Tetrahedral copper(I) complexes of novel N,N-bidentate ligands and photophysical properties

Abstract

A series of copper(I) complexes [Cu(L)(PPh3)2]NO3 (1–5) of bidentate ligands 2-pyridin-2-yl-quinoline (L1), 4-phenyl-2-pyridin-2-yl-quinoline (L2) 2-pyridin-2-yl-quinoxaline (L3), 6,7-dimethyl-2-(pyridin-2-yl)quinoxaline (L4), and 4-phenyl-2-pyridin-2-yl-quinazoline (L5) have been synthesized and characterized by elemental analysis, absorption, emission, IR, 1H, 13C, 31P NMR spectroscopies and redox method. Of these complexes [Cu(L1)(PPh3)2]NO3 (1), [Cu(L3)(PPh3)2]NO3 (3), and [Cu(L4)(PPh3)2]NO3 (4) are structurally characterized by single-crystal X-ray analysis. They exhibited distorted tetrahedral coordination geometries around the copper(I) center with τ4 values of 0.77–0.86. In the solid-state, all these complexes have exhibited emission in the range of 450–750 nm and their excited-state lifetimes were measured as of 1.9–8.9 μs. However, all the complexes were found to be weak emissive in solution due to the excited state structural rearrangement. Further, Time-dependent density-functional theory (TDDFT) calculations showed that the charge transfers are mainly caused by the contribution of HOMO-2 → LUMO, HOMO-1 → LUMO and HOMO → LUMO orbitals.