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[Display omitted] • Four-coordinate N-heterocyclic carbene (NHC) Cu(I) complexes with nonconjugated NHC ligand are synthesized and characterized. • The photophysical properties of the corresponding complexes is studied. • Complexes show deep blue emission in 452–466 nm region. • DFT and TDDFT calculations were employed to rationalize the photophysical properties. In the present study, a series of the four-coordinate N-hetercycle carbene (NHC) copper (I) complexes [Cu(MethyIm-Meth-benzTriazole)(POP)]PF 6 (P1), [Cu(BenzyIm-Meth-benzTriazole)(POP)]PF 6 (P2), and [Cu(BenzyBenzoIm-Meth-benzTriazole)(Xantphos)]PF 6 (P3), MethyIm-Meth-benzTriazole = 1-((1-benzyl-1 H -1,2,3-triazol-4-yl)methyl)-3-methyl-1 H -imidazolylidene, BenzyIm-Meth-benzTriazole = 1-((1-benzyl-1 H- 1,2,3-triazol-4-yl)methyl)-3-phenyl-1 H -imidazolylidene, BenzyBenIm-Meth-benzTriazole = 3-benzyl-1-((1-benzyl-1 H -1,2,3-triazol-4-yl)methyl)-1 H -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. [ABSTRACT FROM AUTHOR]