Aggregation-induced emission enhancement (AIEE)-active tetraphenylethene (TPE)-based chemosensor for CN?

Article abstract of DOI:10.1016/j.saa.2020.118928

An aggregation-induced emission enhancement (AIEE)-active fluorescent sensor has been successfully designed and synthesized, combining the AIE effect of tetraphenylethylene (TPE) with the cyanide acceptor of phenanthro[9,10-d]imidazole. The sensor exhibit

Full text of DOI:10.1016/j.saa.2020.118928

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 245 (2021) 118928
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Aggregation-induced emission enhancement (AIEE)-active
−
tetraphenylethene (TPE)-based chemosensor for CN
a
a,
a
a,b,
Yilan Wang , Hongliang Liu ⁎, Zhao Chen , Shouzhi Pu ⁎⁎
a
Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology Normal University, Nanchang 330013, PR China
Department of Ecology and Environment, Yuzhang Normal University, Nanchang 330103, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 July 2020
Received in revised form 25 August 2020
Accepted 5 September 2020
Available online 10 September 2020
An aggregation-induced emission enhancement (AIEE)-active fluorescent sensor has been successfully designed
and synthesized, combining the AIE effect of tetraphenylethylene (TPE) with the cyanide acceptor of phenanthro
2
[9,10-d]imidazole. The sensor exhibits not only the property of AIEE in DCM/n-hexane or THF/H O, but also the
phenomenon of mechanofluorochromic (MFC). It displays large Stokes shift (107 nm) due to the intramolecular
charge transfer (ICT) process. The cation of CN− boosts the ICT process to make the greater Stokes shift (184 nm)
with the fluorescent color vary from blue-green to sodium-yellow and visually turning from light yellow to dark
yellow in the naked eyes. The results of Job's plot, ESI-MS and the DFT calculations provide the stoichiometric
ratio and electronic properties of the sensor. Furthermore, the sensor could be applied to qualitative and quanti-
tative detection of CN− on test paper strips.
Keywords:
Aggregation-induced emission enhancement
Mechanofluorochromic
Fluorescent sensor
Cyanide
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
ions colorimetric and fluorescence sensors are usually combined by
binding sites and signal groups in a certain way to achieve the purpose
Cyanide compounds are vital in chemical, medicine, fuel industry
of detection [20,21]. According to the different binding modes, it is
mainly divided into the following categories: hydrogen bonding type,
deprotonation type, addition reaction type and coordination action
type [22–25]. For example, Kasushik and co-works [26] reported that
hydrogen-bond-based thiourea recognition sites would rapidly detect
fluoride ions and cyanide ions in the naked eyes, but the disadvantage
was that it would not achieve specific recognition [26]. Bhattacharya
and group members synthesized sensor molecules with anthraquinone
imidazoie as the framework [27]. The compound was indentified fluo-
ride ions and cyanide ions in acetonitrile by intramolecular electron
transfer mechanism, and achieved a single colorimetric recognition of
cyanide ions by changing the solvent system [27].
With the research of colorimetric and fluorescent sensors, more and
more sensors have been reported and proposed, such as imidazole de-
rivatives, rhodamine derivatives and coumarin fluorescent derivatives,
which have high fluorescent quantum yield, good photostability and
molar extinction coefficient [28–30]. But they also exhibit fatal irre-
pressible drawbacks such as aggregation-caused quenching (ACQ),
small stoke shifts (<10 nm) and background interference, limiting
their practical applications [31,32].
and heavy industry fields, because of not only the wide range of sources
but also the wide range of uses [1,2] such as gold mining, electroplating,
metallurgy, synthetic fiber and resin industry [3]. However, cyanide
compounds are one of the most toxic substances to the environment
and human health [4,5]. Cyanide is absorbed through the skin, the
eyes or gastrointestinal tract into the body, breaking down toxic cyanide
ions, which can inhibit the activity of 42 enzymes in the cell [6–9] taking
cytochrome oxidase, peroxidase and decarboxylase [10,11] for example.
Among them, cytochrome oxidase is susceptible to prussiate which can
easily bind to trivalent iron in oxidized cytochrome oxidase to inhibit its
lessening to divalent iron, break the oxidation process of transmitting
electrons, and eventually lead to respiratory failure and death [12–15].
Therefore, the urgent problem to be solved at present is how to quickly,
efficiently and easily detect cyanide ions in the environment and daily
life. Traditional methods for detecting cyanide ions require expensive
instruments and complicate operations, which limit the application of
these methods [16,17]. In recent years, colorimetric and fluoresent
methods have become the research hotpot in ion detection field, be-
cause of their simple operation and cheap instrument [18,19]. Cyanide
Academician Tang Benzhong and members of his research group
proposed aggregation-induced emission (AIE) for the first time in
⁎
Corresponding author.
2
001 to overcome the notorious ACQ phenomenon [33–35].
⁎
⁎ Correspondence to: S. Pu, Department of Ecology and Environment, Yuzhang Normal
Aggregation-induced emission was the opposite process of the
aggregation-caused quenching, showing weak fluorescence or even no
fluorescence in the non-aggregating state, but enhancing fluorescence
University, Nanchang 330103, PR China.
E-mail addresses: liuhongliang03@163.com (H. Liu), pushouzhi@tsinghua.org.cn
(
S. Pu).
https://doi.org/10.1016/j.saa.2020.118928
386-1425/© 2020 Elsevier B.V. All rights reserved.
1

Y. Wang, H. Liu, Z. Chen et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 245 (2021) 118928
in the aggregated state [36,37]. For instance, hydrazone imide deriva-
tives, anthracene derivatives and tetraphenylene derivatives exhibited
AIE phenomena and would be applied to biological detection [38,39].
Among them, tetraphenylene was the characteristics of simple synthe-
sis and easy modification, so many tetraphenylene derivatives had
been designed and proposed. For example, (E)-1,2-di([1,1′:4′,1″-
terphenyl]-4-yl)-1,2-diphenylethene [40], tetra(4-pyridylphenyl)eth-
ylene [41], 9,9′-bixanthenylidene [42], but there were few studies on
linking tetraphenyl to imidazole. Combination the application of imid-
azole derivatives in the field of ion detection with the advantages of
tetraphenylene [43,44], An AIEE-active fluorescent sensor (Scheme 1)
Synthesis of TPI by compound 1 (0.1 g, 0.23 mmol) was dissolved in
methanol (15 mL) and placed in a one-neck flask, and phenanthrene-
9,10-dione (0.07 g, 0.3 mmol) and ammonium acetate (0.7 g, 9 mmol)
were added to the solution to allow the reaction mixture to be at
360 K. The mixture was stirred at reflux temperature until a solid pre-
cipitated. It was cooled to room temperature, washed with methanol
until no impurities, and dried to give a yellow solid (0.08 g, yield:
1
55%). H NMR (500 MHz, DMSO-d
6
): δ (ppm) 6.60 (d, 1H, J = 4 Hz),
6.99 (d, 3H, J = 7.5 Hz), 7.15–7.06 (m, 4H), 7.27–7.22 (m, 6H), 7.29
(d, 3H, J = 8.0 Hz), 7.33 (d, 1H, J = 7.0 Hz), 7.37 (t, 3H, J = 6.5 Hz),
7.59 (d, 1H, J = 4.0 Hz), 7.81 (d, 3H, J = 25 Hz), 8.78 (d, 2H, J =
7.5 Hz), 9.02 (d, 2H, J = 3.5 Hz), 13.76 (s, 1H,), 13C NMR (126 MHz,
2
[
-(5-(4-(1,2,2-triphenylvin-yl)phenyl)thiophen-2-yl)-1H-phenanthro
9,10-d]imidazole (TPI) was designed and synthesized for cyanide ion
identification.
DMSO-d
125.76, 125.99, 127.08, 127.18, 127.27, 127.30, 127.36, 137.65, 127.73,
27.99, 128.03, 128.25, 128.31, 128.42, 128.51, 131.14, 131.19, 131.24,
131.80, 132.05, 133.35, 137.35, 140.42, 141.48, 143.48, 143.59, 144.47,
6
): δ (ppm) 122.30, 122.38, 122.56, 124.27, 124.68, 125.20,
1
2. Experimental
+
1
45.03. MS-ESI (m/z): 631.21 [M + H] (calcd 631.1) (Fig. S2).
2.1. General methods
3
. Results and discussion
All chemicals and solvents were acquired the analytical grade by
bargain and utilized without further purification. 1H NMR and
13
C
3.1. Optical characterization
NMR spectra were noted on a Bruker AV500 (500 MHz) NMR spec-
trometer utilizing tetramethylsilane as the internal standard. Mass
spectra were obtained using an Agilent 1100 ion trap LC/MS MSD sys-
tem. Fluorescence spectra and UV–Vis absorption spectra were
measured with a Hitachi F-4500 fluorescence spectrophotometer and
an Agilent 8453 UV–Vis spectrophotometer, respectively. The fluores-
cence quantum yield was resolved the QYC11347-11 (absolute PL quan-
tum yield spectrometer). XRD researches were performed in the
Shimadzu XRD-6000 diffractometer with Ni-filtered and graphite-
The UV–Vis absorption spectrums of TPI in pure THF
−5
−1
(2.0 × 10 mol L ) and solid state were recorded in Fig. 1A. The ab-
sorption peaks of TPI in pure THF were 321 nm and 394 nm, in that a
relatively weaker absorption peak at 321 nm was due to the π-π* tran-
sitions, and a main absorption peaks at 394 nm was due to the intramo-
lecular charge transfer (ICT) process [38]. The absorption band of solid
TPI (λmax = 401 nm) was slight red-shifted, compared with that of
TPI (λmax = 394 nm) in pure THF, presumably on account of the aggre-
gation formation and the intermolecular interactions occurrence in the
solid state [45]. The fluorescence spectrum of TPI showed bright blue
fluorescence at 501 nm in THF when excited at 394 nm (Fig. 1A), and
exhibited large stock shift (107 nm), whereas this solid state showed
bright blue-green fluorescence at 522 nm. The photograph of TPI in
THF solutions and solid state were shown in Fig. 1B. In addition, the fluo-
rescence lifetime of TPI was found to be 0.05 ns in THF solutions,
whereas the fluorescence lifetime was found to be 0.49 ns in the solid
state. The longer fluorescence lifetime could be due to the restriction
of intramolecular rotations in the solid state [46]. At the same time
photophysical data of TPI were summarized in Table 1.
a
monochromated Cu K radiation (λ = 1.54 Å, 40 kV, 30 mA). Dynamic
light scattering (DLS) studies were measured using Brookhaven
NanoBrook 90 Plus and scanning electron microscopy (SEM) were re-
−
−
−
−
−
3 3
corded on a SEM, Zeiss, Sigma. Anions (CN , F , Cl , CH COO , NO ,
−
2−
−
−
2−
−
−
−
−
−
3−
I , CO
3
, HCO
3
, HSO
3
, SO
4 2 4 4 4 4
, H PO , SCN , ClO , HSO , Br , PO ,
2
−
2−
S
2
O
3
and HPO ) from their tetrabutylammonium salts were pre-
pared, which was diluted to 0.1 mol L by deionized water to obtain
the stock solution.
4
−1
2.2. Synthesis of TPI
As shown in Scheme 1, synthesis of compound 1 by Suzuki coupling,
compound 1 was prepared by reacting (2-(4-bromophenyl)ethene-
,1,2-triyl)tribenzene (0.800 g, 2 mmol) with (5-formylthiophen-2-yl)
boronic acid (0.624 g, 4 mmol) in the presence of Pd(PPh and
Na CO (4 g, 38 mmol) in tetrahydrofolate (THF, 30 mL containing
0% water). Refluxing at 360 K was continued until TLC revealed that
3.2. Aggregation induced emission enhancement (AIEE) properties
1
3
)
4
To research the probable AIEE behavior of TPI, this spectral behavior
was explored in the good and poor solvents. AIEE characteristics of com-
pound TPI was based on emission and UV–Vis absorption spectral as-
2
3
1
the reaction was complete, after being extracted with DCM. Purification
by silica gel column chromatography in petroleum ether and ethyl ace-
tate (45: 1) to compound 1 (56%) pale green solid after drying the sol-
h
sessments in various n-hexane fraction (f = 0–98%) of DCM/n-
hexane mixtures (Fig. 2A). The emission of TPI was weak in DCM solu-
tion and increased slowly until the ratio of n-hexane increased to 80%.
Afterwards, the remarkable emission enhancement was recorded for
vent. 1H NMR (500 MHz, DMSO-d
): δ (ppm) 6.99–7.10 (m, 8H),
.13–7.24 (m, 9H), 7.62 (d, 1H, J = 9.5 Hz), 7.71 (d, 1H, J = 4.5 Hz),
.03 (d, 1H, J = 4.5 Hz), 9.91 (s, 1H). (Fig. S1).
6
7
8
TPI at f
h
of 90% and 98%, which were 2-fold (90%) and 6-fold (98%)
altered from 0 to
higher than that in pure DCM, respectively. As f
h
Scheme 1. Synthetic route of TPI.
2

Y. Wang, H. Liu, Z. Chen et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 245 (2021) 118928
A 1.2
1.2
Solid
TPI in the pure THF
0.9
0.6
0.3
0.0
0.9
0.6
0.3
0.0
300
400
500
600
700
Wavelength (nm)
Fig. 1. (A) The absorption and fluorescence spectra of TPI compound in pure THF solution and in solid states and (B) their photographic images under 365 nm UV light.
9
0%, the absorption bands of TPI in DCM/n-hexane had little changed
compared to it in DCM solution. However, the absorption peak intensi-
ties of TPI slightly increased as f increasing to 98% (Fig. S3). Addition-
3.3. Mechanofluorochromic behavior of TPI
h
The mechanofluorochromic characteristics of compound TPI were
further investigated by emission spectral (Fig. 3A). The solid sample
was then crushed with a pestle, and the fluorescence emission color of
the sample changed (Fig. 3B). The blue green luminescence (521 nm)
transformed into bright green luminescence (542 nm) with a moderate
red-shift (21 nm) after crushing (Fig. 3C). Significantly, after treating
the ground sample with DCM vapor, the fluorescence emission could
be essentially reverted to its initial emission with the color changing
(Fig. 3D). This mechanochromic luminescence transition of TPI would
be repeated many times between the blue green luminescence and
bright green luminescence by alternating grinding and fuming pro-
cesses (Fig. S6). The powder X-ray diffraction (PXRD) technique was
used to reveal the reason for the mechanofluorochromic behavior of
TPI, and the results indicated that this phenomenon occurred due to
the change in molecular packing modes [52]. As shown in Fig. S7, the
diffraction patterns of the solid sample and the solvent fumed powders
clearly exhibited sharp and intense reflections, indicating TPI form mi-
crocrystals. In contrast, the ground powders did not exhibit any notice-
able diffraction in the PXRD profile, reflecting its amorphous.
ally, limiting the intramolecular motions of TPI in aggregation states
made the fluorescence quantum yield of TPI remarkably increase from
0
h h
.042 (f = 0%) to 0.101 (f = 98%) and resulted in the emission im-
provement [47,48]. These results indicated that TPI displayed AIEE char-
acteristics in DCM/n-hexane mixtures. Further, the morphological
transition of the TPI in the DCM/n-hexane mixture solution (f
h
=
98%) was determined by scanning electron microscopy (SEM) and dy-
namic light scattering (DLS) as shown in Fig. S4 and Fig. S5. DLS result
revealed that the particulate size of aggregates changed with increasing
various n-hexane fraction in the DCM/n-hexane mixture. SEM images of
TPI clearly indicated the morphological aggregates state.
Different luminescence response was present with the alter-
ation of water, a polar and poor solvent, in THF solution (Fig. 2B).
The fraction of water ranging from 0% to 20%, the emission inten-
sity descended mildly. Subsequently the emission intensity
ascended slowly with the f
sity improved dramatically with the f
more than 80% the emission converted to decrease. The emission
w
from 20% to 70%, the emission inten-
w
from 70% to 80%, and the
f
w
color appeared red-shift (34 nm) from blue-green (501 nm) to
pure green (535 nm) with the reason that the dye molecules had
different conformations and packing modes at the aggregation
3.4. Analytical studies of TPI
−
−
states [49]. In the mixture of the higher water content (f
w
> 80%),
The binding ability of TPI with different anions including CN , F ,
−
−
−
−
2−
−
−
2−
−
−
the dye molecules might rapidly agglomerated in an irregular
way to induce less emission [50,51]. The fluorescence quantum ef-
Cl , CH COO , NO , I , CO , HCO , HSO , SO4 , H PO4 , SCN ,
3
3
3
3
3
2
−
−
−
3−
2−
2−
4 4 4 2 3
ClO , HSO , Br , PO , S O and HPO4 was also investigated by
−5
−1
ficiency of TPI raised from 0.039 (f
w
= 0%) to 0.09 (f
w
= 80%). Thus,
fluorescence spectroscopy in DCM (2.0 × 10 mol L ) at room tem-
perature. When excited at 441 nm, upon adding 9.0 equiv. of CN , the
fluorescence emission peak of TPI exhibited a theatrical enhancement
−
TPI featured the unique AIEE characteristics in THF/water mix-
tures, also. In addition, the AIEE behavior could be further con-
firmed by DLS and SEM measurements, as shown in Fig. 2C and D.
The Optical properties for TPI under different environment were
summarized in Table S1.
(~8.3 folds) and transformed from 500 nm to 595 nm due to the TPI-
−
−
CN complex form (Fig. 4A). Simultaneously, TPI-CN complex exhib-
ited greater stock shift (184 nm) than that in TPI (107 nm), which
would be easy to facilitate ICT processes [50]. The apparent fluorescence
color turned from blue-green to sodium-yellow (Fig. 4C) with the visi-
ble color changing from light yellow to dark yellow (Fig. S7). After addi-
tion 9.0 equiv. of other anions, no obvious fluorescence variations were
observed. The results indicated that TPI could be used as a fluorescent
Table 1
Optical properties for TPI.
e
Sample THF
Δλ Solid
−
sensor for the naked-eye detection of CN in DCM. In order to evaluate
the TPI anti-jamming capability for detecting CN in the presence of
max (nm)a
λ
em (nm)b τ(ns)c
501 0.05
λ
max (nm)a
λ
em(nm)b τ(ns)c
522 0.49
−
λ
TPI
321, 394
107 290, 401
various anions (Fig. 4B), the experiment of anti-interference was carried
out. There was scarcely any interference in the emission intensity was
a
b
c
Absorption wavelength.
The wavelength of emission maximum.
The fluorescence lifetime.
−
seen by addition CN (9.0 eq.) to TPI solution in the presence of various
anions (10 eq.). Thus, these results indicated TPI could be served as an
3

Y. Wang, H. Liu, Z. Chen et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 245 (2021) 118928
B 2000
A 2
400
2500
2
000
500
8
0%
1
9
8%
1000
1500
1000
500
0
500
0
1600
0
20
40
60
80
100
fh(vol %)
90%
n-hexane fraction
fh
9
8%
fw
0%
99%
800
9
0%
0%
99%
0
%-70%
0
%-80%
0
500
600
700
5
00
600
700
Wavelength (nm)
Wavelength (nm)
C 100
664nm
80
60
40
20
0
200
400
600
800
1000
Side (d.nm)
Fig. 2. (A) The fluorescence spectra of TPI in THF/n-hexane with different fractions (inset: photos of TPI in DCM/n-hexane under 365 nm excitation and PL relative intensity of TPI). (B) The
fluorescence spectra of TPI in THF/H
2
O with different fractions (inset: photos of TPI in THF/H
O (f = 99%).
2
O under 365 nm excitation and the PL relative intensity of TPI). (C) Size distribution of TPI in
THF/H O. (D) SEM images of TPI in THF/H
2
2
w
excellent fluorescent sensor for CN− detection with favorable selectivity
and enjoyable anti-interference.
solution of TPI (2.0 × 10−5 mol L−1), the peak at 595 nm ascended grad-
ually with the peak at 500 nm descending (Fig. 5B). Accompanied by the
fluorescent color of the solution transforming from blue-green to
sodium-yellow, simultaneously the fluorescence quantum yield re-
To further estimate the dose-dependent fluorescence response of
−
TPI to CN was decided by fluorescence titration in DCM at room tem-
−
−
perature (Fig. 5A). As the CN from 0 to 9.0 equiv. dropped into the
markable was increased from 0.042 (TPI) to 0.23 (TPI-CN complex).
A
1.2
Uground
Ground
Treated with DCM
0.8
0.4
0.0
500
600
700
Wavelength (nm)
Fig. 3. (A) Solid state fluorescence spectra of TPI before and after the grinding, and after treatment with DCM vapor (λem = 400 nm). Photographic images of TPI under 365 nm UV light:
(B) the solid sample, (C) the ground solid sample, (D) the solid sample after the treatment with DCM vapor.
4

Y. Wang, H. Liu, Z. Chen et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 245 (2021) 118928
A 600
50
TPI+anions
B
-
TPI+CN +anions
40
30
20
10
0
4
00
00
0
-
CN
2
None + anions
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
k
2
2
3
2
4
I
4
3
r
3
2
4
3
N
3
3
4
F
O
4
4
Cl
O
O
O
B
O
500
600
700
800
an
C
O
O
CN
O
l
O
O
l
NO
CO
P
S
C
S
S
CO
3
C
2
P
B
HS
HS
H
HP
H
Wavelength (nm)
CH
Fig. 4. Alteration in the fluorescence spectra of TPI induced by the anions mentioned above in the DCM solution: (A) fluorescent spectral changes, (B) the change of fluorescence color
induced by various ions (Photographic images under 365 nm UV light), (C) Competitive tests for the emission intensities of TPI in the presence of CN− and other competing anions
(9.0 eq.).
These results indicated that the sensor TPI could also be used as a latent
increased with the addition of n-hexane until 80%. The emission wave-
length was blue-shifted, meanwhile the maximum n-hexane content
was 98%, the I/I value probably reached to 4.3, and the fluorescence
0
−
−
CN fluorescent sensor application. For the CN in a concentration
ranging from 0 to 9.0 eq., the emission intensities revealed a fine linear
relationship (Y = 44.8*X + 68.02857, R = 0.99098) (Fig. 5C). The de-
quantum yield were 0.23 and 0.419, respectively. The results indicated
−
1
−
tection limit was calculated to be 0.09258 μm L based on reported
that TPI-CN complex also had an AIE behavior.
means [53], which was much lower than the maximum contaminant
level (1.9 μm L ) for CN in drinking water set by the WHO.
With the purpose of confirming the feasibility of practical application
of sensor TPI, the test strips were made for the CN detection. Firstly, test
−1
−
−
strips were prepared by immersing filter papers into the DCM and n-
−5
−1
3
.5. Detection mechanism for CN−
hexane solutions of TPI (2 × 10 mol L ) for 10s and then dried in
air. As listed in Fig. S11, test paper strips showed that the blue-green fluo-
rescence was visible in the naked eyes under the 365 nm UV light, and the
result was consistent with the various n-hexane fraction. With the
1
The H NMR analysis further demonstrated the sensor TPI binding
−
−
from with CN in DMSO-d
–
6
(Fig. 6). Upon gradual adding of CN , the
−
NH proton signal (located at 13.76 ppm) of TPI declined gradually
treating of CN , the test strips quickly changed from blue-green to
until disappeared, which indicated the interaction of highly electroneg-
sodium-yellow in aggregation state and dark-yellow in non-aggregation
state. The test strip in aggregation state was more suitable for the CN de-
−
−
ative CN with –NH proton. To further verify the binding stoichiometry
−
of TPI-CN , Job's plot experiment was constructed by varying the molar
tection with more dramatic color changing than that in non-aggregation
state (Fig. S12). After treating different anions into the test strips of aggre-
−
fraction of CN from 0 to 1 under a constant total concentration
−5
−1
−
−
(
2.0 × 10
mol L ). The concentration of TPI + CN complex
gation state, it could be apparently noticed that only CN made a notable
achieved the maximum when the molar fraction of [TPI]/
fluorescence color change from blue-green to sodium-yellow under the
365 nm UV light (Fig. 7A), and the color of the test strips gradually
changed from dark yellow to light yellow under natural light (Fig. 7B).
The result indicated that the sensor TPI could be served as facilitation
−
(
[TPI] + [CN ]) was 0.5, which suggested stoichiometry between TPI
−
−
and CN was 1:1 (Fig. S8). The formation of TPI + CN complex was
further verified by the ESI mass spectrometry analysis (Fig. S9). TPI re-
vealed a main peak at 631.1 m/z ([TPI + H] ) and another major peak
+
−
test strips for a rapid detection of CN . Furthermore, the fluorescent
−
+
produced at 656.6 m/z as 9 eq. of CN added owing to [TPI-CN + H]
calculated 656.2). These results reinforced that the binding stoichiom-
color of the test strips gradually turned from blue-green to sodium-
−
(
yellow under the 365 nm UV light with the concentration of CN raising
−
−4
−1
etry between TPI and CN was 1:1.
from 0 to 2.5 × 10 mol L (Fig. 7C). All the above results demonstrated
the facilitation test strips of sensor TPI could be successfully used for
−
3.6. Practical application of aggregation induced emission
quantitative detecting CN .
To further elucidate the effect of cyanide ion on the AIE behavior of
3.7. The density functional theory (DFT)
TPI, the fluorescence changes of TPI-CN− complex in DCM/n-hexane
mixtures with the volume ratio of n-hexane were studied. The Fig. S10
To supplementary comprehended the relationship between the op-
tical property and electronic structure, the density functional theory
−
shown the fluorescence intensity of TPI-CN complex gradually
5

Y. Wang, H. Liu, Z. Chen et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 245 (2021) 118928
600
400
200
0
A
B 10
-
Original+CN
8
6
4
2
-
9
.0 eq / CN
0
500
600
700
800
0
2
4
6
8
10
-
Wavelength (nm)
CN equiv
Fig. 5. (A) The fluorescence variation of TPI induced by CN−. (B)The curve of fluorescent intensity ratio at 595 nm with the addition 0–9 eq. of CN−. (C) The limit of detection (LOD) was
determined to be 0.09258 μm/L.
(
DFT) calculations was by B3LYP/6-311G (d) basis set with the G09 pro-
transfer [54,55]. Nevertheless, the TPI-CN− compound, the electron dis-
tribution of HOMO was distributed the entire molecule. In contrast, the
electron distribution of LUMO was distributed in 5-phenyl-thiophene
and phenanthro[9,10-d]imidazole unit. Such a spatial frontier orbital
gram. As displayed in Fig. 8, for TPI molecule, the electron distribution of
HOMO was a majority of localizing on 5-phenyl-thiophene, phenanthro
[9,10-d]imidazole unit, while that of the LUMO was distributed in the
−
part of the 5-phenyl-thiophene and imidazole unit. The electrons of
LUMO orbital was mostly similar to the HOMO orbital electron distribu-
tion, which led to the certain restriction on intramolecular charge
distributions revealed that TPI-CN was easy to facilitate ICT processes
[50,56]. The calculated HOMO and LUMO energy levels for TPI were
− 0.19286 eV and − 0.06996 eV, respectively. However, TPI-CN− ex-
hibited a deeper HOMO (−0.20209) and LUMO (−0.08360) energy
−
level. The HOMO-LUMO band gaps in the TPI-CN (0.11849 eV) was
found to be lower than the TPI (0.1229 eV), which could be due to the
−
TPI-CN strong electron-withdrawing ability. These results of investi-
gations also corroborated, for instance, experimental observations of
red-shifted emission and large Stokes shifts (Table S2).
4
. Conclusion
In summary, a fluorescent sensor of CN− was successfully synthe-
sized based on a phenanthro[9,10-d]imidazole AIEgen-based (TPI),
and its utilization in highly selective and sensitive real-time naked-eye
detection was proved according to the transforming fluorescence and
visible color. Meanwhile, the sensor could be applied to qualitative
−
and quantitative detection of CN on test paper strips. The MFC behav-
ior, AIEE properties in two different solvent systems (DCM/n-hexane
and THF/H O), the large stokes shift, ICT process and outstanding optical
2
properties strongly proved the feasibility of our sensor design strategy.
The results in this paper would support new methods for the fluores-
cence sensors in practical application in the future.
Fig. 6. The 1H NMR spectra of TPI (red), TPI-CN− (blue) and TPI-CN− (black) in DMSO-d
6
−
upon the addition of 0 eq., 5.0 eq. and 9.0 eq. CN
.
6

Y. Wang, H. Liu, Z. Chen et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 245 (2021) 118928
Fig. 7. Photograph showing: (A) fluorescent color change of TPI on test paper strips after treating with various anions under 365 nm light, (B) visible color change of TPI on test paper strips
after treating with various anions under natural light, (C) Fluorescence photos of different concentrations of CN−(× 10 mol L ) on test paper strips.
−5
−1
Fig. 8. Optimized structures of TPI and TPI-CN−, HOMO and LUMO energy levels of TPI and TPI-CN−
.
CRediT authorship contribution statement
“Polymer Engineering Research Center”, Jiangxi Science and Technology
Normal University (KFGJ19019).
Yilan Wang: Investigation, Writing - original draft. Hongliang Liu:
Writing - review & editing, Supervision. Zhao Chen: Validation.
Shouzhi Pu: Project administration, Funding acquisition.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.saa.2020.118928.
Declaration of competing interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
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