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X. Wang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 226 (2020) 117650
the AIE molecules to design a pH-response AIE fluorescence probe.
By utilizing coumarin and quinoline as electron donors and elec-
tron acceptors respectively, N, N0-diformylhydrazine bond as the
linkage, a novel pH-responsive fluorescent probe CHBQ with AIE
effect for the broad range pH detection have been synthesized
successfully.
dicyclohexylcarbodiimide (DCC) (0.68 g, 3.3 mmol) in of DMF (8 mL)
were stirred for about 8 h at room temperature. After filtration, the
filtrate was added to the mixture solvent (50 mL) of isopropanol-
hexane mixture (1/20) to obtain the intermediate 2,5-
dioxopyrrolidin-1-yl-2-oxo-2H-chromene-3- carboxylate (DC) [44].
Next, the mixture of the intermediate DC, QA (0.70 g, 3.2 mmol) and
4-Dimethylaminopyridine (0.39 g, 3.2 mmol) in of DMF (10 mL) were
reacted at 85 ꢀC for 24 h. Then, pour the mixture into deionized
water, extracting with dichloromethane. Collecting the organic
phase, washed with saturated sodium chloride solution, and then
dried by anhydrous sodium sulfate. The solvent was removed under
reduced pressure to get crude product. The crude product was pu-
rified by column chromatography on silica gel with the eluent of
methanol/dichloromethane (1/30, v/v) to obtained a pale yellow
solid 2-oxo-N’-(2-(quinolin-8-yloxy)acetyl)-2H-chromene-3-carbo-
The synthesized probe CHBQ exhibited good AIE characteristics.
In a mixed solvent of acetonitrile and water, the fluorescence
located at 415 nm gradually increased with the increase of water
proportion. In addition, a different fluorescence response could be
observed in the presence of acids and bases. Under acidic condi-
tions, the fluorescence emission peak of the probe CHBQ gradually
decreased and generated blue shift from 475 nm to 415 nm with the
pH changed from 2.00 to 6.00 and the color of solution changed
from cyan to blue under UV365 nm lamp. Under alkaline conditions,
as the pH gradually increased, the fluorescence at 415 nm was
decreased, and the blue color of the solution gradually became
darkened under UV365 nm lamp. Furthermore, the response time of
probe CHBQ towards pH was extremely short as 30 s, rapid recog-
nition of acid and base could be realized and almost impervious to
other ions, such as some metal cations and anions. Finally, the
probe CHBQ could be developed as a pH test strip to achieve a faster
detection of a broad range pH in the actual sample.
1
hydrazide (CHBQ) 0.61 g, yield (52%). H NMR (600 MHz, CH3CN-d)
d
(ppm): 11.72 (b, 1H), 10.82 (s, 1H), 9.00 (m, 1H,) 8.97 (s, 1H), 8.37 (d,
J ¼ 8.4 Hz, 1H), 7.97 (d, J ¼ 7.8 Hz, 1H), 7.79 (m, 1H), 7.67 (d, J ¼ 8.4 Hz
1H), 7.60 (m, 2H), 7.52 (d, J ¼ 8.4 Hz,1H), 7.48 (t, J ¼ 7.2 Hz,1H), 7.41 (d,
J ¼ 7.8 Hz, 1H), 4.99 (s, 4H); 13C NMR (100 MHz, DMSO-d6)
d (ppm)
165.87, 160.37, 159.04, 154.51, 154.45, 149.92, 148.56, 140.43, 136.59,
134.93, 130.87, 129.63, 127.27, 125.72, 122.51, 121.81, 118.80, 118.45,
116.74, 113.09, 68.70. HRMS-ESI calcd for C21H15N3O5 (m/z) [M þ H]þ:
390.1084, found: 390.1085.
2. Experimental
2.3. Fluorescence and UV-Vis measurements
2.1. Materials and instruments
The stock solution of CHBQ (1.0 ꢁ 10-3 mol/L) was prepared in
CH3CN. In the pH response experiment, the pH meter was adjusted
by using standard solution of potassium hydrogen phthalate
(pH ¼ 4.00) and mixed phosphate (pH ¼ 6.86). Unless otherwise
stated, the pH of the solution is adjusted by HCl and NaOH. In the
interfering experiment, the pH ¼ 4.00 buffer solution was prepared
by dissolving potassium hydrogen phthalate in deionized water,
and the pH ¼ 9.18 buffer solution of was prepared by dissolving
sodium tetrabrate in deionized water. The stock solutions of ions
(1.0 ꢁ 10-2 mol/L) were prepared by dissolving them in deionized
water. All of the experiments were performed at barometric pres-
sure and room temperature. Excitation and emission slit widths
was 5 nm and 10 nm, respectively.
Unless otherwise stated, all chemical reagents were obtained
from commercial suppliers and used without further purification.
4-Dimethylaminopyridine (DMAP), N,N0-dicyclohexylcarbodiimide
(DCC), N-hydroxysuccinimide (NHS), Coumarin-3-Carboxylic acid,
8-hydroxyquinoline, and methanol (HPLC) were purchased from
Energy Chemical (Shanghai, China) without any further purifica-
tion. Metal ions were all nitrates salts, and anions were all sodium
salt. All the salts were provided from Alfa Aesar (Tianjin, China).
Hydrogen nuclear magnetic resonance (1H NMR) and carbon nu-
clear magnetic resonance (13C NMR) spectra were recorded on
Bruker ARX600 and Bruker ARX400 spectrometer. Chemical shifts
for hydrogens are reported as ppm (tetramethylsilane as an internal
standard) and are referenced to the residual protons in the NMR
spectra (DMSO: d
2.50). 13C NMR spectra were recorded at 100 MHz.
2.4. Calculation of pKa
Chemical shifts for carbons are reported as ppm (tetramethylsilane
as an internal standard) and are referenced to the carbon resonance
The pKa value was calculated by the Henderson-Hasselbach
type mass action equation [45]: pKa ¼ pH - log ((Fmax-F)/(F-Fmin)),
where F is the fluorescence intensity of CHBQ at corresponding pH.
Fmax and Fmin is minimal and maximal fluorescence intensity at
detection range, respectively.
of the solvent (DMSO:
d 39.5). High Resolution Liquid Chromatog-
raphy Mass Spectra (HPLC-MS) were acquired on Thermo Scientific
Q Exactive instrument (Thermo Fisher Scientific, USA), which
equipped with an electroscope ionization (ESI) source. UV-vis
spectra were measured on Hitachi 5300 absorption spectropho-
tometer in a cuvette (1 cm in diameter) with 2 mL solution. Fluo-
rescence spectra were recorded on Hitachi F-4600 fluorescence
spectrophotometer using an excitation wavelength of 330 nm, and
the excitation slit widths was 5 nm and emission slit widths was
10 nm, respectively. The pH value of solution was measured and
controlled with a PHS-3C pH meter (Shanghai LeiCi Device Works,
China). Density functional theory (DFT) (B3LYP/6-31G (d) level of
theory) was utilized to model the structure geometry and elec-
tronic properties of relevant molecular.
2.5. Preparation of test paper strips
The test paper strips were obtained by cutting filter paper with
the size of 10 mm ꢁ 20 mm. Prepared filter paper was placed in
acetonitrile solution of the CHBQ (2.0 ꢁ 10-3 mol/L), and dried in
the air. Then 50 mL solutions of different pH were added to the filter
paper. After placing the test paper 30 mm above the solvent and
keeping it for 30s, the color of test paper above acetic acid and
ethylenediamine changed to cyan and dark under UV365 nm lam,
respectively The color changes of the test paper strips were
observed under UV365 nm lamps. In order to detect the fluorescence
of the test paper discoloration, CHBQ was painted to the wall of the
cuvette, and the fluorescence emission spectrum was recorded in
different pH condition. The excitation wavelength was 330 nm, and
the excitation and emission slits was 10 nm and 20 nm,
respectively.
2.2. Synthesis
The intermediate compounds of ethyl 2-(quinolin-8-yloxy)ace-
tate and 2-(quinolin-8-yloxy) acetohydrazide (QA) were synthesized
according to the previously reported reference [43]. A mixture of
coumarin-3-carboxylic acid (0.57 g, 3.0 mmol), N-hydrox-
ysuccinimide
(NHS)
(0.37 g,
3.2 mmol)
and