A fluorescent chemosensor for fluoride anions based on a hemicyanine dye

Article abstract of DOI:10.1007/s11164-012-0859-4

A hemicyanine dye with imidazole as the acceptor was designed and prepared as a chemosensor for fluoride anions. The experimental results demonstrated that it is a fluorometric probe for fluoride anion with good sensitivity and high selectivity. This probe showed obvious changes in UV-Vis absorption and fluorescence spectra in the presence of fluoride anions, which are attributed to the deprotonation of N-H on the imidazole moiety with fluoride anions.

Full text of DOI:10.1007/s11164-012-0859-4

Res Chem Intermed
DOI 10.1007/s11164-012-0859-4
A fluorescent chemosensor for fluoride anions based
on a hemicyanine dye
Liang Yu
•
Tingting Li Ligong Chen
•
Received: 13 September 2012 / Accepted: 9 October 2012
Ó Springer Science+Business Media Dordrecht 2012
Abstract A hemicyanine dye with imidazole as the acceptor was designed and
prepared as a chemosensor for fluoride anions. The experimental results demon-
strated that it is a fluorometric probe for fluoride anion with good sensitivity and
high selectivity. This probe showed obvious changes in UV–Vis absorption and
fluorescence spectra in the presence of fluoride anions, which are attributed to the
deprotonation of N–H on the imidazole moiety with fluoride anions.
Keywords Fluorescent probe Á Hemicyanine Á Fluoride anion Á Imidazole
Introduction
Owing to its relative size and electronegativity, fluoride plays a fundamental role in
industrial and biological processes [1–4]. Fluoride is associated with dental caries,
treatment for osteoporosis, and the refinement of uranium used in nuclear weapon
manufacture [5–7]. However, excess fluoride can lead to fluorosis; for example,
ahigh level of fluoride has been reported to be implicated in dental and skeletal
fluorosis, as well as inhibition of neurotransmitter biosynthesis in fetuses [8–10]. In
a word, the diversity of its function, both beneficial and otherwise, makes the careful
control of fluoride of great importance. As a consequence, the methodologies for
indicating fluoride, which are developed to provide critical information for fluoride,
have attracted growing attention [11–13]. Among these techniques, fluorescent
molecular sensing, which can translate molecular recognition into tangible
fluorescence signals, has received much attention [14–16].
L. Yu Á T. Li Á L. Chen (&)
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072,
People’s Republic of China
e-mail: lgchen@tju.edu.cn
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L. Yu et al.
A general approximation to the development of anion chemosensors is the
coupling of at least two units: the binding site (receptor) and the signaling subunit
(
fluorophore) [17, 18]. Up to now, a variety of anion binding motifs appended to the
fluorophore core for effective anion binding have been employed [19]. For most of
the reported anion fluorescent sensors, molecules containing H-bond donors toward
anions are widely used as receptors for recognition and sensing purposes [20].
Among these molecules, the N–H fragment of a receptor can be a most promising
motif, because the H-bond donor tendency changes when interact with the fluoride
anion [21, 22]. Kong et al. [21] reported a probe synthesized under microwave
irradiation. The probe shows red shift and absorbance intensity changes in spectra in
the presence of fluoride anions. Qu Yi et al. [22] presented a red fluorescent
chemosensor based on diketopyrrolopyrrole; the addition of fluoride results in vivid
orange-to-red absorption color change and yellow-to-red emission color change.
Both of them are based on the deprotonation of N–H with fluoride anions.
Here, we present an easy-to-prepare fluorescent probe, 2-(2-(1H-imidazol-4-yl)
vinyl)-1,3,3-trimethyl-3H-indolium iodide, for fluoride anion sensing based on
incorporating an imidazole heterocycle via a methine linker into a fluorogenic
indolium core. It is reported and used as a fluorescent chemosensor for fluoride
anions for the first time. The interaction of anions with H-bond-donating receptors
(
imidazole) will lead to a change of the electron distribution of the whole molecule,
which can be amplified to a macroscopic level—the color and the spectra—thus
providing colorimetric and fluorescent sensing of the recognition event.
Experimental
Chemicals and instruments
All chemicals and reagents were commercially available and used without further
purification. All solvents were carefully dried and freshly distilled according to
1
standard procedures. H NMR and C NMR spectra were recorded in DMSO-d on
13
6
a Varian Inova 500 MHz NMR spectrometer using TMS as an internal standard.
Mass spectra were obtained with Bruker Daltonics Autoflex tof/tof III. UV–Vis
absorption spectra were recorded on a PerkinElmer Lambda 750 spectrophotometer.
Fluorescence spectra were obtained on a Varian Eclipse fluorescence spectropho-
tometer at room temperature.
Synthesis of the probe 2
1
,2,3,3-tetramethyl-3H-indolium iodide (1) was prepared according to the literature
procedure [23] described in Scheme 1.
,2,3,3-tetramethyl-3H-indolium iodide (1) (1.54 g, 5 mmol) and imidazole
1
carbaldehyde (0.58 g, 6 mmol) were added to 20 mL ethanol. The mixture was
stirred at 85 °C for 6 h under a nitrogen atmosphere. The reaction mixture was
cooled, filtered, and washed with ethanol, to afford a yellow powder 0.94 g, yield
1
4
9.9 %. H NMR (500 MHz, DMSO-d ): d 1.74 (s, 6H), 3. 98 (s, 3H), 7.36 (d, 1H,
6
1
23

A fluorescent chemosensor for fluoride anion
Scheme 1 Synthetic routes of the fluorescent probe 2
J = 15.74 Hz), 7.53–7.60 (m, 2H), 7.83 (t, 2H, J = 7.27 Hz), 8.08 (m, 2H), 8.46 (d,
1
3
1
1
H, J = 15.74 Hz). C NMR (500 MHz, DMSO-d ): d 26.28, 34.25, 52.04,
6
08.44, 115.00, 123.29, 129.06, 129.33, 142.35, 143.42, 181.75. HRMS: calculated
-
for [M–I ]: 252.1495, measured: 252.1500.
Results and discussion
The fluorescent probe was successfully synthesized as shown in Scheme 1, and was
characterized by NMR spectroscopy and mass spectrometry. Its optical properties
were investigated by UV–Vis and fluorescence spectroscopy. The probe was
composed of a imidazole heterocycle and a fluorogenic indolium core, and the
electron-rich imidazole was designed to be the receptor group.
Spectra titration of 2 with 10 eq of halide anions
According to reports, the N–H fragment of imidazole can interact with the fluoride
selectively. To confirm this assumption, we first investigated the selectivity of the
-
probe. In the experiments, n-Bu NX (TBAX) (X stands for F Cl Br I ) as the
-
- -
4
halide anions source was gradually added to a dichloromethane (DCM) solution of
the probe.
-
As can be seen from Fig. 1, when Cl was added to the solution, the maximum
absorption wavelengths (kmax) of the probe red shifted from 426 to 443 nm, while
the absorbance intensity showed no obvious change. The results of Br and I were
-
-
-
similar to that of Cl , except for the intensity differences. Addition of TBAF
exhibited remarkable spectral variations, revealing a new red-shifted absorption
band at 491 nm, which is attributed to the deprotonation with fluoride anions, and
the absorbance showed a sharp decrease, from 0.25 to 0.03.
Upon addition of halide anions, no significant change in the fluorescence spectra
-
were observed; with the addition of Cl or Br , the other two halide anions showed
-
-
different responses. The spectra of the probe with I and F exhibited a small blue
-
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L. Yu et al.
-5
Fig. 1 UV–Vis absorption (left) and emission (right) spectra of 2 measured in DCM (1.0 9 10 M)
?
4
upon addition of 10 equivalents of halide anions (as n-Bu N )
Scheme 2 Mechanism of the probe 2 sensing on fluoride anion
-
Fig. 2 Changes in emission spectra of 2 after addition of F
-
shift and gradually diminished. While the reason may be different, the one with I
-
may have resulted from the heavy atom effect, while the F resulted from
deprotonation of the imidazole (Scheme 2).
With comprehensive consideration, the selectivity of designed probe 2 for
fluoride anions over the other anions is remarkably high and efficient.
1
23

A fluorescent chemosensor for fluoride anion
Fluorescence spectra titration of 2 with fluoride anion
After the determination of the selectivity, the sensitivity was also investigated. The
result is presented in Fig. 2. Because the absorption spectra titration showed no
apparent change, we mainly studied emission spectra. After the addition of different
equivalences of fluoride anions, the fluorescence gradually diminished with the
increase of fluoride. When the equivalence is 4 times that of the probe, it exhibited
greatly decreased fluorescence intensity. The intensity of the probe went from 625
-
-
(
shift from 525 to 500 nm. The change of the fluorescence spectra is attributed to the
with 0 F ) to 145 (4eq F ), and the maximum emission wavelengths (k ) blue
em
deprotonation with fluoride anions of the imidazole.
Conclusion
We have presented a hemicyanine dye as both a colorimetric and fluorescent
selective chemosensor for fluoride anions in DCM, which operates by interaction of
the H-bond contained in imidazole with the fluoride anions. The obvious absorption
and fluorescence variation upon the addition of fluoride anions can be observed both
-
-
by the naked eye and by optical responses. Other halide anions such as Cl , Br and
-
I
spectra.
were not found to induce any variation in either the absorption or fluorescence
References
1
2
3
. Y. Li, L. Cao, H. Tian, J. Org. Chem. 71, 8279–8282 (2006)
. R. Mart ´ı nez-Man eˆ z, F. Sancen o´ n, Coord. Chem. Rev. 250, 3081–3093 (2006)
. A. Susumu, G.D. Matthew, M.F. Thomas, T.G. Hibbert, T.D. James, G.I. Kociok-K o¨ hn, Chem.
Commun. 14, 1640–1641 (2004)
4
5
6
. I.H.A. Badr, M.E. Meyerhoff, J. Am. Chem. Soc. 127, 5318–5319 (2005)
. G. Zhou, Y. Cheng, L. Wang, X. Jing, F. Wang, Macromolecules 38, 2148–2153 (2005)
. Y.P. Zhao, C.C. Zhao, L.Z. Wu, L.P. Zhang, C.H. Tong, Y.J. Pan, J. Org. Chem. 71, 2143–2146
(2006)
7. M. Takeuchi, T. Shioya, T.M. Swager, Angew. Chem. Int. Ed. 40, 3372–3376 (2001)
8. C. Suksai, T. Tuntulani, Chem. Soc. Rev. 32, 192–202 (2003)
9. T. Mizuno, W.H. Wei, L.R. Eller, J.L. Sessler, J. Am. Chem. Soc. 124, 1134–1135 (2002)
10. S.H. Mashraqui, R. Betkar, M. Chandiramani, D. Quinonero, A. Frontera, Tetrahedron Lett. 51,
596–599 (2010)
1
1
1
1. L. Panzella, A. Pezzella, M. Arzillo, P. Manini, A. Napolitano, Tetrahedron 65, 2032–2036 (2009)
2. X.F. Yang, H.P. Qi, L.P. Wang, Z. Su, G. Wang, Talanta 80, 92–97 (2009)
3. E. Galbraith, T. Fyles, M.F. Marken, M.G. Davidson, T.D. James, Inorg. Chem. 47, 6236–6244
(2008)
1
1
1
1
1
1
2
4. E.J. Cho, B.J. Ryu, Y.J. Lee, K.C. Nam, Org. Lett. 7, 2607–2609 (2005)
5. K.H. Lee, H.Y. Lee, D.H. Lee, J.I. Hong, Tetrahedron Lett. 42, 5447–5449 (2001)
6. C.H. Lin, S. Selvi, J.M. Fang, P.T. Chou, C.H. Lai, Y.M. Cheng, J. Org. Chem. 72, 3537–3542 (2007)
7. R.W. Sinkeldam, N.J. Greco, Y. Tor, Chem. Rev. 110, 2579–2619 (2010)
8. M. Sameiro, T. Gon c¸ alves, Chem. Rev. 109, 190–212 (2009)
9. V. Amendola, D. Esteban-Goamez, L. Fabbrizzi, M. Licchelli, Acc. Chem. Res. 39, 343–353 (2006)
0. B. Liu, H. Tian, J. Mater. Chem. 15, 2681–2686 (2005)
123

L. Yu et al.
21. F.P. Kong, Q.J. Liu, X. Wu, Z. Wang, Q. Chen, L.S. Chen, J. Fluoresc. 21, 1331–1335 (2011)
22. Y. Qu, J. Hua, H. Tian, Org. Lett. 12, 3320–3323 (2010)
23. L. David, J. Gallaher, J. Mitchell, Analyst 124, 1541–1546 (1999)
1
23