Solvent-dependent self-assembly and morphological transition of low-molecular-weight azobenzene organogel

Article abstract of DOI:10.1016/j.tet.2017.05.027

A novel low molecular weight organogelator (LMOG) containing an azobenzene group has been designed and synthesized. Stable gels could be formed in various organic solvents. UV–Vis spectroscopy indicated that the sol-gel transition of the organogels could be reversibly tuned by UV/visible light irradiations. Importantly, scanning electron microscopy (SEM) revealed that the characteristic gelation morphologies would vary from solvents of different polarities. FT-IR, XRD and rheological measurements demonstrated that the different nanostructures in polar and non-polar solvents might result from the differences in the intermolecular hydrogen bonding, π-π stacking driving forces as well as the different stacking models for the formation of the gels. Moreover, as an efficient phase-selective gelator, this photo-switchable gel could perform as an efficient absorbent and water cleaner to remove pollutants (e.g. rhodamine B).

Full text of DOI:10.1016/j.tet.2017.05.027

Accepted Manuscript
Solvent-dependent self-assembly and morphological transition of low-molecular-
weight azobenzene organogel
Zhiwei Zhang, Shaoze Zhang, Junji Zhang, Liangliang Zhu, Dahui Qu
PII:
S0040-4020(17)30501-X
10.1016/j.tet.2017.05.027
TET 28693
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 13 March 2017
Revised Date: 3 May 2017
Accepted Date: 8 May 2017
Please cite this article as: Zhang Z, Zhang S, Zhang J, Zhu L, Qu D, Solvent-dependent self-assembly
and morphological transition of low-molecular-weight azobenzene organogel, Tetrahedron (2017), doi:
10.1016/j.tet.2017.05.027.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Solvent-dependent Self-assembly and Morphological Transition of Low-Molecular-
Weight Azobenzene Organogel
a
b
a,
c
a
Zhiwei Zhang , Shaoze Zhang , Junji Zhang *, Liangliang Zhu , Dahui Qu *
a
Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry & Molecular Engineering, East China University of Science and
Technology, Shanghai 200237, China
b
Key Laboratory for Advanced Materials, School of Chemistry & Molecular Engineering, East China University of Science and Technology, Shanghai 200237,
China
c
State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A novel low molecular weight organogelator (LMOG) containing an azobenzene group has been
designed and synthesized. Stable gels could be formed in various organic solvents. UV-Vis
spectroscopy indicated that the sol-gel transition of the organogels could be reversibly tuned by
UV/visible light irradiations. Importantly, scanning electron microscopy (SEM) revealed that the
characteristic gelation morphologies would vary from solvents of different polarities. FT-IR,
XRD and rheological measurements demonstrated that the different nanostructures in polar and
non-polar solvents might result from the differences in the intermolecular hydrogen bonding, π-π
stacking driving forces as well as the different stacking models for the formation of the gels.
Moreover, as an efficient phase-selective gelator, this photo-switchable gel could perform as an
efficient absorbent and water cleaner to remove pollutants (e.g. rhodamine B).
Available online
keywords:
Low-Molecular-Weight Organogel
Solvent-dependent
Morphological Transition
Azobenzene
2
016 Elsevier Ltd. All rights reserved.
1
. Introduction
gelator-solvents would have a significant effect on the self-
assembly, resulting in different morphologies and properties of
Supramolecular gels, generated from self-assembly of small
35-38
the organogels.
For instance, Duan et al. showed that the
gelators, have attract considerable attentions in the past decades,
due to their wide applications including tissue engineering,
biomaterials, sensors, optoelectronic devices, nanomaterials,
supramolecular chirality of an azobenzene LMOG based
39
organogel could be modulated via solvent polarity. Recently,
Zhang et al. reported a Fmoc-amino acid gelator based
supramolecular gel, whose morphology could also be tuned by
1-9
pollutants removal, control of crystal, and so on. During the
formation of the gels, the noncovalent interactions, such as
hydrogen-bonding, π−π stacking, host-guest interactions, charge-
transfer (CT) interactions, metal ion to ligand coordination and
40
changing the solvent polarity. Therefore, it is essential to
investigate how solvents can influence the self-assembly and
gelation of the LMOGs, which could help understand the gelation
mechanism and further facilitate their potential applications.
10-17
electrostatic interactions,
play a significant role in driving the
small gelators to form the one-dimensional (1D) aggregate to
further 3D network. As a typical supramolecular gelator, low-
molecular-weight organogelators (LMOGs) take advantages of
accurate molecular weight, easy modification, multifarious
9
nanostructures, and stimuli-responsive properties. Compared
with traditional gels, it is easier for these supramolecular gels to
form and dissociate because of the weak interactions between the
gelator molecules, giving an access to possess stimulate-
responsive sol-gel phase transition performances. The stimulus
Scheme 1. The structure of azo-BDAD.
Herein, we constructed a novel photoresponsive LMOG (azo-
BDAD) based on an azobenzene derivative (Scheme 1) and
investigated its solvent-dependent self-assembly behavior in
various solvents. In non-polar solvents, the gelators self-
assembled to nanorod structure with the model of an
interdigitated bilayer, whereas the gelators stacked with a one-
above-the-other bilayer model to form lamellar structures in polar
solvents. All the assembled organogels would undergo reversible
18
2,19-21
22
23
24-
could be heat, light,
complexation, and oxidative/reductive reactions, etc., and
the combination of several independent/synergetic stimuli creates
sound, pH, host-guest interaction,
25
26
27
28-34
multifunctional smart gels.
In these LMOG gels, solvents are
the major components gelled by the minor gelators. Not only the
gelator-gelators but also the gelator-solvents interactions play
important roles in the formation of gels. Meanwhile, different
degrees of the noncovalent interactions of gelator-gelators and

2
Tetrahedron
sol-gel transitions tuned by UV/visible ligh
A
t
C
irr
C
ad
E
ia
P
tio
T
ns
E
for MAth
D
N
e d
U
ec
S
re
C
as
R
e
I
o
P
f π-π* absorbance band at 328 nm and the blue-
T
several cycles. Moreover, the gelators show selective gelation
from aromatic solvents-water at room temperature, and the self-
assembled organogels can be capable of adsorbing cationic dyes,
such as rhodamine B, which implies a potential application in
pollutants removal from water.
shift of n-π* absorbance band from 450 nm to 441 nm suggested
that the transformation from trans form to cis form. The cis form
returned to the trans form after visible light irradiation for 3 min
(Fig. 1A). The isomerization ratio for trans-cis and cis-trans are
over 60% and 80%, respectively (Fig. S2). Besides, the
photoswitching cycles between trans and cis isomers can be
operated several times without obvious degradation, showing a
good fatigue resistance for azo-BDAD (Fig. 1C). Similar results
were also observed in the organogel state (Fig. 1B). The photo-
switchable sol-gel transition was then conducted in a quartz cell.
After UV light (λ = 365 nm) irradiation for 20 min at room
temperature, the organogel in toluene gradually collapsed and
transformed into a viscous solution (Fig. 1D), demonstrating the
dissociation of the gel into solution phase. The transparent gel
formed again after visible light irradiation for 5 minutes (λ > 400
nm). Similar phenomena were obtained when i-butanol was used
as the solvent (Fig. S3). Surprisingly, compared to the photo-
switchable organogel in toluene, the backward sol-gel transition
didn’t occur under visible irradiation in i-butanol. The relatively
stiff structure of gels in i-butanol may attribute to the failure in
sol-gel transition reversibility under photo-irradiation.
2
.
Results and Discussion
.1. Gelation Properties
The gelation ability of azo-BDAD in various organic solvents
2
4
1
was investigated by inverting the vials upside down. The
gelator and solvent were first mixed in a screw-capped sample
tube, and the resulted mixture was then heated until the solid was
dissolved completely. After cooling down to the room
temperature, the corresponding gels were formed as the sample
stayed intact even the vial was inversed upside down. The
gelation testing results and the critical gelation concentration
(CGC, mg/mL) data were summarized in Table 1.
Table 1. Results of Gelation Testing in Various Organic
Solvents and Water at Room Temperature
a
Solvent
Phase(CGC)
Solvent
Phase(CGC)
n-hexane
I
ethyl acetate
i-propanol
chloroform
1,4-dioxane
acetone
S
cyclohexane
TG (2.5)
S
CCl
4
TG (1.7)
S
toluene
diethyl ether
i-butanol
DCM
TG (5.0)
S
P
G (10)
PG (13)
ethanol
P
G (7)
S
S
PG
S
acetonitrile
DMF
n-butanol
THF
methanol
DMSO
P
dichloroethane
P
S
a
G = turbid gel; TG = transparent gel; PG = partial gelation; P = precipitate; I
=
insoluble upon heating.
As shown in Table 1, azo-BDAD presented a good gelation
ability in a wide range of organic solvents. Transparent gels were
Fig. 1 A) Absorption spectra of azo-BDAD in toluene under UV
light (365 nm) and visible light irradiation for different times. B)
Absorption spectra of azo-BDAD gels from toluene under UV (365
nm) and visible light for different times. C) The cycles of absorbance
intensity at 328 nm in toluene. D) The reversible gel-sol transition
under UV/Vis light irradiation. All the concentration of the solution
formed in several non-polar solvents, such as cyclohexane, CCl4
and toluene, whereas turbid gels were obtained in polar solvents,
such as acetone, acetonitrile, i-butanol. The different appearances
may be resulted from the different microstructures and refractive
42
indexes between the organolges. In addition, the CGC of the
organogels in non-polar solvents is lower than that in polar
solvents, which shows that the gelator has a better gelling ability
-4
and gel are 1.0×10 M, 5 mg/mL, respectively.
2
.3. Rheological Measurements
in non-polar solvents (CCl has a lowest CGC of 1.7 mg/mL of
4
The mechanical properties of the formed gels from toluene, i-
all the tested solvents). All these organogels are very stable and
can endure more than half a month without obvious phase
separation at room temperature. Similar with organogels
butanol and acetone were then checked by rheological
measurements at 25 ℃ . The storage modulus (G′) is an order of
magnitude higher than the loss modulus (G″) at all the testing
frequencies in all solvents, indicating the formation of the
organogels (Fig. 2). In toluene and i-butanol, G′ and G″ at high
frequencies are always slightly higher than those at low
frequencies, possibly resulting from the slow rearrangement of
38-39
previously reported,
the azo-BDAD based organogels can
undergo thermoreversible gelation cycles, which the organogels
were melted upon heating and turned into gels upon cooling (Fig.
S1).
47
2
.2. Photoisomerization investigation in solution and gel states
azo-BDAD molecules in gels at high stress. It should be noted
that G′ and G″ values of azo-BDAD gels in i-butanol and acetone
become larger than those in toluene. For example, at ω = 10 Hz,
As a typical photochromic molecule, azobenzenes can
5
transform between trans and cis isomers when irradiated by
the G′ and G″ in i-butanol and acetone reach 1.56 × 10 , 6.38 ×
43-46
4
5
4
alternate UV/Vis light.
Thus, photochromic performances of
1
0 Pa and 1.90 × 10 , 3.19× 10 Pa respectively4, whereas those in
4
Azo-gels were first investigated in both solvents and gel states, as
shown in Fig. 1.
toluene only attain 9.85 × 10 and 2.30 × 10 Pa, respectively.
The results indicated that the gel formed from i-butanol and
acetone were more rigid than toluene, which might result from
the different self-assembly of these azo-gels in different
Photochromism of azo-BDAD was first examined in toluene
-
4
(
1.0×10 M). Upon irradiation with light of 365 nm for 10 min,

solutions. Also, as mentioned above, the azo-BDAD gives access
than that in i-butanol gel. In other words, hydrogen bonding is
probably the more preferred driving force in gels from non-polar
solvents. Similar trend can be observed in gels generated from
other solvents as shown in Table 2. Taking the molecular
structure of the gelator into considering, besides the hydrogen
bonding proved by FT-IR spectra, π-π interaction is also expected
to be one of the major driving forces for self-assembly. To
explore the π-π stacking interactions between azobenzene
chromophores, we investigated UV-Vis spectra of azo-BDAD in
gradual increasing concentrations (Fig. S5). The absorption band
in i-butanol showed a red-shift of about 2 nm, whereas no
changes were seen in toluene, indicating a more preferred π-π
ACCEPTED MANUSCRIPT
to transparent and turbid organogels in non-polar and polar
solvents, respectively. The different appearance of the gels
together with the different gel rigidities prompted us to shed light
on the possible intrinsic interactions and self-assembly models of
the resultant gels from different solvents.
48
stacking interaction in gels from polar solvents. Combined with
these results above, it could be summarized that the hydrogen
bonding and π-π stacking interactions are expected to be the two
major driving forces for gel formation. In non-polar solvents,
intermolecular hydrogen bonding via amide groups is the more
preferred driving force form gelation, while gelation counts more
on π-π stacking when polar solvents are used.
Fig. 2 Viscoelastic behaviors of organogels at 75 mg/mL from A)
toluene, B) i-butanol, C) acetone.
2
.4. Aggregation Morphology Studies
In order to explore the intrinsic factors for different gel
appearances, the micromorphologies were first examined by
monitoring the corresponding air-dried xerogels via SEM in Fig.
3
. The microstructure of the organogels obtained from toluene
was stubbly rod-like structure of more than 4 micrometers in the
length and about 1 micrometer in the width (Fig. 3A). In i-
butanol, azo-BDAD self-assembled orderly into lamellar
structures with about 5-10 micrometers in length and 2-4
micrometers in the width (Fig. 3B). In acetone, the aggregates of
the turbid organogels indicated that nanofibers were formed of
about 10−20 nanometers in the width and up to several
micrometers in the length and seemed to stack on top of each
other at intersections to yield an entangled structure (Fig. 3C).
Similar rod-like nanostructures and nanofibers were observed in
the CCl and acetonitrile, respectively (Fig. S4). The different
4
micromorphologies present the different assembly of the gelator,
which is determined by the gelator-gelators/gelator-solvents
35
interactions. From toluene/CCl4 to i-butanol and then to
acetone/acetonitrile, the microstructures gradually changed from
three-dimensional rod-like structures to lamellar structure and
then to nanofibers, demonstrating a solvent polarity-induced
regulation of the microstructures of the gel 3D networks.
Fig. 4 A) FT-IR spectra of azo-BDAD in DMF solution and gel
states from toluene and i-butanol. B) XRD patterns of the xerogels
obtained from toluene gels (5 mg/mL) and i-butanol gels (13
mg/mL). C) Staking models for the gelator arrangements in the
toluene gel. D) Stacking models for the gelator arrangements in i-
butanol gel.
-1
Table 2. Characteristic Vibrations (cm ) of the azo-BDAD
Obtained in Solvent (s) and Xerogel (x) States.
States
υ(N-H)
υ(C=O)
δ(N-H)
DMF (s)
3459
1667
1497
1522
1522
1524
1523
Fig. 3 SEM images of the organogels in various solvents at their
CGCs: A) toluene, B) i-butanol C) acetone.
toluene (x)
3366,3312
3363,3313
3363,3316
3365,3318
1734,1685,1629
1735,1685,1629
1731,1686,1630
1735,1686,1630
2
.5. Determination of the Driving Forces in Self-Assembly
4
CCl (x)
i-butanol (x)
In order to investigate the driving forces in self-assembly, we
monitored the FT-IR spectroscopies of azo-BDAD in solvent and
acetone (x)
xerogel states. As shown in Fig. 4A, the νN−H signals of azo-
−
1
BDAD in DMF solution appeared at about 3459 cm , and amide
carbonyl stretching (N−C=O, amide I) and N−H bending (amide
2
.6. XRD Studies and DFT analysis
To further understand the molecular arrangements and the
−1
II) bands appeared at around 1667 and 1497 cm , respectively,
indicating a non-hydrogen bonding state. In the gel state, the
peaks of N−H stretching and N−C=O stretching vibrations red-
shifted to 3312-3318 cm and 1629-1630 cm , respectively. Also,
the peak at 1522-1524 cm appeared, which was ascribed to the
amide II stretching frequency. Furthermore, the carboxylate
41
orientation of azo-BDADs in the gel state from different solvents,
the xerogels from toluene and i-butanol were examined by XRD.
In Fig. 4B, two broad diffraction peaks corresponding to the d
spacing of 3.13, 1.54 nm in the low angle region were observed
in toluene. The approximate d spacing ratio of 1:1/2 was
-
1
-1
-
1
−1
39
(
O−C=O) band at 1731-1735 cm was shown in xerogels. All
consistent with a lamellar structure. Taking the intermolecular
these results indicated that all the N−H and N−C=O are hydrogen
strong hydrogen bonding interaction into consideration, it could
be speculated that an interdigitated bilayer structure was obtained
in toluene, which was proved by computational method of
density functional theory (DFT) in Fig. 4C. The azo-BDADs
packed into interdigitated bilayer structures mainly through the
41
bonded in the gel state. On the other hand, comparing with
DMF solution, N−H stretching of the xerogel from toluene red-
shifted more wavenumbers than that from i-butanol, indicating a
more strengthened hydrogen bonding interactions in toluene gel

4
Tetrahedron
), MA
hydrogen-bonds of the N−H···N type bin
A
din
C
g
C
(F
E
ig
P
.
T
S
E
7A
D
w
N
ere
U
d
S
isc
C
ov
R
er
I
ed in non-polar and polar solvents, respectively. In
P
T
which agreed with our previous experimental conclusion.
Whereas, the length of 3.13 nm corresponded neither with the
extended molecular length of azo-BDAD (3.0 nm) nor with twice
the length (6.0 nm), which was the results of the interdigitation of
the alkyl chains in the aggregates. With the aliphatic alkyl chain
interdigitated together, the amide moieties organized into a well-
defined array which leads to the strong hydrogen bonding
interaction between gelator molecules. Similar results were also
non-polar solvents, an interdigitated stacking model was
preferred in the self-assembled 3D micromorphology of the gels,
due to the inversed strong hydrogen bonding interactions and
weak π-π stacking interactions; Whereas in polar solvents, the
gelator self-assembled into 3D nanostructure via a one-above-
the-other stacking model due to strong π-π stacking and weak
hydrogen bonding interactions. More importantly, as an efficient
room-temperature phase-selective gelator, it could offer a simple
and feasible approach for removing the RhB dye from water with
purification efficiency as high as 97%.
35
observed in the xerogels from CCl (Fig. S6A).
4
Nevertheless, as for the xerogels from i-butanol, three
pronounced peaks corresponding to the d spacing of 4.90, 2.49,
and 1.67 nm appeared in the low-angle region. The approximate
d spacing ratio of 1:1/2:1/3 was also indicative of the formation
4
. Experimental Section
4
.1. Materials
41
of a lamellar structure. According to the preceding results, we
suspected gelators formed gels in one-above-the-other assembly
model in i-butanol, which was also verified by computational
method of density functional theory (DFT) in Fig. 4D. In
hydrogen bond breaking polar solvents (e.g. i-butanol), the
formation of intermolecular hydrogen bonds are weakened. As a
result, intermolecular π-π stacking interaction becomes the
dominant driving forces, which prefer the one-above-the-other
assembly model (Fig. S7B). It should be noted that the width of
the column as calculated from the energy minimized orientations
was longer (5.3 nm) than the distance (4.9 nm) obtained from the
low-angle diffraction peaks presented in i-butanol xerogel, which
could be explained by some degree of tilt for the stacking
All starting reagents were commercially available and of
analytical purity and used without further purification. Solvents
used were analytical grade without further treatment, except the
dimethylformamide for amidation reaction and those for optical
tests, which were purified according to standard laboratory
methods. Thin layer chromatography (TLC) analysis was
performed on silica-gel plates. Column chromatography was
operated using silica-gel purchased from Qingdao Haiyang
Chemical (China).
4
.2. Instruments
NMR spectra were recorded on Bruker AM-400 spectrometers,
39
planes. Similar results were also observed in the xerogel from
acetone (Fig. S6B).
and high resolution mass (HRMS) spectra were recorded on a
Waters LCT Premier XE spectrometer. UV/Vis spectra were
recorded on Varian Cary 500 (1 cm quartz cell) at 25 ºC. Fourier
transform-infrared (FT-IR) spectra of samples were recorded on
IR Trace-100 (Shimadzu) spectrometer, and the samples were
ground with anhydrous KBr and pressed into thin wafers and
2
.7. Pollutants removal study
Water purification with gel-like materials is one of the most
7
popular water treatment methods nowadays. Phase-selective
gelation, which is used for removing aromatic pollutants (which
is always highly carcinogenic and toxic) from waters, is urgently
−1
scanned between the wavelengths of 4000 and 400 cm .
Scanning electron microscope (SEM) images were obtained on a
JEOL JSM-6360LV, and the samples were prepared by the air-
drying method and then coated with gold. Oscillatory rheology
measurements were performed using a Physica MCR501 (Anton
Paar GmbH, Austria) rheometer equipped with 25 mm parallel
plate geometry. All the gels were tested at a 0.1% of strain. X-ray
diffraction (XRD) was achieved on a Rigaku D/Max-2550 X-ray
diffractometer with Cu Kα radiation (λ = 1.5406 Å), which was
operated at 40 kV, 100 mA. Irradiation at 365 nm was carried out
27
required but challenging. To check the phase-selective gelation
performances of azo-BDAD for potential application in the water
purification, the commonly used RhB dye was selected as the
“
pollutant” due to its good solubility in water while relatively
lower solubility in common organic solvents. To a 2 mL of RhB
aqueous solution (0.03 mM), 1.0 mL of toluene was added. Then
1
0 mg of the gelator was added to the mixture and heated until
the gelator was dissolved in the toluene layer. Cooling to the
room temperature gave the azo-BDAD gel in the above toluene
layer. After 36 hours, the original purple red aqueous layer with
RhB gradually turned colorless, indicating that almost all of the
RhB was removed from aqueous layer to the gel. As a control
experiment, the color of RhB solution without organogels had
almost no change in the same condition (in Fig. S8B). The dye
was adsorbed in the toluene gel and purified water could be
collected by simple filtration. The purification efficiency was
determined using UV-Vis adsorption spectroscopy and calculated
as high as 97% (Fig. S8A). Thus, though the azobenzene gelator
itself is toxic, it could be used for absorbing water-soluble
organic dyes from water, providing a feasible and efficient proof-
of-concept approach for removing the toxic dyes from water.
2
using a hand-held UV lamp (the power density is ca. 2.0 W/m ),
and visible irradiation using a flashlight (the power density is ca.
2
1
50 W/m ) with a broad band interference filters (Shenyang HB
optical Technology) for λ irr > 400 nm).
4
.3. Synthesis
The target compound azo-BDAD was prepared from the
amidation reaction of p-(Phenylazo)benzoic acid (1) and N-Boc-1,
12-diaminododecanein (2) in the presence of BOP/TEA. The
detailed synthetic approach and methods are provided in
Supporting Information, Scheme S1.
Acknowledgements
3
. Conclusion
This research is supported by the National Natural Science
Foundation of China (21402050, 21420102004), the Programme
of Introducing Talents of Discipline to Universities (B16017).
We successfully designed and synthesized an efficient
photoresponsive organogel based on an azobenzene derivative,
which can achieve the sol-gel transition reversibly by heat/cool
process or UV/visible light irradiation. The gelator shows a good
gelation ability in organic solvents ranging from non-polar
solvents to polar solvents due to hydrogen bonding and π-π
stacking. Interestingly, two different kinds of packing models

References and notes
37. Zhu, P.; Yan, X.; Su, Y.; Yang, Y.; Li, J. Chem.– Eur. J. 2010, 16,
ACCEPTED MANUSCRIPT
3
176-3183.
1
.
Babu, S. S.; Praveen, V. K.; Ajayaghosh, A. Chem. Rev. 2014, 114,
973-2129.
3
3
4
4
8. Yan, N.; Xu, Z.; Diehn, K. K.; Raghavan, S. R.; Fang, Y.; Weiss, R. G.
J. Am. Chem. Soc. 2013, 135, 8989-8999.
1
2
3
4
.
.
.
Draper, E. R.; Adams, D. J. Chem. Commun. 2016, 52, 8196-8206.
Voorhaar, L.; Hoogenboom, R. Chem. Soc. Rev. 2016, 45, 4013-4031.
Yu, X.; Chen, L.; Zhang, M.; Yi, T. Chem. Soc. Rev. 2014, 43, 5346-
9. Duan, P.; Li, Y.; Li, L.; Deng, J.; Liu, M. J. Phys. Chem. B 2011, 115,
3
322-3329.
0. Zhang, Y.; Li, S.; Ma, M.; Yang, M.; Wang, Y.; Hao, A.; Xing, P. New
J. Chem. 2016, 40, 5568-5576.
5
371.
5
6
.
.
Foster, J. A.; Piepenbrock, M. O.; Lloyd, G. O.; Clarke, N.; Howard, J.
A.; Steed, J. W. Nat. Chem. 2010, 2, 1037-1043.
1. Geng, H.; Ye, L.; Zhang, A. Y.; Li, J.; Feng, Z. G. Langmuir 2016, 32,
4
586-4594.
Kaufmann, L.; Kennedy, S. R.; Jones, C. D.; Steed, J. W. Chem
Commun. 2016, 52, 10113-10116.
4
4
2. Toshiaki, D.; Masahiro, N.; Hiromi Y. Langmuir 2004, 16, 6530-6534.
3. Meng, X.; Gui, B.; Yuan, D.; Zeller, M.; Wang, C. Sci. Adv. 2016, 2,
e1600480.
4. Baroncini, M.; d'Agostino, S.; Bergamini, G.; Ceroni, P.; Comotti, A.;
7
8
9
1
.
.
.
Okesola, B. O.; Smith, D. K. Chem. Soc. Rev. 2016, 45, 4226-4251.
Zhang, L.; Wang, X.; Wang, T.; Liu, M. Small 2015, 11, 1025-1038.
Sangeetha, N. M.; Maitra, U. Chem. Soc. Rev. 2005, 34, 821-836.
4
Sozzani, P.; Bassanetti, I.; Grepioni, F.; Hernandez, T. M.; Silvi, S.;
Venturi, M.; Credi, A. Nat. Chem. 2015, 7, 634-640.
0. Piepenbrock, M. O. M.; Lloyd, G. O.; Clarke, N.; Steed, J. W. Chem.
Rev. 2010, 110, 1960-2004.
4
4
5. Manna, D.; Udayabhaskararao, T.; Zhao, H.; Klajn, R. Angew. Chem.
Int. Ed. 2015, 54, 12394-12397.
1
1. Bai, B. L.; Zhang, M. G.; Wei J.; Yan H. Y.; et al. Tetrahedron 2016,
6. Feringa, B. L.; Browne, W. R. Molecular Switches; Wiley-VCH:
Weinheim, 2001.
7
2, 5363-5368.
1
1
2. Buerkle, L. E.; Rowan, S. J. Chem. Soc. Rev. 2012, 41, 6089-6102.
3. Yu, G.; Yan, X.; Han, C.; Huang, F. Chem. Soc. Rev. 2013, 42, 6697,
4
4
7. Xie, Z.; Zhang, A.; Ye, L.; Feng, Z.-g. Soft Matter 2009, 5, 1474-1482.
8. Yan, N.; He, G.; Zhang, H.; Ding, L.; Fang, Y. Langmuir 2010, 26,
6
722.
5
909-5917.
1
4. Zhu, L.; Li, X.; Wu, S.; Nguyen, K. T.; Yan, H.; Agren, H.; Zhao, Y. J.
Am. Chem. Soc. 2013, 135, 9174-9180.
1
1
5. Wang, G.; Kang, Y.; Tang, B.; Zhang, X. Langmuir 2014, 31, 120-124.
6. Chung, J. W.; Yoon, S.-J.; Lim, S.-J.; An, B.-K.; Park, S. Y. Angew.
Chem. Int. Ed. 2009, 48, 7030-7034.
1
1
1
2
2
2
7. Xu, L.; Hu, Y. L.; Liu, M. C.; Chen, J. X.; et al. Tetrahedron 2015, 51,
2
079-2088.
8. Chung, J. W.; An, B. K.; Park, S. Y. A Chem. Mater. 2008, 20, 6750-
755.
9. Yu, J. J.; Cao, Z. Q.; Zhang, Q.; et al. Chem. Commun. 2016, 52,
2056-12059.
0. Zhang, W.; Chen, Y.; Yu, J.; Zhang, X.-J.; Liu, Y. Chem. Commun.
016, 52, 14274-14277.
1. Wang, S.; Shen, W.; Feng, Y.; Tian, H. ogelator. Chem. Commun. 2006,
4, 1497-1499.
6
1
2
1
2. Malicka, J. M.; Sandeep, A.; Monti, F.; Bandini, E.; Gazzano, M.;
Ranjith, C.; Praveen, V. K.; Ajayaghosh, A.; Armaroli, N. Chem. – Eur.
J. 2013, 19, 12991-13001.
2
2
2
2
3. Draper, E. R.; Eden, E. G.; McDonald, T. O.; Adams, D. J. Nat. Chem.
2
015, 7, 848-852.
4. Ni, M.; Zhang, N.; Xia, W.; Wu, X.; Yao, C.; Liu, X.; Hu, X. Y.; Lin,
C.; Wang, L. J. Am. Chem. Soc. 2016, 138, 6643-6649.
5. Chen, H.; Ma, X.; Wu, S.; Tian, H. Angew. Chem. Int. Ed. 2014, 53,
1
4149-14152.
6. Sarkar, S.; Dutta, S.; Chakrabarti, S.; Bairi, P.; Pal, T. ACS Appl. Mater.
Interfaces 2014, 6, 6308-6316.
2
2
7. Wang, Y.; Liu, Y.; Jin, L.; Yin, B. Soft Matter 2016, 12, 6373-6384.
8. Dasgupta, D.; Srinivasan, S.; Rochas, C.; Ajayaghosh, A.; Guenet, J. M.
Langmuir 2009, 25, 8593-8598.
2
9. Ji, X.; Jie, K.; Zimmerman, S. C.; Huang, F. Polym. Chem. 2015, 6,
1
912-1917.
3
3
3
0. Liu, M.; Zhang, L.; Wang, T. Chem. Rev. 2015, 115, 7304-7397.
1. Maeda, H. Chem. Eur. J. 2008, 14, 11274-11282.
2. Mondal, S.; Chakraborty, P.; Bairi, P.; Chatterjee, D. P.; Nandi, A. K.
Chem. Commun. 2015, 51, 10680-10683.
3
3. Van Herpt, J. T.; Areephong, J.; Stuart, M. C. A.; Browne, W. R.;
Feringa, B. L. Chem. Eur. J. 2014, 20, 1737-1742.
3
3
3
4. Zhu, G.; Dordick, J. S. Chem. Mater. 2006, 18, 5988-5995.
5. Wang, X.; Xie, F.; Duan, P.; Liu, M. Langmuir 2016. 32, 12534-12541.
6. Adhikari, B.; Banerjee, A. Soft Matter 2011, 7, 9259-9266.