Heteroleptic Copper(I) complexes of bipyridine glycoluril and phosphine ligands: Photophysical and computational studies

Abstract

A series of heteroleptic copper(I) complexes of the type [Cu(bpg)(PP)]PF6 (1–4) have been synthesized where bpg = [4b,5,7,7a-tetrahydro-4b,7a-epiminomethanoimino-6H-imidazo[4,5-f] [1,10]-phenanthroline-6,13-dione] and PP are phosphine derived ancillary ligands (triphenyl phosphine (PPh3), 1,2 bis(diphenylphosphino)ethane (dppe), bis[(2-diphenylphosphino)phenyl]ether (POP) and 1,3 bis(diphenylphosphino)propane (dppp)). All copper(I)-phosphine complexes were thoroughly characterized by elemental analyses, IR, 1H NMR, 13C NMR, 31P NMR and ESI-MS, UV–visible, emission spectroscopy and DFT calculations. The crystal structure of 1 contains two Cu(I) molecules in asymmetric unit which localizes in distorted tetrahedral geometry with N2P2 coordination core. The UV–visible spectra indicated that ancillary phosphine ligands significantly affect the MLCT band of the copper(I) complexes. The bands in the UV–visible spectra fit well with the TD-DFT calculations and are assigned to the contribution of HOMO-2 → LUMO, HOMO-1 → LUMO and HOMO → LUMO orbitals. These Cu(I) complexes exhibit green emission in CH2Cl2 at room temperature with emission wavelengths at 545–572 nm. Cyclic voltammetric data revealed that steric hindrance of diphosphine ligands affected the oxidation potential of Cu(I) complexes.