A novel fluorescent sensor based on triphenylamine with AIE properties for the highly sensitive detection of CN?

Article abstract of DOI:10.1016/j.dyepig.2021.109534

In this study, a novel fluorescent sensor 1 built on triphenylamine was designed for the extremely sensitive detection of trace cyanide anions. The UV absorbance and fluorescence emission intensity of sensor 1 with aggregation-induced emission (AIE) prope

Full text of DOI:10.1016/j.dyepig.2021.109534

Dyes and Pigments 193 (2021) 109534
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
A novel fluorescent sensor based on triphenylamine with AIE properties for
the highly sensitive detection of CNꢀ
Bin Zuo, Lian Liu, Xicheng Feng, Denghui Li, Wanfang Li, Mingxian Huang, Qinyue Deng*
College of Science, University of Shanghai for Science and Technology, Shanghai, 200093, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
In this study, a novel fluorescent sensor 1 built on triphenylamine was designed for the extremely sensitive
detection of trace cyanide anions. The UV absorbance and fluorescence emission intensity of sensor 1 with
aggregation-induced emission (AIE) properties vary with water fraction (fw). In the 1% DMSO aqueous solution,
sensor 1 exhibits the optimal aggregation state and fluorescence intensity, and has high selectivity and sensitivity
for cyanide ions (CNꢀ ). From formula 3δ/S, it is clear that sensor 1 has an extremely low limit of detection (LOD)
for CNꢀ (LOD = 2.95 × 10ꢀ 8 mol/L). Excellent anti-interference performance and broad pH response scope
(1.0–9.0) are also advantages of sensor 1. Fluorescence spectroscopy, 1H NMR, 13C NMR spectroscopy, HRMS,
Job’s plot analysis and density functional theory calculations have been employed to elucidate the sensing
mechanism between TPEB and CNꢀ . Through colorimetry and fluorescence approach, the sensor 1 test strip can
easily detect CNꢀ . Therefore, the novel sensor 1 provides a broad application prospect for detecting toxic
environmental pollutants.
Fluorescent probes
Cyanide anions
Aggregation induced emission
DFT
Test strip
1. Introduction
synthesized a novel fluorescent probe built on tetraphenylethylene for
detecting CNꢀ [27]. Wen et al. developed a triphenylamine-based sensor
With the development of science and technology, water pollution
and food safety issues caused by poisonous anions have attracted
widespread attention [1–5]. Cyanide and cyanide-containing com-
pounds are currently extensively found in various areas of industrial
manufacturing, including paint, electroplating, rubber, herbicides, and
so on, causing CNꢀ to reach the organism through the drinkable water
system [6–9]. In turn, cyanide is toxic and can cause damage to human
health and the ecological environment [10–12]. However, the World
Health Organization (WHO) specifies 1.9 × 10ꢀ 6 mol/L as the permis-
sible acceptable concentration of drinking water [13]. As a result,
developing a quick, reliable, ultra-sensitive and selective detection
method for CNꢀ is crucial for environmental science.
for the detection of CNꢀ and Hg2+ [28]. Therefore, the sensitivity and
selective detection of fluorescent probes is an ongoing hot topic.
Currently, the majority of the fluorescent sensing probes are organic
solvent-soluble rather than water-soluble [29–32]. However, CNꢀ often
present in the aqueous phase of the industrial wastewater. Therefore, it
is of great importance to design a fluorescence sensor capable of
detecting CNꢀ in the aqueous phase. Since Tang and coworkers’ dis-
covery of the AIE phenomenon of organic molecules in 2001 [33],
growing number of fluorescent probes with AIE effect has been pub-
lished [34–37]. The construction of AIE fluorescent sensors for the
identification of CNꢀ in the aqueous phase would become a current
research trend relying on the special properties of AIE molecules [38,
39].
There are several methods for detecting CNꢀ , including electro-
chemical tests, colorimetric analyzers, and fluorescent probes [14–19].
Among these reported methods, fluorescent probes are regarded as the
most promising detection methods due to their high sensitivity, high
selectivity, low detection limits, simple operation, and online moni-
toring [20–22]. The significant advancements in the chemical charac-
teristics and composition of fluorescent sensors make them more
sensitive and selective than other tests [23–26]. For example, Li et al.
In this paper, sensor 1 was synthesized with triphenylamine (TPA) as
an electron donor and two barbituric acids (BA) units as electron ac-
ceptors, while sensor 2 was formed with TPA as an electron donor and
three BA units as electron acceptors (Scheme 1). The experimental re-
sults show that sensor 1 has good AIE and ICT effects in the DMSO-H2O
solution system, however, sensor 2 has weak ICT effects in the DMSO-
H2O solution system and therefore cannot detect CNꢀ . Compared with
* Corresponding author.
E-mail address: dqy1991@usst.edu.cn (Q. Deng).
https://doi.org/10.1016/j.dyepig.2021.109534
Received 28 April 2021; Received in revised form 27 May 2021; Accepted 3 June 2021
Available online 9 June 2021
0143-7208/© 2021 Elsevier Ltd. All rights reserved.

B. Zuo et al.
Dyes and Pigments 193 (2021) 109534
Scheme 1. The synthetic routes of sensor 1 and sensor 2.
the previously reported TPA fluorescent probe [28], sensor 1 has higher
sensitivity to CNꢀ (LOD = 2.95 × 10ꢀ 8 mol/L). Sensor 1 has an excellent
selectivity and anti-interference capacity, and it has a well linear rela-
tionship with the CNꢀ concentration at 581 nm. NMR spectroscopy,
HRMS, Job’s plot analysis and DFT computation were utilized to study
the sensing mechanism of sensor 1. Besides, we also prepared the
detection test paper for CNꢀ based on sensor 1.
was synthesized followed by Mallegol’s procedure [40]. POCl3 (9.5 mL,
101.9 mmol) was added dropwise at 0 ◦C under N2 to DMF (7.3 mL, 93.8
mmol) and the reaction mixture was stirred for 1 h. Triphenylamine (1.0
g, 4.1 mmol) was added, and the resulting mixture was stirred at 95 ◦C
for 4 h. After cooling to r. t., the mixture was poured into ice-water (200
mL), and basified with 1 M NaOH. After extraction with CH2Cl2 (200
mL), the organic layer was washed with water (3 × 50 mL), dried
(Na2SO4) and filtered over a short pad of silica gel. 4,4′-diformyl-
triphenylamine (brown solid, 85%): 1H NMR (400 MHz, CDCl3, 298 K):
δ = 9.90 (s, 2H), 7.78 (d, J = 8.7 Hz, 4H), 7.40 (t, J = 7.8 Hz, 2H),
7.29–7.24 (m, 2H), 7.22–7.16 (m, 6H). 13C NMR (101 MHz, CDCl3, 298
K): δ = 190.51, 151.99, 145.48, 131.29, 130.14, 128.49, 127.05,
126.25, 122.74.
2. Material and methods
2.1. Chemicals and instruments
All reagents obtained from Sinopharm Chemical Reagent Co. Ltd.
and Aladdin Reagent Shanghai Co. Ltd. are analytical grade without
further purification in procedures except for special instructions. Anions
(Fꢀ , Clꢀ , Brꢀ , Iꢀ , CO32ꢀ , NO3ꢀ , HCOꢀ3 , HSOꢀ3 , SO42ꢀ , H2POꢀ4 , HPO24ꢀ , AcOꢀ ,
OHꢀ , CNꢀ ) from their tetrabutylammonium salts were prepared, which
was diluted to1.0 mM by deionized water to obtain the stock solution.
The sizes and morphologies of the aggregation states of sensor 1 and
sensor 1+CNꢀ were observed in the scanning electron microscope (SEM,
TESCAN). 1H NMR and 13C NMR were recorded on Jeol ECA-400 and
Bruker 400 DRX spectrometers, respectively. UV–Vis spectra and fluo-
rescence spectra are recorded on a UV–Vis spectrophotometer (UV-
3900, Hitachi, Japan) and fluorescence spectrometer (FL-7000, Hitachi,
Japan), respectively. The pH data are obtained by a pH meter (pH400,
Alalis Co. China). High-resolution mass spectra (HRMS) were obtained
from Bruker solanX 70 FT-MS system.
Under nitrogen, a mixture of 4,4′-diformyltriphenylamine (0.3 g, 1.0
mmol) and BA (0.4 g, 3.1 mmol) in ethanol (10 mL) was refluxed for 4 h.
The residue was purified using column chromatography on silica to
afford the product as a red powder after vacuum drying at 50 ◦C over-
night [41]. The sensor 1 (red solid, 91%): 1H NMR (400 MHz, DMSO‑d6,
298 K): δ = 11.31 (s, 2H), 11.17 (s, 2H), 8.28 (d, J = 8.8 Hz, 4H), 8.19 (s,
2H), 7.48 (t, J = 7.7 Hz, 2H), 7.33 (t, J = 7.3 Hz, 1H), 7.25 (d, J = 7.9 Hz,
2H), 7.07 (d, J = 8.7 Hz, 4H). 13C NMR (101 MHz, DMSO‑d6, 298 K): δ =
164.27, 162.48, 154.38, 150.62, 150.35, 145.00, 137.12, 130.83,
127.82, 127.42, 121.81, 116.44.
Synthetic procedures of the sensor 2. Tris (4-formylphenyl)amine
was synthesized followed by Mallegol’s procedure [40]. The 4,
4′-diformyltriphenylamine (0.3 g, 1.0 mmol) was added on an ice-cooled
mixture of POCl3 (3.0 mL, 32.2 mmol) and DMF (2.3 mL, 29.5 mmol).
The resulting mixture was stirred at 95 ◦C for 1.5 h, and after cooling to
r. t., poured into ice-water (100 mL), and basified with 1 M NaOH. After
extraction with CH2Cl2 (100 mL), the organic layer was washed with
water (3 × 50 mL) and dried (Na2SO4). After evaporation of the solvent,
2.2. Synthetic procedures
Synthetic procedures of the sensor 1. 4,4′-diformyltriphenylamine
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B. Zuo et al.
Dyes and Pigments 193 (2021) 109534
Fig. 1. (a) Absorbance of the sensor 1 (1 × 10ꢀ 5 mol/L) in DMSO/H2O (v/v); (b) The fluorescence spectra of the sensor 1 (1 × 10ꢀ 5 mol/L) in DMSO/H2O (v/v)
mixed solvent with varying fw at λex = 365 nm; (c) Sensor 1’s fluorescent wavelength (red) and emission intensity (blue) against the fw are plotted. (d) Absorbance of
the sensor 2 (1 × 10ꢀ 5 mol/L) in DMSO/H2O (v/v); (e) The fluorescence spectra of the sensor 2 (1 × 10ꢀ 5 mol/L) in DMSO/H2O (v/v) mixed solvent with varying fw
at λex = 365 nm; (f) Sensor 2’s fluorescent wavelength (red) and emission intensity (blue) against the fw are plotted.
the crude product was purified by column chromatography (CH2Cl2) to a
yellow solid. Tris (4-formylphenyl)amine (yellow solid, 80%): 1H NMR
(400 MHz, CDCl3, 298 K): δ = 9.95 (s, 3H), 7.85 (d, J = 8.6 Hz, 6H), 7.25
(d, J = 8.7 Hz, 6H). 13C NMR (101 MHz, CDCl3, 298 K): δ = 190.45,
151.17, 132.57, 131.48, 124.51.
2.4. Computational details
DFT and TD-DFT calculations of sensor 1 and sensor 1+CNꢀ are
carried out in Gaussian 16 software package. The geometries of sensor 1
and sensor 1+CNꢀ are optimized by using density functional theory
(DFT) calculations at the M06–2X/6–31 g(d) level of theory. Transition
energy is calculated by using time-dependent density functional theory
(TD-DFT). The binding pattern of sensor 1 with CNꢀ is further proposed
from the calculation results using DFT/TDDFT.
Under nitrogen, a mixture of tris(4-formylphenyl)amine (0.2 g, 0.6
mmol) and BA (0.3 g, 2.3 mmol) in ethanol (10 mL) was refluxed for 4 h.
The residue was purified using column chromatography on silica to
afford the product as a red powder after vacuum drying at 50 ◦C over-
night [41]. The sensor 2 (red solid, 82%): 1H NMR (400 MHz, DMSO‑d6,
298 K): δ = 11.35 (s, 2H), 11.30 (d, J = 6.9 Hz, 1H), 11.23 (d, J = 9.6 Hz,
2H), 11.17 (s, 1H), 8.28 (t, J = 7.2 Hz, 6H), 8.24–8.13 (m, 3H), 7.18 (t, J
= 8.9 Hz, 5H), 7.04 (d, J = 8.8 Hz, 1H). 13C NMR (101 MHz, DMSO‑d6,
298 K): δ = 164.11, 162.37, 154.04, 150.62, 149.38, 136.84, 128.96,
123.86, 117.55.
2.5. Effect of pH on sensor 1
To investigate the effect of pH on the fluorescence properties of
sensor 1 and sensor 1+CNꢀ , the fluorescence spectra are measured at
the same conditions shown in various acidity. The pH is adjusted by
0.01 mol/L sodium hydroxide and hydrochloric acid solution. Relevant
data are recorded by the fluorescence spectrometer. In addition, the
fluorescence spectra were measured more than 3 times, and the average
values were used to determine the fluorescence intensity.
2.3. Spectroscopic detections
A sensor 1 stock solution of 1 × 10ꢀ 2 mol/L is prepared by DMSO and
sensor 1. A series of 1 × 10ꢀ 3 mol/L anionic stock solutions are obtained
via different anions dissolved into deionized water. Except for special
instructions, the typic fluorescence detection system with sensor 1 at 1
× 10ꢀ 5 mol/L is made from 0.01 mL TPEB stock solution, 0.09 mL
DMSO, several anion stock solutions, dropped into the volumetric flask
and added some deionized water to 10 mL. Meanwhile, the solution pH
is adjusted to 7 by 0.01 mol/L hydrochloric acid solution and sodium
hydroxide solution. The fluorescence emission spectra of all detection
systems are recorded in the wavelength range from 400 to 800 nm under
365 nm excitation. In addition, the fluorescence spectra were measured
more than 3 times, and the average values were used to determine the
fluorescence intensity. The sensor 1+CNꢀ : 1H NMR (400 MHz,
DMSO‑d6, 298 K): δ = 9.08 (s, 4H), 7.25 (dd, J = 18.1, 8.0 Hz, 6H),
6.98–6.91 (m, 3H), 6.89 (d, J = 8.5 Hz, 4H), 5.19 (s, 2H), 2.52–2.49 (m,
6H). 13C NMR (101 MHz, DMSO‑d6, 298 K): δ = 163.62, 152.38, 146.07,
133.99, 129.81, 128.70, 126.63, 123.86, 123.59, 122.75, 121.97, 81.50,
58.00.
2.6. The determination of LOD
The detection limit (LOD) was determined according to formula (1)
by emission data of sensor 1 upon gradual addition of CNꢀ .
LOD = 3δ/S
(1)
where δ was the standard deviation of blank ample, S represented the
absolute value of the slope between fluorescence intensity and CNꢀ
concentration.
3. Results and discussion
3.1. The AIE effect of sensor 1 and sensor 2
Sensor 1 and sensor 2 are very soluble in the organic phase rather
than the aqueous phase. We used DMSO/water as solvent systems in our
quest for the best specific solvent for industrial application, and we
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Dyes and Pigments 193 (2021) 109534
electronic transition type of sensor 2 is HOMO to LUMO+1 (Figure S2 in
the ESI†). Both sensor 1 and sensor 2 have charge separation, but the
degree of charge separation of sensor 2 (f = 1.1645) is weaker than that
of sensor 1 (f = 1.5774). It is speculated that the addition of the third BA
may cause the local symmetry of sensor 2 molecule, which weakens the
ICT effect, which leads to weaker fluorescence intensity. Therefore, we
selected sensor 1 with good AIE and ICT effects as the fluorescence
sensor for the detection of CNꢀ .
3.2. The sensing performance of sensor 1
3.2.1. Selectivity and anti-interference of sensor 1
Fig. 2. Under sunlight and 365 nm UV light, color variations were caused by
the addition of 2.0 equiv. of different anions to sensor 1 solution in 99%
aqueous DMSO solution.
The fluorescence spectra of sensor 1 solution (1 × 10ꢀ 5 mol/L) (fw
=
99%) were documented with different anions (Fꢀ , Clꢀ , Brꢀ , Iꢀ , CO23ꢀ
,
NOꢀ3 , HCOꢀ3 , HSOꢀ3 , SO42ꢀ , H2PO4ꢀ , HPO42ꢀ , AcOꢀ , OHꢀ , CNꢀ ) (Fig. 2).
Except for CNꢀ , the tested anion solution is colorless under sunlight and
pink fluorescence under ultraviolet light (365 nm). Only the sensor with
CNꢀ added appears transparent under sunlight and non-fluorescence
under 365 nm UV light. The results of the fluorescence intensity test
in Fig. 3a also correspond to corresponding observations. According to
these observations, sensor 1 has high selectivity for CNꢀ . The results
showed that the competing anions had little effect on the color of the
solution.
investigated the AIE behavior of sensor 1 and sensor 2 using UV–visible
and fluorescence spectroscopy. As shown in Fig. 1a and d, sensor 1 and
sensor 2 both have two absorption peaks in the UV–visible spectrum.
The activated
π→π* electron transition of TPA and BA is primarily
responsible for the absorption peak in the 350–400 nm region, while the
intramolecular charge transfer (ICT) impact of TPA to BA is responsible
for the absorption peak at 474 nm.
The addition of water to DMSO will facilitate aggregation of sensor 1
and sensor 2 as water is an undesirable solvent. The fluorescence vari-
ations of sensor 1 and sensor 2 are observed by modifying the DMSO to
H2O proportion in the solvent situation (Fig. 1b and e). The results show
that sensor 1 (1 × 10ꢀ 5 mol/L) has very weak fluorescence (fw = 0%) in
pure DMSO under the irradiation of the 365 nm ultraviolet lamp. The
enhancement of polarity when fw < 90% leads to the ICT effect, so the
We performed an anti-interference test on sensor 1 by adding 2.0
equivalents of different anions to DMSO/H2O (fw = 99%) to further
investigate its usefulness as an ion-selective fluorescence sensor for CNꢀ
(Fig. 3b). But for the decline in the fluorescence intensity of OHꢀ , the
inclusion of other anions has little effect on the fluorescence intensity in
the single intervening ion system. The fluorescence intensity in the
coexistence system of disturbance ions system with CNꢀ is significantly
lower than in the single intervening ion system. The results of the pre-
ceding study indicate that sensor 1 has strong selectivity and stable anti-
interference capability for CNꢀ .
fluorescence of sensor 1 will become very weak. However, when fw
≥
90%, sensor 1 aggregates, so it presents a fluorescence enhancement
state. Besides, sensor 1 emits bright red fluorescence when fw = 90%
(Figure S1 in the ESI†). All these observations show that sensor 1 has AIE
activity. According to related literature [42,43], as the proportion of
water increases, the emission intensity of sensor 1 shifts to the
long-wave direction, which may be caused by the electronic transition
3.2.2. Sensing ability of sensor 1 for CNꢀ
The scanning electron microscope (SEM) was utilized to study the
aggregation state of sensor 1 after adding CNꢀ to the solution. As
depicted in Fig. 4, sensor 1 had a granular morphology with a rough
surface before the addition of CNꢀ and an aggregated form with a
smooth surface after the addition of CNꢀ .
(π-π*) inside the sensor 1 (Fig. 1c). However, the fluorescence intensity
of sensor 2 was weak in the DMSO-H2O solution system and cannot be
recognized by the machine. The possible reason was that sensor 2 has a
locally symmetric molecular structure (three-arm BA units) and the ICT
effects within the molecular structure cancel each other out, resulting in
a significant decrease in the fluorescence intensity of sensor 2 compared
to sensor 1 (two-arm BA units). In order to confirm the above point of
view, we further studied the luminescence mechanism of sensor 2 in the
DMSO-H2O solution system and implemented it on the M06–2X/6-31G*
level of the Gaussian 16 package. We found through calculations that the
We further investigated the sensing performance of sensor 1 for
different CNꢀ concentrations in 99% DMSO aqueous solution by fluo-
rescence emission spectroscopy. As seen in Fig. 5a, the fluorescence
intensity at 581 nm steadily decreased with increasing CNꢀ concentra-
tion (0.1–2.0 equiv.) due to the interruption of ICT of sensor 1. Fig. 5b
shows the fluorescence intensity of sensor 1 at 581 nm as a function of
Fig. 3. (a) The fluorescence spectra of sensor 1 (1 × 10ꢀ 5 mol/L) with multiple anions (2.0 equiv.) in 99% aqueous DMSO solution. (b) Competitive experiments in
the sensor 1+CNꢀ system with interfering anions at λex = 365 nm.
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Fig. 4. The SEM images of sensor 1 (a, b) and sensor 1+CNꢀ (c, d).
Fig. 5. (a) The fluorescence spectra of sensor 1 (1 × 10ꢀ 5 mol/L) with steadily rising concentrations of CNꢀ (0–2.0 equiv.) in fw = 99%; (b) The detection limit of
sensor 1 for CNꢀ (0–2.0 equiv.).
CNꢀ concentration. The fluorescence intensity gradually decreases as
the CN- concentration rises from 0 to 1.6 × 10ꢀ 5 mol/L, with a strong
linear relationship (y = 526.94–27.50x, R2 = 0.998). As the concen-
tration of CNꢀ > 1.6 × 10ꢀ 5 mol/L, the fluorescence intensity remains
almost constant, meaning that CNꢀ is surplus in the solution. According
to equation 3δ/S, the LOD of sensor 1 for CNꢀ was determined to be
2.95 × 10ꢀ 8 mol/L (0–1.6 × 10ꢀ 5 mol/L), which is significantly lower
than the permitted amount of CNꢀ in drinking water (1.9 × 10ꢀ 6 mol/L).
The conclusions demonstrate that the designed sensor 1 has enough
sensitivity to detect CNꢀ conveniently.
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Dyes and Pigments 193 (2021) 109534
Fig. 6. (a) The influence of pH on the fluorescent intensity of the sensor 1 and sensor 1+CNꢀ ; (b) The time-dependent fluorescent intensity of sensor 1 toward CNꢀ .
Fig. 7. 1H NMR spectra of the sensor 1 and sensor 1+CNꢀ .
3.2.3. Analysis of pH and reaction time toward sensor system
We studied the fluorescence spectrum of sensor 1+CNꢀ over time
(Fig. 6b). The fluorescence intensity of sensor 1+CNꢀ decreased rapidly
after the addition of CNꢀ for the first 5 min, then stayed nearly constant
for the next 30 min. The results show that at room temperature, the
reaction time of sensor 1+CNꢀ can be completed within 5 min. There-
fore, the swift response of sensor 1 to CNꢀ provides a promising
application.
We used fluorescence spectroscopy to study the stability of sensor 1
and sensor 1+CNꢀ under different pH conditions (Fig. 6a). When the pH
changes from 1.0 to 9.0, sensor 1 has a stable emission intensity, and as
the pH rises above 9, the fluorescence intensity diminishes sharply. After
adding CNꢀ to sensor 1, the fluorescent intensity is relatively stable in
the pH range of 4.0–9.0. The fluorescence intensity changed consider-
ably in the pH range of 5.0–8.0 before and after the addition of CNꢀ ,
meaning that sensor 1 can detect CNꢀ in the pH range and has a sig-
nificant fluorescence response. In the following experimental testing, we
preferred pH = 7 as the experimental condition.
3.3. The detection mechanism of sensor 1
1H NMR and Job’s titration were used to investigate the process of
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Dyes and Pigments 193 (2021) 109534
the intrusion detection between sensor 1 and CNꢀ [44,45].
Fig. 9 depicts the optimum structures of sensor 1 and sensor 1+CNꢀ .
By sp2 hybridization of vinyl, the sensor 1 molecule exhibits a rigid
planar configuration. Sensor 1+CNꢀ , on the other hand, shows the non-
planar confirmation through the sp3 hybridization of the carbon-carbon
bond. The results show that the apparent structural difference between
sensor 1 and sensor 1+CNꢀ leads to significant changes in the conjugate
system, which leads to changes in its fluorescence properties.
Besides, Fig. 9 also lists the TD-DFT calculations. As an electron
acceptor, the BA fragment has a strong electron-withdrawing ability in
sensor 1. The electron distribution of HOMO in sensor 1 molecule was
primarily distributed in triphenylamine and part of barbiturate, while
that of LUMO was concentrated in the whole barbiturate and part of
triphenylamine. However, for sensor 1+CNꢀ molecules, the electron
distribution of LUMO and HOMO is limited to the unit, which means that
the ICT phase is interrupted, resulting in a significant decrease in fluo-
rescence. The results indicate that the addition of CNꢀ has an appre-
ciable impact on the phase change performance. The disruption of the
ICT mechanism is caused by the transition in the conjugate scheme,
which is compatible with our previous discussion. Furthermore, the
Fig. 8. Job’s plot for sensor 1 in fw = 99% (The total concentration was 1 ×
10ꢀ 5 mol/L).
sensor 1 detecting CNꢀ . In the 1H NMR spectrum (Fig. 7), sensor 1 shows
two proton peaks at 11.17 ppm and 8.19 ppm, respectively, corre-
sponding to the Ha of BA and H1 of the vinylidene. As CNꢀ were applied
to sensor 1, the peak at H1 (8.19 ppm) vanished entirely, whereas a new
peak at 5.19 ppm appeared, attributed to H2. Simultaneously, the Ha
(11.17 ppm) moved to the low-frequency magnetic field Hb (9.08 ppm).
From Fig. 7, we can observe that the H0 peak attributed to the BA group
of sensor 1+CNꢀ is submerged by the water peak (3.34 ppm). Besides,
the initial molecular structure is broken by the addition of CNꢀ , and
some of the proton peaks attached to the aromatic group move to a high
field. The ICT between the electron donor (TPA) and the electron
acceptor (BA) is blocked by CNꢀ , which has nucleophilicity and attacks
the C = C bond of sensor 1. To further determine the detection mech-
anism, Job’s titration experiment was conducted on sensor 1. As shown
in Fig. 8, the stoichiometric ratio of sensor 1 to CNꢀ is 1–2. As a result,
sensor 1 detects CNꢀ since it is a strong nucleophilicity that attacks
vinylidene.
rupture of the π-conjugated structure results in a higher HOMO-LUMO
energy difference for sensor 1+CNꢀ (6.91 eV) than sensor 1 (4.57 eV).
As a result, theoretical calculations indicated that CNꢀ attacked the C =
3.4. Theoretical calculations
The density functional theory (DFT) and time-dependent density
functional theory (TDDFT) were used to compute the composition,
electron density, and electronic structure of sensor 1 and sensor 1+ CNꢀ
by the M06–2X/6-31G* level of the Gaussian 16 package to investigate
Fig. 10. The photographs of sensor 1-based test strips with OHꢀ , CNꢀ , and
HCO23ꢀ under 365 nm UV light and sunlight.
Fig. 9. Calculation of HOMO and LUMO electron distributions for sensor 1 and sensor 1+CNꢀ .
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Dyes and Pigments 193 (2021) 109534
Table 1
Sensor 1 compared to other previously recorded probes.
Fluorescence sensors
Solvent system (v/v)
THF/H2O (9:1)
LOD/mol Lꢀ 1
2.1 × 10ꢀ 6
References
[46]
H2O/THF (9:1)
3.83 × 10ꢀ 6
[47]
THF/H2O (1985:15)
DMSO/H2O (7:3)
3.9 × 10ꢀ 8
[48]
[49]
1.4 × 10ꢀ 7
H2O/THF (8:2)
1.3 × 10ꢀ 7
4.0 × 10ꢀ 8
[50]
[28]
DMSO/H2O (1:99)
Sensor 1
DMSO/H2O (1:99)
2.95 × 10ꢀ 8
This work
C bond and interrupted the conjugation structure in the molecule,
drinking water, the LOD of the first and second probes did not fulfill the
actual detection demand, as shown in Table 1 [46,47]. The third and
fourth probes have excellent selectivity and anti-interference perfor-
mance for CNꢀ , but there are disadvantages such as poor linear fit and
long-time process [48,49]. Despite the good linear fit of the last two
probes, their LOD was poor compared with this work [28,50]. In
contrast, sensor 1 synthesized in this work has the advantages of
excellent selectivity, easy operation, and outstanding LOD.
resulting in no ICT in sensor 1+CNꢀ .
3.5. Test strips based on sensor 1
We prepared sensor 1 test strips to make the detection of CNꢀ easier.
Sensor 1 (100 μM) was applied on filter paper and dried in an oven to
obtain test strips, and then OHꢀ , CNꢀ and HCO32ꢀ (fw = 100%) were
added dropwise to the test strips to detect the anions. Fig. 10 reveals that
4. Conclusions
when CNꢀ (50
μM) is added dropwise to the filter paper, the fluores-
cence of the test strip based on sensor 1 varies from red to light blue
To summarize, we have successfully produced a novel sensor 1 for
the detection of CNꢀ that uses TPA as an electron donor and two BA as
electron acceptors. The fluorescent sensor 1 has excellent AIE activity in
DMSO/H2O mixing system. Besides, the detection limit of sensor 1 for
CNꢀ is extremely low (LOD = 2.95 × 10ꢀ 8 mol/L), and it has the ad-
vantages of strong anti-interference ability, excellent selectivity, and
easy operation. Theoretical calculations show that the sensing mecha-
nism of sensor 1 is due to the addition of CNꢀ , which interrupts the
conjugated structure in the molecule and leads to the blocking of ICT.
Sensor 1-based test strips can be used to detect CNꢀ in a qualitative
manner by colorimetric method. Thus, sensor 1 offers a promising
under 365 nm UV light, which is readily visible with the naked eye. The
fluorescence intensity of the test paper with drops of OHꢀ (50
μM) and
HCO23ꢀ (50
μM) was marginally weakened and improved, respectively,
in contrast to the sensor 1-based test strips, which was compatible with
the above fluorescence sensors performance. These observations showed
that the sensor 1-based test strips can be used to detect CNꢀ in a qual-
itative manner by colorimetric method.
3.6. Sensor 1 compared to other previously recorded probes
According to standards of WHO on the cyanide concentration in
8

B. Zuo et al.
Dyes and Pigments 193 (2021) 109534
alternative for the detection of CNꢀ in water.
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CRediT authorship contribution statement
Bin Zuo: Methodology, Writing – original draft. Lian Liu: Data
curation, Software. Xicheng Feng: Investigation. Denghui Li: Valida-
tion. Wanfang Li: Investigation. Mingxian Huang: Investigation.
Qinyue Deng: Supervision, Writing – review & editing.
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based on beta-formylBODIPY dyes by an unprecedented nucleophilic addition
reaction. Spectrochim Acta A 2021;247:119102. https://doi.org/10.1016/j.
saa.2020.119102.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
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Acknowledgment
Financial support from the Shanghai Young Teachers Training and
Support Program (No. slg20035), Shanghai Engineering Research Cen-
ter for Food Rapid Detection and the College of Science, University of
Shanghai for Science and Technology is gratefully acknowledged.
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