A supramolecular bottlebrush polymer assembled on the basis of cucurbit[8]uril-encapsulation-enhanced donor–acceptor interaction

Article abstract of DOI:10.1016/j.cclet.2017.03.029

A supramolecular bottlebrush polymer has been constructed in water through the self-assembly of a rigid electron-deficient building block and an electron-rich monomer which bears two tetraethylene glycol chains, driven by CB[8]-encapsulation-enhanced donor–acceptor interaction. The as-formed supramolecular bottlebrush polymer has been characterized by ¹H NMR titration experiment, UV–vis spectroscopy, DLS and 2D ¹H NMR DOSY.

Full text of DOI:10.1016/j.cclet.2017.03.029

Accepted Manuscript
Title: A supramolecular bottlebrush polymer assembled on the
basis of cucurbit[8]uril-encapsulation-enhanced
donor-acceptor interaction
Authors: Zhi-Jian Yin, Zong-Quan Wu, Feng Lin, Qiao-Yan
Qi, Xiao-Na Xu, Xin Zhao
PII:
S1001-8417(17)30104-3
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.cclet.2017.03.029
CCLET 4024
To appear in:
Chinese Chemical Letters
Received date:
Revised date:
Accepted date:
6-2-2017
1-3-2017
17-3-2017
Please cite this article as: Zhi-Jian Yin, Zong-Quan Wu, Feng Lin, Qiao-Yan Qi, Xiao-
Na Xu, Xin Zhao, A supramolecular bottlebrush polymer assembled on the basis of
cucurbit[8]uril-encapsulation-enhanced donor-acceptor interaction, Chinese Chemical
Lettershttp://dx.doi.org/10.1016/j.cclet.2017.03.029
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Original article
A supramolecular bottlebrush polymer assembled on the basis of cucurbit[8]uril-
encapsulation-enhanced donor-acceptor interaction
a,b
a
b
b
b,
b,*
Zhi-Jian Yin , Zong-Quan Wu , Feng Lin , Qiao-Yan Qi , Xiao-Na Xu , Xin Zhao
a
Department of Polymer Science and Engineering, School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009, China
Key Laboratory of Synthetic and Self-assembly Chemistry for Organic Functional Molecules, Shanghai Institute of Organic Chemistry, Chinese Academy of
b
Sciences, Shanghai 200032, China

Corresponding authors.
E-mail addresses: xuxiaona@sioc.ac.cn (X.-N. Xu); xzhao@sioc.ac.cn (X. Zhao)
ARTICLE INFO
Article history:
Received 7 February 2017
Received in revised form 1 March 2017
Accepted 8 March 2017
Available online
Graphical abstract
CB[8]
+
Self-assembly
in water
A supramolecular bottlebrush polymer has been constructed in water through cucurbit[8]uril-mediated self-assembly of a rigid
electron-deficient building block and an electron-rich monomer which bears two tetraethylene glycol chains.
ABSTRACT
A supramolecular bottlebrush polymer has been constructed in water through the self-assembly of a rigid electron-deficient building block and an
electron-rich monomer which bears two tetraethylene glycol chains, driven by CB[8]-encapsulation-enhanced donor-acceptor interaction. The as-
1
1
formed supramolecular bottlebrush polymer has been characterized by H NMR titration experiment, UV-vis spectroscopy, DLS and 2D H NMR
DOSY.
Keywords:
Self-assembly
Supramolecular polymer
Cucurbit[8]uril
Donor-acceptor interaction
Bottlebrush polymer
1
.
Introduction
Supramolecular polymer originates from the merging of supramolecular chemistry and polymer science [1]. Different from the
classic polymers in which building parts are linked by covalent bonds, in supramolecular polymers, their components are connected
through weak intermolecular interactions such as hydrogen-bonding [2-4], coordination interaction [5], host-guest interaction [6-9],
—
——

donor-acceptor interaction [10,11], C-H··· interaction [12], and dimerization of radicals [13,14]. Since the first supramolecular
polymer was reported by Lehn in 1990 [15], over the past decades a myriad of supramolecular polymers have been fabricated. Among
them some interesting properties have been demonstrated and useful applications have been exploited. However, while supramolecular
polymers play more and more important roles in the fabrication of functional soft materials, especially the so-call “smart materials”
which can respond to the external stimuli [16,17], their structural diversities are still quite limited in comparison with the traditional
polymers.
Polymer bottlebrushes, also known as molecular bottlebrushes, are a unique type of polymers which have drawn considerable
attention in recent years [18]. A polymer bottlebrush consists of a long liner backbone on which short densely grafted side chains are
attached. While traditional polymer bottlebrushes can be fabricated through grafting strategy [19], more recently self-assembly has
emerged as a powerful tool to construct this unique type of polymeric materials, which lead to a new type of molecular bottlebrushes,
that is, supramolecular bottlebrush polymers. In principle there are two approaches that can be applied to the construction of
supramolecular bottlebrush polymers. The first one is to noncovalently attach side chains onto linear covalent backbones [20]. For the
second approach, polymeric backbones are constructed through self-assembly driven by noncovalent bonds, while side chains are
covalently linked to the building blocks of the backbones [21]. It is generally believed that the second approach is more useful because
it is synthetically more accessible and easier to be implemented. However, so far most studies in this field are focused on utilizing
hydrogen bonding [22] and aromatic stacking [23] as the main driven forces for the assembly of polymeric chains. To our surprise,
cucurbit[8]uril(CB[8])-based host-guest interaction [24], as one of the most widely used driven forces for the fabrication of main-chain
supramolecular polymers [25], has rarely been employed to construct supramolecular bottlebrush polymers. In this letter, we report the
construction of a supramolecular bottlebrush polymer in water via CB[8]-encapsulation-enhanced donor-acceptor interaction between a
rigid electron-deficient building block and an electron-rich monomer which bears two tetraethylene glycol chains. To the best of our
knowledge, it is the first example of supramolecular bottlebrush polymer constructed through the CB[8]-based host-guest chemistry.
2
. Results and discussion
Compound T1 was prepared according to our previous work [26]. For the synthesis of compound T2, as shown in Scheme 2, the
reaction of tetraethylene glycol and p-toluenesulfonyl chloride led to the formation of monosulfonate 1 in 82% yield, which was further
heated with 2,5-dibromohydroquinone in the presence of K CO in anhydrous acetonitrile to afforded compound 2 in 94% yield.
2
3
Compound 2 was then coupled with 6-methoxy-2-naphthaleneboronic acid to generate the target compound T2 in 80% yield.
1
The self-assembly process was monitored by H NMR titration experiment. As can be seen in Fig. 1, compound T1 exhibits a high-
resolution spectrum, suggesting no self-aggregation of T1 itself in water. The addition of 1 equiv. of compound T2 results in almost no
change of the spectrum of T1 and peaks corresponding to T2 can not be observed. It could be attributed to the extremely low solubility
of T2 in water. However, upon the continuous addition of CB[8] into the mixture of T1 and T2, the peaks of T1 become broad and
some new peaks appear. The peaks appear in the range of 7.50-6.25 ppm are attributed to the protons of naphthalene units of T2.
However, they can not be unambiguously assigned due to the low resolution of the spectra. Moreover, the peaks corresponding to the
tetraethylene glycol chains of T2 can also be observed in the range of 3.9-2.7 ppm, the intensities of which increase with the
incremental addition of CB[8]. When 2 equiv. of CB[8] was added, the peaks of free T1 almost disappear and a spectrum with very
broad peaks and low-resolution was obtained, indicating the formation of polymeric structures and a 1:1:2 stoichiometry for T1, T2
and CB[8].
The formation of the supramolecular bottlebrush polymer is believed to be driven by donor-acceptor interaction between the
electron-rich naphthalene unit and the electron-deficient viologen segment, which has already been well-established in the previous
studies [27]. To acquire direct evidence for the existence of donor-acceptor interaction, UV-vis spectroscopy was carried out for the
solution of a mixture of T1, T2 and CB[8] (1:1:2) in water. For comparison, UV-vis spectrum of compound T1 in water was also
recorded. As shown in Fig. 2, while T1 exhibits almost no absorption in the region of 450-900 nm, the solution of T1, T2 and CB[8]
(1:1:2) displays a broad absorption peak between 500-700 nm. It is the typical charge-transfer absorption resulted from donor-acceptor
interaction [27], confirming the driven force for the formation of the supramolecular bottlebrush polymer is donor-acceptor interaction
between the naphthalene units of T2 and the viologen segments of T1.
The formation of the supramolecular bottlebrush polymer in water has been further evidenced by the dynamic light scattering (DLS)
experiment (Fig. 3). Increasing the concentration of the mixture of T1, T2 and CB[8] (1:1:2) leads to increase of the hydrodynamic
diameters of the aggregates formed in solution, indicating a higher degree of polymerization at higher concentration. For example, the
aggregates in water have an average hydrodynamic radius of around 340 nm at the concentration of T1 being 0.025 mmol/L. The value
increases to ca. 710 nm at a T1 concentration of 0.1 mmol/L. When the concentration of T1 increases to 0.4 mmol/L, the aggregates
with an average hydrodynamic radius of around 1300 nm were observed.
1
2
D H NMR diffusion ordered spectroscopy (DOSY) was also carried out to characterize the polymeric structures formed in water.
-
10
2
2
It was found that T1 itself has a value of diffusion coefficient (D) to be 5.62 × 10 m /s at a concentration of 1.0 mmol/L in D O.

O displays a diffusion coefficient of 3.09 × 10-10 m /s at the
2
However, the solution of the mixture of T1, T2 and CB[8] (1:1:2) in D
same concentration, strongly suggesting the formation of the expected supramolecular bottlebrush polymer.
2
3
. Conclusion
In summary, we have successfully constructed a supramolecular bottlebrush polymer in water by taking advantage of CB[8]-
encapsulation-enhanced donor-acceptor interaction between naphthalene units and the viologen segments. The as-prepared
supramolecular bottlebrush polymer has a rigid supramolecular polymeric backbone as the handle and flexible tetraethylene glycols as
the bristles. Compared with its analogs reported in literature which are fabricated in organic solvents, supramolecular bottlebrush
polymers assembled in water is more attractive because they are more biocompatible and thus have potential applications in the field of
biomaterials. On the other hand, construction of bottlebrush polymers through CB[8]-based self-assembly is facile and the resulting
polymeric structures are extremely stable. In this context, fabricating more supramolecular bottlebrush polymers in aqueous phase and
further exploiting their applications are expected in the future.
4
. Experimental
Synthesis of compound 1: NaOH (2.74 g, 68 mmol) in water (15 mL) was added to a THF (15 mL) solution of tetraethylene glycol
(60 g, 309 mmol). p-Toluenesulfonyl chloride (8.4 g, 44 mmol) in 50 mL of THF was added slowly when the reaction mixture was
kept in an ice bath. After stirring for 5 h, the reaction mixture was poured into 250 mL of ice water. The organic layer was separated,
and the aqueous layer was extracted with dichloromethane. The combined organic layer was washed with water and dried over
anhydrous MgSO
8
2
4
, and the solid was filtered. The solvent was evaporated under reduced pressure to afford 1 as a clear oil (12.6 g,
2%). H NMR (500 MHz, CDCl ): δ 7.80 (d, 2H, J = 8.1 Hz), 7.34 (d, 2H, J = 8.1 Hz), 4.16 (t, 2H, J = 4.9 Hz), 3.59-3.74 (m, 14H),
.45 (s, 3H).
3
Synthesis of compound 2: A mixture of 2,5-dibromohydroquinone (500 mg, 1.87 mmol), K CO (1.03 g, 7.45 mmol) and anhydrous
1
3
2
acetonitrile (20 mL) was refluxed under an argon atmosphere for 1 h and then a solution of 1 (1.62 g, 4.65 mmol) in anhydrous
acetonitrile (5 mL) was added dropwise within 0.5 h. After completing the addition, the reaction mixture was stirred for 24 h. The
solvent was removed and the residue was treated with 10% aqueous HCl and then extracted with dichloromethane. The organic layer
was washed with water three times and dried over anhydrous MgSO
column chromatography (dichloromethane/methanol 200:3) to give compound 2 (1.15 g, 94%) as a white solid. H NMR (500 MHz,
CDCl ): δ 7.16 (s, 2H), 4.13-3.60 (m, 32H).
Synthesis of compound T2: To a mixture of 6-methoxy-2-naphthaleneboronic acid (147 mg, 0.73 mmol), compound 2 (150 mg,
.24 mmol), and Pd[P(Ph )] (28 mg, 0.024 mmol) in a 25 mL flask, a mixture of toluene (3 mL), ethanol (1 mL) and 2 M potassium
4
. After filtration and evaporation, the crude was purified by flash
1
3
0
3
4
carbonate aqueous solution (0.2 mL) was added. The mixture was degassed through three freeze–pump–thaw cycles under an argon
atmosphere and then stirred at 100 °C for 48 h. After being cooled to room temperature, the reaction mixture was extracted with
dichloromethane. The organic layer was washed with water, dried over MgSO
purified by flash column chromatograph (dichloromethane/methanol 40:1) to give compound T2 (150 mg, 80%) as a gray solid. H
NMR (500 MHz, CDCl ): δ 8.00 (s, 2H), 7.79 (d, 2H, J = 9.7 Hz), 7.77 (d, 4H, J = 0.9 Hz), 7.20-7.16 (m, 4H), 7.15 (s, 2H), 4.16-4.10
4
, filtered and evaporated. The crude product was
1
3
1
3
(
m, 4H), 3.96 (s, 6H), 3.78-3.71 (m, 4H), 3.69-3.63 (m, 4H), 3.62-3.48 (m, 20H). C NMR (125 MHz, CDCl
3
): δ 157.77, 150.65,
1
6
33.62, 133.58, 131.06, 129.67, 128.89, 128.52, 128.00, 126.11, 118.80, 117.12, 105.59, 72.38, 70.78, 70.56, 70.29, 69.85, 69.56,
1.72, 55.36. MS (ESI): m/z 775.6 [M] . HRMS (ESI): Calcd. for C44H O12 [M] : 775.3688. Found: 775.3685.
54
+
+
Acknowledgment
We thank the National Natural Science Foundation of China (No. 21402228) for financial support.
References
[
[
[
[
[
1] L. Yang, X. Tan, Z. Wang, X. Zhang, Supramolecular polymers: historical development, preparation, characterization, and functions,
Chem. Rev. 115 (2015) 7196-7239.
2] T. Xiao, X. Feng, S. Ye, et al., Highly controllable ring–chain equilibrium in quadruply hydrogen bonded supramolecular polymers,
Macromolecules 45 (2012) 9585-9594.
3] P. Du, J. Kong, G. Wang, et al., Hydrogen bonded supramolecular polymers in both apolar and aqueous media: self-assembly and
reversible conversion of vesicles and gels, Chin. J. Chem. 29 (2011) 2597-2605.
4] T.G. Zhan, T.Y. Zhou, Q.Y. Qi, et al., The construction of supramolecular polymers through anion bridging: from frustrated hydrogen-
bonding networks to well-ordered linear arrays, Polym. Chem. 6 (2015) 7586-7593.
5] D. Tian, X.J. Liu, R.Y. Chen, Y.H. Zhang, Syntheses, structures, luminescent and magnetic properties of two coordination polymers based
on a flexible multidentate carboxylate ligand, Chin. Chem. Lett. 26 (2015) 499-503.

[
[
[
[
[
[
[
[
[
[
[
6] Y.S. Su, J.W. Liu, Y. Jiang, C.F. Chen, Assembly of a self-complementary monomer: formation of supramolecular polymer networks and
responsive gels, Chem. Eur. J. 17 (2011) 2435-2441.
7] S. Dong, B. Zheng, F. Wang, F. Huang, Supramolecular polymers constructed from macrocycle-based host-guest molecular recognition
motifs, Acc. Chem. Res. 47 (2014) 1982-1994.
8] H. Qian, D.S. Guo, Y. Liu, Cucurbituril-modulated supramolecular assemblies: from cyclic oligomers to linear polymers, Chem. Eur. J. 18
(2012) 5087-5095.
9] T.T. Cao, X.Y. Yao, J. Zhang, Q.C. Wang, X. Ma, A cucurbit[8]uril recognized rigid supramolecular polymer with photo-stimulated
responsiveness, Chin. Chem. Lett. 26 (2015) 867-871.
10] S. Burattini, B.W. Greenland, W. Hayes, et al., A supramolecular polymer based on tweezer-type π−π stacking interactions: molecular
design for healability and enhanced toughness, Chem Mater. 23 (2011) 6-8.
11] Y.K. Tian, Y.G. Shi, Z.S. Yang, F. Wang, Responsive supramolecular polymers based on the bis[alkynylplatinum(II)] terpyridine
molecular tweezer/arene recognition motif, Angew. Chem. Int. Ed. 53 (2014) 6090- 6094.
12] Z. Zhang, Y. Luo, J. Chen, et al., Formation of linear supramolecular polymers that is driven by CH interactions in solution and in
the solid state, Angew. Chem. Int. Ed. 50 (2011) 1397-1401.
13] L. Chen, Y.C. Zhang, W.K. Wang, et al., Conjugated radical cation dimerization-driven generation of supramolecular architectures, Chin.
Chem. Lett. 26 (2015) 811-816.
14] T.G. Zhan, T.Y. Zhou, F. Lin, et al., Supramolecular radical polymers self-assembled from the stacking of radical cations of rod-like
viologen di- and trimers, Org. Chem. Front. 3 (2016) 1635-1645.
15] C. Fouquey, J.M. Lehn, A.M. Levelut, Molecular recognition directed self-assembly of supramolecular liquid crystalline polymers from
complementary chiral components, Adv. Mater. 2 (1990) 254-257.
16] J.F. Xu, Y.Z. Chen, D. Wu, et al., Photoresponsive hydrogen-bonded supramolecular polymers based on a stiff stilbene unit, Angew.
Chem. Int. Ed. 52 (2013) 9738-9742.
[17] D.H. Qu, Q.C. Wang, Q.W. Zhang, X. Ma, H. Tian, Photoresponsive host-guest functional systems, Chem. Rev. 115 (2015) 7543-7588.
[18] M. Zhang, A.H.E. Müller, Cylindrical polymer brushes, J. Polym. Sci. Part A: Polym. Chem. 43 (2005) 3461-3481.
[19] S.S. Sheiko, B.S. Sumerlin, K. Matyjaszewski, Cyclindrical molecular brushes: synthesis, characterization, and properties, Prog. Polym.
Sci. 33 (2008) 759-785.
[
[
[
[
20] S. Liu, Q. Chen, Y. Sheng, et al., Unraveling the forming mechanism of hierarchical helices via self-assembly of an achiral
supramolecular polymer brush, Polym. Chem. 6 (2015) 3926-3933.
21] S. Catrouillet, L. Bouteiller, O. Boyron, et al., Patchy supramolecular bottle-brushes formed by solution self-assembly of bis(urea)s and
tris(urea)s decorated by two incompatible polymer arms, Langmuir 32 (2016) 8900-8908.
22] S. Catrouillet, J.C. Brendel, S. Larnaudie, et al., Tunable length of cyclic peptide-polymer conjugate self-assemblies in water, ACS Macro
Lett. 5 (2016) 1119-1123.
23] N. Dingenouts, S. Klyatskaya, S. Rosenfeldt, M. Ballauff, S. Höger, Temperature-induced switching between aggregated and
nonaggregated states in coil-ring-coil block copolymers, Macromolecules 42 (2009) 5900-5902.
24] J. Lagona, P. Mukhopadhyay, S. Chakrabarti, L. Isaacs, The cucurbit[n]uril family, Angew. Chem. Int. Ed. 44 (2005) 4844-4870.
25] Y. Liu, H. Yang, Z. Wang, X. Zhang, Cucurbit[8]uril-based supramolecular polymers, Chem. Asian J. 8 (2013) 1626-1632.
26] Y. Fan, F. Lin, X.N. Xu, J.Q. Xu, X. Zhao, Construction of a rod-coil supramolecular copolymer through CB[8]-encapsulation-enhanced
donor-acceptor interaction, Acat Polym. Sinica (2017) 80-85.
[
[
[
[27] H.J. Kim, J. Heo, W.S. Jeon, et al., Selective inclusion of a hetero-guest pair in a molecular host: formation of stable charge-transfer
complexes in cucurbit[8]uril, Angew. Chem. Int. Ed. 40 (2001) 1526-1529.

1
Fig. 1. Partial H NMR spectra of (a) T1, (b) T1 + T2 (1:1), (c) T1 + T2 + CB[8] (1:1:0.5), (d) T1 + T2 + CB[8] (1:1:1), (e) T1 + T2 + CB[8] (1:1:1.5), and (f)
o
T1 + T2 + CB[8] (1:1:2) in D
2
O at 25 C. The concentration of T1 was 1.0 mmol/L.
0.75
0.50
0.25
0.00
T1
T1-T2-CB[8]
500
600
700
800
900
1000
Wavelength (nm)
o
Fig. 2. UV-vis spectra of T1 and T1-T2-CB[8] (1:1:2) in water at 25 C. The concentration of T1 was 0.2 mmol/L.
0
0
0
0
.4 mmol/L
.2 mmol/L
.1 mmol/L
.05 mmol/L
40
30
20
10
0
0.025 mmol/L
100
1000
10000
D (nm)
Fig. 3. DLS profile of T1-T2-CB[8] (1:1:2) in water at different concentrations of T1.

D = 5.62 × 10-10 m2s-1
D = 3.09 × 10-10 m2s-1
1
o
Fig. 4. 2D H NMR DOSY-NMR spectra of T1 (left) and T1-T2-CB[8] (1:1:2) (right) in D
2
O at 25 C. The concentration of T1 was 1.0
mmol/L.
=
=
=
Scheme 1. Chemical structures of T1, T2 and CB[8], and cartoon representation of formation of the supramolecular bottlebrush polymer
assembled from T1, T2 and CB[8].
Scheme 2. The synthesis of compound T2.