In this analysis, the single crystal of schiff base has been synthesized and the purity of material has been increased by repeated recrystallization process. Single crystal was grown by adopting the method growing in a slow evaporation solution using ethanol as solvent at room temperature. A new fluorescent molecule based on Schiff base has been synthesised and its binding properties investigated by fluorescence spectroscopy to show that it can selectively bind Cu2+ with fluorescence quenching.
Because of structural flexibility and their application for switching materials and so on, Schiff base compounds are one of the most extensively used ligands in the field of coordination chemistry [
In previous work, we have reported the synthesis and developed their function as selective fluorescent chemsensors for Cu2+ [
Preparation of 1 [6-8]: To a solution of 2-oxo-2H-chromene-3-carbohydrazide (0.3 g, 1.5 mmol) in ethanol (20 ml) was added 2-hydroxybenzaldehyde (0.3 ml, 3mmol). The reaction mixture was stirred for about 5 h. Subsequently, it was cooled to room temperature. The resultant orange solution was filtered. Yellow precipitate obtained was dissolved in ethanol (1.5 g, 31.8%). The synthesis of the shciff base molecules 1 is re presented in the following equation :
Yellow crystals suitable for XRD formed after a few days of slow evaporation of the solvent at room temperature over several days. Yellow single crystals of the title compound is shown in
All reagents obtained from commercial sources were of analyzed grade. Melting points were determined with XT4A micromelting point apparatus and were uncorrected. The 1H NMR was recorded on a Mercury Plus-400
spectrometer with TMS as internal reference and CDCl3 as solvent. IR were recorded on a Perkin-Elmer PE-983 IR spectrometer as KBr pellets with absorption in cm−1. MS were obtained with Finnigan Trace MS instrument using EI method. Elemental analyses were carried out on a Vario EL III instrument. Fluorescence spectra were determined on a Hitachi F-4500.
Single crystal X-ray diffraction studies were carried out on the grown crystals. The X-ray date were collected using X-ray diffractometer (Model: Bruker Smart APEXCCD). The observed results indicate that the crystal belongs to triclinic crystal system and the determined unit cell parameters are a = 17.505 (5) Å, b = 6.3135 (18) Åc = 16.578 (5) Å, α = 90˚, β = 97.255 (5)˚, γ = 90˚ and V = 1817.5 (9) Å3.
Compound of 1. M.p. 145.2˚C - 147.8˚C (dec.). (KBr, cm−1): 3620, 1645, 1600, 1503, 1445. 1H NMR d: 5.2 (s, 2H, OH), 6.8 (d, 4H, PhH), 7.2 (q, 2H, PhH), 7.6 (d, 2H, PhH), 8.8 (s, 2H, CO2CH2CH3), 7.26 - 7.45 (m, 4H, ArH). MS (EI): m/z = 241 [M + H] + Anal. Calcd for C14H12N2O2 (240.26): C, 69.99; H, 5.03; N, 11.66; O, 13.32, Found: C, 69.67; H, 5.33; N, 11.57; O, 13.53.
The binding properties of the Schiff base with various metal ions were investigated by fluorescent spectroscopy titration experiments. Changes of the fluorescence properties of Schiff base (2 × 10−5 M in acetonitrile) solution caused by 15 equiv. of various metal ions (Co2+, Cr3+, Sn4+, Cu2+ , Sr2+ , Ag+, Ni2+, Pb2+, Fe3+) were measured until their emission intensity were constant.
The result showed that Cu2+ produced significant quenching in their fluorescent emission. The other metal ions that were tested only show a relatively insignificant change (
The sensitivity of the fluorescence emission response of 1 towards Cu2+ was also examined under the same conditions with various Cu2+ concentrations (
reduced to 80% of the initial value. From a Stern-Volmer plot (
A new Schiff base molecule as fluorescent chemosensor has been designed and synthesized. They display high selectivity for Cu2+ revealed by fluorescence quenching. In future work, our efforts will be focused on the elucidation of the detailed mechanisms of these fluorescent chemosensor.
We thank the Hubei provincial Department of Education (Grant No.D20112503) for financial support.