A novel dibenzimidazole-based fluorescent organic molecule as a turn-off fluorescent probe for Cr3+ ion with high sensitivity and quick response

Article abstract of DOI:10.1016/j.molstruc.2020.127696

Due to the toxicity and ubiquity of chromium contamination, fluorometric detection of chromium ions (Cr³⁺) has attracted much attention. Here, a new fluorescent probe 4PBI-Cz based on novel dibenzimidazole group was designed and synthesized to

Full text of DOI:10.1016/j.molstruc.2020.127696

Journal of Molecular Structure 1206 (2020) 127696
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
A novel dibenzimidazole-based fluorescent organic molecule as a
turn-off fluorescent probe for Cr3þ ion with high sensitivity and quick
response
Aiyun Zhu, Jie Pan, Yan Liu, Feng Chen, Xinxin Ban*, Suyu Qiu, Yuhui Luo**,
Qingzheng Zhu, Jianmin Yu, Weiwei Liu***
Jiangsu Key Laboratory of Function Control Technology for Advanced Materials, School of Chemical Engineering, Jiangsu Ocean University, Lianyungang,
Jiangsu, 222005, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Due to the toxicity and ubiquity of chromium contamination, fluorometric detection of chromium ions
(Cr3þ) has attracted much attention. Here, a new fluorescent probe 4PBI-Cz based on novel dibenzimi-
dazole group was designed and synthesized to identify chromium ions. The photophysical and elec-
trochemical properties of 4PBI-Cz were characterized in detail. In view of the strong complexation
property, the fluorescence of 4PBI-Cz exhibit gradually turn-off phenomenon with the addition of
chromium ions. In particular, the response time of the probe with chromium ions was less than 1 s, faster
than most of the reported fluorescence probes. Moreover, the detection limit for chromium ions is only
3.5 nM, which can be attributed to the high sensibility of dibenzimidazole to the ions. This research
indicates that the new proposed dibenzimidazole group is an exciting recognition receptor for designing
Received 9 October 2019
Received in revised form
4 January 2020
Accepted 5 January 2020
Available online 6 January 2020
Keywords:
Bibenzimidazole
Fluorescent probe
Chromium ions
High sensitivity
quick response and ultrasensitive fluorescent probes for the determination of Cr3þ
.
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
absorption spectroscopy (AAS) and so on. However, the application
of mentioned traditional analytical methods are limited because of
the high cost of the instrument, the complexity of the operation,
and the time-consuming sample preparation [7e10]. Therefore, the
emergence of fluorescence method with the advantages of simple
operation, low cost, high selectivity, high sensitivity and rapid
response attracted the focus of researchers [11e14]. At present, no
specific recognition group to be complexed with Cr3þ [15e17],
which results in few articles about the fluorescence probe for
detecting chromium ion [18e21]. The most important thing is that
in this few articles, more research is based on different materials to
detect hexavalent chromium ions. For example, Wang et al. syn-
thesized a colorimetric fluorescent material based on metal-
organometallic framework to detect hexavalent chromium with a
Chromium is recognized as one of the eight micronutrients that
are indispensable to the human body [1]. From a medical point of
view, chromium can effectively regulate blood sugar and has a good
preventive effect on cardiovascular diseases caused by high
cholesterol [2,3]. In addition, chromium-based stainless steel plays
an important role in people’s lives. However, excessive levels of
chromium in the body inevitably cause irreparable damage to the
digestive system, and improper discharge of the plant using chro-
mium and its compounds will also cause dreaded heavy metal
contamination [4e6]. Therefore, it is very necessary and desirable
to find a method that can quickly, sensitively and selectively
identify chromium ions in the environment and test samples.
With the gradual advancement of detection technology, there
are many methods for detecting metal ions, such as atomic
detection limit of 0.21 mM [22]. Chen et al. proposed a method for
simultaneously identifying trivalent chromium and hexavalent
chromium by using chlorophyll fluorescence of moss [23]. Based on
the doped carbon point, Zhang et al. developed a fluorescence
method for hexavalent chromium ions whose detection limit is
5 nM and can be used in actual water samples [24]. Therefore, it is
still worthwhile to develop a novel fluorescent probe that can be
* Corresponding author.
** Corresponding author.
*** Corresponding author.
E-mail addresses: banxx@hhit.edu.cn (X. Ban), luoyh@hhit.edu.cn (Y. Luo),
liuww323@aliyun.com (W. Liu).
utilized to detect Cr3þ
.
https://doi.org/10.1016/j.molstruc.2020.127696
0022-2860/© 2020 Elsevier B.V. All rights reserved.

2
A. Zhu et al. / Journal of Molecular Structure 1206 (2020) 127696
In this work, a new group, dibenzimidazole, was proposed to
2.0 mmol), 1,10-Phenanthroline hydrate (0.40 g, 2.0 mmol) and
DMF (30.0 mL) were added to a 100 mL flask. The mixture was
heated to 160 ꢀC under nitrogen for 24 h. After cooling to room
temperature, the reaction mixture was extracted with dichloro-
methane and water. The combined organic layers were dried over
Na2SO4, filtered, and evaporated under reduced pressure. The crude
residue was purified by column chromatography with dichloro-
methane and petroleum ether as eluent to afford 3.80 g of white
design novel probe to detection of Cr3þ. The 4PBI-Cz was synthe-
sized by the palladium-catalyzed Suzuki reaction from the diben-
zimidazole and carbazole core. The fluorescence and absorption
spectra of the probes related to the concentration of chromium ions
were studied. When Cr3þ ions were added, the fluorescence in-
tensity of the probe was significantly quenched and had a linear
relationship with the chromium ion concentration ranging from
0 to 200 nM. Moreover, after adding chromium ions, the absorption
peak of the probe at 315 nm gradually disappeared, and a new
absorption peak appeared at 280 nm. Importantly, the response
time of the probe to Cr3þ is less than 1 s, which means that it can be
used for the immediate detection of chromium ions. Meanwhile,
the probe also exhibited high sensitivity to chromium ions with the
detection limits as low as 3.5 nM. These results demonstrated that
this new fluorescent probe base on dibenzimidazole group has the
advantages of high sensitivity and fast response property, which
would open up opportunities for design more probe used for the
detection of chromium ions.
solid, in 92.9% yield. 1H NMR (500 MHz, CDCl3,
d
): 7.94 (d, J ¼ 8.2 Hz,
2H), 7.65 (t, J ¼ 7.6 Hz, 2H), 7.54-7.47 (m, 5H), 7.40 (t, J ¼ 8.2 Hz, 2H).
2.3.2. 2-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-5-(1-
phenyl-1H-benzo[d]imidazol-2-yl)phenyl)-1-phenyl-1H-benzo[d]
imidazole
2-(3-bromo-5-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)-1-
phenyl-1H-benzo[d]imidazole (5.41 g, 10.0 mmol), bis(pinacolato)
diboron (3.05 g, 12.0 mmol), K2CO3 (4.17 g, 30 mmol), Pd(dppf)Cl2
(1.46 g, 2 mmol) and DMSO (30.0 mL) were added to a 100 mL flask.
The mixture was heated to 80 ꢀC under nitrogen for 24 h. After
cooling to room temperature, the reaction mixture was extracted
with dichloromethane and water. The combined organic layers
were dried over Na2SO4, filtered, and evaporated under reduced
pressure. The crude residue was purified by column chromatog-
raphy with dichloromethane and petroleum ether as eluent to
afford 3.25 g of white solid, in 55% yield. 1H NMR (500 MHz, CDCl3,
2. Experimental
2.1. General information
All reactants and solvents, unless otherwise stated, were pur-
chased from commercial sources and used as received. 1H NMR and
13C NMR spectra were measured on a BRUKER AMX 500-MHz in-
strument with tetramethylsilane as the internal standard. TGA was
recorded with a Netzsch simultaneous thermal analyzer (STA)
system (STA 409 PC) under a dry nitrogen gas flow at a heating rate
of 10 ꢀC minꢁ1. Glass-transition temperature was recorded by DSC
at a heating rate of 10 ꢀC minꢁ1 with a thermal analysis instrument
(DSC 2910 modulated calorimeter). The film surface morphology
was measured with AFM (Bruker, Dimension Edge). Absorption
spectra were recorded with a UVevis spectrophotometer (Agilent
8453) and PL spectra were recorded with a fluorospectropho-
tometer (Jobin Yvon, FluoroMax-3). Cyclic voltammetry was per-
formed on a Princeton Applied Research potentiostat/galvanostat
model 283 voltammetric analyzer in CH2Cl2 solutions (10ꢁ3 M) at a
scan rate of 100 mV sꢁ1 with a platinum plate as the working
electrode, a silver wire as the pseudo-reference electrode, and a
platinum wire as the counter electrode. The supporting electrolyte
was tetrabutylammonium hexafluorophosphate (0.1 M) and
ferrocene was selected as the internal standard. The solutions were
bubbled with argon for 10 min before measurements.
d
): 8.20 (s, 2H), 7.88 (d, J ¼ 7.9 Hz, 2H), 7.50 (s, 1H), 7.41 (t, J ¼ 7.2 Hz,
6H), 7.33 (dd, J ¼ 14.6, 7.3 Hz, 3H), 7.25 (d, J ¼ 5.4 Hz, 3H), 7.16 (d,
J ¼ 7.2 Hz, 4H), 1.27 (s, 12H). 13C NMR (500 MHz, CDCl3,
d): 137.2,
129.8, 128.7, 127.4, 119.7, 110.5, 84.0, 24.8. MS (MALDI-TOF) [m/z]:
calcd for C38H33BN4O2, 588.51; found, 588.43. Anal. Calcd. for
C
9.56.
38H33BN4O2: C, 77.55; H, 5.65; N 9.52. Found: C, 77.45; H, 5.70; N
2.3.3. 2,7-bis(3,5-bis(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)-
9-phenyl-9H-carbazole (4PBI-Cz)
2,7-dibromo-9-phenyl-9H-carbazole (1.0 g, 2.0 mmol), 2-(3-
(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-5-(1-phenyl-1H-
benzo[d]imidazol-2-yl)phenyl)-1-phenyl-1H-benzo[d]imidazole
(2.95 g, 5.0 mmol), K2CO3 (4.17 g, 12 mmol), Pd(PPh3)4 (0.012 g,
0.01 mmol), Toluene (30.0 mL), EtOH (15.0 mL) and H2O (5.0 mL)
were added to a 100 mL flask. The mixture was heated to 85 ꢀC
under nitrogen for 12 h. After cooling to room temperature, the
reaction mixture was extracted with dichloromethane and water.
The combined organic layers were dried over Na2SO4, filtered, and
evaporated under reduced pressure. The crude residue was purified
by column chromatography with dichloromethane and petroleum
ether as eluent to afford 1.40 g of white solid, in 60% yield. 1H NMR
2.2. Quantum chemical calculations
(500 MHz, CDCl3,
d
): 8.03 (d, J ¼ 8.1 Hz, 2H), 7.92 (s, 2H), 7.89 (d,
The geometrical and electronic properties of PPO-Cz and PPO-
3Cz were performed with the Gaussian 09 program package. The
calculation was optimized at the B3LYP/6-31G(d) level of theory.
The molecular orbitals were visualized using Gauss View.
J ¼ 7.8 Hz, 4H), 7.84-7.62 (m, 8H), 7.54 (d, J ¼ 7.3 Hz, 2H), 7.43 (t,
J ¼ 7.4 Hz, 10H), 7.38-7.24 (m, 21H), 7.11 (s, 2H), 7.00 (d, J ¼ 8.1 Hz,
2H). 13C NMR (500 MHz, CDCl3,
d): 144.88, 144.43, 138.94, 133.01,
132.58, 132.28, 132.13, 131.79, 131.78, 131.51, 131.45, 130.75, 130.46,
130.28, 130.07, 126.83, 126.45, 126.05, 125.19, 123.13, 122.65, 122.34,
113.21, 110.61. MS (MALDI-TOF) [m/z]: calcd for C82H53N9, 1164.3;
found, 1164.2. Anal. calcd for C82H53N9: C, 84.59; H, 4.59; N 10.83.
Found: C, 84.55; H, 4.62; N 10.74.
2.3. Synthesis
All reagents were used as purchased without further purifica-
tion. The DMF and DMSO were purified according to standard
procedures and distilled under nitrogen. The intermediate 2-(3-
bromo-5-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)-1-phenyl-
1H-benzo[d]imidazole was prepared according to the literature
procedure [25].
3. Results and discussion
3.1. Synthesis and characterization
The synthetic routes toward 4PBI-Cz was illustrated in Scheme
1. 4PBI-Cz was synthesized by the palladium-catalyzed Suzuki re-
action from benzimidazole and carbazole. The final product 4PBI-Cz
was obtained as a white solid in a yield of 60%. The target
2.3.1. 2,7-Dibromo-9-phenyl-9H-carbazole
2,7-dibromo-9H-carbazole (3.25 g, 10.0 mmol), 1-iodobenzene
(2.45 g, 12.0 mmol), K2CO3 (4.17 g, 30 mmol), CuI (0.38 g,

A. Zhu et al. / Journal of Molecular Structure 1206 (2020) 127696
3
Scheme 1. Synthetic routes toward 4PBI-Cz.
compounds were characterized by 1H NMR and 13C NMR.
3.2. Thermal properties
The thermal stability of 4PBI-Cz were investigated by thermal
gravimetric analyses (TGA) and differential scanning calorimetry
(DSC) under a nitrogen atmosphere at a heating rate of 10 ꢀC minꢁ1
.
As shown in Fig. 1, the fluorescent probe has high glass transition
temperature (Tg) and decomposition temperature (Td, corre-
sponding to 5% weight loss) of 192 and 485 ꢀC, respectively, which
can be attributed to the non-planar structure and higher molecular
weight of 4PBI-Cz. The excellent thermal stability is beneficial to
facilitate the morphological stabilities and the guarantee long-term
reliability of the fluorescent sensors. In order to demonstrate the
superiority of the fluorescent probe in film forming ability, the
solution-processed thin films of 4PBI-Cz were analysed by atomic
force microscope (AFM). As shown in Fig. 2, the roughness of the
4PBI-Cz is 0.64 nm and no aggregation is observed, which is
beneficial to improving the sensitivity of fluorescent probe and the
preparation of fluorescent sensors.
3.3. Theoretical calculations and electrochemical properties
Using tetrabutylammonium hexafluorophosphate (TBAPF6) as
the supporting electrolyte, the electrochemical behaviors of 4PBI-
Cz was investigated by cyclic voltammetry analyses (CV) in CH2Cl2
for anodic sweeping and anhydrous DMF for cathodic scans. As
shown in Fig. 3, the compound exhibited distinct oxidation and
reduction behaviors, and it was also observed that the initial
oxidation potential was 0.80 eV, whereby the highest occupied
Fig. 2. AFM 3D height image (6
m
m ꢂ 6
mm) of 4PBI-Cz.
Fig. 3. Cyclic voltammogram of 4PBI-Cz measured at room temperature in CH2Cl2 with
the scanning rate of 100 mV sꢁ1
.
molecular orbital (HOMO) and the lowest unoccupied molecular
orbital (LUMO) values of the compound were calculated
as ꢁ5.60 eV and ꢁ2.16 eV in combination with the previously
Fig. 1. TGA trace of 4PBI-Cz recorded at a heating rate of 10 ꢀC minꢁ1; inset: DSC
measurement recorded at a heating rate of 10 ꢀC minꢁ1
.

4
A. Zhu et al. / Journal of Molecular Structure 1206 (2020) 127696
obtained energy gap value.
increase of dipole moment from the ground state to the excited
state was calculated by Lipper-Mataga calculation. To determine
the change in dipole moment upon excitation, Lippert-Mataga
equation is used to express the Stokes shift as a function of the
To further understand the relationship of the physical properties
of the fluorescent probe, density functional theory (DFT) calcula-
tions were carried out on their molecular energy levels (Fig. 4). The
carbazole core is distinctly twisted by the phenyl benzimidazole
(PBI) moieties, leading to a nonplanar structure in 4PBI-Cz. The
HOMO and LUMO level of 4PBI-Cz are located at the carbazole units
solvent polarity parameter
Df (ε, n). The relevant values are calcu-
lated by following formulas:
À
Á
2
ꢀ
ꢁ
ꢀ
ꢁ
2
me
ꢁ
mg
and the benzene ring conjugated moieties. The HOMO and LUMO
energy of 4PBI-Cz were calculated to be -5.49 and -1.34 eV,
hc na
ꢁ
nf ¼ hc n0a
ꢁ
nf0
ꢁ
fðε; nÞ
(1)
(2)
a3
respectively, and the Eg was also calculated to be 4.15 eV. The en-
ergy levels of the FMOs can provide the referable information for
evaluating the carrier-injecting ability. The symmetrical structure
of 4PBI-Cz results in the close HOMO and HOMO -1 as well as LUMO
and LUMO þ1, which facilitates the intermolecular charge transfer.
For further simulating the emission properties, the TD-DFT was also
performed to calculated the exciton energy of the emitter. As the
result, the calculated singlet and triplet energies are 3.59 and
2.68 eV, respectively.
ε ꢁ 1
n2 ꢁ 1
fðε; nÞ ¼
ꢁ
2n2 þ 1
2ε þ 1
In Equation (1), G refers to the orientational polarizability of the
solvent, a-nf is the Stokes shift when G is zero, e corresponds to
the excited state dipole moment, g represents the ground-state
n
m
m
dipole moment; a is the solvent cavity (Onsager) radius, ε and n
refer to the solvent dielectric and the solvent refractive index,
respectively; f(ε,n) and a can be calculated respectively by Equation
(2). Through the investigation of the fitted line in high-polarity
solvents, the slope value of the fitted line was acquired
as ꢁ1324.54 cmꢁ1, and with Equation (1), the dipole moment can
be calculated as ꢁ1.05 ꢂ 10ꢁ3 D. It can be seen that the dipole
moment is small, suggesting that the absorption and emission
spectra are not affected by the polarity of the solvents, which is
beneficial to broaden the detection range and application condi-
tions of the probe, and the probe is not easily affected by a small
amount of other solvents in the sample during detection.
3.4. Photophysical properties
Fig. 5a shows the UV absorption spectrum of 4PBI-Cz in aceto-
nitrile. The absorption peak at 250 nm is attributed to
sition, while the absorption peak at 325 nm is attributed to n-
p-p* tran-
p*
transition. The energy gap value of 4PBI-Cz can be calculated from
the initial absorption band to be 3.52 eV. In the state of acetonitrile
as the solvent, the photoluminescence spectrum of the compound
was presented in Fig. 5b, the spectrum shows that the compound
peaks at 420 nm, which is a blue luminescent material. Moreover,
Fig. 5c exhibits the phosphorescence spectra at 77 K in toluene, and
the triplet energies is 2.58 eV for the compound based on the first
phosphorescent emission peak, which is in good agreement with
the theoretically calculated values.
To further investigate the photophysical properties, The PL
spectrum of the 4PBI-Cz was tested in solvents of different polar-
ities, as shown in Fig. 6 and Table 1, The compound exhibited a
significant solvation tendency, showing a pronounced red shift
from non-polar n-hexane to high polar DMSO. Meanwhile, this
3.5. Optical response of probe
In order to investigate the response of the probe to chromium
ions, the fluorescence and absorption spectra of the probe and
fluorescence titration were investigated. On the one hand, as shown
in Fig. 7a, with the addition of chromium ions, the absorption peak
at 315 nm gradually weakened and a new absorption peak
appeared at 280 nm which indicated that probe may be complexed
with Cr3þ. Moreover, the correlation relationship between the
Fig. 4. Molecular orbital amplitude plot calculated by B3LYP/6-31G(d).

A. Zhu et al. / Journal of Molecular Structure 1206 (2020) 127696
5
Fig. 5. (a) UVevis absorption in various solutions. (b) PL features in acetonitrile. (c) The PL spectra at low temperature 77 K. Inset the phosphorescence spectra of 4PBI-Cz after
delay.
Table 1
Spectral properties of 4PBI-Cz in different solvents.
solvents
D
f (ε, n)
4PBI-Cz
va
vf
Dv(va-vf)
n-hexane
toluene
CH2Cl2
THF
ethanol
methanol
DMF
0.0012
0.013
0.218
0.21
0.29
0.31
201 nm, 310 nm
206 nm, 311 nm
202 nm, 313 nm
204 nm, 309.5 nm
238 nm, 314 nm
244 nm, 315 nm
247 nm, 322 nm
414 nm
417 nm
415 nm
420 nm
419 nm
419 nm
418 nm
8103
8173
7852
8501
7981
7879
7132
0.27
between the intensity of the probe and the concentration of chro-
mium ions (R2 ¼ 0.99734) as we can see from Fig. 7c. Moreover, the
limit of detection can be calculated through the absolute value of
the slope in Fig. 7c after measuring the standard deviation of the
fluorescence intensity at 405 nm of ten blank samples by the
Fig. 6. Lipperte-Mataga plot of 4PBI-Cz in various solutions.
equation (LOD ¼ 3
x/k, where x is the standard deviation and k is the
absolute value of the slope). Hence, the LOD of probe was obtained
to be 3.5 nM which is much lower than the highest level of chro-
mium ions in drinking water regulated by WHO. As shown in
Fig. 7d, with the addition of Cr3þ, the probe responded to it and
completed the identification within 1 s, indicating that the probe
could be used for the instant identification of chromium ions. The
inset is derived from Fig. 7d, which is curve of the fluorescence
intensity at 405 nm related to time. In order to explore the com-
bination of chromium ions and probes, the Job’s plot experiment
was explored. The total concentration of metal ions and the probe
absorbance of the probe and the concentration of added chromium
ions was explored. As shown in Fig. S1, the absorption peak of the
probe at 315 nm showed an excellent linear correlation with the
Cr3þ concentration when the concentration was within the range
of 0e200 nm (R2 ¼ 0.98864). On the other hand, the fluorescence
response of probe was also studied. As we can see from Fig. 7b,
while with the advancing concentration of Cr3þ, the original fluo-
rescence intensity of the probe was clearly annihilated by metal
ions on account of the combination of probe and chromium ions.
It is worth noting that there is a good linear relationship
was 10
mM. As shown in Fig. 8, the turning point of the curve was at
the probe: chromium ion ¼ 0.5: 0.5. Therefore, it could be

6
A. Zhu et al. / Journal of Molecular Structure 1206 (2020) 127696
Fig. 7. (a) Normalized absorption spectra of probe in THF at 20 nM upon addition of Cr3þ (0e200 nM). (b) Fluorescence response of probe (20 M) upon addition of increasing Cr3þ
m
concentration in THF solution (0e10 eq). (lex ¼ 300 nm, EX slit ¼ 2.5 nm, EM slit ¼ 2.5 nm). (c) Linear fit between the intensity of probe at 405 nm and the titration concentration of
Cr3þ ranging from 0 to 200 nM lex ¼ 300 nm, Slits: 2.5 nm/2.5 nm. (d) Fluorescence intensity of probe (20 nM) versus time curve with the addition of 20 nM Cr3þ, insert: Time-
dependent fitting of fluorescence intensity at 405 nm.
Fig. 9. Molecular structure and the Cr3þ-sensing process of 4PBI-Cz.
fluorescent probe exhibited strong blue luminescence with an
emission band at 420 nm and further showed sensitive turn-off
fluorescence response to Cr3þ ion. Importantly, the response time
of the probe to chromium ions is as low as 1 s, which is the fastest
testing speed ever reported for Cr3þ ion. Moreover, the detection
limit of chromium ions is 3.5 nM, which is attributed to the
excellent coordination ability of benzimidazole units with chro-
Fig. 8. Job’s plot analysis.
mium ions. The results show that the novel fluorescent probe has
the advantages of high sensitivity and fast response, and can be
used for the detection of Cr3þ ion.
estimated that the binding ratio of chromium ions to the probe was
1: 1 (see Fig. 9).
4. Conclusions
Author contributions
In summary, we have designed and synthesized a novel fluo-
rescent probe 4PBI-Cz based on dibenzimidazole for identify
chromium ion. 4PBI-Cz exhibits excellent thermal stability with Td
and Tg temperatures of 485 and 192 ꢀC, respectively. The
Aiyun Zhu and Jie Pan conceived and designed the study. Yan
Liu, Feng Chen and Xinxin Ban performed the experiments. Suyu
Qiu and Yuhui Luo provided the theoretical calculation. Aiyun Zhu,
Jie Pan, Yan Liu, and Feng Chen wrote the paper. Qingzheng Zhu,

A. Zhu et al. / Journal of Molecular Structure 1206 (2020) 127696
7
[9] S.L. Yang, Y.Y. Yuan, P.P. Sun, T. Lin, C.X. Zhang, Q.L. Wang, 3D water-stable
Jianmin Yu, and Weiwei Liu reviewed and edited the manuscript.
All authors read and approved the manuscript.
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a multi-responsive luminescent
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Acknowledgements
We are grateful for the Grants from the National Natural Science
Foundation of China (21805106), the Natural Science Foundation of
Jiangsu Province (BK20181073), the Natural Science Fund for Col-
leges and Universities in Jiangsu Province (17KJB150007), the
Postdoctoral Science Foundation of China (1107040175), and the
Science Foundation of Huaihai Institute of Technology (KQ16025,
Z2016010). We also thank for the project supported by Scientific
and Technological Program of Lianyungang (JC1603, CG1602).
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