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 ·2H 2 O) and zinc(II) bis-(2-methyl-8-hydroxyquinoline) monohydrate (Zn(MQ) 2 ·H 2 O) were successfully prepared by a room-temperature solid-state chemical reaction using zinc acetate (Zn(CH 3 COO) 2 ·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 ·2H 2 O and Zn(MQ) 2 ·H 2 O. The scanning electron microscopy (SEM) images and the transmission electron microscopy (TEM) images showed that the products ZnQ 2 ·2H 2 O and Zn(MQ) 2 ·H 2 O had sheet-like morphology with a thickness of about 50   nm. The UV–vis absorption spectra of ZnQ 2 ·2H 2 O and Zn(MQ) 2 ·H 2 O indicated that they existed charge transfer from the metal to the ligand (MLCT bands). The room-temperature photoluminescence (PL) spectra of ZnQ 2 ·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 ·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.