Abstract
Copper (II) complexes containing mixed ligands were synthesized in dimethyl formamide (DMF). The intense cyan emission at an ambient temperature is observed for solid copper (II) complexes with salicylic acid and a 12% quantum yield with a fluorescent lifetime of approximately 10 ms. Hence, copper (II) complexes with salicylic acid are excellent candidates for photoactive materials. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) reveal that the divalent copper metal centers coordinate with the nitrogen and oxygen lone pairs of conjugate ligands. XPS binding energy trends for core electrons in lower-lying orbitals are similar for all three copper (II) complexes: nitrogen 1s and oxygen 1s binding energies increase relative to those for undiluted ligands, and copper 2p3/2 binding energies decrease relative to that for CuCl2. The thermal behavior of these copper complexes reveals that the thermal stability is characterized by the following pattern: Cu(1,10-phenanthroline)(salicylic acid) > Cu(1,10-phenanthroline)(2,2’-bipyridine) > Cu(1,10-phenanthroline)(1-benzylimidazole)2.
Highlights
Accepted: 20 February 2022Transition metal ions and complexes have attracted much attention due to their incompletely occupied d-orbitals and highly ordered solid-state structures [1]
These results provide guidelines for future research on copper (II) complexes that exhibit luminescent emissions with a significant quantum yield and measurable lifetimes
The highest quantum yield in dimethyl formamide (DMF) is achieved for copper (II) complexes with salicylic acid
Summary
Transition metal ions and complexes have attracted much attention due to their incompletely occupied d-orbitals and highly ordered solid-state structures [1]. Due to the influence of organic ligands that quench emission, the luminescent studies of Cu2+ complexes are very scarce in the research literature [20–22] This investigation of Cu2+ complexes, with a high quantum yield, is very challenging. Combining structural and luminescent factors, the primary objective of this research investigation is to obtain an enhanced blue-green emission of copper (II) complexes that contain favorable conjugate ligands with a light-harvesting ligand-to-metal energy transfer. Previous research in our laboratory focused on several metal–ligand frameworks based on nitrogen- and oxygen-containing organic ligands for lanthanide emission [8,32] In this investigation of copper (II) emission, the following three Cu2+ complexes were designed and synthesized in DMF: A = Cu(phen)(bim) , B = Cu(phen)(bipy), and C = Cu(phen)(SA), where bim = 1-benzylimidazole, bipy = 2,2’-bipyridine, SA = salicylic acid, and phen = 1,10phenanthroline. The significance for agricultural harvest improvement is very important
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