Control of self-assembly of twin-tapered dihydrazide derivative: Mesophase and fluorescence-enhanced organogels

Article abstract of DOI:10.1039/c3ra40835c

A twin-tapered (six-chained) low-molecular-mass organic gelator bearing hydrazine linkage and end-capped by phenyl, 1,4-bis[(3,4,5-trihexyloxy phenyl)hydrazide]phenylene (TC6) was designed and synthesized. Quadruple hydrogen bonds between the dihydrazide

Full text of DOI:10.1039/c3ra40835c

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Control of self-assembly of twin-tapered dihydrazide
derivative: mesophase and fluorescence-enhanced
organogels3
Cite this: RSC Advances, 2013, 3,
12109
Binglian Bai,{*ab Chunxue Zhang,{a Jue Wei,b Jie Ma,b Xiaolong Lin,b Haitao Wanga
and Min Li*a
A twin-tapered (six-chained) low-molecular-mass organic gelator bearing hydrazine linkage and end-
capped by phenyl, 1,4-bis[(3,4,5-trihexyloxy phenyl)hydrazide]phenylene (TC6) was designed and
synthesized. Quadruple hydrogen bonds between the dihydrazide units are the main driving force in
forming supramolecular liquid crystals and organogels. The association constants (K) of the quadruple
hydrogen bonds between the hydrazide units in chloroform are 7.13 6 103 M21 and 1.53 6 103
M
21 on
the basis of NH-1 and NH-2, respectively. Depending on the environmental conditions, compound TC6 can
self-assemble into a hexagonal columnar mesophase in the condensed state, in which two molecules
constitute the slice of the column, or into a smectic mesomorphic-like organization in the presence of
apolar solvents such as 1,2-dichloroethane, or into a rectangular columnar mesomorphic-like organization
in the presence of polar solvents such as ethanol, in which one molecule constitutes the slice of the
column. Aggregation-induced emission enhancement (AIEE) has been observed after gelation though
conventional chromophore units are not incorporated in TC6.
Received 19th February 2013,
Accepted 29th April 2013
DOI: 10.1039/c3ra40835c
www.rsc.org/advances
assembling of low-molecular-weight compounds (organogela-
tors) through noncovalent interactions, and the networks can
Introduction
Spontaneous self-assembly of simple molecules is a powerful
tool that allows complex supramolecular structures to be built.
Such systems are suitable for the development of materials
with organization-dependent properties. This strategy has
been successfully applied to the creation of soft materials,
such as liquid crystals and organogels.1 Hydrogen bonds play
an important role in building superstructures in these self-
assembled systems due to their specificity and directionality.2
Since Meijer and co-workers first reported a series of 2-ureido-
4(1H)-pyrimidone derivatives that can dimerize through
intermolecular quadruple hydrogen bonds,3 quadruple hydro-
gen-bonded systems have attracted much attention and have
been used in the field of materials science to synthesize, for
the first time, supramolecular polymers through the self-
association of self-complementary monomers.4
absorb a large amount of solvent therein. Organogelators
containing amides,5 hydroxyls,6 and urea7 groups are the most
studied gelators whose driving force for the formation of one-
dimensional self-associated chains is hydrogen bonding.
However, organogels based on quadruple hydrogen bonds
were rather limited. Wan and co-workers reported a hydrazide
quinolinone-based quadruple hydrogen bonded building
block, which can gel dichloromethane/hexane at concentra-
tions higher than 2 wt%.8 Aparicio et al.9 reported tetra-amides
derivatives, which self-assembled cooperatively into fibrillar
structures, acted as efficient crystal growth media for common
pharmaceutical ingredients. We reported the synthesis and
self-assembly of twin-tapered bi-dihydrazide derivatives (six-
chained), oxalyl acid N9,N9-di(3,4,5-trialkoxybenzoyl)-hydrazide
(FH-Tn), which self-assembled in chloroform at concentrations
higher than 255 mM or in bulk through intermolecular
quadruple H-bonding. The association constants (K) in chloro-
form were 447.5 and 217.2 M21 based on NH-1 and NH-2 in
FH-T7, respectively. The FH-Tns can form a stable columnar
mesophase and showed strong gelation ability in ethanol with
Low-molecular-weight organogels are materials in which
three-dimensional networks are formed due to the self-
aKey Laboratory for Automobile Materials (JLU), Ministry of Education, College of
Materials Science and Engineering, Jilin University, Changchun, 130012, P. R. China.
E-mail: minli@mail.jlu.edu.cn; Tel: +86 431 85168254
bCollege of Physics, Jilin University, Changchun, 130012, P. R. China.
critical gelation concentrations of 2.1 6 1023 mol L21 10
The
.
E-mail: baibinglian@jlu.edu.cn; Tel: +86 431 85168254
linear-shaped bi-dihydrazide derivative, oxalyl acid N9,N9-di(4-
(2-ethylhexyloxy)benzoyl)-hydrazide (FH-Z8) could gel dichlor-
omethane efficiently with the critical gelation concentration
(CGC) of 0.14 wt%, and spontaneously crystallized from the gel
Electronic supplementary information (ESI) available. See DOI: 10.1039/
3
c3ra40835c
{ Chunxue Zhang contributed with Binglian Bai, and they are both the first
author.
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during storage, but it was non-mesomorphic. The association
constants (K) in chloroform were 2.2 6 103 and 1.8 6 103 M21
based on NH1 and NH2 in FH-Z8, respectively.11 However,
Symmetrical four-chained (tetracatenar) di-hydrazide deriva-
tives, oxalyl N9,N9-bis(3,4-dialkoxybenzoyl)-hydrazide (BFH-n, n
= 4, 6, 8, 10), cannot gel any solvent.12 Recently, our group
reported the synthesis and self-assembly of symmetric dumb-
bell-shaped (four-chained) low-molecular-mass organic gela-
tors (LMOGs) bearing hydrazide linkage and end-capped by
phenyl,
1,4-bis[(3,4-bisalkoxyphenyl)hydrozide]phenylene
(BPH-n, n = 4, 6, 8, 10), which show great ability to gel a
variety of organic solvents to form stable organogels, and
showed enhanced fluorescence emission after gelation. In
addition, the BPH-n (n = 6, 8, 10) exhibited a thermotropic
hexagonal column (Colh) mesophase.13
Fig. 1 DSC curves of TC6 in the first cooling run and in the second heating run.
Aggregation-induced emission enhancement (AIEE) is one
of the interesting challenges for the prevention of emission
quenching by aggregation. Gelators possessing the AIEE
feature have attracted an extremely large amount of attention
since organogels are thermoreversible, and accordingly ther-
mal fluorescence modulation can be realized.14 A number of
possible mechanisms, including excimers/exciplex formation,
conformational planarization, J-aggregate formation, restric-
tion of intramolecular rotation (RIR), and twisted intramole-
cular charge transfer (TICT), were considered to be responsible
for the AIEE effect.15
min21), and the texture does not change even when it is cooled
to 15 uC. Variable temperature X-ray diffraction was performed
on TC6 to get further information on the molecular arrange-
ments of its mesophases. The X-ray diffraction pattern of TC6,
as shown in Fig. 3, taken at 20 uC in the first cooling run
revealed a hexagonal columnar structure, the d-spacings of
2.65 (100), 1.53 (110), 1.35 (200) nm in the low angle region
showed the ratio 1 : 1/!3 : 1/2. The lattice constant (a) of the
columnar phase is 3.08 nm. The average number of molecules
Our interest in the design of organized hydrogen bonded
soft materials through the control of supramolecular colum-
nar assemblies led us to design a twin-tapered (six-chained)
low-molecular-mass organic gelator bearing hydrazide linkage
and end-capped by phenyl, 1,4-bis[(3,4,5-trihexyloxy phenyl)-
hydrazide]phenylene (TC6), which is also part of our continu-
ing efforts towards hydrazide derivatives. The association
constants (K) of quadruple hydrogen bonds between the
hydrazine units in chloroform were 7.13 6 103 M21 and
1.53 6 103 M21 on the basis of NH-1 and NH-2, respectively.
TC6 showed thermotropic hexagonal columnar mesophase
and strong gelation ability in some organic solvents. And the
structures of the organogels are controllable by the polarity of
the gelling solvent. In addition, enhanced fluorescence
emission was observed after gelation, although the solution
of TC6 was almost non-fluorescent.
(m) in a column slice can be calculated through the equation
pffiffiffi
2
:
: :
m~( 3NA a h r)=2M for the hexagonal phase, where NA is
Avogadro’s number, a is the lattice constant, h is the intraco-
lumnar periodicity (h = 0.42 nm), r is the density (assumed to be 1
g cm23), and M is the molecular weight of the compound. For
TC6, it can be estimated that approximately two molecules (2.08 as
calculated) are included in a unit cell on average. The observation
of hydrogen bonded N–H stretching bands (3284 cm21), and an
intense absorption of bonded CLO stretching vibrations (1687
cm21 and 1635 cm21) at 100 uC in the first cooling stage suggests
that the hydrazide group is strongly H-bonded in the liquid
crystalline state (Fig. S2, ESI ).16,17
3
Results and discussion
Mesophase properties of the compound TC6
The phase behavior of TC6 was studied by POM, DSC, and
XRD. Fig. 1 shows the DSC curves of TC6 in the first cooling
run and in the second heating run (enthalpies, kJ mol21, in
brackets). TC6 showed one exothermic peak at 217 uC,
corresponding to the I–Colh (hexagonal columnar mesophase)
transition upon cooling from its isotropic phase, and there
was one endothermic peak at 225 uC, corresponding to the
Colh–I transition during heating. Fig. 2 shows the focal-conic
texture of TC6 in its mesophase on the cooling run (10 uC
Fig. 2 Optical texture observed for TC6 at 25 uC (6200).
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Fig. 5 Concentration dependence of the chemical shifts of NH-1 and NH-2 in
the 1H NMR spectra of TC6 in CDCl3.
Fig. 3 XRD pattern of TC6 in the first cooling run at 20 uC.
Self-assembly behaviors in solution
supramolecules at concentrations higher than 8.0 mM, which
is the main driving force for supramolecular aggregation. The
association constant for TC6 was estimated using the simplest
(isodesmic) model (i.e. Kn = K, for n ¢2) from eqn (1)
To understand the self-assembly behaviors of TC6, tempera-
ture-dependent 1H NMR spectroscopic experiments (500 MHz,
20% DMSO-d6/CDCl3) were carried out. Generally, internally
hydrogen-bonded amides are expected to show a much smaller
shift with temperature (,3.0 6 1023 ppm K21) compared to
those directed externally and accessible for hydrogen bonding
to a polar solvent (.4.0 6 1023 ppm K21).18 As shown in
Fig. 4, both NH-1 (near to alkoxyphenyl) and NH-2 (near to
central phenyl) of TC6 showed large shifts (6.45 6 1023 ppm
KCT = (P 2 Pa)(Pj 2 Pa)/(Pj 2 P)2
(1)
Where Pa and Pj are the chemical shifts for monomers and
molecules within a stack, P is the observed chemical shift, K is
the association constant, and CT is total molar concentration
of the compounds.19,10a In the present case, Pa was assigned to
8.94 and 9.20 ppm on the basis of NH-1 and NH-2,
respectively. The data from the diluting experiment fit well
with the calculated curves, giving association constants (K) of
7.13 6 103 M21 and 1.53 6 103 M21 on the basis of NH-1 and
NH-2, respectively. The chemical shifts of the phenyl protons
K
21 and 6.05 6 1023 ppm K21, respectively) with temperature
in 20% DMSO-d6/CDCl3, suggesting the primary involvement
of N–H protons in intermolecular hydrogen bonding.
Intermolecular hydrogen bonding in TC6 was further
confirmed by concentration-dependent 1H NMR spectroscopic
experiments. The dependence of the chemical shifts of NH-1
and NH-2 in TC6 on concentrations is shown in Fig. 5. The
chemical shift of NH-1 and NH-2 increased almost linearly
with increasing concentration and then slowed down and
appeared to level off at 8.0 mM. The above results demon-
strated that the two kinds of amide protons (quadruple
hydrogen bonds) in TC6 cooperatively participated in forming
are almost unchanged by comparison (Fig. S3 and S4, ESI ).
3
Gelling behavior
The gelation potential was examined for eight different
organic solvents, and the minimum gel concentrations are
summarized in Table 1. Fig. 6 shows the gel–sol transition
temperature (Tgel) of TC6 gels in ethanol and 1,2-dichlor-
oethane as a function of concentration.
In order to investigate the aggregation morphology of the
organogels, the xerogels TC6 in 1,2-dichloroethane and
ethanol were prepared and subjected to field emission
scanning electron microscopy (FE-SEM) and transmission
electron microscopy (TEM). Long nanofibers are observed in
ethanol and 1,2-dichloroethane (Fig. 7 and 8). The width of
these fibers ranged from 60 nm to several micrometers, and
Table 1 Gelation properties of TC6 (G: gel, S: solution. For gels the minimum
gelation concentration at 20 uC are given.)
Solvents
State
Solvents
State
Benzene
Toluene
1,2-Dichloroethane
Chloroform
G (2.59%)
G (1.44%)
G (0.18%)
S
Ethanol
G (0.44%)
Fig. 4 Chemical shifts of NH-1 and NH-2 of TC6 (8 6 1023 mol L21) in 20%
DMSO-d6/CDCl3 versus temperature (500 MHz; NH-1: near to alkoxyphenyl;
NH-2: near to central phenyl).
Tetrahydrofuran
Dimethylformamide
Dimethylsulfoxide
S
S
S
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Fig. 9 FT-IR spectra of the xerogels of TC6 from 1,2-dichloroethane (0.44 wt%)
Fig. 6 Concentration-dependent melting temperature of TC6 gels in 1,2-
and ethanol (0.67 wt%).
dichloroethane and ethanol.
(weak) cm21 (ethanol gel)) and the intense absorption of
bonded CLO stretching vibrations 1643 cm21 (and 1684 cm21
weak) clearly indicates that the N–Hs of the central hydrazide
…
group are associated with the CLO groups via N–H OLC
intermolecular hydrogen bonding in the gelation process and
the intensity of the intermolecular hydrogen bonding in the
xerogels from 1,2-dichloroethane is stronger than that of
ethanol. Such hydrogen bonding interactions are considered
to be the main driving forces for the formation of the fibers.20
The measurement of the XRD of the gel can provide
information about the long-range regulation of the molecular
self-assembly, thereby the packing model of molecules in the
gel phase can be supposed. Fig. 10a shows the XRD spectrum
of the xerogel obtained from the 1,2-dichloroethane gel. The
good diffraction pattern was characterized by two reflection
peaks of 2.68 and 1.31 nm, which were exactly in the ratio of
1 : 1/2, thus indicating a lamellar organization within the
aggregates of the 1,2-dichloroethane gel with an interlayer
distance of 2.68 nm. The XRD pattern (as seen in Fig. 10b) of
the ethanol xerogel (0.67 wt%) of TC6 consists of several peaks
at 1.79 (200), 1.68 (110), 0.91 (400), 0.79 (220), 0.60 (600), 0.52
Fig. 7 Field emission scanning electron microscopy (FE-SEM) images of xerogels
derived from (a) 1,2-dichloroethane (0.44 wt%), (b) ethanol (0.44 wt%).
their length can be extended to tens of micrometers or even
longer. These long fibers entangled with each other to form a
3D network, which is typical of the gel structures.
The formation of elongated fiber-like aggregates indicates
that the self-assembly of TC6 is driven by strong directional
intermolecular interactions. To ascertain whether hydrogen
bonding plays a role in the gelation process, infrared spectrum
of the TC6 organogel was examined. Fig. 9 shows the IR
spectra of the xerogels from 1,2-dichloroethane and ethanol.
The observation of hydrogen bonded N–H stretching bands
(3187 cm21 (1,2-dichloroethane gel), 3183 cm21 and 3260
Fig. 8 Transmission electron microscopy (TEM) images of xerogels derived from
(a) 1,2-dichloroethane (0.27 wt%, scale bar: 2 mm), (b) ethanol (0.67 wt%, scale
bar: 5 mm).
Fig. 10 XRD patterns of TC6: (a) xerogel from 1,2-dichloroethane (0.44 wt%),
(b) xerogel from ethanol (0.67 wt%) and (c) crystal.
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(330) and 0.48 (530) nm, which correspond to a rectangular
columnar packing (a = 3.58 nm, b = 1.86 nm). The average
number of molecules (m) in a column slice can be calculated
through the equation m = (NA?a?b?h?r)/2M for the rectangular
phase, where NA is Avogadro’s number, a and b are lattice
parameters, h is the intracolumnar periodicity (h = 0.44 nm), r
is the density (assumed to be 1 g cm23), and M is the
molecular weight of the compound. For TC6, it can be
estimated that approximately one molecule (0.8 as calculated)
is included in a unit cell on average. A plausible explanation
for this finding is based on the interactions established
between the molecule and the different solvents. The interac-
tions in ethanol must be stronger than those in 1,2-
dichloroethane since the minimum gelation concentration of
TC6 in ethanol is much larger than that in 1,2-dichloroethane.
It is also possible that the differences in the degree of
interaction depending on the solvent are more significant for
the central dihydrazide groups of the molecule (which is the
polar group). That is to say it is more possible for the polar
ethanol solvent to interact with the polar group, namely the
dihydrazide group, and takes part in hydrogen bonding,
meanwhile impairing the intermolecular hydrogen bonding
interactions of gelator–gelator to some extent (as can be seen
Fig. 9). In this situation, more or less solvent interaction with
the central core of the molecule could influence the type of
organization.
On the basis of the results described above (NMR, TEM,
SEM, IR and XRD), a possible formation processes of the gel
networks of TC6 in 1,2-dichloroethane can be proposed and is
schematically represented as shown in Scheme 1. The
monomers firstly self-assemble to form a one-dimensional
supramolecular chain mainly through intermolecular quad-
ruple hydrogen bonds between dihydrazides, namely elemen-
tal fibrils, whose diameter is equal to the layer spacing (d) of
TC6 as confirmed by XRD measurements. Then the elemental
fibrils assemble into fibrous bundles as the secondary
structure of the gel forms through van der Waals interactions
between the outside alkyl chains. The fibrous bundles finally
weave into a 3D network and fix the solvents into the network
Fig. 11 Absorption spectra of TC6 gel (0.23 wt%) and solution (4 6 1026 mol
L
21) in 1,2-dichloroethane.
fibrils assemble into fibrous bundles, and further into a 3D
network.
Gelation-induced enhanced fluorescence emission
Even though a dilute solution of TC6 was almost non-
fluorescent, a strongly enhanced fluorescence emission was
induced by the gelation process. To examine the fluorescent
properties of the self-assembled aggregates, UV-vis and
photoluminescence spectra of the gelator TC6 were measured
in solution and gels. The xerogels of TC6 from 1,2-dichlor-
oethane and ethanol showed similar fluorescent emission
behaviors (fluorescence quantum yield both equal to 7.6%)
although their structures of aggregates in the gels from 1,2-
dichloroethane and ethanol are different (XRD). So, we
typically discuss the fluorescent properties of TC6 in 1,2-
dichloroethane in detail. The absorption spectrum of TC6 in
dilute solution (1,2-dichloroethane, 4 6 1026 mol L21
)
exhibited a maximum at 281 nm (Fig. 11). Relative to the
solutions, a red shift of 16 nm was observed in the UV-vis
absorption spectrum of the gel (1,2-dichloroethane, 0.23 wt%),
thus indicating the formation of the J-aggregate in the gel
phase.1f,21 The J-aggregate can be further confirmed as a red
shift of about 9 nm with spectrum broadening is observed in
the UV-vis absorption spectrum of the gelling process (Fig. S7,
to form
a gel. While in ethanol, the one-dimensional
supramolecular chains formed through intermolecular quad-
ruple hydrogen bonds self-assemble into rectangular colum-
nar packing (namely elemental fibrils), and then the elemental
ESI ).
3
Fig. 12a shows the fluorescence spectra of TC6 in gel and the
dilute solution forms. TC6 in the dilute solution (1,2-
dichloroethane, 7.2 6 1025 mol L21) exhibited one fluores-
cence maximum with a lmax at 368 nm. The emission centered
at 425 nm was observed in the gel state (1,2-dichloroethane,
0.23 wt%), with an impressive increase in the photolumines-
cence intensity compared with that in the solution. In
agreement with the fluorescence spectrum of the gel, the
xerogel emits blue light as shown in Fig. 12b, where the
fluorescence microscopy image of the xerogel is displayed.
Indeed, the fluorescence intensity enhancement after gelation
can be easily distinguished by the naked-eye (see photos under
UV light illumination in Fig. 12a insets). Such a fluorescence
intensity enhancement was likely due to the formation of self-
Scheme 1 Schematic representation of the formation mechanisms of the
aggregates of TC6 in 1,2-dichloroethane.
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oethane at 20 uC displayed a strong peak at 425 nm. With the
increase of temperature, the aggregation is partially dissolved,
and hence, the intensity of the emission is decreased. Above 75
uC, the gels turned into a fluid solution. A hypsochromic shift
of the emission bands was observed from 425 nm in the gel
state (at 20 uC) to about 391 nm in solution (at 80 uC). These
results are also in line with the formation of molecular
J-aggregation.
Isolated TC6 molecules in a dilute chloroform solution are
considered to be significantly twisted, because the two
aromatic rings are joined by flexible linking groups (–CO–
NH–), which generally suppresses the radiative decay chan-
nel.20a,22 However, in the gel state aggregation induced a more
planar structure, which is evidenced by the absorption band of
the gel with a large red-shift and spectrum broadening relative
to that in solution (Fig. 11 and S7, ESI ).5a,5d In addition the
3
conjugated conformation of TC6 due to strong intermolecular
hydrogen bonding extends the effective p-conjugation length
in the TC6 molecules, which activates the radiation pro-
cess.20a,23 The compound TC6 forming J-aggregates in the
organogel may be another contribution to the enhanced
emission. Consequently, the aggregation-induced enhanced
emission (AIEE) phenomenon in the gelation process was
attributed to the synergistic effect of aggregation induced
planarization and J-aggregate formation.
Conclusions
Fig. 12 (a) Fluorescence spectra of TC6 gel (0.23 wt%) and solution (7.2 6 1025
mol L21) in 1,2-dichloroethane, excitation wavelength (lex) = 320 nm. The insets
are photographic images of the corresponding gel and solution observed upon
UV irradiation at 365 nm (right). (b) Fluorescent microscopic image of the
xerogels obtained from compound TC6 in 1,2-dichloroethane (61000).
A twin-tapered dihydrazide derivative was designed and
synthesized. Quadruple hydrogen bonds between dihydrazide
units are the main driving force in forming supramolecular
liquid crystals and organogels. The association constants (K) of
quadruple hydrogen bonds between hydrazine units in chloro-
form are 7.13 6 103 M21 and 1.53 6 103 M21 on the basis of
NH-1 and NH-2, respectively. TC6 displayed a thermotropic
Colh mesophase, which is stable at room temperature.
Interestingly, the structures of TC6 xerogels are controlled by
the polarity of the gelling solvent. In apolar solvents such as
1,2-dichloroethane, compound TC6 can self-assemble into a
smectic mesomorphic-like organization. In polar solvents such
as ethanol, it can self-assemble into a rectangular columnar
mesomorphic-like organization, in which one molecule con-
stitutes a slice of the column. In addition, TC6 showed
gelation-induced enhanced fluorescence emission, which was
attributed to the synergistic effect of aggregation induced
planarization and J-aggregate formation.
assembly aggregates of TC6 during the gelation process
according to previous investigations.5a,13,21
The intensity of the fluorescence of TC6 in the gel state
decreased as the temperature increased. As shown in Fig. 13,
the emission spectrum obtained from the gel of 1,2-dichlor-
Experimental
Synthesis of TC6
The compound TC6 was synthesized according to the route
shown in Scheme 2 which was similar to that of BPH-n13 and
FH-Tn.10 Terephthaloyl chloride was regularly injected into the
THF solution of 3,4,5-trihexyloxy-benzoyl hydrazine (molchlor-
ide/molhydrazine = 1/2) with vigorous stirring at room temperature
for 8 h. The crude product was isolated and further purified by
Fig. 13 Temperature-dependence of the fluorescence emission of TC6 organo-
gel in 1,2-dichloroethane (0.23 wt%).
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21072076, 51103057, 51073071), the
Natural Science Foundation of Jilin Province (201215009), and
the Project 985-Automotive Engineering of Jilin University.
Notes and references
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Scheme 2 Synthetic route of TC6.
recrystallization from tetrahydrofuran for further 1H NMR, FT-
IR measurements, and elemental analysis; yield = 80%.
1H NMR (300 MHz, DMSO) (ppm, from TMS): 10.67 (s, 2H),
10.48 (s, 2H), 8.05 (s, 4H), 7.24 (s, 4H), 4.02 (t, J = 6.28 Hz, 8H),
3.93 (t, J = 6.38 Hz, 4H), 1.80–1.60 (m, 12H), 1.51–1.41 (m,
12H), 1.31 (m, J = 7.20, 4.02 Hz, 24H), 0.89 (m, J = 7.31, 3.65 Hz,
18H). FT-IR (KBr, pellet, cm21): 3188, 2956, 2930, 2871, 2850,
1642, 1603, 1852, 1488, 1468, 1459, 1425, 1383, 1340, 1231,
1179, 1133, 1112, 1000, 857, 721, 666. Elemental analysis:
calculated for C58H90N4O10 (%), C, 69.43; H, 9.04; N, 5.58;
found: C, 69.32; H, 9.07; N, 5.47.
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Characterization
1H NMR spectra were recorded with a Bruker Avance 500 MHz
or Mercury-300BB 300 MHz spectrometer, using chloroform-d
or DMSO-d6 as solvent and tetramethylsilane (TMS) as an
internal standard (d = 0.00). Transmission electron microscopy
(TEM) images were taken with a JEOL2010 microscope,
operating at an acceleration voltage of 100 kV. Field emission
scanning electron microscopy (FE-SEM) images were taken
with a JSM-6700F apparatus. X-Ray diffraction was carried out
with a Bruker Avance D8 X-ray diffractometer. FT-IR spectra
were recorded with a Perkin-Elmer spectrometer (Spectrum
One B). The xerogels were obtained by freezing and pumping
the organogel of TC6 for 12 h, and then the xerogels were
pressed into a tablet with KBr for FT-IR measurements. UV-Vis
absorption spectra were recorded on a Shimadzu UV-2550
spectrometer, and photoluminescence was measured on a
Perkin-Elmer LS 55 spectrometer. Differential scanning
calorimetry (DSC) curve was obtained on a Netzsch DSC 204
instrument. Optical textures were observed under a Leica
DMLP microscope equipped with a Leitz 350 heating stage.
Gelation test: the weighted gelator was mixed in a capped
sealed test tube [3.5 cm (height) 6 0.5 cm (radius)] with an
appropriate amount of solvent, and the mixture was heated
until the solid dissolved. The sample vial was cooled
spontaneously to 20 uC, and then turned upside down. When
an opaque gel formed, the solvent therein was immobilized at
this stage. Melting temperature (Tm) was determined by the
‘falling drop’ method. An inverted gel was immersed in a water
bath initially at room temperature. The water bath was heated
slowly up to the point at which the gel fell due to the force of
gravity, i.e. the Tm.
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