A Colorimetric and Fluorescent Probe Based on Michael Acceptor Type Diketopyrrolopyrrole for Cyanide Detection

Article abstract of DOI:10.1007/s10895-017-2079-1

A new probe 1 was synthesized by incorporating an α,β-unsaturated ketone to a diketopyrrolopyrrole fluorophore. The probe exhibited a selective and sensitive response to cyanide against other anions. Addition of CN^? aqueous solution to 1 result

Full text of DOI:10.1007/s10895-017-2079-1

J Fluoresc
DOI 10.1007/s10895-017-2079-1
ORIGINAL ARTICLE
A Colorimetric and Fluorescent Probe Based on Michael
Acceptor Type Diketopyrrolopyrrole for Cyanide Detection
Lingyun Wang1 & Shaochun Zhou1 & Derong Cao1
Received: 24 November 2016 /Accepted: 4 April 2017
#
Springer Science+Business Media New York 2017
Abstract A new probe 1 was synthesized by incorporating an
α,β-unsaturated ketone to a diketopyrrolopyrrole
fluorophore. The probe exhibited a selective and sensitive
response to cyanide against other anions. Addition of CN−
aqueous solution to 1 resulted in a rapid color change from
pink to light yellow together with a blue shift from 518 to
421 nm, while other anions did not induce any significant
color change. Furthermore, the Michael addition of cyanide
to 1 elicited 98% fluorescence quenching at 608 nm, which
constituted the fluorescence signature for cyanide detection.
The detection limit was 0.67 μM using the fluorescence spec-
tra changes, which was far lower than the WHO guideline of
1.9 μM. Moreover, 1-based test strips could successfully de-
tect CN− solutions.
release of cyanide to the environment causes serious problems
[1–3]. Therefore, the maximum permissive level of cyanide in
drinking water is set at 1.9 μM by the World Health
Organization (WHO). Nevertheless, cyanide salts are still
widely used as industrial materials in gold mining,
electroplating, plastics production and other fields.
Therefore, it is highly desirable to develop sensitive, selective
and quick detection methods for toxic cyanide anions.
Compared with detection approaches for cyanide based on
hydrogen bonding or supramolecular interactions [4–7], the
burgeoning field of reaction-based indicators has made prog-
ress in this area because of the unique reactivity of CN− to-
ward a variety of organic functional groups including C = O,
C = N, C = C, and so on [8–11]. The irreversible formation of
chemical bonds can provide chemodosimetric information
and develop ratiometric fluorescent probes. Unfortunately,
none of these is ideal. Many of them suffer from the require-
ment of a long reaction time and elevated reaction tempera-
ture, the need for surfactant media and a slow response
[12–20]. There is an ever-present need to develop new
reaction-based CN− sensors, as these can help overcome lin-
gering obstacles in its detection, such as selectivity, sensitivity,
response times, sensor stability, reaction conditions, etc.
As brilliant red and strong fluorescent high performance
pigments, diketopyrrolopyrrole (DPP) and its derivatives have
gained wide attention in recent years due to its ease of syn-
thetic modification, high fluorescence quantum yields and
good light and thermal stability [21–25]. To date, only limited
DPP-derived probes for reaction-based cyanide detection have
been reported [26, 27]. In the present work, probe 1 for cya-
nide was designed and synthesized (Scheme 1), in which DPP
was used as the fluorophore and an α,β-unsaturated ketone
moiety was introduced as the cyanide receptor. The probe
displays high selectivity and sensitivity for CN− over other
anions with a fast response.
.
.
.
Keywords Michael acceptor Cyanide anion Colorimetric
Diketopyrrolopyrrole
Introduction
Anion recognition is an area of growing interest in supramo-
lecular chemistry due to its crucial role in a wide range of
chemical, biological and environmental processes. Among
various anions, cyanide is well known as one of the most toxic
species and is extremely harmful to mammals. Any accidental
* Lingyun Wang
lingyun@scut.edu.cn
1
Key Laboratory of Functional Molecular Engineering of Guangdong
Province, School of Chemistry and Chemical Engineering, South
China University of Technology, Guangzhou 510641, China

J Fluoresc
Scheme 1 Synthesis of probe 1
H
N
O
O
O
O
CHO
O
O
O
CH2OH
CH2OH
O
O
O
O
O
t-C5H11OH
N
H
NH2SO3H
CN
t-C5H11ONa
CN
3
2
C8H17
N
C8H17
N
O
O
O
CHO
O
O
O
C8H17Br
HCl/H2O
THF
OHC
O
O
N
N
t-C4H9OK
C8H17
C8H17
4
5
OH
O
O
OH
C8H17
N
O
OH
O
O
N
CH2Cl2/EtOH
NO2
C8H17
6
NO2
NO2
O2N
O
O
C8H17
F
NO2
O2N
N
O
O
O
NMP, K2CO3
rt , 8h, 52%
O
N
C8H17
1
Experimental
Synthesis of 1
Chemicals and Instruments
111.0 mg (0.2 mmol) coumpond 6, 111.6 mg (0.6 mmol)
2,4-dinitrofluorobenzene and 1.00 g (7.25 mmol) K2CO3
were mixed in 10 mL of N,N-dimethylformamide. After
stirring overnight at room temperature, the resultant was
neutralized with dilute HCl solution and extracted by
methylene chloride. The solvent was evaporated under
reduced pressure to get the crude product, which was fur-
ther purified by column chromatography using hexane/di-
chloromethane/ethylacetate (10/60/1) as an eluent to ob-
tain 120 mg pure compound 1 in 52% yield. m.p. 212–
Nuclear magnetic resonance spectra were recorded on Bruker
Avance III 400 MHz and chemical shifts are expressed in ppm
using TMS as an internal standard. The UV-vis absorption
spectra were recorded using a Helios Alpha UV-Vis scanning
spectrophotometer. Fluorescence spectra were obtained with a
Hitachi F-4500 FL spectrophotometer with quartz cuvette
(path length = 1 cm). The THF solutions of anions (F−,
CN−, Cl−, Br−, I−, AcO−, HSO4 , H2PO4 , NO3 , ClO4 ) were
prepared from their tetrabutylammonium salts with distilled
tetrahydrofuran.
Other solvents were obtained from commercially
available resources without further purification. 2,5-
Dioctyl-3,6-bis(4′-formylphenyl)pyrrolo[3,4-c] pyrrole-
1,4-dione (compound 5) was synthesized according to
our published literature [28]. Compound 6 was synthe-
sized according to the literature [29].
The recognition between 1 and different anions was inves-
tigated by UV–Vis and fluorescence spectroscopy in THF
solution at room temperature. The stock solution of 1 and
anions was at a concentration of 10.0 mM. After the 1 and
anions with desired concentrations were mixed, they were
measured by UV–Vis and fluorescence spectroscopy.
−
−
−
−
1
213 °C. H NMR (CDCl3, 400 MHz, δ, ppm): 8.84 (d,
J = 2.8 Hz, 2H), 8.31 (dd, J = 2.8 Hz, 2H), 7.87(t,
J = 8.4 Hz, 6H), 7.73 (d, J = 8.4 Hz, 4H), 7.70–7.61
(m, 4H), 7.51 (t, J = 7.6 Hz, 2 H), 7.42 (d, J = 15.6 Hz,
2H), 7.21(d, J = 8 Hz, 2H), 6.93(d, J = 9.2 Hz, 2H), 3.77
(t, J = 7.6 Hz, 4H), 1.60 (t, J = 5.2 Hz, 4H), 1.21 (d,
J = 6.4 Hz, 20H), 0.84 (t, J = 6.8 Hz, 6H), 13C NMR
(CDCl3, 100 MHz, δ, ppm): 190.05, 162.5, 155.96,
151.31, 147.66, 144.43, 141.7, 139.01, 136.74, 133.88,
132.59, 131.33, 130.21, 129.28, 129.03, 127.15, 126.24,
122.25, 121.82, 118.35, 110.66, 42.10, 31.69, 29.43,
29.07, 28.98, 26.69,22.57, 14.04. HRMS-ESI: m/z calcd
(%) for C48H52N10O10: 1136.4066 [M + Na]+; Found:
1159.4060.

J Fluoresc
Results and Discussions
showed a major emission peak at 608 nm. Upon addition of
CN− aqueous solution to 1, the PL intensity at 608 nm was
decreased gradually and blue-shifted to 572 nm. A single
crossover point at 570 nm was observed at low concentration
of cyanide ion (0–10 equiv). A plateau with the addition of 30
equiv. of CN− with 98% fluorescence quenching at 608 nm
was achieved. Fig. 2c showed the emission color photographs
of 1 in the presence of CN− under excitation at 365 nm, where
strong red emission was absent.
To exploit its sensing behavior, we examined the time de-
pendent changes in the absorption spectra of 1 (10 μM) upon
reaction with CN− at room temperature. Generally, reaction-
based chemosensors suffer from a long response time. In our
case, the response of 1 to CN− was found to be very fast. The
absorption increase around 421 nm reached maximum at 4
and 1 min in presence of 10 and 30 equiv. CN−, respectively,
indicating nucleophilic addition reaction between the vinyl
group and CN− was completed (Fig. 3). It is well known that
the nucleophilicity of anions is greatly decreased in water due
to hydrogen bond formation between the anions and water
Spectral Characteristics of 1 with CN−
To get insight into sensing behavior of 1 with CN−, the ab-
sorption spectra of 1 in THF upon titration with CN− solution
were recorded. As shown in Fig. 1a, free 1 showed two major
absorption peaks at 336 and 518 nm. Upon addition of CN−,
the absorption peaks of 1 at 336 and 518 nm gradually de-
creased following the formation of two new bands centered at
370 and 421 nm. Meanwhile, two isosbestic points at 358 and
476 nm were observed, which implied new species with less
conjugation were formed. Notably, the ratios of A370/A518 and
A
421/A518 increased over 18.8 and 46.8-fold in presence of 30
equiv. CN−, respectively. The corresponding color changes of
1 with the increasing concentrations of cyanide anion are
shown in Fig. 1c, resulting in a rapid color change from pink
to light yellow.
The CN− sensing property was further examined through
fluorescent titration studies in detail. As shown in Fig. 2a, 1
Fig. 1 a, b UV-Vis spectral
(a)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
336nm
changes and c color changes of 1
in THF (10 μM) with increasing
concentrations of cyanide anion
0eq
370 nm
518nm
421 nm
358nm
8eq
476nm
300
400
500
600
Wavelength(nm)
(b)
336 nm
8 eq.
0.3
0.2
0.1
0.0
495 nm
30 eq.
300
400
500
600
Wavelength(nm)
(c)

J Fluoresc
Fig. 2 a, b Fluorescence spectral
changes and c emission color
changes of 1 (10 μM) in THF
with the increasing concentrations
of cyanide anion
(a)
608 nm
1400
1200
1000
800
600
400
200
0
0 eq
10 eq
570 nm
550
600
650
700
Wavelength(nm)
(b)
600
400
200
0
10eq
593 nm
30eq
550
600
650
700
Wavelength(nm)
(c)
30 equiv
10 equiv
molecules. For instance, Guo’s group reported that the reac-
tion of anthracene-indanedione Michael receptor and cyanide
could be completed within 2 min at an elevated temperature of
50 °C in 9:1 CH3CN-water, and 10 equiv. of cyanide was
required to reach the spectral saturation [30]. Herein, in the
presence of 10 equiv. of cyanide, the nucleophilic CN− addi-
tion to 1 occurred very rapidly (within 4 min), indicating high
reactivity was the unique feature of 1, which was impressive
as many reported cyanide probes require high equivalents of
cyanide and long reaction time to reach a maximal spectral
signal [31–41].
0.30
0.25
0.20
0.15
0.10
0.05
0
2
4
6
8
10
12
14
16
18
20
Selectivity of 1 with CN−
Time(min)
Fig. 3 Time-dependent UV-vis absorption strength of probe 1 (10 μM)
in THF at 421 nm in the presence of CN− (10 equiv. ▲ in green, 30 equiv.
● in red) at room temperature
For the purpose of evaluating selectivity of 1 to cyanide, the
absorption spectral change of 1 upon addition of other anions

J Fluoresc
Fig. 4 a UV-vis absorption
spectra and b color changes of 1
in THF (10 μM) upon addition of
10 equiv. of each anion
(a)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1+cyanide
1+other anions
350
400
450
500
550
600
Wavelength(nm)
(b)
was also investigated. Dramatic change of the absorption
spectrum induced by CN− was observed, while almost no
changes could be found in presence of other anions, including
presence of CN−, while other anions did not induce any sig-
nificant color change, which suggested that naked-eye selec-
tive detection of CN− became possible (Fig. 4b).
F−, CN−, Cl−, Br−, I−, AcO−, HSO4 , H2PO4 , NO3 , ClO4
Meanwhile, only CN− rendered a remarkable BTurn-Off^
fluorescence response, whereas all other anions revealed a
negligible change in the fluorescent spectra of 1 (Fig. 5a). In
−
−
−
−
(Fig. 4a). More importantly, the color change from pink to
light yellow can be clearly observed by the naked eye in
Fig. 5 a Fluorescence and b
emisson color changes of 1 in
(a)
1400
1
THF (10 μM) upon addition of 10
1200
equiv. of each anion aqueous
solution
1000
1+other anions
800
600
400
200
0
1+cyanide
600
700
Wavelength(nm)
(b)

J Fluoresc
-
1400
1200
1000
800
600
400
200
0
Competing ions and CN
Competing ions
0.010
0.008
0.006
0.004
0.002
0.000
y = a + b*x
No Weightin
6.15551E-7
Equation
Weight
Residual
Sum of
Squares
Adj. R-Squar
0.99157
Value
Standard Erro
Intercept
Slope
3.59435E- 8.01678E-5
8.09164E- 2.15324E-10
B
B
A
0
200000
400000
600000
800000 1000000 1200000
- 2
1/[(I -I )(CN ) ]
0 min
Fig. 8 Benesi-Hildebrand plot of 1 (10 μM) using 1:2 stoichiometry for
association between 1 and cyanide ions
Fig. 6 Selectivity of 1. The black bars represent fluorescence intensity at
601 nm of 1 (10 μM) in THF in the presence of other anions (300 μM)
produced similar optical spectral changes. These results
showed that the selectivity of sensor 1 toward CN− was
not affected by the presence of other anions.
the presence of 30 equivalents of CN −, an emission peak at
601 nm with 98% fluorescence quenching was observed.
Fig. 5b showed the photographs of 1 in the presence of
different anions under excitation at 365 nm using a por-
table UV lamp. The disappearance of intense red color of
the solution upon interaction of 1 with CN− was present.
However, other anions did not induce any significant
emission color change.
Another important feature of 1 is its high selectivity
toward the CN− in presence of other competitive anions.
Changes of fluorescence spectra of 1 (10 μM) caused by
CN− (30 equiv) and miscellaneous competing species (30
equiv) were recorded in Fig. 6. As can be seen, these
competitive species, did not lead to any significant inter-
ference. In the presence of these ions, the CN− still
For determination of stoichiometry between 1 and CN−,
Job’s plot analyses were used. The method is that keeping total
concentration of 1 and CN− at 10.0 μM, and changing the
molar ratio of CN− (XM; XM = [CN−]/{[1] + [CN−]}) from
0.1 to 0.9. From Fig. 7, when molar fraction of CN− was 0.3,
the I0-I value got to maximum, indicating that forming a 1:2
complex between 1 and CN−.
Moreover, the binding stoichiometry and the binding
constant to CN− were determined by Benesi–Hildebrand
double reciprocal method following Eq. (1). Here I0 and
Imin are the fluorescence intensities at zero and the max-
imum concentrations of CN−, [CN−] is the total CN− con-
centration, Kb is the binding constants for 1:2 binding
mode. For receptor 1, a good linear fit could be obtained
by Eq. (1), indicative of the binding stoichiometry of 1:2,
180
160
140
120
100
80
y = a + b*x
Equation
1380
No Weighting
163.73333
Weight
Residual Sum
of Squares
1360
1340
1320
1300
1280
1260
1240
1220
1200
1180
0.99363
Adj. R-Square
Value
1366.6
Standard Error
2.659
Intercept
Slope
B
B
-3.73333E6 99615.42212
60
40
20
0
0.0
0.2
0.4
0.6
0.8
1.0
-
0.00000
0.00001
0.00002
0.00003
0.00004
0.00005
X= 1 /{ 1 + CN
}
-
[CN ]
Fig. 7 Job’s plot for the evolution of binding stoichiometry between 1
and cyanide ions in THF solution. The total concentration of cyanide ions
and 1 was 10 μM
Fig. 9 The linear relation for concentration of CN− vs fluorescence
intensity of 1

J Fluoresc
Fig. 10 a Color and b emission
changes of 1-based test strips be-
fore and after addition of CN−
which conformed to the presence of two a,b-unsaturated
ketone moiety in receptor 1 (Fig. 8). The binding constant
was found to be 1.24 × 108 M−2.
Conclusions
In summary, we developed a new type of DPP-based BTurn-
Off^ fluorescence chemodosimeter, which displayed high se-
lectivity and sensitivity for the detection of cyanide. Addition
of CN− aqueous solution to 1 in THF resulted in a rapid color
change from pink to light yellow, while other anions did not
induce any significant color change, suggesting naked-eye
selective detection of CN− using 1 became possible. In the
presence of CN−, the strong red emission of 1 was completely
quenched. Test strips for use in practical applications are suc-
cessfully realized.
1
1
1
¼
þ
ð1Þ
2
KðI0−IminÞ½CN−Š
I0−I
I0−Imin
The detection limit of 1 for CN− was calculated based
on the fluorescence titration data according to a reported
method [42]. Under optimal conditions, calibration graphs
for the determination of CN− were constructed. The de-
creased fluorescence intensity of the system showed a
good linear relationship (R2 = 0.998), as shown in
Fig. 9. The detection limit for CN− was determined as
0.67 μM based on S/N = 3, which was far lower than
the WHO guideline of 1.9 μM cyanide [43–47].
Acknowledgements The supports by National Natural Science
Foundation of China (No. 21274045), the Fundamental Research Funds
for the Central Universities (2015ZZ037), and the Natural Science
Foundation of Guangdong Province (2015A030313209,
2016A030311034) are gratefully acknowledged.
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