Four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes bearing functionalized 3-benzyl-1-(pyridyl)-1H-imidazolylidene ligands: Synthesis, photophysical properties and computational study

Seven luminescent copper(l) complexes bearing four-coordinate N-heterocyclic carbene (NHC) ligands with varying electron-withdrawing substituents including -CF3, -CN, -COCH3, and -CHO groups at the pyridine ring part of the carbene are reported in this study. P1-P4 without the methyl group show better light absorption in low-energy region compared with P5-P7 with the methyl group at the a-position of the pyridine ring. The emitting state of all the complexes is regarded as the (MLCT)-M-3/(LLCT)-L-3 character. P1-P4 exhibit the emission maximum in the range of 537-547 nm with the photoluminescence quantum yields (PLQY) of 12.7-21.9% in PMMA films and excited state lifetimes (tau) of 14.7-22.6 mu s. The emission wavelengths of P5-P7 are blue-shifted to 505-513 nm compared with those of P1-P4, showing the higher PLQY of 38.0-57.3% and longer tau of 36.2-84.8 mu s. Theoretical calculations were used to rationalize the photophysical properties. (C) 2019 Elsevier Ltd. All rights reserved.