Preparation of a fixed-tetraphenylethylene motif bridged ditopic benzo-21-crown-7 and its application for constructing AIE supramolecular polymers

Article abstract of DOI:10.1016/j.cclet.2020.10.037

Benzo-21-crown-7 (B21C7) is one of the most important crown ethers, which not only shows excellent physicochemical properties but also exhibits promising binding capability with dialkylammonium salts. In this paper, we designed and synthesized a fixed-tetraphenylethylene (FTPE) motif bridged ditopic benzo-21-crown-7 molecule (H). The fixed tetraphenylethylene motif endows H with aggregation induced emission (AIE) property. In the presence of a ditopic dialkylammonium salt guest molecule (G), a fluorescent supramolecular polymer with golden luminescent property could be fabricated. This B21C7-based host-guest supramolecular polymer with golden fluorescence may have potential application in dynamic luminescent materials.

Full text of DOI:10.1016/j.cclet.2020.10.037

Chinese Chemical Letters 32 (2021) 1377–1380
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
Communication
Preparation of a fixed-tetraphenylethylene motif bridged ditopic
benzo-21-crown-7 and its application for constructing AIE
supramolecular polymers
a
a
a
a
a
Tangxin Xiaoa, , Jie Wang , Yong Shen , Cheng Bao , Zheng-Yi Li , Xiao-Qiang Sun ,
*
Leyong Wangb
a
School of Petrochemical Engineering, Changzhou University, Changzhou 213164, China
School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
b
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 31 August 2020
Received in revised form 14 October 2020
Accepted 23 October 2020
Available online 24 October 2020
Benzo-21-crown-7 (B21C7) is one of the most important crown ethers, which not only shows excellent
physicochemical properties but also exhibits promising binding capability with dialkylammonium salts.
In this paper, we designed and synthesized a fixed-tetraphenylethylene (FTPE) motif bridged ditopic
benzo-21-crown-7 molecule (H). The fixed tetraphenylethylene motif endows H with aggregation
induced emission (AIE) property. In the presence of a ditopic dialkylammonium salt guest molecule (G), a
fluorescent supramolecular polymer with golden luminescent property could be fabricated. This B21C7-
based host-guest supramolecular polymer with golden fluorescence may have potential application in
dynamic luminescent materials.
Keywords:
Benzo-21-crown-7
Host-guest interaction
Supramolecular polymer
Fluorescent materials
AIE
© 2020 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.
Published by Elsevier B.V. All rights reserved.
Supramolecular polymers, as a result of the combination of
conventional polymer science and supramolecular chemistry, are
promising materials that generally exhibit dynamic properties [1–
5]. In contrast to covalent bonded polymers, repeating units of
supramolecular polymers are integrated together by non-covalent
interactions, such as multiple hydrogen bonding [6–9], metal-
dialkylammonium salts tightly, leading to excellent host-guest
properties. Fixed-tetraphenylethylene (FTPE) is an analogue of
tetraphenylethylene (TPE), from which two of its benzene groups
are fixed by a covalent bond. Compared with TPE, FTPE is less
studied but is also an outstanding AIE motif [49–51]. To the best of
our knowledge, the integration of B21C7 unit and FTPE motif to one
molecule has not been reported so far.
ligand coordination [10–13], host-guest interaction [14–26],
p-p
stacking [27–30], or a combination of these non-covalent bonds
[31–34]. In recent years, the focus of studying supramolecular
polymers have gradually changed from construction strategy to the
development of new functionality of supramolecular polymers,
which is more important for their real applications. For example,
the development of fluorescent supramolecular polymers has
drawn much attention due to their potential application in
luminescent materials, chemical sensors, and optoelectronics
[35–41].
Since its first report [42], B21C7 has shown promising
properties/applications in various areas including lower critical
solution temperature behavior (LCST) [43–45], adhesive materials
[46,47], bulk supramolecular materials [48]. B21C7 is a specific
member in crown ether family that can accommodate
Based on our experience on B21C7 [52,53], we designed and
synthesized a new host molecule H in this work, which contains
both B21C7 units and FTPE motif (Fig. 1). The FTPE motif endows H
with the property of AIE, while B21C7 unit renders compound H
with the capability to bind dialkylammonium salt. Upon the
addition of compound G, a ditopic dialkylammonium salt guest
molecule, a novel AA/BB type supramolecular polymer could be
formed by macrocycle-based host-guest interaction. Moreover, the
supramolecular polymer could be assembled into macroscopic
fibers with golden fluorescence from concentrated solution. This
crown ether-based supramolecular polymer with beautiful golden
fluorescence in solid state may have potential application in
dynamic luminescent materials.
The synthesis of monomer H and G are straightforward.
Compound H was synthesized from B21C7-based derivative A
[38] and FTPE-based derivative B (Scheme 1). As shown in
Scheme 1, starting from 9-fluorenone, compound 4 was prepared
and further converted to FTPE precursor 5 in toluene solution by
* Corresponding author.
E-mail address: xiaotangxin@cczu.edu.cn (T. Xiao).
https://doi.org/10.1016/j.cclet.2020.10.037
1001-8417/© 2020 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.

T. Xiao et al.
Chinese Chemical Letters 32 (2021) 1377–1380
Fig. 2. Fluorescence emission spectra of H versus hexane fraction in CHCl3/hexane
mixtures (lex = 365 nm, [H] = 5 Â10-5 mol/L).
emission wavelength of H was kept constant at 560 nm in the
mixed solvent when excited at 365 nm.
The formation of supramolecular polymers from H and G was
first studied by concentration-dependent 1H NMR, which was
measured in CDCl3/CD3CN (1:1, v/v) at concentrations in the range
of 2-64 mmol/L (Fig. 3). The concentration-dependent 1H NMR
spectra were complicated due to the slow-exchange complexation
of the B21C7 and the dialkylammonium salt units on the NMR
timescale. Although the spectra are complicated, the splitting of
peaks is relatively clear in the low concentration range (2-8
mmol/L), indicating that cyclic oligomers are predominant species
at low concentration. Upon increasing the monomer concentra-
tion, most of the peaks became broad, providing evidence for the
formation of high-molecular-weight assemblies driven by host-
guest interactions.
In order to further investigate the supramolecular polymers
driven by host-guest self-assembly, viscosity measurements were
carried out in mixed CHCl3/CH3CN solvents (1:1, v/v) by using a
micro-Ubbelohde viscometer. A double logarithmic curve of
specific viscosity against monomer concentration was shown in
Fig. 4a. A slope value of 1.02 was obtained in the low concentration
range, which is the characteristic of cyclic oligomers with
unchanged size. When the monomer concentration reaches
Fig. 1. Schematic illustration of the AIE supramolecular polymer material
constructed from H and G.
Suzuki reaction. Demethylation of compound 5 with boron
tribromide in dichloromethane (DCM) yields compound 6 [49].
Subsequent
afforded compound 7, which could be further hydrolyzed to
produce amino derivative B. Compound was synthesized
reaction with
N-(3-bromopropyl)phthalimide
G
according to literature report [54]. The compounds that have
not been reported previously are fully characterized by 1H NMR,
13C NMR and HR-MS (Figs. S2-S10 in Supporting information).
To examine whether the FTPE motif bridged ditopic B21C7 are
still AIE active, the emission spectra of H in mixed CHCl3/hexane
solutions were tested. As shown in Fig. 2, compound H exhibits
remarkable AIE property. There is no emission when H was
dissolved in pure CHCl3 (a good solvent for H). When the hexane (a
poor solvent for H) content of a solution of H was increased
gradually to 80%, an obvious emission spectrum was observed. As
the hexane content continues to increase to 90%, the fluorescence
intensity of H also shows a dramatic continuous increase. The
Scheme 1. Synthetic route of compound H.
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T. Xiao et al.
Chinese Chemical Letters 32 (2021) 1377–1380
Fig. 3. 1H NMR spectra (300 MHz, CDCl3/CD3CN = 1/1, v/v, 298 K) of individual H and
G, and mixtures of them at different monomer concentrations ([H]/[G] = 1/1).
Fig. 5. (a) Fluorescence spectra of H and H-G in solid state, lex = 365 nm. (b)
Fluorescence decay profiles of H and H-G in solid state. (c) Optical and (d)
fluorescent images of a figure-of-eight fiber.
strong golden yellow fluorescence. This strong luminescence
behavior can be maintained even after several weeks, suggesting
that the supramolecular polymer prepared in this work has
potential applications as dynamic luminescent material.
In summary, we have successfully prepared a golden lumines-
cent supramolecular polymer from a FTPE motif bridged ditopic
B21C7 host molecule and a ditopic dialkylammonium salt guest
molecule. The host-guest polymerization process was character-
ized by a combination of techniques including concentration-
dependent 1H NMR, SEM, and viscosity measurements. Fluores-
cent properties of the supramolecular polymer in solid state are
also investigated, which indicates that the supramolecular
polymer well inherits the AIE activity of the host and emits
beautiful golden yellow fluorescence. The AIE supramolecular
polymer described in this study may have potential applications in
the area of dynamic luminescent materials.
Fig. 4. (a) Specific viscosity of H-G complex versus the monomer concentration in
CDCl3/CD3CN (1:1, v/v) solutions (298 K). (b) SEM image of
a rod-like fiber
constructed from H and G.
13.7 mmol/L, a new curve with a steeper slope 1.75 was obtained,
indicating that the transformation of cyclic oligomers to supra-
molecular polymers are occurred. The concentration range for such
transformation was basically consistent with concentration-
dependent 1H NMR. The formation of supramolecular polymers
was further evidenced by scanning electronic microscopy (SEM)
(Fig. 4b). Rod-like fibers with a diameter of 9
mm can be pulled out
Declaration of competing interest
The authors report no declarations of interest.
Acknowledgment
from a very concentrated solution of H and G (molar ratio of H/
G = 1/1). This kind of fibers can be only made from entanglements
of large aggregates, such as supramolecular polymers. On the
contrary, no fiber can be drawn from the concentrated solution of
individual H or individual G.
The photophysical properties of H-G supramolecular polymers
were further studied by solid-state fluorescence. As shown in
Fig. 5a, the emission wavelength of H in solid state is bath-
ochromically shifted from 560 nm in solution to 610 nm. The H-G
supramolecular polymer in solid state showed stronger emission
intensity but the same maximum emission wavelength with H,
suggesting that the formation of supramolecular polymer does not
weaken but enhance the AIE behavior of H. This might be due to the
incorporation of the guest affected the packing arrangement of the
fluorophores, resulting in enhanced luminescent properties. From
the fluorescence decay profiles (Fig. 5b and Fig. S1 in Supporting
We gratefully thank the financial support from the National
Natural Science Foundation of China (No. 21702020).
Appendix A. Supplementary data
Supplementary material related to this article can be found, in
the
online
version,
at
doi:https://doi.org/10.1016/j.
cclet.2020.10.037.
References
information), we can see that the fluorescence lifetime of H-G (
t =
[1] M. Wehner, F. Würthner, Nat. Rev. Chem. 4 (2020) 38–53.
[2] O. Goor, S.I.S. Hendrikse, P.Y.W. Dankers, et al., Chem. Soc. Rev. 46 (2017) 6621–
6637.
[3] L. Yang, X. Tan, Z. Wang, et al., Chem. Rev. 115 (2015) 7196–7239.
[4] T. Aida, E.W. Meijer, S.I. Stupp, Science 335 (2012) 813–817.
[5] T.F.A. de Greef, E.W. Meijer, Nature 453 (2008) 171–173.
[6] T. Xiao, W. Zhong, L. Qi, et al., Polym. Chem. 10 (2019) 3342–3350.
[7] T. Xiao, L. Xu, J. Götz, et al., Mater. Chem. Front. 3 (2019) 2738–2745.
[8] T. Xiao, H. Wu, G. Sun, et al., Chem. Commun. 56 (2020) 12021–12024.
[9] X. Fu, R.R. Gu, Q. Zhang, et al., Polym. Chem. 7 (2016) 2166–2170.
1.75 ns) is slightly higher than H ( = 1.59 ns), further indicating
t
that the supramolecular polymer maintains the fidelity of AIE from
host molecules. Finally, in order to illustrate the fluorescent
properties of the supramolecular polymer more intuitively, a
figure-of-eight supramolecular polymer fiber was prepared. The
pictures under visible light and ultraviolet (UV) light are shown in
Figs. 5c and d. It can be seen that under UV lamp, the fiber emits
1379

T. Xiao et al.
Chinese Chemical Letters 32 (2021) 1377–1380
[32] P. Wei, X. Yan, F. Huang, Chem. Soc. Rev. 44 (2015) 815–832.
[33] X.Z. Yan, T.R. Cook, J.B. Pollock, et al., J. Am. Chem. Soc. 136 (2014) 4460–4463.
[34] S.L. Li, T. Xiao, C. Lin, et al., Chem. Soc. Rev. 41 (2012) 5950–5968.
[35] B. Li, T. He, X. Shen, et al., Polym. Chem. 10 (2019) 796–818.
[36] C.W. Zhang, B. Ou, S.T. Jiang, et al., Polym. Chem. 9 (2018) 2021–2030.
[37] L.N. Xu, D. Chen, Q. Zhang, et al., Polym. Chem. 9 (2018) 399–403.
[38] C. Lu, M. Zhang, D. Tang, et al., J. Am. Chem. Soc. 140 (2018) 7674–7680.
[39] X. Ji, Y. Yao, J. Li, et al., J. Am. Chem. Soc. 135 (2013) 74–77.
[10] B. Shi, Z. Zhou, R.T. Vanderlinden, et al., J. Am. Chem. Soc. 141 (2019) 11837–
11841.
[11] L. Xu, X. Shen, Z. Zhou, et al., J. Am. Chem. Soc. 140 (2018) 16920–16924.
[12] Y. Ding, P. Wang, Y.K. Tian, et al., Chem. Commun. 49 (2013) 5951–5953.
[13] W. Zheng, L.J. Chen, G. Yang, et al., J. Am. Chem. Soc. 138 (2016) 4927–4937.
[14] T. Xiao, L. Wang, Tetrahedron Lett. 59 (2018) 1172–1182.
[15] T. Xiao, L. Xu, W. Zhong, et al., Isr. J. Chem. 58 (2018) 1183–1193.
[16] D.S. Guo, S. Chen, H. Qian, et al., Chem. Commun. 46 (2010) 2620–2622.
[17] S. Dong, B. Zheng, F. Wang, et al., Acc. Chem. Res. 47 (2014) 1982–1994.
[18] T. Xiao, L. Qi, W. Zhong, et al., Mater. Chem. Front. 3 (2019) 1973–1993.
[19] T. Xiao, L. Xu, L. Zhou, et al., J. Mater. Chem. B 7 (2019) 1526–1540.
[20] A. Harada, Y. Takashima, M. Nakahata, Acc. Chem. Res. 47 (2014) 2128–2140.
[21] M. Cheng, J. Zhang, X. Ren, et al., Chem. Commun. 53 (2017) 11838–11841.
[22] S. Wang, Z. Xu, T. Wang, et al., Nat. Commun. 9 (2018) 1737.
[23] T. Xiao, W. Zhong, L. Xu, et al., Org. Biomol. Chem. 17 (2019) 1336–1350.
[24] T. Xiao, W. Zhong, L. Zhou, et al., Chin. Chem. Lett. 30 (2019) 31–36.
[25] T. Xiao, L. Zhou, L. Xu, et al., Chin. Chem. Lett. 30 (2019) 271–276.
[26] Y. Wang, G. Ping, C. Li, Chem. Commun. 52 (2016) 9858–9872.
[27] T. Xiao, L. Xu, J. Wang, et al., Org. Chem. Front. 6 (2019) 936–941.
[28] W. Wagner, M. Wehner, V. Stepanenko, et al., J. Am. Chem. Soc. 141 (2019)
12044–12054.
[40] M.M. Zhang, S.Y. Li, X.Z. Yan, et al., Proc. Natl. Acad. Sci. U. S. A. 113 (2016)
11100–11105.
[41] M. Zhang, S. Yin, J. Zhang, et al., Proc. Nat. Acad. Sci. 114 (2017) 3044–3049.
[42] C. Zhang, S. Li, J. Zhang, et al., Org. Lett. 9 (2007) 5553–5556.
[43] D. Huang, Q. Zhang, Y. Deng, et al., Polym. Chem. 9 (2018) 2574–2579.
[44] S. Wu, Q. Zhang, Y. Deng, et al., J. Am. Chem. Soc. 142 (2020) 448–455.
[45] Y. Deng, X. Li, C. Han, et al., Chin. Chem. Lett. 31 (2020) 3221–3224.
[46] S. Dong, J. Leng, Y. Feng, et al., Sci. Adv. 3 (2017) eaao0900.
[47] Q. Zhang, T. Li, A. Duan, et al., J. Am. Chem. Soc. 141 (2019) 8058–8063.
[48] L. Wang, L. Cheng, G. Li, et al., J. Am. Chem. Soc. 142 (2020) 2051–2058.
[49] X. Gu, J. Yao, G. Zhang, et al., Adv. Funct. Mater. 22 (2012) 4862–4872.
[50] J.H. Wang, H.T. Feng, J. Luo, et al., J. Org. Chem. 79 (2014) 5746–5751.
[51] H. Jin, H. Li, Z. Zhu, et al., Angew. Chem. Int. Ed. 59 (2020) 10081–10086.
[52] T. Xiao, L. Zhou, X. Wei, et al., Chin. J. Org. Chem. 40 (2020) 944–949.
[53] T. Xiao, X. Feng, Q. Wang, et al., Chem. Commun. 49 (2013) 8329–8331.
[54] X. Li, L. Wang, Y. Deng, et al., Chem. Commun. 54 (2018) 12459–12462.
[29] X. Wang, Y. Han, Y. Liu, et al., Angew. Chem. Int. Ed. 56 (2017) 12466–12470.
[30] J. Zhan, Q. Li, Q. Hu, et al., Chem. Commun. 50 (2014) 722–724.
[31] T. Xiao, L. Zhou, X.Q. Sun, et al., Chin. Chem. Lett. 31 (2019) 1–9.
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