Luminescence color tuning of the four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes with imidazolylidene ligand functionalized by thiazole/benzoxazole moiety

•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.