Fluorescence detection of iodide anion using a donor-acceptor (D-A) thiourea derivative

Article abstract of DOI:10.1016/j.jphotochem.2014.07.015

1-(4-acetyl-phenyl)-3-(4-N,N-dimethylaminophenyl)-thiourea is synthesized and characterized by NMR, IR, MS and elemental analysis. The probe exhibits the "turn-off" fluorescence response to iodide anion in THF/H₂O (v/v = 9/1) pH = 7.4 Tris-HCl buffer solution, which is attributed to the intramolecular charge transfer (ICT). It is found that the probe has a detection limit of 0.336 μM. Such interesting results could be further supported by quantum chemical calculation, UV and ¹H NMR titration. Moreover, the probe is applied to determine iodide in powdered milk and urine samples. This experiment shows a good agreement between added and detected concentration of the iodide in real samples.

Full text of DOI:10.1016/j.jphotochem.2014.07.015

Journal of Photochemistry and Photobiology A: Chemistry 292 (2014) 49–55
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Fluorescence detection of iodide anion using a donor–acceptor (D–A)
thiourea derivative
Wen Yang, Jie Shao, Yunlong Xu, Weiqun Zhou∗, Juan Xie
School of Chemistry & Chemical Engineering and Material Science, Soochow University, 199 Ren’ai Road, Suzhou 215123, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
1-(4-acetyl-phenyl)-3-(4-N,N-dimethylaminophenyl)-thiourea is synthesized and characterized by
NMR, IR, MS and elemental analysis. The probe exhibits the “turn-off” fluorescence response to iodide
anion in THF/H2O (v/v = 9/1) pH = 7.4 Tris–HCl buffer solution, which is attributed to the intramolecular
charge transfer (ICT). It is found that the probe has a detection limit of 0.336 ␮M. Such interesting results
could be further supported by quantum chemical calculation, UV and 1H NMR titration. Moreover, the
probe is applied to determine iodide in powdered milk and urine samples. This experiment shows a good
agreement between added and detected concentration of the iodide in real samples.
Received 18 March 2014
Received in revised form 9 July 2014
Accepted 15 July 2014
Available online 29 July 2014
Keywords:
Donor–acceptor (D–A) thiourea
Fluorescence recognition
Iodide anion
© 2014 Elsevier B.V. All rights reserved.
Intramolecular charge transfer
1. Introduction
[29], taking sulfur amide group as anion binding sites based on the
formation of the intermolecular hydrogen bonding.
The development of fluorescence probes for biological anions
is of great interest due to the important role that anions play in
the areas of medicinal, biochemistry, and environmental chem-
istry [1–6]. For example, iodine is an indispensable microelement to
humans and is instrumental in several biological activities such as
brain functions, neurological activity, cell growth, metabolism and
thyroid function [7–10]. Iodide deficiency or excess could lead to
disorder of physiological functions [11–13]. Therefore, the deter-
mination of iodide anion in biological system will become very
important. Recently, increasing attentions are paid to developing
simple fluorescence probes for fast and convenient detection of
anions. However, the probes for iodide anion are rarely shown
because of iodide’s large anionic radius, low charge density, and
low hydrogen-bonding ability [14–18]. In particular, the iodide
anions widely exist in aqueous systems in nature and most of the
probes shown for iodide are incompatible with aqueous systems.
For practical applications, it is necessary to design and prepare the
fluorescence probes for iodide anions in aqueous systems. Recently,
a few fluorescence probes for iodide anions in aqueous systems are
reported [19–24].
In this work, we designed a highly selective probe for recogni-
tion of iodide anion with a strong donor–acceptor (D–A) ␲-electron
system taking N,N-dimethylamino moiety as the electron donor
and acetyl group as the electron acceptor. In general, the D–A
molecules, exhibiting ICT fluorescence characteristics, show good
photo-physical properties and are applied to sensing anions
[30–32].
Although there are a lot of sensors for I− based on “turn-off” flu-
orescence [20,33,34], suitable in aqueous systems is rare. Our probe
displays the “turn-off” fluorescence responses to I− in THF/H2O
(v/v = 9/1) pH = 7.4 Tris–HCl buffer aqueous solution. The probe
is also applied to determine iodide in powdered milk and urine
samples as actual detection. The results show a good agreement
between added and detected concentration of the iodide in real
samples. The probe of this work is very prospective to be a good
sensor due to its characteristics, such as small molecule, simple
structure, easy to synthesis, and high selectivity and sensitivity for
detecting I−.
2. Experiment
Thiourea group as fluorophore is often exploited for detecting
F− [2–6], AcO− [4–6,25], CN− [3,26,27], H2PO4 [5,28] and PO4
−
3−
2.1. Instruments and materials
Melting points were determined on a Kofler melting point appa-
ratus and remained uncorrected. IR spectra were obtained in KBr
pellets using a Nicolet 170SX FT-IR spectrometer. 1H NMR and
13C NMR spectra have been recorded on INOVA 400 at 400 and
∗
Corresponding author. Tel.: +86 0512 65884827.
E-mail address: wqzhou@suda.edu.cn (W. Zhou).
http://dx.doi.org/10.1016/j.jphotochem.2014.07.015
1010-6030/© 2014 Elsevier B.V. All rights reserved.

50
W. Yang et al. / Journal of Photochemistry and Photobiology A: Chemistry 292 (2014) 49–55
S
100 MHz, respectively (TMS as internal standard and CDCl3-d as
deuterated solvents with chemical shifts reported as ppm). Ele-
mental analyses were performed on a Yannaco CHNSO Corder MT-3
analyzer. Absorption and fluorescence spectra were recorded using
a CARY50 UV–vis spectrophotometer and an FLS920 fluorescence
spectrophotometer, respectively. Mass spectra were recorded on
a Finnigan MAT95 mass spectrometer (ESI+). Measurement of pH
was performed using a REX PHS-3c acidmeter (INESA Instrument,
China).
CS2
CuSO4
N
NHCSNH4
N
NH2
N
NCS
.
NH3 H2O
(2)
(1)
(3)
COCH3
N
S
1-(4-aminophenyl)ethanone (4)
N
H
N
H
(5)
Scheme 1. The synthetic route of the probe.
THF were used as HPLC grade and purchased from COSMOSIL
(CHINA). CDCl3-d, tetrabutyl-ammonium salts of halides, quinine
sulfate, NaH2PO4, Na2HPO4, Na2SO4, NaHCO3, NaNO3, NaAc as ana-
lytical reagent (AR) and the standard buffer solution of Tris–HCl
were purchased from J&K (J&K CHEMICA, CHINA). The fluorescence
quantum yield was evaluated using quinine sulfate in 0.05 mol L−1
(0.05 M) sulfuric acid as the standard.
(Ka) of probe •I− was determined by the Benesi–Hildebrand
Eq. (1) [43]:
1
1
1
=
+
(1)
{Ka × (F0 − Fmax) × [I−]}
F0 − F
(F0 − Fmax
)
where F was the fluorescence intensity at 520 nm at any given I−
concentration, F0 was the fluorescence intensity in the absence of
I−, and Fmax was the maxima fluorescence intensity in the presence
of I−. The association constant Ka was evaluated graphically by plot-
ting 1/(F0 − F) against 1/[I−]. Data were linearly fitted according to
Eq. (1) and the Ka value was obtained from the slope and intercept
of the line.
A stock solution of the probe (200 ␮M) was prepared in water
with Tris–HCl (10 mM, pH = 7.4) buffer solution. Then, it was diluted
to the concentration (20 ␮M) with THF and water to the determined
solution of the probe (THF/H2O, V/V = 9/1). A 0.08 mol L−1 of iodide
stock solution was prepared by dissolving 1.328 g of potassium
iodide (J&K CHEMICA, CHINA) in water and diluting to 100 mL in a
volumetric flask.
The detection limit (DL) of I− was determined from the following
equation: DL = K × SD/S [44], where K = 3, SD was the standard devi-
ation of the blank solution, and S was the slope of the calibration
curve.
2.2. Calculation
DFT (B3LYP) method [35–37] had been employed to optimize
the ground structure of the free probe. The stable structure and
properties of the complex probe •I− were obtained by PM3 semi
empirical method. The harmonic vibration frequency calculations
confirmed the stability of the structures.
2.5. Preparation of sample
28 g of milk sample was placed in a porcelain crucible, and 10 g
of Na2CO3, 10 mL of a 6 mol L−1 NaOH solution and 40 mL of MeOH
were added. This mixture was allowed to dry slowly in a heater at
110 ◦C. Then it was placed in a cold muffle furnace, the tempera-
ture of which was slowly increased to 500 ◦C, to prevent analyte
losses. Approximately 3 h later, when incineration was complete
(white ash), the crucible was cooled down in a desiccator to room
temperature. Then the ash was redissolved in 10 mL of hot water.
The dissolve residue was filtered and the filtrate was condensed to
1 mL [45]. 10 mL of urine sample was also heated and condensed to
1 mL.
0.5 mL of the above concentrate was added to 0.5 mL stock solu-
tion of probe, and diluted to 10 mL with THF. Another 0.5 mL of the
concentrate was added to 1 ␮L 0.08 mol L−1 iodide stock solution
and 0.5 mL stock solution of probe, then diluted to 10 mL with THF.
The analytical procedure was applied afterwards.
2.3. Synthesis of probe
The probe was synthesized according to the references [38–41]
and the structure was defined by elemental analysis, 1H NMR, 13
NMR, MS and FT-IR (Figs. S1–S4).
C
Probe, Green powder. Yield: 54.1%. m.p.: 163.2 ◦C. Anal. Calc. for-
mula, C17H19N3OS (%): C, 65.18; N, 13.42; H, 6.07. Found (%): C,
64.86; N, 13.36; H, 6.42. 1H NMR (ppm): ı = 2.09 (s, 3H, COCH3), 2.89
(s, 2CH3, 6H), 6.74–6.76 (d, J = 8.4 Hz, 2H), 7.21–7.23 (d, J = 8.4 Hz,
2H), 7.68–7.70 (d, J = 8.4 Hz, 2H), 7.89–7.91 (d, J = 8.4 Hz, 2H), 9.80
(s, 1H), 9.84 (s, 1H). 13C NMR (ppm): ␦ = 196.604 (1C, C O), 179.162
(1C, C S), 148.130 (1C), 144.505 (1C), 131.949 (1C), 128.830 (1C),
127.956 (2C), 125.586 (2C), 121.512 (2C), 112.270 (2C), 109.343
(1C), 98.385 (1C), 26.536 (1C). HRMS (ESI) calcd. for (M + H+)+ 314.1,
found 314.1. FTIR (cm−1): 3406 (␯N1–H1), 3032 (␯Ph–H), 2970
(␯N2–H2), 2856 (␯CH3, s), 1679 (␯C O), 1604 (␯Ph), 1588 (␯C C),
3. Results and discussion
1529 (␯N
C
N, as), 1509 (␯C N), 1416 (␯C N), 1361 (␯Ph N),
3.1. Preparation
1285 (␯C S), 1079 (␯C N), 1019 (␯C N), 732 (␯C S).
The Synthetic route of the probe was depicted in Scheme 1.
Carbon disulfide of 4.3 mL and ammonia of 9.0 mL were taken
into a 250 mL flask cooled by ice water. After mixed adequately,
the alcohol solution (10 mL) of 4-N,N-dimethylaminoaniline (1)
(5.5 g) was dropwised into the flask under stirred. The solid of
4-N,N-dimethylaminoanilino thiocarbamoyl ammonium (2) was
obtained. The 20 mL aqueous solution of (2) was added to the sat-
urated copper sulfate solution (50 mL). After extracted by ethyl
acetate (20 mL twice) and evaporated under reduced pressure,
the phenyisothiocyante (3) was gained. Then, the equimolar 1-(4-
aminophenyl) ethanone (4) was added into the acetonitrile solution
(10 mL) of (3) (5.0 g). The probe (5) was obtained by reduced pres-
sure and purified by washed with alcohol (10 mL, twice) and dried
over Na2SO4.
2.4. The pH dependence, the binding stoichiometry, the
association constants and the detection limit
The pH dependence of the probe (20 ␮M) was investigated in
THF/water (v/v = 9/1) of different pH. The stock solution of the
probe (200 ␮M) obtained different pH value in water with HCl and
NaOH, and the pH value was calibrated by an acidimeter. Then, it
was diluted to the concentration (20 ␮M) with THF to the deter-
mined solution (THF/H2O, V/V = 9/1). The binding stoichiometry
of probe •I− was determined from a Job’s plot [42]. The fluores-
cence intensity at 520 nm was plotted against the molar fraction of
the probe with 0-2.0 equivalents of I−. The association constant

W. Yang et al. / Journal of Photochemistry and Photobiology A: Chemistry 292 (2014) 49–55
51
the band at ꢀmax = 295 nm had formed. Then, the bands increase
gradually along with the increase of iodide anions from 0.8 to
2.0 equiv. Meanwhile, in the presence of 0.4 equivalents of iodide,
a weak absorption band appeared at about 370 nm through an
isosbestic point at 315 nm, which indicated the formation of
probe •I−.
3.3. 1H NMR titration
1H NMR titration (Fig. 2) was employed to gain a clear under-
standing of the interaction between the probe and I−. Because
of magnetic performance and electron withdrawing effect, iodide
anions must affect the proton signals of probe binding to I− site.
When I− approached to the probe, the deshield effect of the
adjacent protons increased and the signs shifted downfield. For
example, the chemical shifts of H(1) and H(2) of
N H of thiourea
shifted downfield from 9.84 and 9.80 ppm (I− absent) to 9.96 and
9.91 ppm (2 equiv. of I−) respectively. The chemical shifts of H (3)
also showed a slight lower field shift (7.70 → 7.73 ppm) upon addi-
tion of 2.0 equiv. of I−. All these changes in the chemical shifts
indicated the complex could be formed by the manner of I− closing
to the thiourea moieties.
Fig. 1. UV–vis spectra of the probe (20 ␮M) upon addition of different equiv. iodide
anions.
3.2. UV Spectra of probe
The anion binding property of the probe was determined by
UV–vis absorption spectra in the absence and the presence of differ-
ent anions as shown in Fig. 1. In the absence of anions, the free probe
(20 ␮M) showed two characteristic absorption peaks at ꢀmax = 275
and 318 nm (ε ≈ 8000 and 9000 mol−1 L cm−1, respectively) in THF
solution, corresponding to ␲ → ␲* electronic transitions. Adding
0 to 0.4 equiv. of iodide anions, the intensities of the absorption
bands at ꢀmax = 275 nm increased gradually and the absorp-
tion bands were covered by the strong bands at ꢀmax = 318 nm.
Adding 0.6 equiv. of iodide anions, the band at ꢀmax = 318 nm
began shift blue, and increasing to 0.8 equiv. of iodide anions,
3.4. Turn-off fluorescence response for iodide anions
The fluorescent property of the probe was investigated in differ-
ent solvents upon excitation at 295 nm (Fig. S5). Dual fluorescence
emissions at ꢀmax = 360 and 501 nm were observed in THF. The flu-
orescence quantum yield was 0.034 and 0.082, respectively. The
fluorescence band at ꢀmax = 360 nm having the moderate Stokes
shift (≈154,000 cm−1) was attributed to ␲* → ␲ transition [46].
The fluorescence band at ꢀmax = 501 nm was considered as a ICT
fluorescence [47–50] due to the fluorescence characteristic of the
Fig. 2. 1H NMR titration of the probe (370 ␮M) upon the absence and the presence of iodide anions in CDCl3-d.

52
W. Yang et al. / Journal of Photochemistry and Photobiology A: Chemistry 292 (2014) 49–55
wide band and the large Stokes shift (≈48,600 cm−1). The fluores-
cence recognition properties of the probe in THF were investigated
upon the excitation at 295 nm in the absence and the presence of
2.0 equiv. different sodium salts of anions, such as F−, Cl−, Br−,
I−, H2PO4−, HPO42−, SO42−, HCO3−, NO3 and AcO−. Upon addi-
−
tion of F−, the first fluorescence band (ꢀmax = 360 nm) showed
an obvious increase in intensity, which was considered as the
hydrogen bonding interaction between F− and the probe. And the
Stokes’ fluorescence band only had a slight increase upon addi-
tion of F−. Moreover, the fluorescence response of both bands in
THF/water (v/v = 9/1) solution was similar to that in THF. When
adding I− to the probe, both fluorescence bands were quenched.
Considering the strong hydrogen bonded of water, and avoiding
F− and water interfering the recognition of I−, the fluorescence
recognition of the probe was investigated based on the Stokes flu-
orescence band in THF/water (v/v = 9/1, pH = 7.4 Tris–HCl) buffer
solution.
Upon the excitation at 350 nm, only Stokes fluorescence accom-
panying a red shift at the ꢀmax (from 501 to 520 nm) was observed
due to the polarity increase of the solvent. Fig. 3(a) showed the flu-
orescence changes of the probe in the absence and the presence of
2.0 equiv. different a−nions, such as F−, Cl−, Br−, I−, H2PO4−, HPO4
,
2−
SO42−, HCO3−, NO3 and AcO−. Obviously, some increases were
observed upon addition of the anions except for I−. When I− was
introduced little by little, the fluorescence emission was quenched
gradually (Fig. 3(b)). The maximum fluorescence quenching effi-
ciency ((F − F0)/F0) of iodide anion (2.0 equiv.) at 520 nm reached
to 81% (Fig. 3(c)).
In general, the anions were widely found in the aqueous medium
and therefore, an interested sensor should be suitable to recog-
nize analytes in aqueous system. A suitable pH range of the probe
was conducted to determine fluorescence intensity at 520 nm in
different pH THF/water (v/v = 9/1) solution. Fig. 4(a) showed the
small fluorescence changes at a pH range of 6–8. The emission
intensity decreased dramatically when the pH value was lower
than 5, which was attributed to the protonation of dimethylamino
[51], destroyed the donor–acceptor system. So, the ICT fluorescence
disappeared. When the pH value was higher than 9, the obvious
decrease of fluorescence resulted from the deprotonation of HN
group of thiourea moieties was observed. Because of the protona-
tion of dimethylamino group of the probe in more acidic solution
and the deprotonation of HN of thiourea in the higher pH, the best
pH range of the probe for I− sensing was approximately 6–8.
To determine the binding stoichiometry of the complex, the
emission intensity of the probe at 520 nm was plotted as a func-
tion of its molar fraction under a constant total concentration.
Fig. 4(b) showed the resulting Job’s plot. The maximum quenching
appeared at a molar fraction of 0.5, which indicated a 1:1 ratio for
probe •I−. The association constant Ka of probe •I− was evaluated
graphically by plotting 1/ꢁF against 1/[I−] (Fig. 4(c)). The data were
linearly fitted to the Benesi–Hildebrand equation, and the Ka value
obtained from the slope and intercept of the line was 1.766 × 104.
The detection limit of the probe from the plot of fluorescence inten-
sity as a function of the concentration of I− (Fig. 4(d)) was 0.336 ␮M
(SD = 22.4, n = 12).
Fig. 3. Fluorescence changes of the probe (20 ␮M) upon addition of different tested
anions (40 ␮M) (a), different equiv. iodide anions (b), and the changes in fluores-
cence emission at 520 nm upon addition of 2 equivalents of various anions tested
(c) (ꢀex = 350 nm) in THF/H2O (v/v = 9/1) Tris–HCl (pH = 7.4) buffer solution.
3.5. Selectivity, competition and reversibility
the iodide anion was similar to that in the absence of competitive
anion.
The competition experiment (Fig. 5(a)) displayed the variations
of fluorescence at 520 nm of the probe •I− (20 ␮M, 1:1) in THF/water
buffer solution caused by miscellaneous anions including F−, Cl−,
Br−, H2PO4−, HPO42−, HCO3−, NO3−, SO42− and AcO− (40 ␮M). The
miscellaneous competitive anions did not lead to any significant
spectral change (Fig. 5(a)). That was to say, under the coexistence of
the competitive anions, the fluorescence quenching resulted from
The reversibility of the probe was investigated by adding Ag+.
The quenched fluorescence resulted from iodide anion could be
released by the addition of Ag+ (Fig. 5(b)). Adding 0.9 equivalents
of Ag+, the maximum restored fluorescence signal was 58.6% of
its original. The fluorescence reversion mechanism adding Ag+ for
probe •I− was depicted in Scheme 2. incomplete reversion of the
fluorescence signal could be attributed to the tight binding between

W. Yang et al. / Journal of Photochemistry and Photobiology A: Chemistry 292 (2014) 49–55
53
Fig. 4. Fluorescence intensity (F0) of the probe in different pH values THF/H2O (v/v = 9/1) solution (a), the stoichiometry analysis of complex probe •I− by Job’s plot analysis
(b), Benesi–Hildebrand plot of probe •I− (c), and the calibration curve (d) of probe •I− in THF/H2O (v/v = 9/1) buffer (Tris–HCl, pH = 7.4) solution. The monitored wavelength
is 520 nm.
the probe and I−, which resulted in an imperfect displacement of
iodide anion from the complex.
3.6. Recognition mechanism
The frontier molecular orbitals (HOMO and LUMO) obtained
by the optimized structure of the probe were shown in Fig. 6(a)
using DFT(B3LYP) method at the level of 6-31G(d). Obviously, the
first excited transition (HOMO → LUMO) in free probe underwent
a charge transfer transition from amino-phenyl ring to 4-acetyl-
phenyl ring. Thus, the free probe exhibited good ICT characteristic.
As iodide ion had a large nuclear charge number, the complex
(supported by 1H NMR and UV titration) between the probe and
iodide ion was optimized by PM3 semi-empirical method, and
the HOMO and LUMO of the complex were depicted in Fig. 6(b).
Upon the formation of the complex, probe •I−, the excitation of
the electron from the HOMO to the LUMO enabled the inter-
molecular charge transfer from the HOMO of the donor iodide
anion to the LUMO of the thiourea group [52]. The primary ICT
transition of the free probe was blocked, the fluorescence was
quenched.
Br− didn’t result in the fluorescence quenching of the probe,
so the heavy-atom effect [53–55] could be excluded in this work.
Furthermore, the exclusion of the self-absorption of I− was testified
by the UV–vis spectrum in THF/H2O (v/v = 9/1) (Fig. S6). As shown
in Fig. S6, two absorption peaks at about 273 nm and 350 nm were
observed. The molar absorptions of two peaks were about 4540
(for 273 nm) and 570 mol−1 L cm−1 (for 350 nm). Comparing to the
Fig. 5. Fluorescence competitions between iodide and the other anions (a), the flu-
molar absorption of the probe (about 9000 mol−1 L cm−1), the self-
orescence changes of probe •I− upon the addition of Ag+ (b) in THF/H2O (v/v = 9/1)
absorption of I− at about 350 nm was insignificant.
buffer (Tris–HCl, pH = 7.4) solution. ([probe] = 20 ␮M, [I−] = 40 ␮M).

54
W. Yang et al. / Journal of Photochemistry and Photobiology A: Chemistry 292 (2014) 49–55
Scheme 2. The proposed fluorescence reversion mechanism upon addition of Ag+ for probe •I−
.
Fig. 6. The frontier molecular orbital (HOMO and LUMO) of the probe at the level of B3LYP/6-31G (d), (a) and the frontier molecular orbital (HOMO and LUMO) of the complex
at the level of PM3 (b).
Table 1
the 1:1 stoichiometry between the probe and iodide anion.
The probe was also applied to determine iodide in powdered
milk and urine samples. The results showed a good agreement
between added and detected concentration of the iodide in real
samples.
Determination of iodide in powdered milk and urine samples.
Amount of iodide (mol L−1
)
Samples
Recovery (%)
Added
Found*
9.08( 0.03) × 10−6
1.69( 0.04) × 10−5
1.32( 0.04) × 10−5
2.17( 0.05) × 10−5
98.9
8.0 × 10−6
Powdered milk
Urine
Acknowledgment
8.0 × 10−6
102.3
*
This work was supported by the National Natural Science Foun-
dation of China (no. 51079094) and the Natural Science Foundation
of Jiangsu Province (no. BK2010215, BK2012186).
The Project was funded by the Priority Academic Program Devel-
opment of Jiangsu Higher Education Institutions
Mean SD (n = 3).
3.7. Analytical application
The probe was carried out for the determination of iodide in
powdered milk and urine samples. The possibility of applying this
probe for analysis of samples was tested by determining the recov-
ery of known amounts of iodide anion added to the samples. The
given results in Table 1 showed good agreement between added
and detected concentration of the iodide in real samples.
Appendix A. Supplementary data
Supplementary material related to this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.jphotochem.
2014.07.015.
4. Conclusion
References
We successfully designed and synthesized structurally sim-
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ICT mechanism. The probe (20 ␮M) could detect iodide anion
with fluorescence “turn-off” responses at 520 nm in THF/H2O
(v/v = 9/1) pH = 7.4 Tris–HCl buffer solution. UV and 1H NMR
titrations supported the formation of probe •I−. The character-
istic of HOMO and LUMO of the complex confirmed the ICT
(from iodide anion to the probe) mechanism, which resulted
in the fluorescence quenching. The Job’s curves further showed
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Wen Yang received her Ph.D. in 2007 from Soochow University, China. She is an
instructor and engages in the research of the luminescent chemistry for the biolog-
ical and material purpose.
Jie Shao received his Ph.D. in 2009 from Nankai University, China. His research
interest is fluorescence probes for anions and metal ions.
Yunlong Xu is studying for master in Soochow University. His research interests
include the design and synthesis of fluorescent chemosensors for biological and
material purpose.
Wei-qun Zhou is a professor in College of Chemistry, Chemical Engineering and
Materials Science, Soochow University, China. She is interested in the synthesis and
application of fluorescent chemosensors.
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Juan Xie is studying for master in Soochow University. Her research interests include
the design and synthesis of fluorescent chemosensors for biological and material
purpose.