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[Display omitted] • Four-coordinate N-heterocyclic carbene (NHC) Cu(I) complexes with various substituents are synthesized and characterized. • The photophysical properties of the corresponding complexes is studied. • Complexes exbihit bright photoluminescence with orange-red color. • DFT and TDDFT calculations were employed to rationalize the photophysical properties. Herein, three four-coordinate N-hetercycle carbene (NHC) copper (I) complexes of the types [Cu(BenDimBenIm-CHOPy)(POP)]PF 6 (P1), [Cu(BenDimBenIm-CNPy)(POP)]PF 6 (P2), and [Cu(DimbenDimBenIm-CNPy)(POP)]PF 6 (P3) (BenDimBenIm-CHOPy = 3-benzyl-1-(5-formyl -pyridin-2-yl)-1 H -5,6-dimethylbenzimidazolylidene, BenDimBenIm-CNPy = 3-benzyl-1-(5-cyano -pyridin-2-yl)-1 H -5,6-dimethylbenzimidazolylidene, DimbenDimBenIm-CNPy = 3-(3,5-dimethylbenzyl-1-(5-cyano-pyridin-2-yl)-1 H -5,6-dimethylbenzimidazolylidene, POP = bis[2-diphenylphosphino]-phenyl)ether) have been prepared and investigated. All complexes exhibit the lowest energy metal-to-ligand charge transfer (MLCT) characters in 320–360 nm region showing a slight blue-shift of the absorption maxima in the order P1 > P2 > P3. The emissive wavelength can be fine-tuned to cover the orange-red spectral range of 615−638 nm with higher photoluminescence quantum yields (PLQY) of 17.6–40.3 %. Additionally, the photophysical properties are also investigated theoretically using density functional theory (DFT) and time dependent DFT. [ABSTRACT FROM AUTHOR]