-Im)(POP)]PF 6 (P1), [Cu(BenzThiazolyl-BenIm)(POP)]PF 6 (P2), [Cu(BenzBenzoxazolyl-Im)(POP)]PF 6 (P3), and [Cu(BenzBenzoxazolyl-BenIm)(POP)]PF 6 (P4), (BenzThiazolyl-Im=3-benzyl-1-(thiazol-2-yl)-1 H -imidazolylidene, BenzThiazolyl-BenIm=3-benzyl-1-(thiazol-2-yl)-1 H -Benzoimidazolylidene BenzBenzoxazolyl-Im=3-benzyl-1-(benzoxazol-2-yl)-1 H -imidazolylidene, BenzBenzoxazolyl-BenIm=3-benzyl-1-(benzocazol-2-yl)-1 H -imidazolylidene, POP=bis[2-diphenylphosphino]-phenyl)ether). Thiazole/benzoxazole moiety were functionalized onto imidazolylidene ligand to tune the photophysical properties of the corresponding complexes. P1 and P2 exhibit the metal-to-ligand charge transfer (MLCT) absorption band with the onset at 406–412 nm, while P3 and P4 have similar MLCT band with the onset at 380–389 nm. The emission wavelengths of all NHC Cu(I) complexes can be fine-tuned to cover the spectral range of 517–551 nm with the phosphorescent origin in PMMA films. P2 show the highest photoluminescence efficiency of 40.9% with the red-shifted emission wavelength at 551 nm, whereas P4 has the lowest photoluminescence efficiency of 1.80% with the blue-shifted emission wavelength at 517 nm. Density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations were employed to rationalize the differences for photophysical properties of the NHC Cu(I) complexes. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present study, a series of the four-coordinate N-hetercycle carbene (NHC) copper (I) complexes [Cu(Ph-Im-cyPy)(Xantphos)]PF 6 (P1), [Cu(DimBenPh-Im-cyPy)(Xantphos)]PF 6 (P2), and [Cu(BenDimBenIm-CNPy)(Xantphos)]PF 6 (P3), Ph-Im-cyPy=3-benzyl-1-(4-cyano-pyridin-2-yl)-1 H -imidazolylidene, DimBenPh-Im-cyPy=3-(3,5-dimethylbenzyl-1-(4-cyano-pyridin-2-yl)-1 H -imidazolylidene, BenDimBenIm-CNPy=3-benzyl-1-(4-cyano-pyridin-2-yl)-1 H -5,6-dimethylbenzimidazolylidene, Xantphos=9,9-dimethyl-4,5-bis(diphenylphosphino)-9 H -xanthene, have been synthesized and characterized. The molecular structures of P1 – P3 have been established by single-crystal X-ray diffraction study. In the solid state, P1 – P3 exhibit orange-red emission in the range of 621–643 nm with shorter excited-state lifetimes (τ) of 5.73–6.42 μs and the emission quantum yields (Φ) of 1.0–3.9 % at room temperature. Additionally, the photophysical properties are explained by using density functional theory (DFT) and time dependent DFT. [Display omitted] [ABSTRACT FROM AUTHOR]