A new ratiometric and colorimetric chemosensor for cyanide anion based on Coumarin-hemicyanine hybrid

Article abstract of DOI:10.1039/c2ob25516b

A hybrid coumarin-hemicyanine dye, Cou-BT, was developed as a new ratiometric and colorimetric sensor for cyanide with a sensing mechanism via nucleophilic addition of cyanide anion to the benzothiolium group. Cou-BT shows high sensitivity and selectivity for cyanide detection over other common anion species in aqueous acetonitrile solution. The calculated pseudo-first-order rate constant for cyanide anion addition was (2.13 ± 0.08) × 10 ^-2 s^-1 at 298 K, and the detection limit was estimated to be 0.64 μM. The DFT and TDDFT calculation results suggest that the ratiometric and colorimetric sensing behavior of Cou-BT upon its reaction with cyanide was due to the interrupted π-conjugation and blocked ICT progress.

Full text of DOI:10.1039/c2ob25516b

View Online / Journal Homepage
Dynamic Article Links
Organic &
Biomolecular
Chemistry
Cite this: DOI: 10.1039/c2ob25516b
www.rsc.org/obc
PAPER
A new ratiometric and colorimetric chemosensor for cyanide anion based on
Coumarin–hemicyanine hybrid†
a
a,b
a
c
a
d
Zhenghao Yang, Zhipeng Liu,* Yuncong Chen, Xiaoqing Wang, Weijiang He* and Yi Lu
Received 1st February 2012, Accepted 14th May 2012
DOI: 10.1039/c2ob25516b
A hybrid coumarin–hemicyanine dye, Cou-BT, was developed as a new ratiometric and colorimetric
sensor for cyanide with a sensing mechanism via nucleophilic addition of cyanide anion to the
benzothiolium group. Cou-BT shows high sensitivity and selectivity for cyanide detection over other
common anion species in aqueous acetonitrile solution. The calculated pseudo-first-order rate constant for
−
2 −1
cyanide anion addition was (2.13 ± 0.08) × 10
s
at 298 K, and the detection limit was estimated to be
0
.64 μM. The DFT and TDDFT calculation results suggest that the ratiometric and colorimetric sensing
behavior of Cou-BT upon its reaction with cyanide was due to the interrupted π-conjugation and blocked
ICT progress.
fluorescent chemodosimeters have been developed based on
specific chemical reactions. Although these chemodosimeters
Introduction
8
Cyanide is a well-known hazardous chemical both in biology
and the environment due to its extremely high toxicity to
mammals. The cyanide poisoning of mammals can lead to
for cyanide have the advantage of high selectivity due to the
minimized interference of other anions, they may still suffer
from the high detection limit and decreased reaction rate in
1
8k–m
vomiting, loss of consciousness, and finally death. According
aqueous medium.
In addition, sensors displaying both ratio-
to the World Health Organization, the maximum acceptable level
metric and colorimetric response to cyanide are able to offer
quantitative information via their internal calibration of dual
emissions/excitations and show the presence of CN− via
the altered color simultaneously. However, there are very few
chemodosimeters exhibiting both ratiometric and colorimetric
2
of cyanide in drinking water is 1.9 μM. Moreover, the wide-
spread use of cyanide in petrochemical, gold mining, photo-
graphic, and steel manufacturing have caused a serious
1
environmental concern. Thus, there is considerable interest in
8
m–p
the development of effective detection methods of high selec-
tivity and sensitivity for cyanide anion, especially in water and
physiological conditions.
response to cyanide in aqueous solution.
Therefore, the
design of a ratiometric and colorimetric chemodosimeter for
cyanide the quantitative detection of cyanide in the aqueous
solution remains challenging. Herein, we report a coumarin–
hemicyanine hybrid fluorophore, Cou-BT, which exhibits the
specific ratiometric and colorimetric response towards cyanide
anion in aqueous acetonitrile solution.
Recently, fluorescent sensors for cyanide anion have received
great attention owing to their simple, selective, and rapid
3
implementation. Several strategies, such as the coordination of
4
,5
cyanide anions with metal ion/boronic acid derivatives,
6
cyanide-induced aggregation of quantum dots, and hydrogen
bonding interactions for the construction of cyanide anion
7
sensors have been reported. On the other hand, a number of
Results and discussion
Design and synthesis of Cou-BT
a
State Key Laboratory of Coordination Chemistry, Coordination
Coumarin–hemicyanine hybrids are often exploited as fluorophore
Chemistry Institute, School of Chemistry and Chemical Engineering,
Nanjing University, Nanjing, P.R. China. E-mail: heweij69@nju.edu.cn
for chemosensors due to their relatively large Stokes shift and long
b
9
School of Chemistry and Chemical Engineering, Liaocheng University,
emission wavelength. Moreover, the emission of the coumarin
Liaocheng, P.R. China. E-mail: chliuzp@163.com
c
chromophore would be recovered due to the inhibition of π-conju-
School of Material Science and Engineering, Liaocheng University,
gation between the half cyanine and coumarin induced by certain
Liaocheng 252000, P.R. China
d
9b
Department of Chemistry, Beckman Institute for Advanced Science and
chemical reactions. Therefore hybrid coumarin–hemicyanine
Technology, University of Illinois at Urbana-Champaign, Urbana,
IL 61801, USA
†
ESI-MS spectra of Cou-BT, calculated Z-matrix and total energy of
Cou-BT and Cou-BT-CN . See DOI: 10.1039/c2ob25516b
derivatives are valuable platforms for the construction of ratio-
metric fluorescent sensors. The synthesis of Cou-BT is depicted
in Scheme 1. The starting materials 7-diethylamino-2-aldehyde-
coumarin and 3-carboxymethyl-2-methylbenzothiazole-3-ium
1
Electronic supplementary information (ESI) available: H NMR,
−
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem.

View Online
Scheme 1 Synthesis of Cou-BT.
bromide were synthesized according to the reported pro-
10
cedures. Cou-BT was synthesized by conjugating compound 1
and compound 2 in the presence of piperidine as a catalyst.
Compared with 7-dimethyl-2-aldehyde-coumarin, Cou-BT
should display an emission shift to a longer wavelength due to
the expanded π-conjugation and enhanced ICT progress from
coumarin moiety to benzothiolium group. Considering the intrin-
sic nature of high electron deficiency on the 2-C atom of ben-
zothiolium, it is expected that the cyanide anion might be able to
attack this carbon atom, and this nucleophilic addition will not
only interrupt the π-conjugation in the molecule of Cou-BT, but
also block the ICT progress from coumarin moiety to benzothio-
lium group. As a result, both the absorption and emission of cou-
marin moiety should be recovered to those of coumarin
derivative, displaying the expected ratiometric and colorimetric
response to cyanide anion.
Fig. 1 (a) UV-vis spectra of Cou-BT (1 × 10−5 M) obtained at differ-
ent time after the addition of 5 equiv. cyanide anion in CH
3
CN–H
2
O
=
(9 : 1, v : v) at 25 °C; (b) the temporal profile of absorption at λabs
5
43 nm observed from the reaction between Cou-BT and cyanide anion
(
■). The red curve overlaid on the experimental data points is theoretical
−2 −1
fit generated using k′ = (2.13 ± 0.08) × 10
s .
UV-vis absorption and emission spectra of Cou-BT
As shown in Fig. 1, free Cou-BT in aqueous acetonitrile solution
(
CH CN–H O = 9 : 1, v : v) exhibits one main absorption band
3 2
4
−1
−1
centered at 543 nm (ε = 3.1 × 10 M cm ), which can be
assigned to the ICT band of Cou-BT. When cyanide anion was
added, distinct reduction of this band was observed, accom-
panied by the increase of a new band centered at 455 nm (1.4 ×
4
−1
−1
1
0 M cm ). This evident hypsochromic shift of the ICT
band from 543 to 455 nm suggests that the π-conjugation and
ICT progress of Cou-BT were both inhibited by the nucleophilic
addition of cyanide to Cou-BT. Moreover, 5 equiv. cyanide is
sufficient to make this nucleophilic addition be completed within
2
min, and the calculated pseudo-first-order rate constant (k′) for
−2
−1 11
cyanide anion addition was (2.13 ± 0.08) × 10 s . This
result suggests that Cou-BT is highly reactive to cyanide anions.
Cou-BT shows two characteristic fluorescence bands at 488
and 624 nm in the emission spectrum, respectively. The emission
band at 624 nm is attributed to the ICT emission band, while the
emission band at 488 nm should be ascribed to the diethylamino
coumarin moiety. The intensity of the emission band at 624 nm
is significantly decreased upon gradual addition of cyanide anion
to Cou-BT, in the mean time, the increased intensity of the emis-
Fig. 2 Fluorescence responses of Cou-BT (1 × 10− M) toward differ-
ent concentrations of cyanide anion in CH CN–H O (9 : 1, v : v) at
25 °C. Each spectrum was obtained after cyanide anion addition for
2
6
5
3
2
min (Inset: titration profile based on the emission ratio at 488 and
24 nm, F488/F624).
Obviously, Cou-BT is a promising fluorescence ratiometric
sensor for the detection of low level cyanide anion in samples
(Fig. 2).
¬
sion band at 488 nm was observed. The CN induced emission
shift from 624 nm (pink) to 488 nm (bluish-green) also indicates
that the π-conjugation and ICT effect of Cou-BT were both
destroyed after cyanide anion addition. Additionally, the emis-
sion intensity ratio at 488 and 624 nm showed a drastic change
from 2.6 to 29.8 in the presence of 5 equiv. of cyanide anion.
The detection limit was estimated to be 0.64 μM at S/N = 3.
Selective detection of cyanide anion
The selective response of Cou-BT towards cyanide anion was
−
−
evaluated by adding 5 equiv. of various anions such as F , Cl ,
−
−
−
−
−
−
2−
−
Br , I , AcO , H PO , SCN , OCN , S
and HS ,
2
4
Org. Biomol. Chem.
This journal is © The Royal Society of Chemistry 2012

View Online
Fig. 4 Optimized structure of Cou-BT and Cou-BT-CN−.
Table 1 Calculated HOMOs and LUMOs of Cou-BT and
Cou-BT-CN− and electronic contributions to the excitation of Cou-BT
and Cou-BT-CN−
Electronic
contribution
of transition
Molecular orbitals
Cou-BT
HOMO →
LUMO 100%
Cou-BT-CN−
HOMO − 1 →
LUMO 100%
Fig. 3 (a) UV-vis spectra of Cou-BT (1 × 10− M) obtained upon the
5
addition of 5 equiv. of various anions in CH CN–H O (9 : 1, v : v). Each
3
2
spectrum was obtained after mixing at 25 °C for 5 min. (b) Emission
ratio at 488 and 624 nm, F488/F624, of Cou-BT (1 × 10− M) determined
5
upon the addition of various analytes (5 equiv.) in CH
9 : 1, v : v).
3 2
CN–H O
Detailed information regarding the distinct absorption and
emission blue shift upon the formation of Cou-BT-CN can be
(
−
obtained from TDDFT (time-dependent DFT) calculations as
respectively. As shown in Fig. 3, the absorption band at 544 nm
of Cou-BT is slightly decreased in all these cases. Different
from the distinct color change from violet to yellow-green,
which is associated with the reaction between Cou-BT and
cyanide anion, no significant color change was observed by
addition of other anions (Fig. 3a inset). The selective fluor-
escence response of Cou-BT to cyanide anion was also investi-
gated (Fig. 3b). As expected, almost no emission intensity ratio
well. The calculated excitation wavelengths of Cou-BT and
−
Cou-BT-CN are 2.43 eV/509 nm and 3.26 eV/380 nm, respec-
tively, which are slightly lower but in good agreement with the
determined ones, and the simulated absorption spectra of
−
Cou-BT and Cou-BT-CN were shown in Fig. S3.† The calcu-
lated molecular orbitals and the electronic contribution of transi-
−
tion are shown in Table 1. In Cou-BT and Cou-BT-CN ,
−
−
HOMO → LUMO and HOMO − 1 → LUMO transitions con-
tribute respectively 100% to the excitation of Cou-BT and
(
F4 /F ) changes were observed in the presence of F , Cl ,
88 624
−
−
−
−
−
−
2−
−
Br , I , AcO , H PO , SCN , OCN , S and HS .
2
4
−
Cou-BT-CN . From the LUMO of Cou-BT, it is clear that the
ICT progress takes place through a conjugated bridge between
the diethylamino coumarin and benzothiolium groups, while this
is obviously prohibited in Cou-BT-CN due to the cyanide
Rationalization of the photophysical properties of Cou-BT
−
To investigate the mechanism of the ratiometric and colorimetric
response of Cou-BT to cyanide anions, DFT calculations were
carried out for Cou-BT and Cou-BT-CN− with 6-31G* basis
anion addition. This result suggests that the absorption and emis-
−
sion blue shift from Cou-BT-CN ascribed to its weakened ICT
process relative to that in Cou-BT.
1
2
sets using a suite of Gaussian 03 programs. The optimized
structures of Cou-BT and Cou-BT-CN− were shown in Fig. 4.
The diethylamino coumarin and benzothiolium groups of
Cou-BT are well planned via a conjugated bridge (–CvC–), the
dihedral angle between the diethylamino coumarin and benzo-
thiolium group is 2°. The addition of cyanide anion to 2-C atom
of benzothiolium ring inhibited the plantation of diethylamino
coumarin and benzothiolium groups, and the dihedral angle
between diethylamino coumarin and benzothiolium groups of
the reaction product Cou-BT-CN− is 100.3°. This structural
difference between Cou-BT and Cou-BT-CN− shows the sig-
nificant difference in π-conjunction between Cou-BT and
Conclusions
In summary, we have described a new ratiometric and colori-
metric sensor for cyanide, Cou-BT, with a sensing mechanism
of nucleophilic addition of cyanide anion to benzothiolium
group of a coumarin–hemicyanine hybrid dye. Cou-BT shows a
remarkable dual channel response in absorption and emission
specifically for cyanide anion over other common anions in
aqueous acetonitrile. Cou-BT is highly reactive to cyanide anion
and the pseudo-first-order rate constant for cyanide addition was
determined as (2.13 ± 0.08) × 10
−
−2 −1
Cou-BT-CN .
s
at 298 K. The detection
This journal is © The Royal Society of Chemistry 2012
Org. Biomol. Chem.

View Online
limit was estimated to be 0.64 μM. DFT and TDDFT calculations
suggest that the colorimetric and ratiometric sensing behavior of
Cou-BT for cyanide anion was due to the interrupted π-conju-
gation and blocked ICT progress induced by cyanide addition to
Cou-BT.
Notes and references
1
(a) G. C. Miller and C. A. Pritsos, Cyanide: Soc., Ind. Econ. Aspects,
Proc. Symp. Annu. Meet. TMS, 2001, 73–81; (b) K. W. Kulig, Cyanide
Toxicity, U. S. Department of Health and Human Services, Atlanta, GA,
1991.
2
3
4
Guidelines for Drinking-Water Quality, World Health Organization,
Geneva, 1996.
Z. Xu, X. Chen, H. N. Kim and J. Yoon, Chem. Soc. Rev., 2010, 39,
Experimental section
127.
(a) Y. H. Kim and J. I. Hong, Chem. Commun., 2002, 512; (b) X. Chen,
S.-W. Nam, G.-H. Kim, N. Song, Y. Jeong, I. Shin, S. K. Kim, J. Kim,
S. Park and J. Yoon, Chem. Commun., 2010, 46, 8953; (c) C.-F. Chow,
M. H. W. Lam and W.-Y. Wong, Inorg. Chem., 2004, 43, 8387.
Materials and general methods
All reagents were obtained from commercial suppliers and used
1
without further purification unless otherwise indicated. H and
5 (a) R. Badugu, J. R. Lakowicz and C. D. Geddes, J. Am. Chem. Soc.,
2005, 127, 3635; (b) J. V. Ros-Lis, R. Martínez-Máńez and J. Soto,
Chem. Commun., 2005, 5260; (c) R. Badugu, J. R. Lakowicz and
C. D. Geddes, Dyes Pigm., 2005, 64, 49; (d) Y. Kim, H.-S. Huh,
M. H. Lee, I. L. Lenov, H. Zhao and F. P. Gabbaï, Chem.–Eur. J., 2011,
17, 2057.
1
3
C NMR spectra were recorded on a Varian Mercury-plus 400M
spectrometer and referenced to the residual proton signals of the
solvent. Mass spectra were measured with a LCQ (ESI-MS,
Thermo Finnigan) mass spectrometer. UV-vis absorption spectra
were carried out on a Shimadzu UV-160U spectrophotometer. Flu-
orescence spectra were measured on a Perkin Elmer LS55 lumi-
nescence spectrophotometer (the pathlength of the quartz cell is
6
W. J. Jin, M. T. Fernández-Argüelles, J. M. Costa-Fernández, R. Pereiro
and A. Sanz-Medel, Chem. Commun., 2005, 883.
7
(a) S.-S. Sun and A. J. Lees, Chem. Commun., 2000, 1687; (b) H. Miyaji
and J. L. Sessler, Angew. Chem., Int. Ed., 2001, 40, 154;
(c) P. Anzenbacher, D. S. Tyson, K. Jursikova and F. N. Castellano,
J. Am. Chem. Soc., 2002, 124, 6232.
1
cm) with a xenon arc lamp as the light source.
All the stock solutions of anions (1.2 mM) were prepared with
8
(a) J. V. Ros-Lis, R. Martínez-Máńez and J. Soto, Chem. Commun.,
corresponding tetrabutylammonium or sodium salts in aceto-
nitrile. A stock solution of Cou-BT (1.84 mM) was prepared in
acetonitrile. The solution of Cou-BT was then diluted to 10 μM
with acetonitrile and water (9 : 1, v : v). In titration experiments,
2
002, 2248; (b) M. Tomasulo, S. Sortino, A. J. P. White and
F. M. Raymo, J. Org. Chem., 2006, 71, 744; (c) J. Q. Ren, W. H. Zhu
and H. Tian, Talanta, 2008, 75, 760; (d) F. Garcia, J. M. Garcia,
B. Garcia-Acosta, R. Martínez-Máńez, F. Sancenon and J. Soto, Chem.
Commun., 2005, 2790; (e) Y. K. Yang and J. Tae, Org. Lett., 2006, 8,
3
mL solution of Cou-BT (10 μM) was filled in a quartz optical
5721; (f) D. Ryu, E. Park, D. S. Kim, S. Yan, J. Y. Lee, B. Y. Chang and
cell of 1 cm optical path length, and the cyanide anion stock
solution was added into the cuvette gradually by using a micro-
pippet. To determine the sensing selectivity, the test samples
were prepared by adding anions stock solution (5 equiv.) into
K. H. Ahn, J. Am. Chem. Soc., 2008, 130, 2394; (g) Y. M. Chung,
B. Raman, D.-S. Kim and K. H. Ahn, Chem. Commun., 2006, 186;
(h) D. G. Cho, J. H. Kim and J. L. Sessler, J. Am. Chem. Soc., 2008, 130,
12163; (i) J. L. Sessler and D. G. Cho, Org. Lett., 2008, 10, 73;
( j) Y. Chung, H. Lee and K. H. Ahn, J. Org. Chem., 2006, 71, 9470;
(k) S.-J. Hong, J. Yoo, S.-H. Kim, J. S. Kim, J. Yoon and C.-H. Lee,
Chem. Commun., 2009, 189; (l) G.-J. Kim and H.-J. Kim, Tetrahedron
Lett., 2010, 51, 185; (m) X. Wu, B. Xu, H. Tong and L. Wang, Macro-
molecules, 2011, 44, 4241; (n) L. Yuan, W. Lin, Y. Yang, J. Song and
J. Wang, Org. Lett., 2011, 13, 3730; (o) X. Lv, J. Liu, Y. Liu, Y. Zhao,
M. Chen, P. Wang and W. Guo, Org. Biomol. Chem., 2011, 9, 4954;
3
mL solution of Cou-BT (10 μM).
Synthesis of Cou-BT
A mixture of 7-dimethyl-2-aldehyde-coumarin (0.9 g, 3.7 mmol),
piperidine (0.015 g, 0.185 mmol), 3-(carboxymethyl)-2-methyl-
benzothiazol-3-ium bromide (1.16 g, 3.7 mmol) in 20 mL
ethanol was refluxed for 6 h. After being cooled to room temp-
erature, the resulting precipitate was filtered, washed with
ethanol and dried in vacuo, and Cou-BT was obtained as a dark-
(
p) Z. liu, X. Wang, Z. Yang and W. He, J. Org. Chem., 2011, 76, 10286.
9
(a) J.-A. Richard, M. Massonneau, P.-Y. Renard and A. Romieu, Org.
Lett., 2008, 10, 4175–4178; (b) L. Yuan, W. Lin and J. Song, Chem.
Commun., 2010, 46, 7930–7932.
0 (a) J.-S. Wu, W.-M. Liu, X.-Q. Zhuang, F. Wang, P.-F. Wang, S.-L. Tao,
X.-H. Zhang, S.-K. Wu and S.-T. Lee, Org. Lett., 2007, 9, 33;
(b) S. Tatay, P. Gaviňa, E. Coronado and E. Palomares, Org. Lett., 2006,
8, 3857.
1
1
green solid (1.37 g, 85%). M.p. 236–238 °C. H NMR (400 M,
1
1
1 T. J. Dale and J. Rebek, J. Am. Chem. Soc., 2006, 128, 4500.
CD OD), δ 8.33 (s, 1H), 8.19–8.17 (d, 1H, J = 7.85), 8.06–8.02
3
2 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, J. A. Montgomery Jr., T. Vreven, K. N. Kudin,
J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone,
B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson,
H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li,
J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma,
G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith,
M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe,
P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez and
J. A. Pople, Gaussian 03, Gaussian Inc., Wallingford CT, 2004.
(m, 4H), 7.82–7.78 (t, 1H, J = 7.36), 7.73–7.69 (t, 1H, J = 7.56),
7
9
.54–7.52 (d, 1H, J = 9.04), 6.87–6.84 (dd, J = 2.52, J =
1 2
.10), 5.46 (s, 2H), 3.58–3.54 (q, 4H, J = 7.18), 1.27–1.23
13
(t, 6H, J = 7.08). C NMR could not be obtained because of its
poor solubility. ESI-MS: m/z, cal. 435.14, found, 435.25.
Element analysis (%): cal. C H N O S C, 66.19, H, 5.32,
2
4 23 2 4
N, 6.43. found, C, 66.46, H, 5.01, N, 6.56.
Acknowledgements
We thank the Natural Science Foundation of Shandong Province
(ZR2011BQ010) and the Liaocheng University Funds for Young
Scientists (31805) for financial support.
Org. Biomol. Chem.
This journal is © The Royal Society of Chemistry 2012