A thiophene-derived hexaazatriphenylene (HAT) fluorescent sensor for the selective detection of Ag+ ion

Article abstract of DOI:10.1016/j.tetlet.2021.152911

Herein, by symmetrically merging six thiophene units into the hexaazatriphenylene (HAT) core, a HAT-based sensor (1) was designed and synthesized, which was found capable of exhibiting selective recognition of Ag⁺ with detection limit as low as 1.79 × 10^?6 M in chloroform featuring with significant fluorescence “turn-off” property. Through the systematical investigation with UV–Vis absorption, fluorescence spectroscopy and the naked-eye experiments, as well as the ¹H NMR titration and the Job's plot, it was revealed that sensor 1 could complex with Ag⁺ in a stoichiometric ratio of 2:3. We envisage the construction of such a thiophene-derived HAT molecule is conducive to exploring new type of Ag⁺ sensors, and it also will bring potential application in environmental detection.

Full text of DOI:10.1016/j.tetlet.2021.152911

Tetrahedron Letters 68 (2021) 152911
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A thiophene-derived hexaazatriphenylene (HAT) fluorescent sensor
+
for the selective detection of Ag ion
Xiang Zhang a, , Yu Fan , Tian-Guang Zhan , Qiao-Yan Qi , Xin Zhao
⇑
b
c
b
b,
⇑
a
College of Chemical Engineering, Hunan Chemical Vocational Technology College, Zhuzhou 310027, China
Key Laboratory of Synthetic and Self-Assembly Chemistry for Organic Functional Molecules, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai
00032, China
Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, College of Chemistry and Life Science, Zhejiang Normal University, 688 Yingbin Road, Jinhua 321004,
China
b
2
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Herein, by symmetrically merging six thiophene units into the hexaazatriphenylene (HAT) core, a HAT-
Received 17 November 2020
Revised 18 January 2021
Accepted 4 February 2021
Available online 9 February 2021
based sensor (1) was designed and synthesized, which was found capable of exhibiting selective recog-
+
À6
nition of Ag with detection limit as low as 1.79 Â 10 M in chloroform featuring with significant fluo-
rescence ‘‘turn-off” property. Through the systematical investigation with UV–Vis absorption,
1
fluorescence spectroscopy and the naked-eye experiments, as well as the H NMR titration and the
+
Job’s plot, it was revealed that sensor 1 could complex with Ag in a stoichiometric ratio of 2:3. We envis-
Keywords:
+
age the construction of such a thiophene-derived HAT molecule is conducive to exploring new type of Ag
Host-guest systems
+
sensors, and it also will bring potential application in environmental detection.
Ag sensor
Ó 2021 Elsevier Ltd. All rights reserved.
Ion recognition
Hexaazatriphenylene
+
Introduction
tools. In this context, a vast number of Ag sensors with conjugated
aromatic structures such as fluorescein, [23] rhodamine, [24] rho-
The design and construction of chemosensors targeting cations
1-5] or anions [6-10] of biological, chemical and environmental
danine, [25] boron-dipyrromethene,[26,27] 1, 8-naphthalimide,
[28,29] coumarin,[30] anthracene,[31] isoquinoline,[32] phena-
zine,[33,34] as well as polymers[35] have been extensively
explored, benefiting from the distinctive characteristics of exten-
[
importance is one of vibrant areas in supramolecular chemistry.
+
Silver ion (Ag ), on one hand, plays an indispensable role in a wide
range of fields such as pharmacy,[11] catalysis,[12,13] and
supramolecular self-assembly.[14-16] On the other hand, the uti-
lization of silver compounds causes unavoidable negative impact
sive p-electron delocalization and strong fluorescent emission.
Hexaazatriphenylene (HAT),[36] which is a rigid planar conju-
gated motif with the feature of easy derivatization and plentiful
N-containing coordinative sites, has been extensively explored
not only to fabricate self-assembly systems but also as fluorescent
probes for ion recognition. In our previous work, a series of HAT-
based derivatives were developed to achieve the selective detec-
+
on the environment, and long-term and excess intake of Ag will
lead to healthy problem such as stomach distress, skin irritation,
disruptive renal and neurological functions.[17-19] Owing to the
+
duplicitous effects of Ag ion, the development of new chemosen-
À
2+
sors for the excellently selective, instantly responsive and efficient
tion of F ,[37] Cu ,[38] and even proton-anion ion-pair.[39] More-
over, Bu and co-workers have showed that pyridine-derived HAT
+
detection of Ag is highly desirable.
2
+
Traditional approaches such as atomic absorption spectrometry,
molecules could be applied as Cd fluorescent sensors.[40,41]
However, the HAT-based molecules have rarely been used as selec-
[
20] inductively-coupled plasma emission mass spectrometry [21]
+
and electrochemical method [22] have been utilized to monitor the
tive fluorescent probes for Ag so far. Aiming to enrich the struc-
+
+
existence of Ag . However, these strategies commonly suffer from
tural diversity of Ag chemosensors and expand the application
disadvantages of high-cost, time-consuming and labour-intensity.
Comparatively speaking, fluorescent probes featuring with easy
operation, high selectivity and sensitivity are more preferable
scope of HAT-based derivatives, we here report a unique HAT-
based sensor (compound 1 in Scheme 1) containing six symmetri-
cally substituted thiophene units, the introduction of which was
+
found to enable 1 to selectively recognize Ag ion with significant
1
‘
‘turn-off” of emission. The Job’s plot and H MR titration experi-
⇑
Corresponding authors.
E-mail addresses: zhangxiang871229@163.com (X. Zhang), xzhao@sioc.ac.cn (X.
+
ments revealed that 1 could complex with Ag in a ratio of 2:3 with
Zhao).
https://doi.org/10.1016/j.tetlet.2021.152911
0
040-4039/Ó 2021 Elsevier Ltd. All rights reserved.

X. Zhang, Y. Fan, Tian-Guang Zhan et al.
Tetrahedron Letters 68 (2021) 152911
O
OH
O
O
O
Thiamine, DBU
CuSO
4 2
5H O
S
S
S
S
S
DMSO, 60 oC, 5 h
CH CN, H O, 85 oC, 10 min
3
2
3
4%
8
8%
2
3
4
NH
2
H
2
N
NH2
NH
S
N
S
S
H
2
N
2
N
N
N
NH
2
5
S
N
S
S
CH
3
COOH, 140 oC, 24 h
6%
N
1
1
Scheme 1. The synthesis of sensor 1.
7
À1
an apparent association constant of 3.98 Â 10 M , and the limit
The spectroscopic property of 1 in chloroform was then
À6
of detection was calculated to be 1.79 Â 10 M.
revealed by UV–Vis and fluorescent spectroscopic studies. Upon
+
the addition of Ag , it was found that the absorption of 1 at
4
25 nm decreased gradually and a new peak cantered at 450 nm
appeared (Fig. 2a), the dramatic spectral change of which could
be attributed to the coordination between Ag and 1.[25] However,
+
Results and discussion
the characteristic absorption band of
responses when other metal ions were introduced (Fig. 2b), again
suggesting the high selectivity towards Ag .
Fluorescent spectroscopic experiments were further carried out
to investigate the recognition behaviour of 1 towards Ag ion. As
shown in Fig. 3a, upon the addition of 6 equiv. of Ag , the fluores-
cence emission intensity at 475 nm drastically decreased until
1 exhibited negligible
Sensor 1 was synthesized through a facile three-step route as
showed in Scheme 1. The benzoic condensation of 2-thenaldehyde
2) yielded compound 3, which was further efficiently oxidized by
+
(
+
CuSO to give diketone 4. Then, the condensation of 4 with hex-
4
+
aaminobenzene(5) [15] afforded the target compound 1, the chem-
1
ical structure of which was unambiguously assigned by H NMR,
1
3
10
C NMR as well as HR-MS spectroscopies (see ESI for details).
Naked-eye experiments were first carried out in chloroform
completely quenched, which could be attributed to the d config-
uration of silver.[25,30] However, except for the observation of
under ambient condition and UV-lamp irradiation, respectively.
slight decrease for the emission intensity of 1 at 475 nm after
+
3+
2+
As depicted in Fig. 1, the addition of Ag (4 equiv.) into the solution
introducing Fe and Cu ions, the fluorescent spectra of 1 exhib-
ited negligible changes while other metal ions were added to its
solution (Fig. 3b). Furthermore, the detection limit could be calcu-
of 1 led to the development of distinct colour change from light
yellow to dark yellow and discernible fluorescence quenching phe-
nomenon. By contrast, both the colour and fluorescence changes
were negligible when the same amount of other metal ions were
introduced. This result demonstrated that 1 was capable of serving
À6
lated as 1.79 Â 10 M in CHCl ,[42] which suggested a high recog-
3
+
nition sensitivity of 1 for the Ag ion (Fig. S5).
+
To further reveal the selective recognition behavior of 1 to Ag ,
fluorescent spectra of sensor 1 in the presence of various metal
+
as a colorimetric sensor for Ag with a high selectivity, and the
+
detailed recognition behaviour of 1 over Ag was then investigated.
Fig. 1. The solutions of 1 (5 Â 10À6 M) in chloroform before and after the addition of various metal cations (2 Â 10À5 M) under (a) visual light and (b) UV lamp (365 nm)
irradiation.
2

X. Zhang, Y. Fan, Tian-Guang Zhan et al.
Tetrahedron Letters 68 (2021) 152911
À5
Fig. 2. (a) UV–Vis spectra of sensor 1 (1.25 Â 10 M, CHCl
3
) upon the addition of
+
À5
À6
) (a) upon the addition of Ag+ (0
3
Ag (0 to 6 equiv.), (b) UV–Vis spectra of sensor 1 (1.25 Â 10 M, CHCl
3
) upon the
Fig. 3. Fluorescent spectra of 1 (5 Â 10 M, CHCl
addition of 6 equiv. of various metal ions (Fe , Zn , Cu , Ni2+, Co , Cd , Pd
3
+
2+
2+
2+
2+
2+
,
to 6 equiv.), and (b) upon adding 6 equiv. of various other metal ions (Fe , Cu2+
,
Zn , Ni , Co , Cd , Pd , Hg , Ca , Mg , and Na ).
3+
2+
2+
2+
+
2+
2+
2+
2+
2+
2+
2+
2+
+
Hg , Ca , Mg , and Na ).
ions (Fe3+, Zn2+, Cu2+, Ni2+, Co2+, Cd2+, Pd2+, Hg2+, Ca2+, Mg2+, and
structure of 1-Ag+ (2:3) complex (Fig. S8). This further confirmed
the complexation behaviour of 1 and Ag revealed by the experi-
mental investigations.
+
+
Na ) were recorded, and the emission intensity of 1 at 475 nm
+
was further compared with that of after introducing Ag ion. As
exhibited in Fig. 4a, no pronounced signal interference was
observed for the detection of Ag by 1 in the presence of other
To get more insight of the recognition mechanism between 1
+
+ 1
and Ag , H NMR titration experiments were further performed.
As displayed in Fig. 5, the thiophene protons signals (H , H and
) of 1 gradually broadened and then completely disappeared
metal ions, suggesting that 1 exhibited great potential for discrim-
1
2
+
2+
inating Ag from other competing metal ions, especially Cu and
H
3
2
+
+
Hg . In addition, the fluorescent reversibility of 1 was also tested
by alternative addition of Ag and EDTA (Fig. 4b), which showed
fluorescence quenching with Ag and comparable restoration in
during the addition of Ag . Meanwhile, as the concentration of
+
+
Ag increased, the proton signals of the aromatic rings slightly
+
shifted upfield which might be attributed to conformation change
+
fluorescence with EDTA in 6 cycles, accompanied by almost no loss
of fluorescent intensity at each cycle. Moreover, the time depen-
dent plot was generated by correlating the fluorescence intensity
of 1 after its complexion with Ag . We proposed that the structural
rigidification and redistribution of electron density of sensor 1
+
could be induced upon coordination with Ag , which might facili-
+
of 1 to Ag vs. time, from which it was found that the steady com-
tate the intramolecular photoinduced electron transfer (PET) pro-
+
plex between 1 and Ag could be formed in less than 40 s (Fig. S6).
cess,[44] thus causing the fluorescent quench of 1. It is worthy of
+
These results demonstrated that 1 could serve as a quickly respon-
mentioning that the heavy metal atom effect of Ag could also be
+
sive Ag sensor.
responsible for such impressive fluorescent quenching behavior.
[45]
Job’s plot experiments were performed to determine the stoi-
+
chiometry of 1 and Ag . The absorbance value of the mixed solution
+
of 1 and AgNO
3
reached a maximum at 0.4 molar fraction of Ag ,
+
Conclusion
suggesting a 2:3 stoichiometry for 1 and Ag (Fig. S7a). By using
the Benesi-Hildebrand method based on titration data [43], the
+
In summary, a unique HAT derivative (sensor 1) bearing six
thiophene substituents was prepared, and its recognition beha-
viour towards various metal ions was systematically investigated.
It was found that 1 could exhibit a naked-eye detection capability
apparent association constant of 1 and Ag was calculated to be
7
À1
3
.98 Â 10 M (Fig. S7b). In addition, theoretical calculations were
performed, which gave an optimized sandwich-like coordination
3

X. Zhang, Y. Fan, Tian-Guang Zhan et al.
Tetrahedron Letters 68 (2021) 152911
+
gests its unique ability to distinguish Ag without the interference
of mercury ions. These features enabled such a thiophene-derived
HAT sensor to be capable of serving as a new type of colorimetric
and fluorescent chemosensor. More broadly, this work has well-
demonstrated that the modification of HAT core by introducing
heteroaromatic substitutions might be an efficient approach for
the exploration of novel HAT-based chemosensors with unprece-
dented recognition behavior towards a wider range of guest
species.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgment
This work was supported by the Natural Science Foundation of
Hunan Province (No. 2017JJ5021 and No. 19C0644).
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tetlet.2021.152911.
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