Optical Properties Toward Metal Cations
[485]/165
reduced pressure. The general procedures were followed by the indicated references [3].
For the next step, the dye chemosensor was obtained from the prepared intermediates of
2,2-bithiophene-5-carboxaldehyde and benzoxazole moiety. 2 mmol of 2,2-bithiophene-5-
carboxaldehyde and benzoxazole moiety were dissolved in 15 ml of benzene. 5∼6 drops of
piperidine was added dropwise and refluxed for 48 h. The reaction products were filtered
with benzene and dried in vacuum.
(yield: 0.38g, 45%). 1H-NMR (400MHz, acetone-d6) δ 8.82 (s, 1H), δ 8.08 (d, 1H), δ
7.79 (m, 2H), δ 7.68 (d, 1H), δ 7.57 (m, 1H), δ 7.50 (m, 2H), δ 7.40(d, 1H), δ 7.35(s, 3H), δ
7.17(m, 1H), δ 7.00(m, 1H). MS: 402(M+). Anal. Calculated for C22H14N2O2S2: C, 65.65;
H, 3.51; N, 6.96; S, 15.93: found; C, 66.07; H, 3.83; N, 6.82; S, 14.74.
2.2 Measurements
The spectroscopic characteristics and the fluorescence properties of the prepared dye
chemosensor were examined and determined using Agilent 8453 UV-Vis spectrophotome-
1
ter and Shimadzu RF-5301 spectrofluorophotometer, respectively. H NMR spectra and
elemental analyses were recorded with a JNM-AL400 spectrometer operated at 400 MHz
NMR and a Carlo Elba Model 1106 analyzer, respectively. Electron distributions and energy
potentials were calculated with Material Studio 4.3 [15]. Cyclic voltammograms were ex-
amined with a Versa STAT3 using three-electrode conventional electro chemical cell. Cyclic
voltammetry test was conducted in an acetonitrile solution containing tetrabutlyammonium
hexafluorophosphate electrolyte. The reference electrode, Ag/Ag+ was directly immersed
in the reaction cell. The working electrode was a glassy carbon. The counter electrode was
a platinum wire. The scan rate was commonly 100mV/s.
2.3 Job’s plot measurements
Using job’s method determination, the stoichiometrical characteristics of metal binding
ratio with dye sensor were examined. Equimolar solutions of dye sensor and various metal
cations (Cd2+, Cu2+, Hg2+, Ni2+, Zn2+, Al2+ and Fe2+) were mixed in different volume
ratios (1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, 10:0). The maximum absorption of these
mixtures was characterized.
Results and Discussion
In this work, the designed dye chemosensor was synthesized using 2,2-bithiophene as
a donor unit and benzoxazole dye intermediate as a signal unit. UV-Vis absorption and
fluorescence emission spectra were investigated to monitor the optical changes and sensing
properties of the dye sensor with various different metal cations. The UV-Vis absorption
and fluorescence emission spectra of dye sensor (1 × 10−5 M) in MeOH : Water (9:1)
solution with various metal cations (Cd2+, Cu2+, Hg2+, Ni2+, Zn2+, Al2+ and Fe2+, 1 ×
10−4 M) are shown in Figure 1 and 2, respectively.
From Figure 1 and Figure 2, the dye sensor showed the higher selective detection
toward Cu2+ cations. As Figure 1 and Figure 2 show, upon the addition of Cu2+ to the
solution of the prepared dye sensor, the absorption band at 390 nm progressively decreased
in intensity and a weak new peak at 470 nm appeared; an isobestic point at 430 nm
also developed. The appearance of this isobestic point suggests that at least one stable
dye sensor-Cu2+ metal cation species is present in solution and is indicative that a stable
complex formed between dye sensor and Cu2+. In the case of fluorescence emission band at