A pillar[6]arene-based UV-responsive supra-amphiphile: Synthesis, self-assembly, and application in dispersion of multiwalled carbon nanotubes in water

Article abstract of DOI:10.1039/c4cc00590b

A UV-responsive supra-amphiphile based on a water-soluble pillar[6]arene was constructed. Its self-assembly and application in dispersion of multi-walled carbon nanotubes in water were studied.

Full text of DOI:10.1039/c4cc00590b

ChemComm
View Article Online
View Journal | View Issue
COMMUNICATION
A pillar[6]arene-based UV-responsive
supra-amphiphile: synthesis, self-assembly,
and application in dispersion of multiwalled
carbon nanotubes in water†
Cite this: Chem. Commun., 2014,
50, 3993
Received 23rd January 2014,
Accepted 22nd February 2014
Jie Yang, Guocan Yu, Danyu Xia and Feihe Huang*
DOI: 10.1039/c4cc00590b
www.rsc.org/chemcomm
A
UV-responsive supra-amphiphile based on a water-soluble and a UV-responsive guest (G) bearing the 2-nitrobenzyl ester
pillar[6]arene was constructed. Its self-assembly and application in moiety (Scheme S1, ESI†) was constructed (Fig. 1). Furthermore,
dispersion of multi-walled carbon nanotubes in water were studied. its UV-responsive self-assembly in water and application in dispersion
of multi-walled carbon nanotubes (MWNTs) in water were studied.
Supra-amphiphiles, a class of captivating supramolecules, carry both
Firstly, UV irradiation was conducted to investigate the
hydrophilic and hydrophobic parts and can self-assemble in an photocleavage properties of the 2-nitrobenzyl ester moiety of
aqueous phase or an oil phase to form well-defined nanostructures
depending on the repelling and coordinating forces generated from
the interactions of the amphiphiles and surrounding medium.1
In order to get controllable supramolecular architectures from
self-assembly of supra-amphiphiles for applications in controlled
release, gene delivery, and electro-optic materials, the introduction of
stimuli-responsive functional groups into these building blocks is
indispensable. Multitudinous external stimuli such as temperature,
pH, redox, and enzyme have been utilized in the construction of
supra-amphiphiles.2 Among them, photo-stimulus is especially
attractive on account of its easy operation, non-invasiveness, low
cost, sensitivity, and excellent penetration depth.3
Host–guest chemistry has attracted considerable attention
over the past decades because of the topological importance and
application of host–guest structures in the fabrication of artificial
molecular machines, supramolecular polymers, supramolecular gels
and other functional supramolecular systems.4 As a new kind of
macrocyclic hosts, pillar[n]arenes have been investigated by more
and more chemists due to their symmetrical pillar architecture,
facile and high-yield syntheses, and accessible derivatizations.5 The
host–guest chemistry of pillararenes has been employed in the
fabrication of supra-amphiphiles.6 However, its application in
the preparation of photo-responsive supra-amphiphiles has been
rarely investigated.6d Herein, a UV-responsive supra-amphiphile
based on host–guest interactions between a water-soluble pillar-
[6]arene (WP6) containing carboxylate anionic groups on both rims
State Key Laboratory of Chemical Engineering, Department of Chemistry,
Zhejiang University, Hangzhou 310027, P. R. China. E-mail: fhuang@zju.edu.cn;
Fax: +86-571-8795-3189; Tel: +86-571-8795-3189
† Electronic supplementary information (ESI) available: Synthetic procedures,
Fig. 1 Chemical structures of compounds used here and schematic
representation of UV-responsive self-assembly in water studied here.
characterizations, determination of association constants, UV-vis data and other
materials. See DOI: 10.1039/c4cc00590b
This journal is ©The Royal Society of Chemistry 2014
Chem. Commun., 2014, 50, 3993--3995 | 3993

View Article Online
Communication
ChemComm
Fig. 3 TEM images: (a) G; (b) WP6*G; (c) intermediate state of WP6*G;
(d) WP6*G treated with UV light irradiation. Fluorescence microscopic
images: (e) bright field, G; (f) G; (g) WP6*G; (h) WP6*G treated with UV
light irradiation. TEM images: (i) MWNTs; (j) MWNTs treated with WP6*G;
(k) enlarged image of WP6*G–MWNTs; (l) WP6*G–MWNTs treated with
UV light irradiation.
Fig. 2 UV-vis spectra of G (1.00 Â 10À5 M) before and after irradiation
with UV light (365 nm) for 30 min.
the guest molecule. It is well known that the cleavage of
2-nitrobenzyl ester leads to the formation of 2-nitrobenzaldehyde
which weakly absorbs at 360 nm and can be detected using
absorption spectroscopy.7a So the aqueous solution of G was concentration-dependent conductivity, the critical aggregation
subjected to irradiation with UV light (365 nm) for about 30 min, concentration (CAC) of G was determined to be 1.1 Â 10À7
M
as shown in UV-vis spectra; UV absorbance at B360 nm increased (Fig. S18, ESI†). As revealed using TEM, the typical amphiphilic G
clearly, accompanied by the decrease of the absorbances at 320 nm itself self-assembled in water to form two-dimensional nanosheets
and 345 nm (Fig. 2), demonstrating the photo-stimulated (Fig. 3a), which was confirmed by fluorescence microscopy
cleavage of the 2-nitrobenzyl ester moiety and the generation (Fig. 3e and f).
of a 2-nitrobenzaldehyde derivative (Fig. 1).7b
In the presence of WP6, the critical aggregation concentration of
The solubility of G in water is very poor. In order to study the WP6*G increased to 1.0 Â 10À6 M (Fig. S19, ESI†). The enhance-
interactions between G and WP6, we designed a model compound ment of the CAC value was attributed to the stable host–guest
DMPy (Scheme S2, ESI†) and studied its complexation with WP6. complexation between WP6 and G. As shown in TEM images, the
The host–guest complexation between WP6 and DMPy was first nanosheets of G disappeared and nanorods were observed instead
studied by 1H NMR spectroscopy. As shown in Fig. S17 (ESI†), when upon addition of WP6, which was also proved by fluorescence
an equimolar amount of WP6 was added into a solution of DMPy microscopy images (Fig. 3b and g). The average diameter of the
(1.00 mM), the signals related to the protons on DMPy significantly nanorods was about 500 nm. Interestingly, from the enlarged image
shifted upfield. Additionally, extensive broadening effects occurred of the nanorods, we found that the nanorods were full of cores, so
when DMPy interacted with WP6 due to complexation dynamics.6a we supposed that the nanorods were composed of nanospheres.
The reason is that these protons were located within the cavity of Fortunately, we observed the intermediate state, which indicated the
WP6 and shielded by the electron-rich cyclic structure by forming a transition from nanospheres to nanorods (Fig. 3c). Therefore, a
threaded structure between DMPy and WP6.5p
mechanism was proposed to explain the transformation from
For estimation of the binding constant, fluorescence titrations of nanosheets to nanospheres and then to nanorods upon addition
WP6 with DMPy were conducted. As shown in Fig. S13 (ESI†), the of WP6. Because of strong p–p stacking interactions between pyrene
quenching of fluorescence was observed upon gradual addition aromatic rings in water, 2D nanosheets were obtained for G alone.
of DMPy. A mole ratio plot based on the fluorescence titration Upon complexation with WP6, the anionic hosts were introduced
experiments demonstrated that the complex between WP6 and DMPy into the hydrophilic membrane of nanosheets and caused the
has a 1 : 1 stoichiometry (Fig. S14, ESI†) and the association constant increase of the membrane curvature due to the existence of steric
(Ka) was calculated to be (1.24 Æ 0.07) Â 105 MÀ1 in water by using a hindrance and electrostatic repulsion generated by WP6,8 resulting
non-linear curve-fitting method (Fig. S15, ESI†). Further evidence for in the disappearance of nanosheets and the formation of nano-
the formation of the inclusion complex WP6*DMPy was obtained spheres. With the extended self-assembly, the cores of the nano-
from UV-vis absorption spectroscopy. When DMPy and WP6 were spheres expanded and became exposed to water transiently.
mixed in water in a 1 : 1 molar ratio, the spectrum exhibited a broad Consequently, the cores adhered to other nanospheres and formed
absorption above 400 nm, which corresponds to the characteristic nanorods driven by the high interactions between the exposed
absorption of the charge-transfer complex (Fig. S16, ESI†).
pyrene blocks to minimize the portion of the hydrophobic segment.9
Upon irradiation with UV light for about 30 min, the self-
After the establishment of the recognition motif between WP6
and G in water, we utilized it to construct a supra-amphiphile and assembly of the building blocks experienced dramatic changes
investigated its UV-responsive self-assembly in water. By using the as indicated by the transition from nanorods to nanosheets
3994 | Chem. Commun., 2014, 50, 3993--3995
This journal is ©The Royal Society of Chemistry 2014

View Article Online
ChemComm
Communication
and H. W. Gibson, J. Am. Chem. Soc., 2005, 127, 484–485; (d) F. Wang,
C. Han, C. He, Q. Zhou, J. Zhang, C. Wang, N. Li and F. Huang, J. Am.
Chem. Soc., 2008, 130, 11254–11255; (e) F. Wang, J. Zhang, X. Ding,
S. Dong, M. Liu, B. Zheng, S. Li, K. Zhu, L. Wu, Y. Yu, H. W. Gibson and
F. Huang, Angew. Chem., Int. Ed., 2010, 49, 1090–1094; ( f ) W. Jiang,
(Fig. 3d and h). Moreover, we also investigated the aggregation
behavior of pyrene-1-butyric acid alone in water. As shown in
the TEM images, the pyrene-1-butyric acid also self-assembled
to form nanosheet structures through p–p stacking interactions
(Fig. S20, ESI†). Therefore, we drew the conclusion that the
change of the self-assembly of the building blocks was attributed
to the generation of pyrene-1-butyric acid by photo-cleavage of
WP6*G complexes.
Because strong p–p interactions can exist between MWNTs
and pyrenyl rings in water,6b we utilized this supra-amphiphile
to disperse MWNTs in aqueous solution. Direct evidence for the
WP6*G–MWNTs interactions was obtained using TEM. From
TEM images of initiative MWNTs, large aggregates of nano-
tubes were observed (Fig. 3i). Upon addition of a solution of
WP6*G, the hydrophobic pyrenyl ring part of WP6*G clung to
the surface of the MWNTs through p–p interactions, while the
hydrophilic WP6 stuck out into the water. Therefore, well
dispersed MWNTs could be distinguished (Fig. 3g and k).
Furthermore, we could control the dispersion behavior of MWNTs
by UV light irradiation. When the WP6*G–MWNTs complexes
were subjected to UV irradiation for about 30 min, the aggregation
of MWNTs was observed again (Fig. 3l) for the sake of the photo-
cleavage of the hydrophilic segment from the hybrids.
In conclusion, we have successfully constructed a UV-responsive
supra-amphiphile based on the host–guest complexation
between WP6 and G. In contrast to the nanosheets formed by
the amphiphilic molecule G alone, WP6*G self-assembled into
nanorods. Upon irradiation with UV light, the transformation
from nanorods to nanosheets was obtained. Furthermore,
we applied this supramolecular system in the UV-responsive
dispersion of MWNTs in water. This new kind of UV-responsive
supra-amphiphile has numerous potential applications in many
fields, including nanocontainers, nanoelectronics, sensors, drug-
delivery and controlled release.
This work was supported by the National Basic Research
Program (2013CB834502), the National Natural Science Foundation
of China (21125417), the Fundamental Research Funds for the
Central Universities, and the Key Laboratory of Supramolecular
Structure and Materials.
¨
A. Schafer, P. C. Mohr and C. A. Schalley, J. Am. Chem. Soc., 2010, 132,
2309–2320; (g) L. Chen, Y.-K. Tian, Y. Ding, Y.-J. Tian and F. Wang,
Macromolecules, 2012, 45, 8412–8419; (h) V. N. Vukotic and S. J. Loeb,
Chem. Soc. Rev., 2012, 41, 5896–5906; (i) D.-S. Guo and Y. Liu, Chem.
Soc. Rev., 2012, 41, 5907–5921; ( j) S.-L. Li, T. Xiao, C. Lin and L. Wang,
Chem. Soc. Rev., 2012, 41, 5950–5968; (k) Y. Han, Y.-K. Gu, J.-F. Xiang
and C.-F. Chen, Chem. Commun., 2012, 48, 11076–11078; (l) J.-F. Xu,
Y.-Z. Chen, L.-Z. Wu, C.-H. Tung and Q.-Z. Yang, Org. Lett., 2013, 15,
6148–6151; (m) Y. Ding, P. Wang, Y.-K. Tian, Y.-J. Tian and F. Wang,
Chem. Commun., 2013, 49, 5951–5953; (n) Q. Zhang, D.-H. Qu, X. Ma
and H. Tian, Chem. Commun., 2013, 49, 9800–9802; (o) J. Zhan, Q. Li,
Q. Hu, Q. Wu, C. Li, H. Qiu, M. Zhang and S. Yin, Chem. Commun.,
2014, 50, 722–724; (p) C. Y. Ang, S. Y. Tan, X. Wang, Q. Zhang,
M. Khan, L. Bai, S. T. Selvan, X. Ma, L. Zhu, K. T. Nguyen, N. S. Tan
and Y. Zhao, J. Mater. Chem. B, 2014, DOI: 10.1039/C3TB21325K.
5 (a) T. Ogoshi, S. Kanai, S. Fujinami, T. Yamagishi and Y. Nakamoto, J. Am.
Chem. Soc., 2008, 130, 5022–5023; (b) D. Cao, Y. Kou, J. Liang, Z. Chen,
L. Wang and H. Meier, Angew. Chem., Int. Ed., 2009, 48, 9721–9723;
(c) C. Li, L. Zhao, J. Li, X. Ding, S. Chen, Q. Zhang, Y. Yu and X. Jia, Chem.
Commun., 2010, 46, 9016–9018; (d) C. Li, Q. Xu, J. Li, F. Yao and X. Jia, Org.
Biomol. Chem., 2010, 8, 1568–1576; (e) L. Liu, D. Cao, Y. Jin, H. Tao, Y. Kou
and H. Meier, Org. Biomol. Chem., 2011, 9, 7007–7010; ( f ) Z. Zhang,
Y. Luo, J. Chen, S. Dong, Y. Yu, Z. Ma and F. Huang, Angew. Chem., Int.
Ed., 2011, 50, 1397–1401; (g) W. Si, L. Chen, X.-B. Hu, G. Tang, Z. Chen,
J.-L. Hou and Z.-T. Li, Angew. Chem., Int. Ed., 2011, 50, 12564–12568;
(h) Z. Zhang, C. Han, G. Yu and F. Huang, Chem. Sci., 2012, 3, 3026–3031;
(i) C. Han, G. Yu, B. Zheng and F. Huang, Org. Lett., 2012, 14, 1712–1715;
( j) X.-Y. Hu, X. Wu, Q. Duan, T. Xiao, C. Lin and L. Wang, Org. Lett., 2012,
14, 4826–4829; (k) P. J. Cragg and K. Sharma, Chem. Soc. Rev., 2012, 41,
597–607; (l) M. Xue, Y. Yang, X. Chi, Z. Zhang and F. Huang, Acc. Chem.
Res., 2012, 45, 1294–1308; (m) M. Holler, N. Allenbach, J. Sonet and
J.-F. Nierengarten, Chem. Commun., 2012, 48, 2576–2578; (n) X. Shu,
S. Chen, J. Li, Z. Chen, L. Weng, X. Jia and C. Li, Chem. Commun., 2012,
48, 2967–2969; (o) I. Nierengarten, S. Guerra, M. Holler, J.-F. Nierengarten
and R. Deschenaux, Chem. Commun., 2012, 48, 8072–8074; (p) Y. Ma,
X. Chi, X. Yan, J. Liu, Y. Yao, W. Chen, F. Huang and J.-L. Hou, Org. Lett.,
2012, 14, 1532–1535; (q) X.-B. Hu, Z. Chen, G. Tang, J.-L. Hou and Z.-T. Li,
J. Am. Chem. Soc., 2012, 134, 8384–8387; (r) Y. Yao, M. Xue, J. Chen,
M. Zhang and F. Huang, J. Am. Chem. Soc., 2012, 134, 15712–15715;
(s) H. Zhang, X. Ma, J. Guo, K. T. Nguyen, Q. Zhang, X.-J. Wang, H. Yan,
L. Zhu and Y. Zhao, RSC Adv., 2013, 3, 368–371; (t) Y. Fang, L. Wu, J. Liao,
L. Chen, Y. Yang, N. Liu, L. He, S. Zou, W. Feng and L. Yuan, RSC Adv.,
2013, 3, 12376–12383; (u) X. Wang, K. Han, J. Li, X. Jia and C. Li, Polym.
Chem., 2013, 4, 3998–4003; (v) S. Dong, B. Zheng, Y. Yao, C. Han, J. Yuan,
M. Antonietti and F. Huang, Adv. Mater., 2013, 25, 6864–6867;
(w) K. Wang, C.-Y. Wang, Y. Wang, H. Li, C.-Y. Bao, J.-Y. Liu, X.-A.
Zhang and Y.-W. Yang, Chem. Commun., 2013, 49, 10528–10530; (x) H. Li,
D.-X. Chen, Y.-L. Sun, Y. Zheng, L.-L. Tan, P. S. Weiss and Y.-W. Yang,
J. Am. Chem. Soc., 2013, 135, 1570–1576; (y) L. Chen, W. Si, L. Zhang,
G. Tang, Z.-T. Li and J.-L. Hou, J. Am. Chem. Soc., 2013, 135, 2152–2155;
(z) G. Yu, Y. Ma, C. Han, Y. Yao, G. Tang, Z. Mao, C. Gao and F. Huang,
J. Am. Chem. Soc., 2013, 135, 10310–10313.
Notes and references
1 (a) C. Wang, Z. Wang and X. Zhang, Small, 2011, 7, 1379–1383;
(b) C. Wang, Z. Wang and X. Zhang, Acc. Chem. Res., 2012, 45,
608–618; (c) J. Huang, S. Wang, G. Wu, L. Yan, L. Dong, X. Lai,
S. Yin and B. Song, Soft Matter, 2014, 10, 1018–1023.
6 (a) G. Yu, C. Han, Z. Zhang, J. Chen, X. Yan, B. Zheng, S. Liu and
F. Huang, J. Am. Chem. Soc., 2012, 134, 8711–8717; (b) G. Yu, M. Xue,
Z. Zhang, J. Li, C. Han and F. Huang, J. Am. Chem. Soc., 2012, 134,
13248–13251; (c) G. Yu, X. Zhou, Z. Zhang, C. Han, Z. Mao, C. Gao and
F. Huang, J. Am. Chem. Soc., 2012, 134, 19489–19497; (d) D. Xia, G. Yu,
J. Li and F. Huang, Chem. Commun., 2014, DOI: 10.1039/C3CC49686D.
7 (a) M. Kang and B. Moon, Macromolecules, 2009, 42, 455–458;
(b) J. Yin, H. Hu, Y. Wu and S. Liu, Polym. Chem., 2011, 2, 363–371.
8 (a) C. Wang, S. Yin, S. Chen, H. Xu, Z. Wang and X. Zhang, Angew.
Chem., Int. Ed., 2008, 47, 9049–9052; (b) X. Yan, B. Jiang, T. R. Cook,
Y. Zhang, J. Li, Y. Yu, F. Huang, H.-B. Yang and P. J. Stang, J. Am.
Chem. Soc., 2013, 135, 16813–16816; (c) Y. Yao, M. Xue, Z. Zhang,
M. Zhang, Y. Wang and F. Huang, Chem. Sci., 2013, 4, 3667–3672;
(d) X. Ji, J. Chen, X. Chi and F. Huang, ACS Macro Lett., 2014, 3,
110–113.
2 (a) H. Tian, B. Qin, R. Yao, X. Zhao and S. Yang, Adv. Mater., 2003, 15,
2104–2107; (b) S. Silvi, A. Arduini, A. Pochini, A. Secchi, M. Tomasulo,
F. M. Raymo, M. Baroncini and A. Credi, J. Am. Chem. Soc., 2007, 129,
13378–13379; (c) J. Babin, M. Pelletier, M. Lepage, J.-F. Allard,
D. Morris and Y. Zhao, Angew. Chem., Int. Ed., 2009, 48, 3329–3332;
(d) Q. Yan, J. Yuan, Z. Cai, Y. Xin, Y. Kang and Y. Yin, J. Am. Chem.
Soc., 2010, 132, 9268–9270.
3 (a) C. Park, K. Lee and C. Kim, Angew. Chem., Int. Ed., 2009, 48,
1275–1278; (b) T. Dvir, M. R. Banghart, B. P. Timko, R. Langer and
D. S. Kohane, Nano Lett., 2010, 10, 250–254; (c) M. J. Tucker,
J. R. Courter, J. Chen, O. Atasoylu, I. A. B. Smith and
R. M. Hochstrasser, Angew. Chem., Int. Ed., 2010, 49, 3612–3616.
4 (a) F. Huang, F. R. Fronczek and H. W. Gibson, J. Am. Chem. Soc., 2003,
125, 9272–9273; (b) F. Huang and H. W. Gibson, J. Am. Chem. Soc.,
2004, 126, 14738–14739; (c) F. Huang, D. S. Nagvekar, C. Slebodnick
9 I.-H. Lee, P. Amaladass, K.-Y. Yoon, S. Shin, Y.-J. Kim, I. Kim, E. Lee
and T.-L. Choi, J. Am. Chem. Soc., 2013, 135, 17695–17698.
This journal is ©The Royal Society of Chemistry 2014
Chem. Commun., 2014, 50, 3993--3995 | 3995