Synthesis and Luminescence Properties of the Four-Coordinate N-heterocyclic Carbene (NHC) Copper(i) Complexes with Different Bisphosphine Ligands

Here, we report a series of the four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes having the same bidenate NHC ligand and different bisphosphine (P <^> P) ligands, [Cu(CNbenPy-benzIm)(Naphphos)]PF6 ( P1 ), [Cu(CNbenPy-benzIm)(cyc-xantphos)]PF6 ( P2 ), and [Cu(CNbenPy-benzIm) (xantphos)]PF6 ( P3 ), (CNbenPy-benzIm = 3-(3-cyanobenzyl)-1-(5-phenylpyridin-2-yl)-1H- imidazolylidene; BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthalene; cyc-xantphos = (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(dicyclohexylphosphine), xantphos = 9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphine)). P1 exhibits the metal-to-ligand charge transfer (MLCT) absorption band at 366 nm with high molar extinction coefficient of 2.44 x 10 4 M-1 cm(-1), while P2 and P3 show a blue-shift of the MLCT absorption band at 336-341 nm with the molar extinction coefficients of 0.82- 1.16 x 10 4 M-1 cm(-1), which are just a little lower than that of P1 . The emission wavelengths of all NHC-Cu(I) complexes can be fine-tuned to cover the spectral range of 525-555 nm with the phosphorescent origin in PMMA films. P1 has the lowest photoluminescence efficiency of 5.50% with the red-shifted emis-sion wavelength at 555 nm and the emission lifetime of 237 mu s, whereas P3 show the highest photolumi-nescence efficiency of 39.5% with the blue-shifted emission wavelength at 525 nm and the emission life-time of 64.4 mu s. The differences for photophysical properties of NHC-Cu(I) complexes were rationalized using density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. (c) 2023 Elsevier B.V. All rights reserved.