Reversible photoswitching self-assembly of azobenzene-functionalized hyperbranched polyglycerol induced by host-guest chemistry

Article abstract of DOI:10.1007/s11426-011-4421-9

Reversible assembly and disassembly of rod-like large complex micelles have been achieved by applying photoswitching of supramolecular inclusion and exclusion of azobenzene-functionalized hyperbranched polyglycerol and α-cyclodextrin as driving force, promising a versatile system for self-assembly switched by light. Hydrogen-nuclear magnetic resonance ( ¹H NMR) and Fourier transform infrared (FT-IR) spectroscopy were applied to characterize the azobenzene-functionalized hyper-branched polyglycerol. Atomic force microscopy (AFM), transmission electron microscopy (TEM) and dynamic laser light scattering (DLS) were employed to investigate and track the morphology of the rod-like large complex micelles before and after irradiation of UV light.

Full text of DOI:10.1007/s11426-011-4421-9

SCIENCE CHINA
Chemistry
April 2012 Vol.55 No.4: 604–611
doi: 10.1007/s11426-011-4421-9
• ARTICLES •
Reversible photoswitching self-assembly of
azobenzene-functionalized hyperbranched polyglycerol
induced by host-guest chemistry
HAN Yi1, GAO Chao1* & HE XiaoHua2*
1 MOE Key Laboratory of Macromolecular Synthesis and Functionalization; Department of Polymer Science and Engineering,
Zhejiang University, Hangzhou 310027, China
2 Department of Chemistry, East China Normal University, Shanghai 200062, China
Received June 27, 2011; accepted July 15, 2011; published online November 21, 2011
Reversible assembly and disassembly of rod-like large complex micelles have been achieved by applying photoswitching of
supramolecular inclusion and exclusion of azobenzene-functionalized hyperbranched polyglycerol and α-cyclodextrin as driv-
ing force, promising a versatile system for self-assembly switched by light. Hydrogen-nuclear magnetic resonance (1H NMR)
and Fourier transform infrared (FT-IR) spectroscopy were applied to characterize the azobenzene-functionalized hyper-
branched polyglycerol. Atomic force microscopy (AFM), transmission electron microscopy (TEM) and dynamic laser light
scattering (DLS) were employed to investigate and track the morphology of the rod-like large complex micelles before and af-
ter irradiation of UV light.
azobenzene, hyperbranched polyglycerol, reversible self-assembly, host-guest chemistry
switched trans- and cis- transitions of azobenzene are of
1 Introduction
particular interest, if considering the host-guest chemistry
between azobenzene moiety and α-cyclodextrin (α-CD)
[11–19]. Trans azobenzene can be well recognized by α-CD
due to the hydrophobic and van der Waals interactions,
whereas the cis form cannot be included because of mis-
match between the host and α-CD guest [13, 15–18, 20–22].
For instance, Zhang and co-workers used amphiphilic sur-
factants containing azobenzene and α-CD to fabricate a
photo-controlled reversible supramolecular assembly sys-
tem [23]. Jiang and co-workers reported linear poly-
mer-based amphiphiles containing β-CD had dual reversible
self-assembly properties driven by inclusion complexation
between azobenzene and β-CD [24]. However pho-
toswitchable self-assembly of HPBs is yet to be reported.
In this article, we attempt to make use of the pho-
toswitchable inclusion and exclusion of azoben-
zene-functionalized hyperbranched polyglycerol (HPG-azo)
with α-CD to obtain a novel kind of “smart” complex mi-
Supramolecular self-assembly of hyperbranched polymers
(HBPs) represents a new research direction, and has at-
tracted increasing interest in the past years because of its
potential applications in the fields of drug delivery and bi-
omimetics [1–6]. Various topological supramolecular ag-
gregates and hybrids at all scales and dimensions have been
generated, such as nano- or micro-micelles, fibers, tubes,
and honeycomb films following the pioneering work of Yan
et al. [4, 5, 7–10].
Up to date, the obtained self-assembly structures of
HBPs in solution are generally in static station. However, in
life entity or in some other application cases, self-assem-
bling is demanded to be “smart”, which means stimuli-
responsive and reversible. In this respect, the photo-
*Corresponding author (email: chaogao@zju.edu.cn; xhhe@chem.ecnu.edu.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2011
chem.scichina.com www.springerlink.com

Han Y, et al. Sci China Chem April (2012) Vol.55 No.4
605
celles which can undergo reversible assembly and disas-
sembly.
1000 spectrometer was applied to obtain Fourier transform
infrared (FTIR) spectra using KBr disks. Dynamic laser
light scattering (DLS) measurements were performed using
a
BI-200SM Dynamic/static Laser Light Scattering,
2 Experimental
Brookhaven, and the wavelength of the laser was set at 630
nm. AFM images were obtained by using a Digital
Instrument (DI) Nanoscope IIIa scanning probe microscope,
under the tapping mode. Transmission electron microscopy
(TEM) studies were conducted on a JEOL JEM2010
electron microscope at 200 kV. A Varian Cary 100 Bio
UV-vis spectrophotometer was applied to obtain UV-vis
spectra. Induced circular dichroism (ICD) spectra were
recorded on a Biologic MOS-450 spectrometer in DMF
with 1 cm quartz cells.
2.1 Materials
HPG (Mn = 122 kDa, PDI = 1.16, DP = 1650), and 4-oxo-
4-(prop-2-ynyloxy)butanoic acid (alkyne-COOH) were
synthesized according to the previous work [25–28]. CuBr
(purified according to ref. [29] before use, 98%) was pur-
chased from Sigma–Aldrich. 1,1,4,7,7-Pentamethyl-
diethylenetriamine (PMDETA, 98%) was purchased from
Alfa Aesar. 6-(4-Methoxyazobenzene-4'-oxy)hexyl bromide
(azo-Br) was synthesized according to the published proto-
col [30]. All of the other reagents were purchased from Al-
drich and used as recezhaoxiaofen@hotmail.com; ived.
2.3 Synthesis of alkyne-modified HPG
As shown in Scheme 1, HPG (1.170 g, 15.82 mmol hydrox-
yl) and N,N-dimethylformamide (DMF, 4 mL) were added
into a Schlenk flask under nitrogen flow and stirred until the
HPG was totally dissolved and the flask was immerged into
the ice-water bath. Then N,N-dicyclohexylcarbodimide (DCC,
2.2 Characterization
Hydrogen-nuclear magnetic resonance (1H NMR) measur-
ements were carried out on a Varian Mercury 400 MHz
spectrometer using CDCl3 as the solvent. A PE Paragon
Scheme 1 Synthetic protocol for HPG-azo.

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Han Y, et al. Sci China Chem April (2012) Vol.55 No.4
3.300 g, 16.01 mmol), alkyne-COOH (2.540 g, 16.29
mmol), and 4-(dimethylamino)pyridine (DMAP, 0.195 g,
1.58 mmol) were added into the reaction system and the
Schlenk was sealed with a rubber plug. The reaction was
carried out in dark for 24 h at room temperature. During the
reaction, a small amount of dichloromethane could be added
if the system became too viscous. Then the mixture was
filtered and the residual dichloromethane was removed by a
rotary evaporator under reduced pressure. After that, the
mixture was precipitated in de-ionized water followed by
solubilizing the precipitate with acetone as little as possible
and then filtered. The solution was precipitated in
de-ionized water twice. The final product was obtained after
drying in a vacuum oven overnight at 30 °C (0.382 g, yield
38.2%). The final product was light yellow and sticky, and
should be stored in darkness [31].
tain amount of water was added dropwise into the solution
until the solution became opalescence indicating the
self-assembly had occurred. The cloudy dispersion was then
irradiated by UV light at 365 nm for 30 min, affording a
transparent solution again which might indicate the disas-
sembly of the complexation between HPG-azo and α-CD.
DLS was used to track the micelles’ size variation during
the process of adding water. Before and after UV light irra-
diation, DLS, AFM and TEM were applied to characterize
the assembled morphology. UV-vis spectra were also con-
ducted to record transmittance of the solution at 600 nm.
AFM samples were made by the spin-coating method on
freshly-peeled mica substrates before and after irradiation.
TEM samples were made by dropping onto 200 mesh holey
lacey carbon grids on a copper support.
3 Results and discussion
2.4 Synthesis of azo-N3
3.1 Synthesis of alkyne-modified HPG
6-(4-Methoxyazobenzene-4'-oxy) hexyl azide (azo-N3) was
synthesized from the substitution reaction of NaN3 and
azo-Br. To a 200 mL three-neck round-bottom flask
equipped with a condenser were added a solution of sodium
azide (0.781 g, 12 mmol) in DMF (10 mL) and azo-Br (2.35
g, 6 mmol). The flask was immersed in an oil bath at 75–80
oC and kept stirring for 5 days (caution: the azide is quite
explosively sensitive to friction during feeding and when
the temperature is higher than 80 oC). The mixture was pre-
cipitated in de-ionized water followed by filtering and
washing by 100 mL de-ionized water. The precipitation was
dissolved in acetone and then precipitated in de-ionized
water. The precipitation was filtered and dried in vacuum at
room temperature overnight. Yield: 1.512 g, 71.4%.
Similar to our previous work, alkyne-modified HPG was
synthesized by DCC condensation. Figure 1 shows the H
1
NMR and FTIR spectra of HGP-alkyne. All the peaks in the
1H NMR spectrum were coded by letters associated to the
protons of the products. As shown in the 1H NMR spectrum
of HPG-alkyne, two newly appearing peaks: peak b
(OCH2CCH) at 5.18 ppm and peak c (CH2CH2COO) at 2.67
ppm demonstrated the successful linkage of alkyne to HPG.
Because CDCl3 is a poor solvent for HPG (addition with the
shielding effect of the terminal chains), the signal from the
2.5 Synthesis of HPG-azo
To the Schlenk flask, HPG-alkyne (75 mg, 0.276 mmol of
alkyne groups calculated by the 1H NMR spectrum), azo-N3
(195 mg, 0.552 mmol), dichloromethane (4 mL) were added
and the flask was deoxygenated by bubbling nitrogen for 10
min. Then CuBr (8 mg, 0.055 mmol) and PMDETA (11.8
μL, 0.055 mmol) were added to the flask under nitrogen
flow. The reaction was carried out under room temperature
and lasted 12 h in darkness. After the reaction, the mixture
was precipitated in ether for three times. The final product
of HPG-azo was obtained after drying in a vacuum oven at
room temperature overnight [32, 33].
2.6 Self-assembly and disassembly of the complex mi-
celles constructed by HPG-azo and α-CD
In order to test the self-assembly properties of HPG-azo and
α-CD system, we prepared 0.167 mg mL–1 HPG-azo solu-
tion in DMF followed by dissolving excess α-CD (25 times
the amount of azobenzene groups of HPG-azo). Then a cer-
Figure 1 (A) 1H NMR spectrum of alkyne-modified HPG; (B) FT-IR
spectrum of alkyne-modified HPG.

Han Y, et al. Sci China Chem April (2012) Vol.55 No.4
607
core of HPG was slightly weakened. The reaction degree
can be roughly calculated by the following formula in
which Ac, Ae, Ad and Af represent the peak area of peaks c,
e, d and f respectively .
of HPG were transferred into alkyne groups, and all of them
reacted with azo-N3 groups during the step of “click” reac-
tion. The molecular weight of the HPG was 122 kDa, which
meant there were 1649 hydroxyl groups for a single HPG
molecule on average. Therefore, we calculated that on av-
erage one HPG-azo macromolecule possesses around 924
azo-arms.
R = 5/8·[Ac/(Ae + Ad + Af)]
1
From the integration of the signals from the H NMR spec-
Figure 4 shows the photoisomerization behaviors of
HPG-azo examined by UV-vis spectra in DMF. Upon irra-
diation with UV light at 365 nm, the absorption band of
HPG-azo at around 359 nm (ascribed to π-π* transition)
decreased significantly, and simultaneously the absorption
at 448 nm (ascribed to n-π* transition) increased slightly
(Figure 4(A)), indicating that the azobenzene groups of
HPG-azo changed from trans to cis state. By contrast, when
the DMF solution of HPG-azo was put in dark, the absorp-
tion at 359 nm increased gradually again and the absorption
at 448 nm decreased, suggesting that the azobenzene groups
of HPG-azo recovered from cis to trans state [34–36]. The
whole recovering process took about one day at room tem-
perature in dark.
trum, ~ 56% hydroxyl groups of HPG were transferred into
alkyne groups. The absorption peaks in the FTIR spectrum
also confirmed the formation of the expected structure. The
peaks at 2100 and 3280 cm1 were associated with alkyne
groups and the peak at around 1740 cm1 was assigned to
carbonyl groups.
3.2 Synthesis of azo-N3
1
As shown in Figure 2(A), all the peaks were labeled in H
NMR spectrum, and the peak e (CH2N3) was shifted from
3.44 ppm to around 3.30 ppm compared with azo-Br. This
could also be confirmed by the FTIR spectra as shown in
Figure 2(B). The newly appeared sharp peak at 2100 cm–1
was assigned to azido groups in azo-N3.
3.4 Self-assembly and disassembly of the complex mi-
celles constructed by HPG-azo and α-CD
3.3 Synthesis and photoisomerization behaviors of
HPG-azo
In order to test the self-assembly properties of HPG-azo and
α-CD system, we prepared 0.167 mg mL–1 HPG-azo solu-
HPG-azo was synthesized by Cu(I)-catalyzed azide-alkyne
click chemistry between alkyne-modified HPG and azo-N3.
As shown in Figure 3(A), the alkyne peak at 2100 cm–1
disappeared completely showing that the click reaction was
almost 100%. As mentioned above, ~ 56% hydroxyl groups
Figure 3 (A) FTIR spectrum of HPG-azo; (B) 1H NMR spectrum of
Figure 2 (A) 1H NMR spectrum of azo-N3; (B) FTIR spectra for (1)
HPG-azo.
azo-Br and (2) azo-N3

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Han Y, et al. Sci China Chem April (2012) Vol.55 No.4
Figure 4 (A) Absorption spectra of HPG-azo in DMF solution, observed
(a) before and after (b) 20 s, (c) 40 s, (d) 120 s and (e) 600 s of 365 nm
light irradiation at 365 nm. (B) The recovery absorption spectra of
HPG-azo in DMF solution which was irradiated for 15 min by UV light at
365 nm, observed after (f) 24 min, (g) 77 min, (h) 234 min, (i) 974 min and
(j) 24 h of stirring in the darkness.
tion in DMF followed by dissolving excess α-CD. Because
DMF is a good solvent for both HPG-azo and α-CD, the
solution was transparent. After addition of water into the
DMF solution, the solution became opalescence due to the
efficient complexation between the azobenzene moiety and
α-CD in the presence of water. The process was monitored
by DLS (Figure 5(A)). A peak around 800 nm appeared
after 0.5 mL of deionized water was added into 6 mL of the
DMF solution, indicating the self-assembly of HPG-azo and
α-CD. Atomic force microscopy (AFM) and transmission
electron microscopy (TEM) were used to observe the cor-
responding self-assembly morphology, as shown in Figure 6.
Rod-like assembled structures were found. Estimated from
AFM images, the rods have length of around 540 nm and a
diameter of 127 nm on average. In addition, some short rods
fused with two to three dots with in diameter 100 nm were
also observed. From the TEM image, the typical rods are
280 nm in length and 63 nm in width. The rod size meas-
ured by TEM was almost half of that measured by AFM.
The reason is likely attributed to the stained TEM samples
with tungstophosphoric acid hydrate. As the HPG core
binds with tungstophosphoric acid hydrate more tightly, the
colour of the core part would be much darker, which makes
the periphery part of HPG hardly seen under TEM bright
field. Furthermore, as shown in Figure 6(E), we can clearly
distinguish that the rod-like structures are aggregated line-
arly from three or more smaller dots (labeled by red cycles)
that could be unimolecular micelles of α-CD/HPG-azo
complex [37, 38]. This morphology is in agreement with
that observed by AFM. In order to demonstrate that the
rod-like micelles resulted from the complexation of HPG-
azo and α-CD, we prepared control samples without α-CD
or in the absence of water. No similar self-assembly mor-
phology was found in those samples. The formation of
complexation between HPG-azo and α-CD was also con-
Figure 5 DLS charts of HPG-azo and α-CD complex after adding water
(A) before UV irradiation and (B) after UV irradiation.
Figure 6 AFM images of (A) rod-like micelles before irradiation and (B)
its phase image. AFM images of (C) rod-like micelles before irradiation for
the fourth cycle and (D) its phase images. TEM images of (E) rod-like mi-
celles before irradiation and (F) unimolecular micelle after the irradiation.

Han Y, et al. Sci China Chem April (2012) Vol.55 No.4
609
firmed by induced circular dichroism spectra (ICD) meas-
urements (Figure 7). The peak appearing at around 353 nm
was associated to the complexation between HPG-azo and
α-CD. Therefore host-guest inclusion of azobenzene group
and α-CD is the inducing factor for the self-assembly of
HPG-azo in our system [32, 39, 40].
sembly process could be recycled for many times. As shown
in the AFM images in Figure 6(C), for the fourth cycle, the
rod-like aggregates could be again clearly distinguished.
The rods’ size was around 670 nm in length and 200 nm in
width, which was quite similar to the first cycle case. Con-
sidering the morphology errors came from irradiation and
magnetic stirring, we conclude that the self-assembled
morphology kept almost the same in different cycles. The
particle size and transmittance at 600 nm were tracked for
five cycles and the results are depicted in Figure 8(A),
showing the reversible self-assembly and disassembly for
the HPG-azo and α-CD systems through photoswitching. In
fact, the transparency difference before and after irradiation
could be observed by naked eyes and the comparison photo
is shown in Figure 8(B) [42].
The dynamic photoswitching process could be explained
by Scheme 2. Before irradiation, the azobenzene moiety in
the peripheral part is included by α-CD due to the hydro-
phobic interaction. We roughly calculated the ratio of inclu-
sion. The solution before irradiation was precipitated and
washed by water and dried in vacuum. The weight differ-
ence between the precipitate and the original HPG-azo re-
flects the amount of α-CD nesting the azobenzene moiety.
As a result, every azo-arm was included by 0.51 α-CD (i.e.,
about half of azo units were included by α-CD). The low
inclusion ratio is mainly caused by the high density of azo
groups and the simultaneous self-assembly of HPG-azo
during the inclusion of α-CD that might lead to the decrease
of effective azobenzene units. With increasing the inclusion
of α-CD, the interactions between CDs (e.g., hydrogen
bonding and crystallization), drive HPG-azo unimolecular
and multi-molecular micelles to self-assemble into larger
micelles such as rods. When irradiated by UV-light, the
trans-azobenzene units of HPG-azo transform into cis-ones,
and α-CD guests drop from the azo-arms, inducing the dis-
assembly of rod-like micelles. Because the host-guest inclu-
sion of HPG-azo and α-CD can be switched by light, the
self-assembly and disassembly of HPG-azo can be reversi-
bly tuned readily [43].
To demonstrate the photoswitching behaviors of self-
assembly of HPG-azo, the cloudy dispersion was then irra-
diated by UV light at 365 nm for 30 min, affording a trans-
parent solution again. DLS measurements show that the
peak at around 800 nm disappeared as expected, and the
peak around 200 nm appeared again, which corresponds to
the micelles assembled by several HPG-azo molecules.
(figure 5(B)). It is noteworthy that there was also a peak
around 50 nm in Figure 5(B), which corresponds to the
unimolecular micelle of HPG-azo. Because HPG-azo mol-
ecules were amphiphilic with the hydrophilic core and hy-
drophobic arms, they tend to form multi-molecular micelles
when a certain amount of water is added into the system.
The photoswitching behavior could be explained as follows.
During the irradiation process, most of the trans-azobenzene
units transform into cis-ones, making the guest of α-CD
released from the host of azobenzene because of the mis-
match between the host and guest. The TEM image after
irradiation shows that the rod-like structures disassembled
into unimolecular micelles and multi-molecular micelles of
HPG-azo (Figure 6(F)). The ICD spectrum further proved
that the azo moiety was excluded by α-CD because the sig-
nal at around 353 nm disappeared (see in Figure 7) [39, 41].
Therefore, the exclusion of α-CD caused by UV irradiation
was the main reason for the disassembly of rod-like mi-
celles.
Moreover, the clear solution became opalescence again
after being stirred by a magnetic bar for one day in dark,
and the peak around 800 nm in DLS also appeared. Because
DLS is more sensitive to larger particles, the signal from the
unimolecular micelles was sometime much weaker than the
larger one. Therefore we used the peaks around 200 nm
which correspond to the multi-molecular micelles to indi-
cate the disassembly of rod-like micelles for convenience.
With alternating irradiation of the solution with UV light
and stirring in dark for one day, this assembly and disas-
Figure 8 (A) Changes of Rh of the micelles ( triangle line) formed by
HPG-azo and α-CD and transmittance at 600 nm (circle line) of the solu-
tion upon alternating irradiation with UV for 30 min and stirred in
darkness for one day. Five cycles are shown in the figure; (B) the compar-
ison photo of solution of HPG-azo and α-CD before (right) and after (left)
irradiation.
Figure 7 ICD spectra of (1) HPG-azo and α-CD complex and (2) after 30
min of UV irradiation.

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characteristics and perspectives. Chem Commun, 2009(10):
1172–1188
6
7
8
Yan DY, Gao C, Frey H. Hyperbranched Polymers: Synthesis,
Properties, and Applications. New York: Wiley, 2011
Yan DY, Zhou YF, Hou J. Supramolecular self-assembly of
macroscopic tubes. Science, 2004, 303: 65–67
Gao C, Zheng X. Facile synthesis and self-assembly of
multihetero-arm hyperbranched polymer brushes. Soft Matter, 2009,
5(23): 4788–4796
9
Liu C, Gao C, Yan DY. Honeycomb-patterned photoluminescent
films fabricated by self-assembly of hyperbranched polymers. Angew
Chem Int Ed, 2007, 46(22): 4128–4131
10 Whitesides GM, Grzybowski B. Self-assembly at all scales. Science,
2002, 295(5564): 2418–2421
11 Asakawa M, Ashton PR, Balzani V, Brown CL, Credi A, Matthews
OA, Newton SP, Raymo FM, Shipway AN, Spencer N, Quick A,
Stoddart
JF,
White
AJP,
Williams
DJ.
Photoactive
azobenzene-containing supramolecular complexes and related
interlocked molecular compounds. Chem-Eur J, 1999, 5(3): 860–875
12 Chen L, Zhu XY, Yan DY, Chen Y, Chen Q, Yao YF. Controlling
polymer architecture through host-guest interactions. Angew Chem
Int Ed, 2006, 45(1): 87–90
13 Guo MY, Jiang M. Macromolecular self-assembly based on inclusion
complexation of cyclodextrins. Prog Chem, 2007, 19(4): 557–566
14 Harada A, Hashidzume A, Yamaguchi H, Takashima Y. Polymeric
rotaxanes. Chem Rev, 2009, 109(11): 5974–6023
15 Callari F, Petralia S, Sortino S. Highly photoresponsive monolayer-
Scheme 2 The structure of HPG-azo and illustration of the photoswitch-
ing of self-assembly and disassembly of HPG-azo and α-CD complexation.
protected gold clusters by self- assembly of
azobenzene-derived supramolecular complex. Chem Commun,
2006(9): 1009-1011
a cyclodextrin-
16 Chen X, Hong L, You X, Wang YL, Zou G, Su W, Zhang QJ.
Photo-controlled molecular recognition of alpha-cyclodextrin with
azobenzene containing polydiacetylene vesicles. Chem Commun,
2009, 11: 1356–1358
4 Conclusions
17 Luo CH, Zuo F, Ding XB, Zheng ZH, Cheng X, Peng YX. Light-
triggered reversible solubility of alpha-cyclodextrin and azobenzene
moiety complexes in PDMAA-co-PAPA via molecular recognition. J
Appl Polym Sci, 2008, 107(4): 2118–2125
18 Luo CH, Zuo F, Zheng ZH, Cheng X, Ding XB, Peng YX. Tunable
smart surface of gold nanoparticles achieved by light-controlled
molecular recognition effection. Macromol Rapid Commun, 2008,
29(2): 149–154
An azobenzene-functionalized hyperbranched polymer was
readily prepared by efficient Cu(I)-catalyzed alkyne/azide
click chemistry [44, 45]. This polymer showed host-guest
interaction induced assembly and disassembly behaviors
switched by light. Our work provids a novel smart system
which combines photo-chemistry, host-guest chemistry and
self-assembly of HBPs. The “smart” reversible assembly
and disassembly transitions would have potential applica-
tions in intelligent materials and biomimetics [19, 46–49].
19 Liu Z, Jiang M. Reversible aggregation of gold nanoparticles driven
by inclusion complexation. J Mater Chem, 2007, 17(40): 4249–4254
20 Fujimoto T, Nakamura A, Inoue Y, Sakata Y, Kaneda T.
Photoswitching of the association of
a permethylated alpha-
yclodextrin-zobenzene dyad forming a Janus 2 pseudorotaxane.
Tetrahedron Lett, 2001, 42(45): 7987–7989
21 Zheng PJ, Hu X, Zhao XY, Li L, Tam KC, Gan LH. Photoregulated
sol-gel transition of novel azobenzene-functionalized hydroxypropyl
methylcellulose and its alpha-cyclodextrin complexes. Macromol
Rapid Comm, 2004, 25(5): 678–682
22 Luo CH, Zuo F, Zheng ZH, Ding XB, Peng YX. Temperature/ ight
dual-responsive inclusion complexes of alpha-cyclodextrins and
azobenzene-containing polymers. J Macromol Sci Pure, 2008, 45(5):
364–371
This work was financially supported by the National Natural Science
Foundation of China (20974093), the National Basic Research Program of
China (973 Program, 2007CB936004), Qianjiang Talent Foundation of
Zhejiang Province (2010R10021), the Fundamental Research Funds for
the Central Universities (2009QNA4040), Zhejiang Provincial Natural
Science Foundation of China (R4110175) and Research Fund for the Doc-
toral Program of Higher Education of China ( 20100101110049).
23 Wang YP, Ma N, Wang ZQ, Zhang X. Photocontrolled reversible
supramolecular assemblies of an azobenzene-containing surfactant
with alpha-cyclodextrin. Angew Chem Int Ed, 2007, 46(16):
2823–2826
24 Zou J, Guan B, Liao XJ, Jiang M, Tao FG. Dual reversible
self-assembly of pnipam-based amphiphiles formed by inclusion
complexation. Macromolecules, 2009, 42(19): 7465–7473
25 Zhou L, Gao C, Xu WJ. Efficient grafting of hyperbranched
polyglycerol from hydroxyl-functionalized multiwalled carbon
nanotubes by surface-initiated anionic ring-opening polymerization.
Macromol Chem Phys, 2009, 210(12): 1011–1018
1
Guo B, Sun XY, Zhou YF, Yan DY. Supramolecular self-assembly
and controllable drug release of thermosensitive hyperbranched
multiarm copolymers. Sci China Chem, 2010, 53(3): 487–494
Han J, Gao C. Host-Guest Supramolecular Chemistry of Dendritic
Macromolecules. Curr Org Chem, 2011, 15(1): 2–26
2
3
Adeli M, Haag R. Multiarm star nanocarriers containing
a
poly(ethylene imine) core and polylactide arms. J Polym Sci Pol
Chem, 2006, 44(19): 5740–5749
Gao C, Yan DY. Hyperbranched polymers: From synthesis to
applications. Prog Polym Sci, 2004, 29(3): 183–275
Zhou YF, Yan DY. Supramolecular self-assembly of amphiphilic
hyperbranched polymers at all scales and dimensions: Progress,
4
5
26 Zhang Y, He H, Gao C. Clickable macroinitiator strategy to build
amphiphilic polymer brushes on carbon nanotubes. Macromolecules,

Han Y, et al. Sci China Chem April (2012) Vol.55 No.4
611
2008, 41(24): 9581–9594
synthesis of unimolecular polymeric janus nanoparticles and their
unique self-assembly behavior in a common solvent. Macromolecules,
2008, 41(21): 8159–8166
27 Kainthan RK, Muliawan EB, Hatzikiriakos SG, Brooks DE.
Synthesis, characterization, and viscoelastic properties of high
molecular weight hyperbranched polyglycerols. Macromolecules,
2006, 39(22): 7708–7717
28 Gao C, He H, Zhou L, Zheng X, Zhang Y. Scalable functional group
engineering of carbon nanotubes by improved one-step nitrene
chemistry. Chem Mater, 2008, 21(2): 360–370
39 Kodaka M. A general rule for circular dichroism induced by a chiral
macrocycle. J Am Chem Soc, 1993, 115(9): 3702–3705
40 Zhu XY, Chen L, Yan DY, Chen Q, Yao YF, Xiao Y, Hou J, Li JY.
Supramolecular self-assembly of inclusion complexes of a multiarm
hyperbranched polyether with cyclodextrins. Langmuir, 2004, 20(2):
484–490
29 Gao HF, Matyjaszewski K. Synthesis of star polymers by
a
combination of ATRP and the "click" coupling method.
Macromolecules, 2006, 39(15): 4960–4965
41 Zhao YL, Stoddart JF. Azobenzene-based light-responsive hydrogel
system. Langmuir, 2009, 25(15): 8442–8446
30 He X, Zhang H, Yan D, Wang X. Synthesis of side-chain
liquid-crystalline homopolymers and triblock copolymers with
p-methoxyazobenzene moieties and poly(ethylene glycol) as coil
segments by atom transfer radical polymerization and their
thermotropic phase behavior. J Polym Sci Pol Chem, 2003, 41(18):
2854–2864
31 Han Y, Gao C. Miktoarms hyperbranched polymer brushes: One-step
fast synthesis by parallel click chemistry and hierarchical
self-assembly. Sci China Chem, 2010, 53(12): 2461–2471
32 Wu J, He H, Gao C. β-Cyclodextrin-capped polyrotaxanes: One-pot
facile synthesis via click chemistry and use as templates for platinum
nanowires. Macromolecules, 2010, 43(5): 2252–2260
42 Pang Y, Liu JY, Su Y, Zhu BS, Huang W, Zhou YF, Zhu XY, Yan
DY. Bioreducible unimolecular micelles based on amphiphilic
multiarm hyperbranched copolymers for triggered drug release. Sci
China Chem, 2010, 53(12): 2497–2508
43 Yagai S, Kitamura A. Recent advances in photoresponsive
supramolecular self-assemblies. Chem Soc Rev, 2008, 37(8):
1520–1529
44 Kolb HC, Finn MG, Sharpless KB. Click chemistry: Diverse
chemical function from a few good reactions. Angew Chem Int Ed,
2001, 40(11): 2004–2021
45 Ladmiral V, Legge TM, Zhao YL, Perrier S. "Click" chemistry and
radical polymerization: Potential loss of orthogonality.
Macromolecules, 2008, 41(18): 6728–6732
33 Lutz JF. 1,3-Dipolar cycloadditions of azides and alkynes:
A
universal ligation tool in polymer and materials science. Angew Chem
Int Ed, 2007, 46(7): 1018–1025
34 Kumar GS, Neckers DC. Photochemistry of azobenzene-containing
polymers. Chem Rev, 1989, 89(8): 1915–1925
46 Zhai S, Hong HY, Zhou YF, Yan DY. Synthesis of cationic
hyperbranched multiarm copolymer and its application in
self-reducing and stabilizing gold nanoparticles. Sci China Chem,
2010, 53(5): 1114–1121
35 Zimmerman G, Chow LY, Paik UJ. The photochemical isomerization
of azobenzene. J Am Chem Soc, 1958, 80(14): 3528–3531
36 Hartley GS. 113 The cis-form of azobenzene and the velocity of the
thermal cis -> trans-conversion of azobenzene and some derivatives.
J Chem Soc, 1938, 633–642
37 Cheng F, Zhang KK, Chen DY, Zhu L, Jiang M. Self-assembly of
heteroarms core-shell polymeric nanoparticles (HCPNs) and
templated synthesis of gold nanoparticles within HCPNs and the
superparticles. Macromolecules, 2009, 42(18): 7108–7113
38 Cheng L, Hou GL, Miao JJ, Chen DY, Jiang M, Zhu L. Efficient
47 Zhang JX, Ma PX. Polymeric core-shell assemblies mediated by
host-guest interactions: Versatile nanocarriers for drug delivery.
Angew Chem Int Ed, 2009, 48(5): 964–968
48 Wang YP, Zhang M, Moers C, Chen SL, Xu HP, Wang ZQ, Zhang X,
Li ZB. Block copolymer aggregates with photo-responsive switches:
Towards a controllable supramolecular container. Polymer, 2009,
50(20): 4821–4828
49 Sun XY, Zhou YF, Yan DY. Drug release property of
a
pH-responsive double-hydrophilic hyperbranched graft copolymer.
Sci China Ser B Chem, 2009, 52(10): 1703–1710