A series of luminescent Cu(i) complexes based on the diphosphine ligand and diimine ligand: weak intermolecular interactions, terahertz spectroscopy and photoproperties

Abstract

Five novel mononuclear [Cu(Bphen)(bdppmapy)]X complexes showing photoluminescence were synthesized. The same diphosphine ligand and diimine ligand and different Cu(I) salts were used in the one-pot synthesis of complexes 1–5. These complexes are listed as follows: [Cu(Bphen)(bdppmapy)]CF₃SO₃ (1), [Cu(Bphen)(bdppmapy)]BF₄·0.268CH₃OH (2), [Cu(Bphen)(bdppmapy)]ClO₄ (3), [Cu(Bphen)(bdppmapy)]I·CH₃OH (4) and [Cu(Bphen)(bdppmapy)]Br·2CH₃OH (5) (Bphen = 4,7-diphenyl-1,10-phenanthroline, bdppmapy = N,N-bis((diphenylphosphino)methyl)-2-pyridinamine). IR, NMR, elemental analysis, single-crystal X-ray diffraction analysis, UV-vis, fluorescence spectroscopy and terahertz time-domain absorption spectroscopy (THz-TDS) were used to characterize 1–5. Their crystal structures have been elucidated by X-ray crystallography and their photophysical properties have been investigated in detail. These five complexes have a similar coordination center, while their space stacked structures are different, from a 0D dimeric structure to a 3D supramolecular structure. Photophysical studies and density functional theory calculations (DFT) show that the luminescence properties of these five complexes are mainly ascribed to metal-to-ligand charge transfer (MLCT). Among these five complexes, 1 emits luminescence with the highest quantum yield of 36.96% and a lifetime of 11.90 μs at ambient temperature. Different counter-anions lead to the distinction of QYs, maybe due to the influence of weak forces. Terahertz time-domain absorption spectroscopy was used to characterize these ligands and complexes in the range of 0.2–2.4 THz.