New approach to synthesize 8-hydroxyquinoline-based complexes with Zn2+ and their luminescent properties

In this paper, zinc(II) bis-(8-hydroxyquinoline) dihydrate (ZnQ(2)center dot 2H(2)O) and zinc(II) bis-(2-methyl-8-hydroxyquinoline) monohydrate (Zn(MQ)(2)-H2O) were successfully prepared by a room-temperature solid-state chemical reaction using zinc acetate (Zn(CH3COO)(2)center dot 2H(2)O), 8-hydroxyquinoline (HQ) and 2-methyl-8-hydroxyquinoline (2-methyl-8-HQ) as the starting materials. The results of X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and thermal analysis (TG/DSC) demonstrated that the chemical composition of the products were ZnQ(2)center dot 2H(2)O and Zn(MQ)(2)center dot H2O. The scanning electronmicroscopy (SEM) images and the transmission electron microscopy (TEM) images showed that the products ZnQ(2)center dot 2H(2)O and Zn(MQ)(2)center dot H2O had sheet-like morphology with a thickness of about 50 nm. The UV-vis absorption spectra of ZnQ(2)center dot 2H(2)O and Zn(MQ)(2)center dot H2O indicated that they existed charge transfer from the metal to the ligand (MLCT bands). The room-temperature photoluminescence (PL) spectra of ZnQ(2)center dot 2H(2)O revealed that the sample possessed largely blue shift compared with the previous reports. Besides, the two complexes presented a consistent decline situation along with the decline concentration in chloroform solution, which due to solvate effect and structural similarity. The fluorescence quantum yields were measured at 36.58% and 0.07%, and the emission colors were blue-green and light-blue, respectively. The fluorescence quantum yield of ZnQ(2)center dot 2H(2)O was higher than some reported similar structure. The method was believed to largely facilitate the fabrication and application of organometallic complex nanomaterials. (C) 2013 Elsevier B.V. All rights reserved.