A novel dibenzimidazole-based fluorescent probe with high sensitivity and selectivity for copper ions

Article abstract of DOI:10.1016/j.jphotochem.2020.113018

A novel fluorescence probe TPA-BMZ for Cu²⁺, based on intramolecular charge transfer, was designed and synthesized. Probe was composed of triphenylamine as the fluorophore and benzimidazole derivative as the receptor. AFM measurement exhibits that TPA-BMZ possess an amorphous state without any crystallization, which benefits to its long-term stability due to application. Meanwhile, its optical character was studied and the results shown that TPA-BMZ could be used to recognize cupric ions in consequence of intramolecular charge transfer (ICT) and it even could be used to detect the presence of cupric ions in seawater. The Job's plot curve demonstrated the molar ratio of probe to copper is 1:1. Moreover, from the fluorescence titration spectrum of copper ions to probe, the limit of detection of probe is obtained (0.094 μM) and the complex constant is 6.57 × 10^?8 M^?1 which shows a high sensibility towards copper ions. In addition, probe was also used to detect copper ions in tap water, river water and seawater which demonstrated a potential application in seawater. More importantly, the response time of the probe to copper ions is within 1 s.

Full text of DOI:10.1016/j.jphotochem.2020.113018

Journal Pre-proof
A novel dibenzimidazole-based fluorescent probe with high sensitivity
and selectivity for copper ions
Jie Pan, Jianmin Yu, Suyu Qiu, Aiyun Zhu, Yan Liu, Xinxin Ban, Wen
Li, Hui Yu, Liantai Li
PII:
S1010-6030(20)30815-7
DOI:
https://doi.org/10.1016/j.jphotochem.2020.113018
JPC 113018
Reference:
To appear in:
Journal of Photochemistry & Photobiology, A: Chemistry
Received Date:
Revised Date:
Accepted Date:
7 August 2020
25 October 2020
29 October 2020
Please cite this article as: Pan J, Yu J, Qiu S, Zhu A, Liu Y, Ban X, Li W, Yu H, Li L, A novel
dibenzimidazole-based fluorescent probe with high sensitivity and selectivity for copper ions,
Journal of Photochemistry and amp; Photobiology, A: Chemistry (2020),
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A novel dibenzimidazole-based fluorescent probe with high sensitivity and
selectivity for copper ions
Jie Panab, Jianmin Yua, Suyu Qiua, Aiyun Zhua*, Yan Liua, Xinxin Bana*, Wen Lia, Hui Yua, Liantai Lib*
a School of Environmental and Chemical Engineering, Jiangsu Key Laboratory of Function Control Technology for
Advanced Materials, Jiangsu Ocean University, Lianyungang, Jiangsu, 222005, P.R. China
b Jiansu Key Laboratory of Marine Bioresources and Environment, School of Marine Life and Fisheries, Jiangsu
Ocean University, Lianyungang, Jiangsu, 222005, P.R. China
*Corresponding authors.
E-mail addresses: zhuay@jou.edu.cn (AY. Zhu), banxx@jou.edu.cn (XX. Ban), lilt@jou.edu.cn (LT. Li)
Graphical Abstract
The addition of copper ions formed a complex with benzimidazole, which prevented the
intramolecular charge effect and led to fluorescence quenching
Highlights
The bisbenzimidazole group has been demonstrate to coordinate with Cu2+


efficiently.


The response time between the probe and the metal ion is very fast (less than 1s).
The probe can be used as a test strip for actual water samples.
Abstract
A novel fluorescence probe TPA-BMZ for Cu2+, based on intramolecular charge transfer, was
designed and synthesized. Probe was composed of triphenylamine as the fluorophore and
benzimidazole derivative as the receptor. AFM measurement exhibits that TPA-BMZ possess an
amorphous state without any crystallization, which benefits to its long-term stability due to
application. Meanwhile, its optical character was studied and the results shown that TPA-BMZ
could be used to recognize cupric ions in consequence of intramolecular charge transfer (ICT) and
it even could be used to detect the presence of cupric ions in seawater. The Job’s plot curve
demonstrated the molar ratio of probe to copper is 1:1. Moreover, From the fluorescence titration
spectrum of copper ions to probe, the limit of detection of probe is obtained (0.094 μM) and the
complex constant is 6.57×10-8 M-1 which shows a high sensibility towards copper ions. In addition,
probe was also used to detect copper ions in tap water, river water and seawater which
demonstrated a potential application in seawater. More importantly, the response time of the probe
to copper ions is within 1 s.
Keywords: fluorescence probe; cupric; fluorescence; intramolecular charge transfer; optical
character
1. Introduction:
As one of the earliest metals is utilized by mankind, copper has been widely used in electrical and
mechanical manufacturing industries in modern technology, which greatly facilitates people's
daily life [1]. However, on one hand, it is a sensation to be excessive with copper in the human
body, as is the excess copper in the environment. On the other hand, Lack of copper is also a very
scary thing, because it often means that you are more likely to develop Alzheimer’s disease than
the general population [2-4]. Therefore, it is very important to quickly detect the concentration of
copper (II) ions in the surrounding living environment such as water, etc. [5-8]
.

At present, there are many detection methods based on different principles that can be used to
detect metal ions [9-14], whereas their applications are limited due to various shortcomings, such as
complicated operation. In contrast, fluorescent chemical sensors can detect concentration in
different environments including tap water, river water and even sea water, not to mention its
sensitivity and specificity [15-20]. Based on this, the number of researchers focusing on fluorescent
chemical sensors is advancing. Although the copper ion is not match for the other transition metal
ions in terms of heat, it is of necessary for us to enrich the molecular structure of copper ion
fluorescent chemical sensors. Imidazole is a five-membered aromatic heterocyclic compound with
two meta-nitrogen atoms in its molecular structure. and imidazole is also a familiar ligand in
metalloprotein. Tang et al. designed a probe 1 based on benzimidazole derivatives with a detection
limit of only 36 μM but the ability to detect copper ions in an aqueous environment [21]. Wang et al.
synthesized two probes with high sensitivity to copper ions by Schiff reaction [22]. Some literatures
based on benzimidazole also have been reported [23-25]. According to them, we found that the sp2
nitrogen in imidazole has a good binding affinity for Cu (II).
Actually, many fluorescent probes based on benzimidazole have been reported as metal sensors.
But most of them are only using the single benzimidazole unit as the recognition group. In this
work, we designed and synthesized a novel fluorescent chemical sensor TPA-BMZ based on
bisbenzimidazole group and triphenylamine which has a more faster coordination effect with
metal ions and a lower detection limitation than other reported copper ion fluorescent molecule.
The thermal, photophysical and electrochemical properties were investigated in detail. TPA-BMZ
possesses good thermal stability with high Td and Tg of 186 ℃ and 420 ℃, respectively. The
titration experiment of fluorescence and ultraviolet absorption spectra were measured and found to
be useful for identifying copper ions. The Job’s plot curve demonstrated the molar ratio of probe
to copper is 1:1. Meanwhile, the LOD (limit of detection) was measured as low as 0.094 μM by
studying the fluorescence intensity of probe with the changes of solvent, metal ions, amount of
copper ions. Moreover, probe was also used to detect copper ions in tap water, river water and
seawater which demonstrated a potential application in seawater.
2. Experimental section
2.1 Materials and measurements
Paraiodoanisole and parabromoaniline were purchased from Energy Chemical with the purity 99%.
Bis(pinacolato)diborane was obtained from Maya Reagent with the purity of 98%. And
[1,1’-bis(diphenylphosphino)ferrocene] dichloro palladium (II), complex with dichloromethane
was afforded by Shang Hai Macklin Biochemical co., Ltd. with the purity of 98%. All the solvents
were offered by the Tian Jin Yongda Chemical Reagent company Limited with the analytical pure.

All the solvents and the reagents are utilized directly without further purification. Fluorescence
spectra were measured by F4600 fluorescence spectrophotometer. The UV-vis absorption spectra
data are provided at room temperature through TU-1901 double beam UV-visible
spectrophotometer.
2.2 Synthesis
i: KOH, CuI, 1,10-Phenanthroline, Toluene; ii: [1,1’-bis(diphenylphosphino)ferrocene] dichloro palladium (II),
complex with dichloromethane, DMSO; iii: Pd (PPh3)4. toluene: ethanol: water
Scheme 1. The synthesis route of TPA-BMZ
As shown in Scheme 1, we synthesized the TPA-BMZ through three steps of Suzuki-Miyaura
coupling reaction with different reaction systems. Firstly, we synthesized the intermediate
products: 4-bromo-N, N-bis(4-methoxyphenyl) benzenamine (1) and ligand 2 by following the
steps of literatures [26,27]
.
Synthesis of TPA-BMZ
Br-BMZ was obtained from previous work [28]. To a 100 mL single-neck round-bottle flask,
a mixture of Br-BMZ (0.60 g, 1.1 mmol), compound 2 (0.431 g, 1 mmol), Pd(PPh3)4 (0.
0058 g, 0.005 mmol), K2CO3 (0.42 g, 3 mmol) was added into a solution of toluene:etha
nol:water (12 mL: 6 mL: 2mL), the resulting mixture was whisked constantly and refluxed
26 h under nitrogen atmosphere. The reaction was monitored by TLC, after evaporation
of the solvent, the pure product TPA-BMZ was obtained by column chromatography on
silicagel eluented with DCM: ethyl acetate = 10:1. (0.55 g, 71%).1H NMR (500 MHz, CDCl
3) δ 7.99 (d, J = 11.6 Hz, 1H), 7.88 (dd, J = 7.6, 4.5 Hz, 2H), 7.63 - 7.56 (m, 2H), 7.53 - 7.4

2 (m, 6H), 7.38 - 7.32 (m, 2H), 7.28 (dd, J = 9.5, 5.2 Hz, 8H), 7.04 (ddd, J = 8.6, 5.3, 2.9 Hz, 4
H), 6.84 (ddd, J = 11.8, 5.9, 3.1 Hz, 8H), 3.81 (s, 6H);13C NMR (126 MHz, CDCl3) δ 156.03, 151.
77, 148.55, 143.05, 140.71, 140.58, 137.13, 136.86, 131.19, 130.72, 129.96, 128.68, 128.63, 128.4
6, 127.55, 127.43, 126.72, 123.49, 123.06, 120.37, 120.06, 114.76, 110.50, 77.30, 77.05, 76.80, 55.
51.
3. Results and discussion
3.1 Thermal properties
The thermal stability of TPA-BMZ were discussed by TGA (thermal gravimetric analyses) and
DSC (differential scanning calorimetry) under a nitrogen atmosphere at a heating rate of 10 ℃
min-1. Due to the bulky and non-planar structure of TPA-BMZ, as demonstrated in Figure. 1 (a),
(b), the probe has satisfactory glass transition temperature (Tg), melting temperature (Tm) and
decomposition temperature (Td, 5% weightlessness temperature) of 186 ℃, 276 ℃ and 420 ℃,
respectively. The high Td and Tg demonstrate the good thermal stability of TPA-BMZ.
Figure. 1. (a) DSC curve of probe recorded at heating rate of 10 ℃ min-1; (b) TGA analysis of TPA-BMZ
recorded at heating rate of 10 ℃ min-1.
The good thermal stability will benefit to the morphological stability of the fluorescence sensor.
For the sake of further proving the superiority of fluorescent probe in film forming capacity, the
solution-treated probe thin films were analyzed by AFM (atomic force microscope). As exhibited
in Figure. 2, the probe film has no aggregation phenomenon, which improves the sensitivity and
long-term stability of the fabricated fluorescent sensor. Meanwhile, the phase image was also
provided in the manuscript and the average roughness was calculated to be 0.95 nm. Such a small
roughness is benefit for the uniform film formation in the testing paper. As for the concentration

dependent properties, we measured the fluorescence change at different concentration. As shown
in Figure , during the concentration increase from 10-5 to 10-3,the PL intensities are gradually
enhanced, which means no aggregation quenching effect at such a wide concentration range.
Figure. 2. AFM 3D image of TPA-BMZ
3.2 Theoretical calculations and electrochemical properties
The cyclic voltammetry (CV) was used to investigate the electrochemical behavior of compound
in DCM for anode scan while tetrabutylammonium perchlorate was used as supporting
electrolyte. Platinum disk electrode, silver wire and platinum wire are working electrode,
reference electrode and counter electrode respectively. As shown in Figure. 3, the material
demonstrated unique oxidation behaviors, and the initial oxidation potential of 0.76 V was
observed, which corresponds to the highest occupied molecular orbital (HOMO) values of the
compound were calculated as -5.23 eV (HOMO=-(Eox - 0.40 + 4.8) eV).

Figure. 3. Cyclic voltammogram of probe dissolved in DCM
To get inside to the electronic properties of the probe, density functional theory (DFT)
calculations were performed. As shown in Figure. 4, HOMO was distributed to triphenylamine
unit, while LUMO was located on benzimidazole. The calculated HOMO was -4.44 eV, while
LUMO was -1.62 eV, and energy gap (Eg) of the probe was 2.82 eV. To further simulate the
emission characteristics, time dependent DFT (TD-DFT) was also performed to calculate the
exciton energy of TPA-BMZ. As a result, the singlet energy was calculated to be 3.05 eV and
triplet energy was 2.70 eV, which corresponds to the typical blue emission.
Figure. 4. Theoretical calculations of TPA-BMZ
3.3 Photophysical properties of probe
The fluorescence spectra of probe were measured after probe was dissolved in organic solvent. As
shown in Figure. 5a, different fluorescence spectra curves were measured with TPA-BMZ
dissolved in solvents, and it demonstrated an obvious advancing Stokes’ shift with increasing
polarity (toluene, DCM, acetone, acetonitrile, methanol), which put down to the π-π* transition of
conjugated system of the probe TPA-BMZ with the electron-withdrawing group and
electron-donating group. Because of the coactions between donor triphenylamine and acceptor
benzimidazole, the intramolecular charge transfer effect occurred. Meanwhile, Figure. 5b
demonstrated the ultraviolet absorption spectrum of TPA-BMZ in acetonitrile, the absorption peak
at 210 nm is attributed to n-σ transition while the absorption peak at 300 nm is attributed to n-π*
transition. As a result, the energy gap of probe can be calculated to be 3.2 eV.

As shown in Table 1 and Figure. 5a, the solvation of TPA-BMZ was further studied. The probe
material shows up an obvious red-shift phenomenon. Since the stokes displacement was a function
of the solvent polarity parameter △f (ξ, n), the change of dipole moment was determined by
Lippert-mataga equation:
As shown in Figure. 5c, the fitted line in different polarity solvents was studied, and the slope
value of the fitted line was 13803.83 cm-1. Thus, the dipole moment was calculated as 13.5 D.
There is no doubt that the dipole moment of the fluorescent probe is very small, which indicates
that the absorption and emission spectra are affected by the polarity of the solvent.
Figure.5. (a) Fluorescence emission (b)UV-vis absorption spectra of TPA-BMZ in the organic solvent acetone,
DCM, toluene, acetonitrile, methanol, at a probe concentration of 10-5 mol/L. (c) Lipperte-Mataga plot of probe in
different solvents
Table 1. Spectral properties of probe in different solvents
TPA-BMZ
va-vf (cm-1)
solvents
λabs (nm)
λf (nm)
f(ξ,n)

Toluene
DCM
0.013
0.218
0.284
0.305
0.308
307
399
435
448
470
495
7511
10124
8260
230,302
327
Acetone
Acetonitrile
Methanol
210,302
214,297
11836
13400
3.2 Optical properties of the probe
The metal ions chosen are nitrates and were soluble in distilled water. Acetonitrile was selected to
dissolve the probe for the following tests of fluorescence and UV spectroscopy, and considering
water solubility and toxicity. It is the same solvent as the benzimidazole-based probes selected in
other literatures [29,30]. As shown in Figure 6, the fluorescence intensity of the probe with different
metal ions (Na+, Ba2+, Ca2+, Cr3+, Cu2+, Pb2+, K+, Mg2+, Mn2+, Ni2+, Al3+) added were measured. It
is worth noting that the red shift occurs in the probe solution after the addition of metal ions,
which is caused by the increase of polarity of the original pure acetonitrile solution after the
addition of metal ions in the aqueous solution. Therefore, the red shift is not caused by the
complexation between metal ions and the probe. Probe was slightly affected by Al3+ and Na+.
Additionally, compared to other metal ions, the probe was greatly quenched by copper ions.
Figure. 6. (a) Fluorescence intensity (b) absorption spectra of 10-5 M probe with different metal ions (10eq)
To further explore the effect of copper ions on the probe, the spectral properties of dropping
different equivalents of copper ions into TPA-BMZ dissolved in acetonitrile were tested. As seen
in Figure. 7a, excitation wavelength at 350 nm and excitation slit at 2.5 nm, emission slit at 5.0 nm,
the decreasing fluorescence intensity of probe can be found with the addition of Cu2+
concentration, in addition, peak of emission spectrum had a distinct red-shift. It was apparent that
copper ions had a combination with TPA-BMZ. In addition, as Figure. 7b demonstrated, a slight

Stokes shift occurred (from 211 nm to 221 nm). Hence, TPA-BMZ was combined with Cu2+ which
could be used to detect cupric ions.
In order to obtain the limit of detection of TPA-BMZ, as shown in Figure. 7e, fluorescence
intensity of TPA-BMZ was measured with the addition of cupric ions and found a linear
correlation between them (R2 = 0.98846). As a result, detection limit of probe is 94 nM which is
obtained by the formula LOD = 3ξ / k (ξ is the standard deviation of fluorescence intensity at 472
nm of nine blank sample solution, meanwhile k is the absolute value of the slope of the linear
equation of probe intensity at 472 nm and cupric ions concentration).

Figure. 7. (a) Fluorescence intensity of probe with titration of Cu2+ (0-10eq); (b) absorption spectra of TPA-BMZ
with titration of copper (II); (c) Fluorescence intensity of TPA-BMZ at 10 μM with Cu2+ at concentration of 5
equip while other metal ions at concentration of 20 equiv ( in order, Na+, Ba2+, Ca2+, Cr3+, Cu2+, Pb2+, K+, Mg2+,
Mn2+, Ni2+, Al3+ ); (d) Fluorescence spectra changes with advancing pH values; (e)Linear relationship between
fluorescence response at 472 nm of TPA-BMZ and Cu2+ (0-10 μM); (f) Job’s plot curve of TPA-BMZ; (g) Linear
fitting of probe to Cu2+ binding constant
Furthermore, in order to study the practicability and metal ion competition of the probe, the
same equivalent copper ion was added dropwise to the probe solution of metal ions ( in order, Na+,
Ba2+, Ca2+, Cr3+, Cu2+, Pb2+, K+, Mg2+, Mn2+, Ni2+, Al3+ ), and the results were explored. As shown
in Figure. 7c, the probe was quenched significantly by copper (II) ions even in the presence of
other metal ions. To prove its potential application in biology, the pH influence on the optical
spectra of the TPA-BMZ was investigated by measuring fluorescence intensity of probe without
cupric ions and probe with the same number of cupric ions but different pH values. As shown in
Figure. 7d, the fluorescence intensity of TPA-BMZ augmented slightly which can be attributed to
the effect of proton transfer on the probe. Moreover, stabilized optical response towards Cu2+ can
be seen with the pH values range from 4 to 9 which indicated that probe have the possibility of
detecting copper ions in most nature water (lake, river, seawater). Additionally, fluorescence
intensity of TPA-BMZ increased with the pH > 9 excepting pH = 13.
In order to obtain the limit of detection of TPA-BMZ, as shown in Figure. 7e, fluorescence
intensity of TPA-BMZ with the addition of cupric ions were measured and a linear correlation
between them (R2 = 0.98846) was found. As a result, detection limit of probe is 0.094 µM which
is obtained by the formula LOD = 3ξ / k (ξ is the standard deviation of fluorescence intensity at
472 nm of nine blank sample solution, meanwhile k is the absolute value of the slope of the linear
equation of probe intensity at 472 nm and cupric ions concentration). The binding constant was

also calculated from the fluorescence spectrum titration data by using the Benesi-Hildebrand (B-H)
1
1
1
formula: I−I
=
+
. I0 and I respectively represent the fluorescence
−퐼
0
2+
퐾
푎
(퐼
푚푎푥
−퐼 )(퐶푢
)
퐼
0
0
푚푎푥
intensity of probe TPA-BMZ and probe TPA-BMZ after adding copper ions, Imax represents the
maximum fluorescence intensity of the probe when lead ions are excessive, (Cu2+) represents the
concentration of copper ions added. As shown in the Figure 7g, the linear relationship between
1/(I－I0) and 1/(Cu2+), and its linear correlation coefficient R2 = 0.9917, and Ka is 6.57×10-8 M-1.
Job’s plot curve is a common method to obtain the combination ratio in the field of analytical
chemistry. As shown in Figure. 7f, the absorption peak reached its maximum value when the
molar ratio of probe to copper is 1:1, indicating that the complexing constant is 1. Hence, the
possible combination mode of TPA-BMZ and Cu2+ was shown in Figure. 8 (a).
Figure. 8. (a) Mechanism diagram of probe towards cupric ions; (b) infrared spectra of probe and probe
response to Cu (II)
In order to verify the practicability of TPA-BMZ in actual water samples, the probe was used to

measure copper ions in three samples from different environments (river, sea water and tap water),
and the fluorescence spectrum as shown in Figure 9 was used to explore the results. As shown in
Figure. 9a, the probe intensity was slightly quenched in tap water, proving that there was no
excess copper ions in tap water. However, in the case of adding seawater, the fluorescence
intensity of the probe decreased by one third, which was higher than that in tap water and river
water. According to the results in Figure 6, the probe may be slightly quenched due to the presence
of sodium ions in seawater. As shown in Figure. 9b, in the three actual water samples with probes,
the fluorescence intensity after adding copper ions and that of the probes quenched by copper ions
in pure acetonitrile solution had little change. This suggests that water sample differences do not
affect the probe response to copper ions, and TPA-BMZ can be used in complex water sample
environments. In addition, the recovery rate is an essential factor for practicality. As shown in
Table 2, the recovery rate of the three water samples is between 100 plus or minus 2%. The high
recovery and low relative error of the probe prove its excellent performance in the identification of
copper ions in water samples. Moreover, AFM measurement exhibits that TPA-BMZ possess an
amorphous state without any crystallization, which benefits to its long-term stability due to
application. As a result, the sensing of TPA-BMZ to Cu2+ on test paper also need to be tested. As
demonstrated in Figure. 9c, four test paper were prepared, which has strong luminescence under
UV lamp. After drop the sample water, which contains Cu2+ with the same concentration (10-6 M),
the fluorescence was completely quenched at the contacting range. It is demonstrate our newly
designed probe can be successfully used as test paper for actual detection.

Figure 9. Fluorescence intensity of actual water samples with (a) probe concentration of 2 µM; (b) 2 µM of
probe and Cu2+; (c) Probe test paper test (from left to right, arrange in the order of no water
sample, river water sea water, and tap water)
Table 2. Recovery of probe in three kinds of water samples
Sample
River water
Sea water
Tap water
Added (M)
2.0 × 10-6
2.0 × 10-6
2.0 × 10-6
Detected (M)
2.04 10-6
1.98 10-6
1.96 10-6
Recovery (%)
Relative error (%)
102
99
2
1
2
98
Response time is a non-negligible factor in actual sample detection with fluorescent probes. As
shown in Figure 10(a), the probe completes the complexation within 1 s after the addition of
copper ions, and the fluorescence intensity remained basically unchanged after 1 s.
Figure 10. (a) Fluorescence intensity of TPA-BMZ (20 nM) versus time curve with the addition of 20 nM
Cu2+; (b) Response time fitting of fluorescence intensity at 488 nm.
4. Conclusions
In this paper, we have successfully synthesized a novel fluorescence probe TPA-BMZ for Cu2+.
Probe material presents outstanding thermal stability with Tg 186 ℃ and Td 420 ℃. More
importantly, its optical response was studied and results demonstrated that cupric ions quench
probe’s fluorescence intensity by intramolecular charge transfer effect whether the interfering ions
existed or not. In addition, fluorescence response of probe with advancing pH values was detected

and TPA-BMZ can be used in complex water sample environments. Moreover, an admirable
detection limit of TPA-BMZ is 0.094 μM, which was acquired with fluorescence titrimetric
method. The outstanding properties of the probe TPA-BMZ will contribute to extending further
study on selective detection of Cu2+ and providing inspiration for the detection of the other metal
ions.
Author Statement
Jie Pan and Jianmin Yu conceived and designed the study. Aiyun Zhu, Suyu Qiu and
Yan Liu performed the experiments. Xinxin Ban, Wen Li and Hui Yu provided the
theoretical calculation. Jie Pan, Yan Liu, and Suyu Qiu wrote the paper. Aiyun Zhu,
Jianmin Yu, and Liantai Li reviewed and edited the manuscript. All authors read and
approved the manuscript
Declaration of interests
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.
We declare that we do not have any commercial or associative interest that represents a conflict of
interest in connection with the work submitted.
Acknowledgement
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
Colleges and Universities in Jiangsu Province (17KJB150007), the Postdoctoral Science
Foundation of China (1107040175), and the Science Foundation of Huaihai Institute of
Technology (KQ16025, Z2016010). The First-class Undergraduate Majors Construction Program
of Jiangsu Province, the Key Discipline Construction Program of Jiangsu Province, a Project
Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions
(PAPD). The Postgraduate Research & Practice Innovation Program of Jiangsu Province
(KYCX19_2293). We also thank for a project funded by the priority academic program
development of Jiangsu Higher Education Institutions (PAPD) and the project supported by
Scientific and Technological Program of Lianyungang (JC1603, CG1602).

References
[1] He C, Zhou H, Yang N, Niu N, Hussain E, Li Y, et al. A turn-on fluorescent BOPHY probe for
Cu2+ ion detection. New J. Chem. 2018, 42, 2520.
[2] Li Y, Han X, Song Y. An azo-phenol derivative probe: colorimetric and “turn-on” fluorescent
detection of copper (II) ions and pH value in aqueous solution. RSC Adv 2017, 7, 20537.
[3] Xiao N, Zhang C. Selective monitoring of Cu (II) with a fluorescence–on naphthalene–based
probe in aqueous solution. Inorg Chem Commun 2019, 107, 467.
[4] Liu X, Zhang Y. A Readily-Synthesized Fluorescent Probe Based on N, N-Bis
(Pyridin-2-Ylmethyl) Aniline for Copper (II) Detection in Aqueous Solution. J Fluoresc 2016,
26, 2267.
[5] Wu X, Wang H, Yang S, Tian H, Liu Y, Sun B. A novel coumarin-based fluorescent probe
for sensitive detection of copper (II) in wine. Food Chem 2019, 284, 23.
[6] Xu J, Wang Z, Liu C, Xu Z, Zhu B, Wang N, et al. A Colorimetric and Fluorescent Probe for
the Detection of Cu2+ in a Complete Aqueous Solution. Anal Sci 2018, 34, 453.
[7] Y. Li, M. Sun, K. Zhang, Y. Zhang, Y. Yan, K. Lei, L. Wu, H. Yu, S. Wang, A near-infrared
fluorescent probe for Cu2+ in living cells based on coordination effect, Sensors Actuators, B
Chem. 243 (2017) 36–42.
[8] Lee DY, Singh N, Jang DO. A benzimidazole-based single molecular multianalyte fluorescent
probe for the simultaneous analysis of Cu2+ and Fe3+. Tetrahedron Lett 2010, 51, 1103.
[9] R. Sun, L. Wang, C. Jiang, Z. Du, S. Chen, W. Wu, A Highly Efficient BODIPY Based
Turn-off Fluorescent Probe for Detecting Cu2+, J. Fluoresc. 30 (2020) 883–890.
[10] Li G, Zhang D, Liu G, Pu S. A highly selective fluorescent probe for Cd2+and Zn2+ based on a
new diarylethene with quinoline–benzimidazole conjugated system. Tetrahedron Lett 2016,
57, 5205.
[11] Hu Q, Tan Y, Liu M, Yu J, Cui Y, Yang Y. A new highly selective and sensitive fluorescent
probe for Zn2+ and its application in cell-imaging. Dye Pigment 2014, 107, 45.
[12] Bai JY, Xie YZ, Wang CJ, Fang SQ, Cao LN, Wang LL, et al. A Quninolylthiazole
Derivatives as an ICT-Based Fluorescent Probe of Hg (II) and its Application in Ratiometric
Imaging in Live HeLa Cells. J Fluoresc 2018, 28, 795.

[13] Tan Y, Gao J, Yu J, Wang Z, Cui Y, Yang Y, et al. A new fluorescent probe for
2+
distinguishing Zn2+ and Cd
11465.
with high sensitivity and selectivity. Dalt Trans 2013, 42,
[14] Guo B, Liu Q, Su Q, Liu W, Ju P, Li G, et al. A triphenylamine-functionalized fluorescent
organic polymer as a turn-on fluorescent sensor for Fe3+ ion with high sensitivity and
selectivity. J Mater Sci 2018, 53, 15746.
[15] Jung HJ, Singh N, Jang DO. Highly Fe3+ selective ratiometric fluorescent probe based on
imine-linked benzimidazole. Tetrahedron Lett 2008, 49, 2960.
[16] Li Q, Wang Z, Song W, Ma H, Dong J, Quan YY, et al. A novel D-π-A triphenylamine-based
turn-on colorimetric and ratiometric fluorescence probe for cyanide detection. Dye Pigment
2019, 161, 389.
[17] Lai H, Xiao Y, Yan S, Tian F, Zhong C, Liu Y, et al. Symmetric cyanovinyl-pyridinium
triphenylamine: A novel fluorescent switch-on probe for an antiparallel G-quadruplex.
Analyst 2014, 139, 1834.
[18] Tan Y, Liu M, Gao J, Yu J, Cui Y, Yang Y, et al. A new fluorescent probe for Zn2+ with red
emission and its application in bioimaging. J Chem Soc Dalt Trans 2014, 43, 8048.
[19] Wang L, Yang X, Chen X, Zhou Y, Lu X, Yan C, et al. A novel fluorescence probe based on
triphenylamine Schiff base for bioimaging and responding to pH and Fe3+. Mater Sci Eng C
2017, 72, 551.
[20] Zhao M, Deng Z, Tang J, Zhou X, Chen Z, Li X, et al. 2-(1-Pyrenyl) benzimidazole as a
ratiometric and “turn-on” fluorescent probe for iron(iii) ions in aqueous solution. Analyst
2016, 141, 2308.
[21] Tang L, Cai M, Huang Z, Zhong K, Hou S, Bian Y, et al. Rapid and highly selective relay
recognition of Cu (II) and sulfide ions by a simple benzimidazole-based fluorescent sensor in
water. Sensors Actuators, B Chem 2013, 185, 188.
[22] Wang X, Xu T, Duan H. Schiff base fluorescence probes for Cu2+ based on imidazole and
benzimidazole. Sensors Actuators, B Chem 2015, 214, 138.
[23] Misra A, Ali R. Imidazole and oxazole containing fluorescent dyad: Cu2+ induced
fluorescence quenching and cyanide sensing "On-Off-On " via copper displacement approach.
Indian J Chem - Sect B Org Med Chem 2018, 57B, 217.

[24] Grüter A, Hoffmann M, Müller R, Wohland T, Jung G. A high-affinity fluorescence probe for
copper (II) ions and its application in fluorescence lifetime correlation spectroscopy. Anal
Bioanal Chem 2019, 411, 3229.
[25] Mahiya K, Mathur P. Bis-benzimidazolyl diamide based fluorescent probe for copper (II):
Synthesis, structural and fluorescence studies. J Fluoresc 2013, 23, 767.
[26] Hu W, Zhang Z, Cui J, Shen W, Li M, He R. Influence of π-bridge conjugation on the
electrochemical properties within hole transporting materials for perovskite solar cells.
Nanoscale 2017, 9, 12916.
[27] Sil MC, Kavungathodi MFM, Nithyanandhan J. Effect and position of
spiro-bipropylenedioxythiophene π-spacer in donor-π-spacer-acceptor dyes for dye-sensitized
solar cell. Dye Pigment 2019, 161, 313.
[28] Jiang W, Ban X, Sun Y. Enhanced electron affinity and charge balance property of a bipolar
material: highly efficient solution-processed deep blue electrofluorescent and green
electrophosphorescent devices. RSC Adv 2015, 5, 66994.
[29] Okda HE, El Sayed S, Otri I, Ferreira RCM, Costa SPG, Raposo MMM, et al. A simple and
easy-to-prepare imidazole-based probe for the selective chromo-fluorogenic recognition of
biothiols and Cu (II) in aqueous environments. Dye Pigment 2019, 162, 303.
[30] Goswami S, Maity S, Maity AC, Maity AK, Das AK, Saha P. A FRET-based
rhodamine-benzimidazole conjugate as a Cu2+- selective colorimetric and ratiometric
fluorescence probe that functions as a cytoplasm marker. RSC Adv 2014, 4, 6300.