Multistimuli responsive organogels based on a reactive azobenzene gelator

Article abstract of DOI:10.1039/c3sm53145g

A reactive azobenzene based super organogelator was found to rapidly and reversibly transform a range of hydrophobic solvents from gels to solutions upon changes in temperature, light and shear force. More specifically they formed gels at concentrations as low as 0.08 wt%. Upon heating, exposure to UV light, or application of shear, the π-π bonding was disrupted which resulted in a rapid drop of both modulus and viscosity. This was confirmed by ¹H NMR, SAXS, and rheological measurements. Although many examples of organogelators are known in the literature, this is the first time that a reactive group, a benzoyl chloride, has been incorporated in a supramolecular organogel structure. Moreover, this group is available for subsequent synthetic modifications. The presence of benzoyl chloride groups showed a remarkable effect on the formation and properties of the gels. Compared with other approaches, this strategy is advantageous in terms of structural design since it not only produces a multi-responsive soft material but also allows facile modifications which may expand the applications of organogels to other fields.

Full text of DOI:10.1039/c3sm53145g

Soft Matter
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Multistimuli responsive organogels based on a
reactive azobenzene gelator†
Cite this: Soft Matter, 2014, 10, 2188
ab
c
b
*
*
Shuhua Peng and Timothy C. Hughes
Runmiao Yang,
A reactive azobenzene based super organogelator was found to rapidly and reversibly transform a range of
hydrophobic solvents from gels to solutions upon changes in temperature, light and shear force. More
specifically they formed gels at concentrations as low as 0.08 wt%. Upon heating, exposure to UV light,
or application of shear, the p–p bonding was disrupted which resulted in a rapid drop of both modulus
and viscosity. This was confirmed by 1H NMR, SAXS, and rheological measurements. Although many
examples of organogelators are known in the literature, this is the first time that a reactive group, a
benzoyl chloride, has been incorporated in a supramolecular organogel structure. Moreover, this group
is available for subsequent synthetic modifications. The presence of benzoyl chloride groups showed
a remarkable effect on the formation and properties of the gels. Compared with other approaches,
this strategy is advantageous in terms of structural design since it not only produces a multi-responsive
soft material but also allows facile modifications which may expand the applications of organogels to
other fields.
Received 18th December 2013
Accepted 17th January 2014
DOI: 10.1039/c3sm53145g
www.rsc.org/softmatter
attention, since it is a non-contaminating stimulus that
provides a broad range of tunable parameters, e.g., wavelength,
Introduction
intensity, and duration, to manipulate the rheological proper-
ties of photoresponsive systems.10–12
Organogels are capable of forming gels with organic liquids at
relatively low concentrations through non-covalent interac-
tions. They differ from traditional polymer gels which typically
form three-dimensional network structures through covalent
crosslinks.1 Low molecular weight organogels (LMOGs) may be
thermoreversible, viscoelastic materials which can self-
assemble into complex three-dimensional structures via
multiple non-covalent interactions including hydrogen bonds,
hydrophobic interactions, p–p interactions and van der Waals
forces.2–4 Responsive or ‘smart’ LMOGs are new types of self-
assembled materials which have attracted great interest
recently.5,6 They can dynamically respond to external stimuli
and, thus, are of particular interest in both research and
industrial applications such as controlled release systems,
catalyst systems, and nano-reactors.7,8 Several different types of
smart responsive systems have been reported, namely, photo-,
electrochemical, ionic and pH responsive LMOG systems.9
Among these external stimuli, light has attracted considerable
Photo-active groups such as diarylethene substituted buta-
dienes,13 Fe(II) triazoles,14 merocyanines,15 and azobenzenes16–18
have been successfully introduced to LMOGs. Through these
groups the chemical nature of the gel can change the self-
assembly structure upon exposure to different wavelengths of
light. LMOGs incorporating the azobenzene moiety exhibit
trans-to-cis photoisomerisation behavior which inuences the
mechanical properties of the gel upon UV/visible light irradia-
tion.19,20 Recently, multistimuli responsive organogels contain-
ing azobenzene have also been reported. For example, Liu21
designed and synthesized an organogelator (Azo-G3) whose self-
assembly behavior and gel formation ability was investigated in
detail. Meanwhile, Wang22 and Zhang23 designed and studied
multistimuli responsive organogels featuring electroactive tet-
rathiafulvalene (TTF) and photoresponsive azobenzene groups.
Although azobenzene gelators containing relatively inert func-
tional groups, such as alkyl chains, benzene rings, ethers and
esters, have been widely reported,24–26 to the best of our
knowledge, multistimuli-responsive organogelators comprising
reactive functional groups which are capable of forming stable
gels have not been previously described. Typically, LMOGs form
gels at concentrations higher than 1.0 wt% which may limit
their commercial applicability. Zinic et al., dened ‘super
gelator’ as a class of gelators with critical gelation concentration
(CGC) below 0.1 wt%.27 To date relatively few azobenzene based
super gelators have been reported.8,21,27
aDepartment of Material Engineering, Jiangsu University of Technology, Changzhou,
213001, China. E-mail: yangrunmiao@jsut.edu.cn; Tel: +86-519-86953291
bCSIRO Materials Science and Engineering, Bayview Avenue, Melbourne, VIC 3168,
Australia. E-mail: tim.hughes@csiro.au; Tel: +61-3-95452503
cDepartment of Chemical and Biomolecular Engineering, University of Melbourne,
Melbourne, VIC 3010, Australia
† Electronic supplementary information (ESI) available: Synthetic procedures and
characterization data for new compounds; the thermal behaviours, viscosity and
morphologies of the gels in different temperature; modulus and SAXS data on
exposure to UV light. See DOI: 10.1039/c3sm53145g
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Reactive groups which are incorporated into LMOGs not only conducted using an ARES photo-rheometer (TA Instruments,
act as an effective unit to control the morphology of their self- USA) connected to an EXFO Acticure 4000 UV light source
assembly but also play an important role in forming an orga- (365 nm, 200 mW cmꢀ2) and quartz-halogen visible light source
nogel. More importantly, they may provide a bridge to introduce (>540 nm, 38 mW cmꢀ2) via liquid light-guide. A Peltier
further functionalities through synthetic elaboration and temperature controller was also connected to the rheometer to
expand the applications of such smart materials.28–30 With those maintain the temperature. POM was conducted using a Nikon
objectives in mind, we designed and synthesized a new low Eclipse 80i. SAXS experiments were performed at the Australian
molecular weight organogelator (C8-Azo-TPC), composed of an Synchrotron on the small/wide angle X-ray scattering beamline
alkyl chain, an azobenzene unit, and a reactive benzoyl chloride working at 12.0 keV.
moiety. The azobenzene unit provides the possibility of multi-
responsiveness while the benzoyl chloride moiety enables facile
functionalization of the gelator.
Determination of critical gelation concentration (CGC)
Typically, 5 mg of gelator was mixed with 0.5 g of solvent. The
mixture was heated until the organogelator dissolved and a
clear solution was obtained. The solutions were then cooled to
room temperature and gel formation was determined by
inverting the vials.
Experimental section
Synthesis of C8-Azo-TPC, preparation, and characterization are
described in detail in the ESI.† All chemicals were purchased
from Sigma-Aldrich and Merck and used without further puri-
cation. No purication was performed on the solvents except
Results and discussion
for the tetrahydrofuran (THF) and toluene, which was taken The synthesis of the 4-chlorocarbonyl-benzoic acid 40-(400-octy-
from an Innovative Technologies, Inc., solvent purication loxy-phenylazo)-benzyl ester (C8-Azo-TPC, (4)) started from
system. All the chemicals were characterized by 1H and 13C phenol and p-ethylcarboxylate analine in a 4 step procedure
NMR spectroscopy on a 400 MHz Bruker Ultrashiled Spec- outlines in Scheme 1. The synthetic details and characterization
trometer (Bruker, Germany) in CDCl3. Accurate mass spectra data are provided in the ESI.†
were obtained on a Thermo Scientic Q Exactive FTMS,
The gelation ability of C8-Azo-TPC was evaluated in various
employing ASAP probe. Photoisomerization of C8-Azo-TPC was organic solvents by inversion test of cooled solutions. The
measured on a Cary 50-Bio UV-Vis Spectrophotometer (Varian) gelation results with critical gelation concentrations are pre-
against a background of solvent in a quartz cuvette. Trans to cis sented in Table 1. Stable gels were formed when the C8-Azo-TPC
isomerisation was induced by an EXFO Acticure 4000 light was mixed with nonpolar solvents such as alkanes while it was
source via a liquid light-guide working at 365 nm wavelength. soluble in polar solvents, such as chloroform, acetone and THF.
The UV light intensity was about 3.8 mW cmꢀ2. Cis to trans Apart from gels formed in DMF and petroleum fuel, C8-Azo-TPC
isomerisation was induced by visible light at 12.1 mW cmꢀ2
UV-vis data was collected every 30 seconds. Rheology was indicating its ‘super gelator’ properties.31–33 C8-Azo-TPC formed
.
was able to form gels at concentrations less than 0.1 wt%,
Scheme 1 Synthesis of C8-Azo-TPC.
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Table 1 Gelation ability of C8-Azo-TPC in various solvents at room temperaturea
Solvent
State
CGC (wt%)
Solvent
State
CGC (wt%)
Olive oil
Petroleum fuel
THF
S
G
S
S
S
S
S
S
S
S
G
—
2.4
—
—
—
—
—
—
—
—
0.4
Carbon tetrachloride
Engine oil
n-Hexane
n-Heptane
n-Decane
n-Octane
n-Dodecane
DMF
Cyclohexane
n-Dodecane/EtOAc ¼ 10/1
n-Heptane/EtOAc ¼ 10/1
S
S
—
—
G
G
G
G
G
PG
G
G
G
0.4
0.4
0.1
0.1
0.08
1.0
0.5
0.2
0.4
Benzene
Ethyl acetate
Dichloromethane
Acetone
1,4-Dixane
Toluene
Chloroform
Petroleum benzine
a
CGC, critical gelation concentration, the minimum concentration necessary for gelation of solvents; S, soluble; G, gel; PG, partial gel.
n-dodecane at 0.1 wt%. Aer cooling, it formed a light trans-
parent yellow gel, through which the background could be
clearly observed (Fig. 1). The intensity of the color of the gels
and solution depended on the concentration of the C8-Azo-TPC
used.
Thermal induced sol/gel transitions
Representative photographs of sol–gel process are shown in
Fig. 2. An orange colored solution in n-dodecane (1.0 wt%) was
formed by heating. Upon cooling, the yellow colored gel could
be regenerated within 3 minutes (or faster if actively cooled)
(Fig. S12†). This reversible gel–sol phase transition could be
repeated several times as demonstrated by the reversible
changes in optical transmission upon repeated heating and
ꢁ
cooling cycles between 20 and 60 C (Fig. 3). Even aer several
Fig. 1 Photographs of the azobenzene sol (60 ꢁC) and gel (20 ꢁC) in n-
months, the gel remained stable. A rheological study showed a
dodecane at 0.1 wt%.
reversible change in viscosity with change in temperature
(Fig. 4). Initially, at 20 ꢁC the sample was a viscous liquid with a
a translucent yellow gel in alkane or mixed solvents at very low
|h*| ꢂ 210 Pa s. immediately following the increase in
concentrations with CGCs as low as 0.08 wt%, directly compa-
rable to the best know azobenzene gelators.8,21 Fig. 1 shows
photographs of the azobenzene sol (60 ꢁC) and gel (20 ꢁC) in
temperature, a dramatic decrease of viscosity was observed.
Specically, the viscosity reached a new steady state of |h*| ꢂ 5
Pa s at 55 ꢁC which was maintained until the temperature began
Fig. 2 C8-Azo-TPC in n-dodecane (1.0 wt%), multistimuli responsive organogels.
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Fig. 3 Spectra of C8-Azo-TPC in n-dodecane at 1.0 wt% alternating
temperature from 20 ꢁC to 60 ꢁC to 20 ꢁC for six times cycle.
Fig. 5 POM images (200ꢃ magnification) for C8-Azo-TPC in n-
dodecane (1.0 wt%) under (a) visible light at 20 ꢁC, (b) polarized light at
20 ꢁC, (c) visible light at 80 ꢁC, (d) polarized light at 80 ꢁC, respectively.
Fig. 4 Plot of viscosity against the temperature of C8-Azo-TPC in
n-dodecane, (1.0 wt%). (,) |h*| vs. time; (-) temperature vs. time.
to decrease. Upon a reduction in temperature, the viscosity was
restored to the initial state, and the sample regained a gel-like
viscous state. Fig. 5 shows 200ꢃ magnication polarizing
optical microscope (POM) photographs of the C8-Azo-TPC gel in
n-dodecane at 1.0 wt%. The structure of both the gel (20 ꢁC) and
ꢁ
solution (80 C) could clearly be observed. Bright areas in the
POM images indicate the presence of a self-assembled macro-
scale C8-Azo-TPC domain potentially a liquid crystal like struc-
ture. Upon heating the polarization phenomenon mostly
disappeared due to the loss of an organized network structure.
Jung et al. reported similar behavior of organo gels, which were
formed through intermolecular hydrogen bonds, p–p stacking,
and hydrophobic interaction.34
Variable temperature NMR spectroscopy was performed to
investigate the gelation mechanism. In CDCl3, a non-gelling
solvent for C8-Azo-TPC, the 1H NMR the spectrum of C8-Azo-TPC
contains only one set of peaks consistent with the proposed
Fig. 6 Variable temperature 1H NMR studies of the C8-Azo-TPC in
cyclohexane (1.0 wt%).
1
structure (Fig. S4†). In contrast, the H NMR spectrum of C8-
Azo-TPC in cyclohexane show multiple sets of peaks consistent interactions and those of the free molecules, as also observed by
with the coexistence of C8-Azo-TPC in two different states: an Jung.34 Upon heating, the integral of the aggregate peaks
aggregate (peaks at d7.58, 6.94, 6.76 5.42 and 3.92 ppm) and decreased while the integral of the single molecular state peaks
single molecular state (peaks at d8.41, 8.12, 7.74, 7.08, 5.50 and increased. Upon cooling, the reverse changes in peak integrals
4.02 ppm) (Fig. 6). The difference in chemical shi between were observed. Although the integral of each peak changed
protons in the gel and solution state are consistent with mole- depending on the temperature, the integration ratio between
cules associated by p–p stacking and/or the hydrogen-bonding the aggregate and single molecule state was constant. The
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integration ratio of peaks at d3.90–4.10, 5.35–5.60, and 6.70– under mechanical stimuli which overcame the relatively weak
8.50 ppm corresponding to the alkyl chain methylene (h), p–p interactions. Thus, the major reason why the system acted
benzyl methylene (c) and aromatic protons (a, b, e, d, g, f), as a uid gel–sol mixture was associated with its aggregation
respectively, remained at 1 : 1 : 6 at all temperatures. Thus, the mode. Fig. 7b shows the transition state between gel and sol
changes in the NMR spectrum with temperature are consistent which has not previously been reported. Owing to the
with a gelator transitioning between the gel and solution state mechanical stimuli, the brous aggregate was partially broken
resulting from variation in the interactions between the resulting in a mixture of both brous and vesicular structures.
molecules.
Aer resting for a few minutes, the micelles disappear and long
Synchrotron small angle X-ray scattering (SAXS) is a powerful microbers slowly reformed. Regeneration of the bers resulted
method for exploring supramolecular structures.35 Further in the reformation the gel state. The cycle involving vesicle-ber
evidence for the thermally driven dissociation of the self transformation could be repeated many times (Fig. 2).
assembled gels were obtained by SAXS analysis of the C8-Azo-
The mechano-responsive behavior of the organogels repor-
TPC gels. Scattering peaks in the SAXS spectrum of C8-Azo-TPC ted here was further investigated by rheological measurements.
ꢀ1
Plots of storage (G0) and loss (G00) moduli monitored as func-
˚
gel in n-dodecane 1.0 wt% at room temperature at q ¼ 0.13 A
ꢀ1
˚
and q ¼ 0.21 A show the presence of a long-range ordered tions of shear strain were shown in Fig. 8. It can be clearly
structure (Fig. S15†). However, this long-range order decreased observed that at initial strain values, the value of G0 (about 4600
as the sample was heated with the structure almost completely Pa) was greater than G00 (about 1300 Pa), indicating a dominant
ꢁ
disappeared when the mixture was heated to 85 C.
elastic characteristic of the sample. When the strain was initi-
ated, the G0 and G00 values of the gels decreased with increasing
strain at 20 ꢁC. At low strain values, a sharp decrease of G0 and
G00 was observed, representing a partial breakup of the gel.
Furthermore, a pronounced reduction was recorded for the
storage modulus (G0), which dropped from around 4800 Pa to
600 Pa. Specically, the viscosity plummeted from about 1000
Pa s down to around 150 Pa s. Likewise a reduction was recor-
ded for the loss modulus (G00), which dropped from around
1400 Pa to 500 Pa.
Shear induced sol/gel transitions
In addition to temperature, the gel–sol phase transition could
also be triggered by mechanical stimulus. For example, as
shown in Fig. 2, at 1.0 wt% concentration, the gel of C8-Azo-TPC
in n-dodecane became uid as a result of vigorous shaking. This
is consistent with partial disruption of the self-assembled
1
structure. In this system, as indicated by the H NMR analysis
above, C8-Azo-TPC co-existed in both gel and solution at the
same time. In order to obtain a visual insight into the
morphologies, optical microscopy (OM) was used to observe
the gel–sol phase transition (Fig. 7). In the gel state, as shown in
Fig. 7a, the gel exhibited entangled and dense brous aggre-
gates. Three dimensional brous networks containing bers
with widths of several micrometres and lengths of hundreds of
micrometres were observed for the gel state. Similar brous
structures were also observed in other azobenzene containing
gels.21,19 These three dimensional networks, formed from self
assembly of the C8-Azo-TPC into a brous structure, were
responsible for the gelation. By applying force to the gel
between microscope slides, the generated shear caused the gel
to transform into vesicular structures (Fig. 7c). Following
exposure to shear, Lee et al., also reported observing similar
changes to the gel morphologies.36 These observations imply
that without shear C8-Azo-TPC tended to aggregate into linear
Fig. 8 Storage modulus G0 and loss modulus G00 values of a C8-Azo-
TPC organogel (n-dodecane, 1.0 wt%) on rheological experiments of
bers due to p–p interactions but formed vesicular structures strain sweep.
Fig. 7 Optical microscopy images (400ꢃ magnification) of C8-Azo-TPC in n-dodecane (1.0 wt%), 20 ꢁC, (a) gel; (b) transition between gel and
sol; (c) sol.
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Fig. 9 Storage modulus G0 and loss modulus G00 values of a C8-Azo-
TPC organogel (n-dodecane, 1.0 wt%) on rheological experiments of
frequency sweep.
Frequency sweep experiments were conducted to study the
mechanical properties of the gel. In all cases, the value of G00
was below the value of G0 at all frequencies. Furthermore, the G0
and G00 of both gels exhibited very strong frequency dependence
in the range from 0.1 to 10 rad sꢀ1 and minimal frequency
dependence in the frequency range of 10–100 rad sꢀ1. The
results depicted in Fig. 9 showed that a pronounced increased
was recorded for the storage modulus (G0), which increased
from around 2600 Pa to 6000 Pa, as well as the loss modulus
(G00), which increased from around 1500 Pa to 4600 Pa. Specif-
ically, the viscosity dropped markedly from about 2000 Pa s to
around 10 Pa s. Similar thixotropic properties of the organogels
in other solvents were also observed (e.g., see n-heptane results
in the ESI section†).
Fig. 10 C8-Azo-TPC in n-dodecane at 20 ꢁC (0.002 wt%), (a) change
in absorption of UV-Vis spectra over time under UV light (365 nm,
3.8 mW cmꢀ2); (b) change in absorption of UV-Vis spectra over time
under visible light (12.1 mW cmꢀ2).
modulus (G00) with time were clearly observed under UV light
exposure. Initially in the absence of UV exposure, the G0 was
greater than G00 indicating solid-like gel (i.e. beyond the G0, G00
Photo induced sol/gel transitions
Azobenzene compounds are well-known for their reversible crossover point). However, during exposure of the gel to UV light
photoisomerization between the trans and cis forms under (from 3 min) a dramatic decrease of modulus was observed and
alternating UV and visible light irradiation.37 In order to a new plateau value was reached within 1 min (Fig. S13†). A
investigate the light-responsive behavior of the C8-Azo-TPC in corresponding change in viscosity was also observed (Fig. 11).
n-dodecane, UV/Vis spectroscopic studies of the compound The initial highly viscous gel changed to a low viscosity uid
were also performed. C8-Azo-TPC shows a broad absorption under UV irradiation within one minute. Aer a period of UV
around 350 nm mainly due to the trans form of the azo- exposure, a new steady state was established and the UV light
benzene group. The resulting gels were subjected to UV irra- was turned off. At the same time, visible light was turned on.
ꢁ
diation at 365 nm for 20 min at 20 C. The orange gels were The reversibility of the system was demonstrated by the rapid
found to collapse gradually and nally turned into trans- recovery of the rheological properties upon exposure to visible
parent solutions. As shown in Fig. 10(a), UV irradiation results light. Viscosity was restored close to the initial state before UV
in the trans–cis isomerization, indicated by the decay of the light irradiation recommenced, and the sample regained a gel-
maximum absorption band at around 350 nm and the like viscous consistency. Such gel–sol phase transition by UV
generation of a new absorption at 446 nm. Importantly, for and visible light irradiation was reversible and again could be
practical applications, this photo-induced isomerization was repeated many times (Fig. 2).
reversible, as the azobenzene in cis form relaxes to trans form
Real-time synchrotron SAXS measurements38,39 were also
within a few minutes aer exposure to visible light or more carried out to obtain structural information of the gelator in n-
slowly in the dark. Fig. 10(b) showed that the cis to trans iso- dodecane under different light exposure (Fig. 12). Initially, the
merisation was achieved by the subsequent irradiation of SAXS spectrum of the gel was measured in the dark.ꢀ1Upon
˚
visible light.
exposure to UV light, the SAXS peaks at q ¼ 0.21 A dis-
ꢀ1
˚
Following a similar trend to the viscosity measurements, the appeared and peaks at q < 0.10 A decreased signicantly in
dynamic changes to the storage modulus (G0) and the loss intensity. When the UV light was switched off and the visible
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Moreover, multiple cycles of this switching response can be
achieved, demonstrating the reversibility of self-assembly in
the system. The real time SAXS results conrmed that the
changes in bulk properties result from the system transitioning
between gel and sol states as the self-assembled structure
forms and dissociates.
Derivatives of C8-Azo-TPC
C8-Azo-TPC contains a reactive group, an acyl chloride, which
can remain active in the gel and opens the door to further
synthetic elaborations (Scheme 2). In principle, the acyl chlo-
ride of C8-Azo-TPC can react with a number of nucleophiles
enabling a large number of derivatives to be prepared with the
potential to introduce many functionalities. For example, C8-
Azo-TPC is a hydrophobic segment, which can react with
hydrophilic polyethylene glycol methyl ether (MPEG) to form
amphiphilic surfactants (Fig. S7†). These surfactants have
similar multi-stimuli responsiveness with C8-Azo-TPC and can
form a gel in some organic solvents. Not all compounds
generated by reaction with C8-Azo-TPC with nucleophiles have
multiple responsive behavior. For instance, the product from
the reaction of C8-Azo-TPC with ethanol or water did not form a
gel in organic solvents as shown in the Table 2. This may be
because the products disrupt the appropriate intermolecular
forces needed to form a gel. Carboxylic acid and ester groups
may break the multiple non-covalent interactions such as
hydrogen bonding, donor–acceptor and hydrophobic interac-
tions between organic gels, thus losing the possibility of
gelation.
Fig. 11 Real-time photorheology measured over alternating UV
(365 nm, 200 mW cmꢀ2) and visible (38 mW cmꢀ2) light irradiation for
C8-Azo-TPC in n-dodecane (1.0 wt%) at 20 ꢁC. The data were
obtained at a constant frequency of 5 rad sꢀ1 and a strain of 1.0%.
Table 2 Results of gelation tests for 5a–da
Fig. 12 Time resolved synchrotron SAXS patterns for the C8-Azo-TPC
in n-dodecane (1.0 wt%) upon UV light (365 nm, 200 mW cmꢀ2
)
Solvent
5a
5b
5c
5d
exposure and visible light (38 mW cmꢀ2) at 25 ꢁC.
Water
I
I
I
I
Chloroform
Hexane
Benzene
S
I
I
S
I
I
S
G
S
S
G
S
light turned on immediately, all the scattering peaks which
disappeared under UV light re-appeared, indicating a revers-
ible structural rearrangement. The rst ve diffraction peaks
Toluene
n-Dodecane
THF
Cyclohexane
n-Dodecane/EtOAc ¼ 10/1
I
I
S
I
I
I
I
S
I
I
S
G
S
G
G
S
G
S
G
G
(q < 0.10 Aꢀ1) indicated the formation of ber aggregation in
˚
the gel and along with the POM measurements strongly
suggest a liquid crystal like structure (Fig. 12 and S16†).40
a
20 ꢁC, 2.0 wt%; G ¼ gel, S ¼ clear solution aer cooling, I ¼ insoluble.
Scheme 2 Synthesis of compounds containing C8-Azo-TPC.
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Acknowledgements
The authors greatly acknowledge the support of this work by the
National Natural Science Foundation of China (Grant no.
21204032) and Excellent Young Teacher Training Project of
Jiangsu Province. SAXS/WAXS research was undertaken at the
Australian Synchrotron, Victoria, Australia and the authors
thank Dr Adrian Hawley for his assistance. The authors wish to
thank Drs Keith McLean, Richard Evans and Colin Wood
(CSIRO) for helpful discussions about the manuscript.
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