Several hemicyanine dyes as fluorescence chemosensors for cyanide anions

Article abstract of DOI:10.1016/j.saa.2016.02.008

Four hemicyanine dyes as chemosensors for cyanide anions were synthesized easily. Their photophysical properties and recognition properties for cyanide anions were investigated. The results indicate that all the dyes can recognize cyanide anions with obvious color, absorption and fluorescence change. The recognition mechanism analysis basing on in situ ¹H NMR and Job plot data indicates that to the compounds with hydroxyl group, the recognition mechanism is intramolecular hydrogen bonding interaction. However, to the compounds without hydroxyl group, cyanide anion is bonded to carbon-carbon double bond in conjugated bridge and induces N⁺ CH₃ to neutral NCH₃. Fluorescence of the compounds is almost quenched upon the addition of cyanide anions.

Full text of DOI:10.1016/j.saa.2016.02.008

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 160 (2016) 34–38
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Several hemicyanine dyes as fluorescence chemosensors for
cyanide anions
a,
a
Muhan Liang a, Kangnan Wang a, Ruifang Guan a, Zhiqiang Liu b, , Duxia Cao , Qianqian Wu ,
⁎
⁎
Yanyan Shan a, Yongxiao Xu a
a
School of Material Science and Engineering, Shandong Provincial Key Laboratory of Preparation and Measurement of Building Materials, University of Jinan, Jinan 250022, Shandong, China
b
State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, Shandong, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 August 2015
Received in revised form 4 February 2016
Accepted 14 February 2016
Available online 17 February 2016
Four hemicyanine dyes as chemosensors for cyanide anions were synthesized easily. Their photophysical properties
and recognition properties for cyanide anions were investigated. The results indicate that all the dyes can recognize
cyanide anions with obvious color, absorption and fluorescence change. The recognition mechanism analysis basing
on in situ 1H NMR and Job plot data indicates that to the compounds with hydroxyl group, the recognition mecha-
nism is intramolecular hydrogen bonding interaction. However, to the compounds without hydroxyl group, cyanide
anion is bonded to carbon–carbon double bond in conjugated bridge and induces N+CH3 to neutral NCH3. Fluores-
cence of the compounds is almost quenched upon the addition of cyanide anions.
Keywords:
Hemicyanine dye
Photophysical property
Cyanide
© 2016 Elsevier B.V. All rights reserved.
Fluorescence chemosensor
1. Introduction
2. Experimental
As we all know, cyanide has extreme toxicity [1]. A small amount of
cyanide can cause acute symptoms of poisoning, such as vomiting, con-
vulsion, loss of consciousness, and even eventual death [2]. Despite its
toxicity, cyanide is an important raw material of synthetic resin,
pharmaceuticals, pesticides and other industrial areas. In the mean-
while, cyanide is used to dissolve gold and silver ores in the mining in-
dustry, and also used in electroplating, plastics and other industrial
production [1,3,4]. Thus, chemists have paid more and more attention
to compose quickly and highly selective chemosensors for cyanide anions.
In recent decades, optical sensors for cyanide, in which a change in
color, fluorescence intensity, or emission wavelength is monitored
[5–15], have been paid more attention by scholars due to their simple
operation, high sensitivity and low cost. Our group is devoted to the
research on chemosensors for cyanides for several years [16–20].
Here four hemicyanine dyes as fluorescence chemosensors for CN−
were synthesized. These compounds exhibit remarkable response to
CN− with obvious color and fluorescence changes, which allows
naked eye detection.
2.1. Chemical and instruments
5-Bromosalicylaldehyde, p-nitrobenzaldehyde, N-ethyl-3-
carbazolecarboxaldehyde, 4-(diethylamino)salicylaldehyde, 4-
methylpyridine and 2-methylpyridine were purchased from Aladdin
Reagents. Other reagents were purchased from Shanghai Reagents
and used as received directly without further purification. NMR spectra
were recorded on a Bruker Avance III 400 MHz spectrometer at room
temperature.
2.2. Synthesis and characterization
The molecular structures of compounds 1–4 are shown in Fig. 1.
Compounds 1–4 (Table S1) were synthesized by the condensation
reaction between the substituted aldehyde and 4-methyl-N-
methylpyridinium iodide (S1) or 2-methyl-N-methylpyridinium
iodide (S2) [21–23]. The raw materials were put into 50 mL flask with
a stirrer and condenser, and then an amount of ethanol and 3 drops of
piperidine were added in turn. The mixture was heated under reflux
for 4 h. After cooling to room temperature, precipitate of compounds
1, 3 and 4 was filtered and washed by dichloromethane to afford the
products. But the product of compound 2 is an oil-like object, which
was recrystallized from a mixed solution of dichloromethane and
ethanol to give green crystals.
⁎
Corresponding authors.
E-mail addresses: zqliu@sdu.edu.cn (Z. Liu), duxiacao@ujn.edu.cn (D. Cao).
http://dx.doi.org/10.1016/j.saa.2016.02.008
1386-1425/© 2016 Elsevier B.V. All rights reserved.

M. Liang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 160 (2016) 34–38
35
Fig. 1. The molecular structures of compounds 1–4.
2.3. Photophysical property measurement
3. Results and discussion
UV–vis absorption and fluorescence spectra of the compounds in
acetonitrile were recorded at room temperature on a Shimadzu
UV2550 spectrophotometer and a Horiba Fluoromax-4 fluorescence
spectrometer with C = 1.0 × 10−5 M at room temperature, respectively.
The spectral changes were monitored with the addition of a solution of
tetra (n-butyl)ammonium cyanide (TBACN) in acetonitrile as CN−
source at room temperature.
3.1. UV–vis absorption and fluorescence properties
UV–vis absorption, fluorescence emission spectra and excitation
spectra of the compounds in acetonitrile are shown in Fig. 2 and
Fig. S1. From Fig. 2a, we can see that compound 1 exhibits linear
absorption in violet region with the absorption peaks at 374 nm
(ε = 1.41 × 104 M−1 cm−1). The absorption peaks of compounds
2–4 are 490 nm (2, ε = 2.65 × 104 M−1 cm−1), 336 nm (3, ε =
3.58 × 104 M−1 cm−1) and 417 nm (4, ε = 3.18 × 104 M−1 cm−1),
respectively, and they exhibit much stronger linear absorption than
compound 1. The shorter absorption wavelength of compound 3 rela-
tive to compound 4 may be derived from stronger electron accepting
ability of nitro group. (For interpretation of the references to color in
this figure, the reader is referred to the web version of this article.)
As shown in Fig. S1, excitation and absorption spectra of all the
compounds are very similar. The fluorescence spectra were obtained
with the excitation wavelengths at 370 nm (1), 490 nm (2), 340 nm
(3) and 420 nm (4). Compounds 1 and 4 exhibit stronger fluorescence
compared with other compounds (Fig. 2b). The fluorescence intensity
of compound 3 is lower than other compounds significantly, perhaps
because it contains nitro group and nitro group has fluorescence
quenching effect. The fluorescence peak of compound 2 at 607 nm is
the longest, which may be because it has a strong electron donating
group diethylamino.
3.2. Response to cyanide anions
As shown in Fig. 3(a), compound 1 has two absorption peaks in
acetonitrile at 323 nm and 374 nm. When cyanide anions are added, a
new absorption peak at 577 nm appears and increases gradually,
which is accompanied by the decrease at 323 nm and 374 nm, at the
same time, a new absorption peak at 353 nm appears. Three isosbestic
points at 287 nm, 348 nm and 448 nm are observed. Compound 1 also
exhibits fluorescence spectral response to cyanide anions. From the
Fig. 3(b), we can see that the fluorescence intensity at 533 nm decreases
and is almost quenched completely when 1.4 equiv. cyanide anions are
added.
Upon the addition of cyanide anions, compound 2 also exhibits
obvious UV–vis absorption change with the original absorption peak
(490 nm) decreasing and new absorption peak in long wavelength
region (589 nm) appearing (Fig. S2). The fluorescence at 607 nm of
compound 2 decreases and fluorescence intensity finally decreases to
7% of the original fluorescence and fluorescence peak has a 21 nm red
shift. (For interpretation of the references to color in this figure, the
reader is referred to the web version of this article.)
The detection limits [24,25] of compounds 1 and 2 for cyanide anions
with UV–vis absorption and fluorescence as detected signal are also in-
vestigated. From Figs. S3 and S4, the detection limits of compounds 1
Fig. 2. UV–vis absorption (a) and fluorescence spectra (b) of compounds 1–4 in
acetonitrile with C = 1.0 × 10−5 M at room temperature.

36
M. Liang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 160 (2016) 34–38
Fig. 4. UV–vis absorption (a) and fluorescence (b, λex = 420 nm) spectra of 4
(1.0 × 10−5 M) in acetonitrile at room temperature upon the addition of CN−
.
Fig. 3. UV–vis absorption (a) and fluorescence (b, λex = 370 nm) spectra of 1
(1.0 × 10−5 M) in acetonitrile at room temperature upon the addition of CN−
.
anions, the reaction mechanism was investigated. From Fig. 5, we can
see that upon the addition of cyanide anions, the two hydrogens of dou-
ble bonds in 8.20 ppm (d, J = 16.0 Hz) and 7.62 ppm (d, J = 16.0 Hz)
disappear, and two sets of new peaks in 3.76 ppm (d, J = 8.8 Hz) and
5.20 ppm (d, J = 8.8 Hz) appear, which may be because the double
bond of compound 4 changes to single bond by Michael addition reac-
tion, in which cyanide is added to carbon–carbon double bond. Hydro-
gen proton signal of NCH3 is up field shifted from 4.42 ppm to
2.96 ppm, which may be corresponding to the change from N+CH3 to
neutral NCH3. The mechanism of the reaction is also shown in Fig. 5.
The fluorescence decrease of the compounds upon the addition of cya-
nide anions is because cyanide anion is bonded to the CC in conjugated
bridge, which induced to the breaking of charge transfer.
To compounds 1 and 2, after the addition of cyanide anions, the orig-
inal main absorption peaks in short wavelength region decrease, at the
same time, a absorption peak in long wavelength region appears. These
spectral changes are different to that of compound 4. Compared with
compounds 1 and 2, there is no hydroxyl in compound 4. So the absorp-
tion peak in long wavelength region may be derived from hydroxyl
bond interaction between hydroxyl group of the compounds and CN−.
The in situ 1H NMR spectrum of compound 1 in CD3CN before and
after the addition of cyanide anions indicates that CC double
bond dose not disappear. We think that the reaction mechanism of
compounds 1 and 2 to cyanide anions is intermolecular hydrogen
bond interaction (Fig. S9).
and 2 for cyanide anions are 0.38 μM (1, DLabs), 0.21 μM (2, DLabs),
0.00082 μM (1, DLfluo) and 0.0016 μM (2, DLfluo).
Compound 3 also exhibits obvious response to CN− (Fig. S5). As
shown in Fig. S5, with the addition of CN−, absorption peak of com-
pound 3 at 336 nm decreases gradually, while new peaks at 425 nm
and 568 nm appear and an isosbestic point at 373 nm is observed. The
detection limit of compound 3 for cyanide anions with absorption as
the detected signal is 2.7 μM (3, DLabs).
As shown in Fig. 4(a), upon the addition of cyanide anion to an ace-
tonitrile solution of compound 4, the peak at 417 nm decreases gradual-
ly and an isosbestic point at 300 nm is observed and finally is saturated
when 3 equiv. cyanide anions are added. As for Fig. 4(b), we can see that
with excitation at 490 nm, the fluorescence intensity at 570 nm of com-
pound 4 has a decrease when cyanide anions are added. Fluorescence
intensity finally decreased to 11% of the original fluorescence with
6 nm blue shift. From Figs. S6 and S7, the detection limits of compound
4 for cyanide anions are 0.75 μM (DLabs), 0.0004 μM (DLfluo). (For inter-
pretation of the references to color in this figure legend, the reader is
referred to the web version of this article.)
From the fluorescence titration spectra of compounds 1, 2, and 4, we
can see that the compounds exhibit turn-off response to cyanide anions.
From Figs. S8, Job's plots indicates that the complexation between
the compounds and cyanide anions is 1:1. Based on 1H NMR spectrum
of compound 4 in (CD3)2SO before and after the addition of cyanide

M. Liang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 160 (2016) 34–38
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Fig. 5. The 1H NMR spectrum of compound 4 in (CD3)2SO before and after the addition of cyanide anions at room temperature and reaction mechanism.
3.3. Selective detection of cyanide anion
(NaCl), Br− (KBr), I− (NaI), HPO4− (KHPO4), SCN− (KSCN), HSO4−
(NaHSO4) and CO23− (Na2CO3). From Fig. S10, for compounds 2–4, no
significant absorption spectral change upon the addition of other anions
is observed. As expected, compounds 2–4 have pretty well selective de-
tection for cyanide anion. To compound 1, upon the addition of CO32−
and F−, the absorption spectra also change obviously, but the change
is different to that induced by CN−, which means that the selectivity
High selectivity for a chemosensor is very important. The influence
of other anions on the response of the compounds to cyanide
anions in acetonitrile was examined. The selective response of com-
pounds 1–4 towards cyanide anions was evaluated by adding 5 equiv.
of various anions in acetonitrile such as CN− (TBACN), F− (NaF), Cl−
Fig. 6. Photographs showing the color change of compounds 1–4 before (a) and after (b) the addition of cyanide anions in acetonitrile in natural light and 365 nm UV-light.
(For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

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M. Liang et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 160 (2016) 34–38
of compound 1 is also very good. At the same time, the selectivity of
compound 2 (Fig. S11) in test paper was tested. From Fig. S11, we
found that the color of compound 2 with cyanide is obviously different
from that with other anions, so the selective detection of cyanide can be
realized by the change of color in test paper. When cyanide is added, the
color of 2 changes from red to purple.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.saa.2016.02.008.
References
3.4. ‘Naked-eye’ detection of cyanide anions
[1] F. Wang, L. Wang, X.Q. Chen, J.Y. Yoon, Chem. Soc. Rev. 43 (2014) 4312–4324.
[2] K.W. Kulig, Cyanide Toxicity, U.S. Department of Health and Human Services,
Atlanta, 1991.
[3] Z.C. Xu, X.Q. Chen, H.N. Kim, J.Y. Joon, Chem. Soc. Rev. 39 (2010) 127–137.
[4] Y.M. Yang, Q. Zhao, W. Feng, F.Y. Li, Chem. Rev. 113 (2013) 192–270.
[5] J.L. Liu, Y. Liu, Q. Liu, C.Y. Li, L.N. Sun, F.Y. Li, J. Am. Chem. Soc. 133 (2011)
15276–15279.
The color changes of the compounds in acetonitrile upon the addi-
tion of cyanide anions were also researched (Fig. 6). To compounds 1
and 3, upon the addition of cyanide anions, the color changes from col-
orless to blue (1) and light yellow (3) in nature light. Color of compound
2 changes from red to blue. In 365 nm UV-light, compounds 1 and 4
exhibit stronger fluorescence compared with other compounds and
the green (1) or yellow (4) fluorescence are almost quenched upon
the addition of cyanide anions.
[6] Y.K. Yue, F.J. Huo, C.X. Yin, J.B. Chao, Y.B. Zhang, Sensors Actuators 212 (2015)
451–456.
[7] Y.B. Chen, W. Shi, Y.H. Hui, X.H. Sun, L.X. Xu, F. Lei, Z.F. Xie, Talanta 137 (2015)
38–42.
[8] C.I.M. Santos, E. Oliveira, J.F.B. Barata, M.A.F. Faustino, J.A.S. Cavaleiro, M.G.P.M.S.
Neves, C. Lodeiro, Mater. Chem. 22 (2012) 13811–13819.
[9] Y.S. Xie, Y.B. Ding, X. Li, C. Wang, J.P. Hill, K. Ariga, W.B. Zhang, W.H. Zhu, Chem.
Commun. 48 (2012) 11513–11515.
4. Conclusion
[10] Y.T. Yang, C.X. Yin, F.J. Huo, J.B. Chao, Y.B. Zhang, F.Q. Cheng, Sensors Actuators 193
(2014) 220–224.
In summary, the effectiveness of four compounds as chemosensors
for cyanide anions was demonstrated. The results indicate that the com-
pounds exhibit obvious UV–vis absorption and fluorescence change re-
sponse in acetonitrile solution. Especially, all the compounds allow for
‘naked-eye’ detection of cyanide anions with high selectivity and sensi-
tivity. Bonding mechanism analysis indicates that to the compounds 1
and 2 with hydroxyl group, recognition mechanism is intramolecular
hydrogen bond interaction. However, to the compounds 3 and 4 with-
out hydroxyl group, cyanide anion is bonded to CC of conjugated bridge
and induces N+CH3 to neutral NCH3, which breaks the intramolecular
charge transfer and induced to fluorescence decrease.
[11] Y. Xu, X. Dai, B.X. Zhao, Spectrochim. Acta A 138 (2015) 164–168.
[12] R.K. Bhandari, R.P. Oda, I. Petrikovics, D.E. Thompson, M. Brenner, S.B. Mahon, V.S.
Bebarta, G.A. Rockwood, B.A. Logue, J. Anal. Toxicol. 38 (2014) 218–225.
[13] X.H. Zhang, Q. Liu, H.J. Shi, L.Y. Wang, Y.L. Fu, X.C. Wei, L.F. Yang, Dyes Pigments 100
(2014) 232–240.
[14] K.-S. Lee, H.-J. Kim, G.-H. Kim, I. Shin, J.-I. Hong, Org. Lett. 10 (2008) 49–51.
[15] R. Jackson, R.P. Oda, R.K. Bhandari, S.B. Mahon, M. Brenner, G.A. Rockwood, B.A.
Logue, Anal. Chem. 86 (2014) 1845–1852.
[16] D.X. Cao, H.Y. Zhao, F.P. Gabbaï, New J. Chem. 35 (2011) 2299–2305.
[17] Q.Q. Wu, Z.Q. Liu, D.X. Cao, R.F. Guan, K.N. Wang, Y.Y. Shan, Y.X. Xu, L. Ma, Mater.
Chem. Phys. 161 (2015) 43–48.
[18] K.N. Wang, Z.Q. Liu, R.F. Guan, D.X. Cao, H.Y. Chen, Y.Y. Shan, Q.Q. Wu, Y.X. Xu,
Spectrochim. Acta A 144 (2015) 235–242.
[19] Y.Y. Shan, Z.Q. Liu, D.X. Cao, G.Q. Liu, R.F. Guan, N. Sun, C. Wang, K.N. Wang, Sensors
Actuators 221 (2015) 463–469.
[20] H.H. Chen, Z.Q. Liu, D.X. Cao, S.S. Lu, J.Z. Pang, Y.H. Sun, Sensors Actuators 199 (2014)
Acknowledgment
115–120.
[21] D.X. Cao, Y.H. Wang, H.Y. Chen, G.Z. Li, G.H. Zhang, J. Chem. Ind. Eng. 58 (2007)
2115–2119.
[22] A. Shunmugasundaram, T.L. Thanulingam, V. Raj, A. Rajasekhar, Indian J. Chem. 33A
This work was supported by the National Natural Science Foundation
of China (51373069), and the Natural Science Foundation of Shandong
Province (ZR2013BM005, ZR2015BL011), Scientific Research Foundation
for the Returned Overseas Chinese Scholars (20121707), Science and
Technology Plan Project of Zhejiang Province (2014F50035) and the
Fund of Graduate Innovation Foundation of University of Jinan, GIFUJN
(S1504).
(1994) 417–419.
[23] H.H. Chen, Z.Q. Liu, D.X. Cao, Y.L. Deng, Y.H. Sun, F.Y. Li, Dyes Pigments 96 (2013)
563–568.
[24] M. Zhu, M.J. Yuan, X.F. Liu, J.L. Xu, J. Lv, C.S. Huang, H.B. Liu, Y.L. Li, S. Wang, D.B. Zhu,
Org. Lett. 10 (2008) 1481–1484.
[25] J. Isaad, A.E. Achari, Tetrahedron 67 (2011) 5678–5685.