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

Abstract

Seven luminescent copper(I) 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 α-position of the pyridine ring. The emitting state of all the complexes is regarded as the 3MLCT/3LLCT 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 (τ) of 14.7–22.6 μs. 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 τ of 36.2–84.8 μs. Theoretical calculations were used to rationalize the photophysical properties.