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[Display omitted] • Dinuclear N-heterocyclic carbene (NHC) Cu(I) complexes bearing the mixed bis-NHC and POP ligands are synthesized and characterized. • Complexes show intense yellow-green emission in 531–571 nm region originated from the delayed fluorescence. • The photophysical properties were rationalized by DFT and TDDFT calculations. • Green and yellow light-emitting diodes and anti-counterfeiting applications were fabricated successfully. Here, a series of dinuclear N-heterocyclic carbene (NHC) copper(I) complexes having 3,3′-(1,4-phenylenebis(methylene))bis(1-(pyridin-2-yl)-1H-imidazolylidene as bis-NHC ligand and bis[(2-diphenylphosphino)phenyl]ether (POP) as auxiliary ligand have been successfully prepared, and their photophysical properites were investigaged experimentally and theocitcally. The resulting complexes all exhibited intense green to yellow emission that originated from the thermally activated delayed fluorescence (TADF) with a high photoluminescence quantum yield of up to 0.67 and longer excited-state lifetimes on the microsecond time scale in the solid state. Green and yellow light-emitting diode (LED) devices based on Cu(I) complexes have successfully achieved good color rendering indices. Moreover, the anti-counterfeiting patterns and QR codes made of Cu(I) complexes have been applied to clothing, banknotes, books and glass plates with excellent anti-counterfeiting effects. [ABSTRACT FROM AUTHOR]