Luminescent copper(I) complexes bearing benzothiazole-imidazolylidene ligand with various substituents: Synthesis, photophysical properties and computational studies

The synthesis and photophysical investigation of a series of copper(I) complexes bearing benzothiazoleimidazolylidene-type N-heterocyclic carbene (NHC) ligands are reported. Their photophysical properties are tuned by adjusting the different substituens at 6-position of the benzothiazole ring. C1 and C2 exhibit the lowest lying metal-to-ligand charge transfer (MLCT) absorption bands at 325-400 nm, while the MLCT band of C3 is almost unresolved owing to the blue shift of this band. Upon excitation with UV light all the complexes emit bright yellow-green light (lambda(em) = 543-551 nm) with higher emission quantum yields of 24.9-44.1% and excited state lifetimes on the microsecond scale (tau = 13.7-32.7 mu s) in PMMA films. Additionally, the electronic properties, absorption and emission profiles of these complexes were further explored using DFT/TDDFT methods.