Aggregation-induced emission organogel formed by both sonication and thermal processing based on tetraphenylethylene and cholesterol derivative

Article abstract of DOI:10.1016/j.dyepig.2019.02.041

In this work, we designed and synthesized a novel asymmetric tetraphenylethylene-based fluorescence compound, which can form cholesteryl liquid crystal by cooling from the isotropic melt and exhibit typical AIE property with a 180-fold enhancement of fluo

Full text of DOI:10.1016/j.dyepig.2019.02.041

Accepted Manuscript
Aggregation-induced emission organogel formed by both sonication and thermal
processing based on tetraphenylethylene and cholesterol derivative
Miao Luo, Sheng Wang, Chengpeng Li, Wangen Miao, Xiang Ma
PII:
S0143-7208(18)32870-5
https://doi.org/10.1016/j.dyepig.2019.02.041
DYPI 7375
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 28 December 2018
Revised Date: 15 February 2019
Accepted Date: 23 February 2019
Please cite this article as: Luo M, Wang S, Li C, Miao W, Ma X, Aggregation-induced emission
organogel formed by both sonication and thermal processing based on tetraphenylethylene and
cholesterol derivative, Dyes and Pigments (2019), doi: https://doi.org/10.1016/j.dyepig.2019.02.041.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Aggregation-induced emission organogel formed by both sonication
and thermal processing based on tetraphenylethylene and cholesterol
derivative
Miao Luo,a Sheng Wang,*a Chengpeng Li,a Wangen Miao,a and Xiang Ma*b
a College of Basic Education, School of Chemistry and Chemical Engineering,
Lingnan Normal University, Zhanjiang Preschool Education College, Zhanjiang,
524037, Guangdong, P. R. China
b Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China
University of Science and Technology
Meilong Road 130, Shanghai, 200237, P. R. China
*Corresponding author: Prof. Dr. Sheng Wang, College of Chemistry Science &
Technology, Lingnan Normal University, Zhanjiang 524048, P.R. China; Tel:
+86-759-318-2515; Fax: +86-759-318-3510; E-mail: dyesws@126.com;
Prof. Dr. Xiang Ma, Key Laboratory for Advanced Materials and Institute of Fine
Chemicals, East China University of Science and Technology
Meilong Road 130, Shanghai, 200237, P. R. China; Tel: +86-21-64252288, Fax:
+86-21-64252288; E-mail: maxiang@ecust.edu.cn
Abstract ： In this work, we designed and synthesized a novel asymmetric
tetraphenylethylene-based fluorescence compound, which can form cholesteryl liquid
crystal by cooling from the isotropic melt and exhibit typical AIE property with a
180-fold enhancement of fluorescence intensity in 90% water fraction of THF/water
mixture than pure THF. This compound can gelate in cyclohexane via both ultrasound
stimuli and general sol–gel processes accompanied by remarkable enhanced
fluorescence emission. The self-assembly and gelling properties can be controlled by
ultrasound stimuli and renewed by a thermodynamic process. The mechanism of the
process was investigated by UV-Vis absorption, PL emission, scanning electron
microscopy, wide-angle X-ray scattering analysis, and small-angle X-ray scattering
1

ACCEPTED MANUSCRIPT
analysis. The results reveal that the cooperation and relative competition of multiple
intermolecular interactions, which are the main contributors for the formation of gel
influenced by the sonication or thermal stimulus.
Keywords: aggregation-induced emission, tetraphenylethylene derivatives,
organogelator, gelation-induced fluorescence enhancement, liquid crystal
1. Introduction
Research on organic luminescent materials has attracted numerous attentions
because of their vast potential in fluorescent sensors, organic electronics,
optoelectronics, and light-emitting diode fabrication.[1-3] However, conventional
fluorescent molecules containing large planar aromatic rings often suffer from
aggregation-caused quenching (ACQ) due to their intermolecular π-π interactions in
the aggregate state or solid state, which will limit their developments and applications
in fluorescent chemosensors, bioprobes, light detectors, organic light-emitting devices
(OLEDs), etc.[1, 2, 4] Promisingly, the aggregation-induced emission (AIE) effect,
which is opposite to the ACQ phenomenon, was first reported by Tang and
co-workers in 2001. [5] Excitingly, many organic dyes with aggregation-induced
emission (AIE) characteristics have been found successively.[1, 6-10]
In recent years, aggregation-induced emission (AIE) organogelators, which
exhibited remarkable variation in the fluorescence spectrum accompanying a
gel-to-sol or sol-to-gel phase transition process, have received much attention from
2

ACCEPTED MANUSCRIPT
both theoretical and practical viewpoints.[3, 11-27] For example, Park and coworkers
synthesized
a
novel fluorescent molecule, 1-cyano-trans-1, 2-bis-(3’,
5’-bis-trifluoro-methyl-biphenyl)ethylene (CN-TFMBE) without long alkyl chain or
steroidal substituents, showed a typical aggregation-induced enhanced emission
(AIEE) phenomenon.[25] Ihara and Lu reported a new organogelator based on a
salicylideneaniline derivative with cholesterol units, exhibited strong fluorescence
enhancement in the gel state relative to a solution of the same concentration because
of the formation of J aggregations.[26]
Recently, stimuli-responsive low-weight molecular organogels (LMOGs) has been
studied extensively in areas ranging from chemistry and biology to materials science
because of their potential applications in drug delivery, sensors, adaptive materials,
and nano/micro devices.[28-31] However, most of the reported responsive materials
were stimulated by light, reaction, and heat, therefore, a smart gel controlled or even
switched by sound is also very appealing.[28] There are some reports recently
appeared about the gelation formation by ultrasound stimuli.[28, 29, 32-34] Huang’s
group reported a novel family of asymmetric cholesterol-based fluorescent
organogelators, their self-assembly and surface wettability can be controlled by
ultrasound stimuli and restored by a thermal process.[28, 29]
Thus, combining an AIE luminogen and a stimulus-responsive organogelator would
be a promising strategy for constructing smart luminescent systems. In 2016,
Srivatsan and coworkers reported
a
family nucleolipid gels displayed
aggregation-induced enhanced emission and their gelation behavior and photophysical
3

ACCEPTED MANUSCRIPT
properties could be reversibly switched by external stimuli such as temperature,
ultrasound and chemicals.[35] However, low-weight molecular organogel reversibly
switched by ultrasound and thermal stimuli with aggregation-induced emission
property is very rare thus far to the best of our knowledge.[28, 29, 36] It is reported
that the balance of the hydrogen-bonds with other interactions (such as hydrophobic
interactions and π-π interactions, as well as the steric hindrance) are necessary to
satisfy the requirements of ultrasonic stimuli for gelation.[28, 36] Herein, we report a
novel AIE compound derived from tetraphenylethylene and cholesterol moieties with
the structural character of ALS (aromatic group A, linker L, steroidal group S)[28, 29],
the gelling ability, aggregation behavior, and response to ultrasound stimuli are also
elucidated.
Scheme 1
2. Experimental
2.1 Materials and instruments
4-Aminophenylboronic acid, 2-bromo-1,1,2-triphenylethylene, cholesterol, succinic
anhydride, aliquat 336, tetrakis (triphenylphosphine) palladium (0) were purchased
from Aladdin company and used as received. 4-dimethylamiopryidine (DMAP),
1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC-HCl) were
purchased from Shanghai Darui company (China) used as received. Ultra-pure water
was used in the experiments. Tetrahydrofuran (THF) was distilled from
sodium/benzophenone. All other reagents and solvents were purchased as analytical
grade from Zhangjiang Kangbai Company (China) and used without further
4

ACCEPTED MANUSCRIPT
purification. 4-(1,2,2-triphenylvinyl)benzene-amine (TPE-NH2)[12] was prepared
according to the literature methods.
The IR spectra were measured on a Nicolet-6700 FT-IR spectrometer by
incorporating the samples in KBr disks. Proton and carbon nuclear magnetic
13
resonance (1H NMR and CNMR) spectra were measured on a Bruker AVANCE III
spectrometer [CDCl3, tetramethylsilane (TMS) as the internal standard]. The
electronic spray ionization (ESI) high-resolution mass spectra were tested on a HP
5958 mass spectrometer. The SEM images were obtained by using a Hitachi S-4800
spectrometer. The AFM images were obtained by using Veeco/DI Scanning Probe
Microscope and the TEM Images by using JEM-1400 Plus (JEOL Ltd., Japan) at 120
kV. The UV/Vis spectra were determined on a Shimadzu-2550 spectrophotometer.
Wide-angle X-ray diffraction (WAXD) measurement was performed by using a
Philips X’Pert Pro diffractometer with an X-ray source of Cu Ka (λ=0.15406 nm) at
40 kV and 40 mA, at scan rates of 2.4 ° per 1 min. Small-angle X-ray diffraction
(SAXD) measurement was performed by using a Rigaku D/max 2550V with an X-ray
source of Cu Ka (λ=0.15406 nm) at 40 kV and 100 mA, at scan rates of 0.6o per 1 min.
Canon EOS 60D and EOS 70D digital camera was used to take photographs. The
sonication gel (S-gel) was gained by using SK5210HP (Shanghai Kedao Company,
working frequency: 53 kHz, ultrasonic power: 200 W, the power can vary from 40%
to 100%).
The calculations were performed with the periodic density functional theory (DFT)
method using the DMol3 module in the Materials Studio 7.0 software package.[37]
5

ACCEPTED MANUSCRIPT
The DMol3 calculation: Task: Geometry Optimization; Quality: Medium; Functional:
GGA, PW91. Basis set: DND; Basis file: 3.5. The DMol3 electronic options: SCF
tolerance: 1.0 × e−5; Max. SCF cycles: 500.
2.2 Synthesis of 3-Cholesteryloxycarbonylpropanoic acid (1):
A solution of cholesterol (5.80 g, 15 mmol), succinic anhydride (1.50 g, 15 mmol),
pyridine (1.00 mL), and dry heptane (150 mL) were heated to reflux for 21 h and
cooled to room temperature. The resulting precipitate was recrystallized twice from
acetone. Yield: 70%.
2.3 Synthesis of TPE-Ch:
TPE-NH2 (0.30 g, 0.86 mmol) and 1 (0.42 g, 0.99 mmol) were dissolved in THF
(50 mL), and then EDC-HCl (0.01 g) and DMAP (0.01 g) were added. The solution
was stirred at room temperature for 12 hours. After removing the solvent under
reduced pressure, the residue was crystallized from ethanol to give white crystalline
powder TPE-Ch (0.44 g, 62.8% yield). IR (KBr): υ=3433 cm-1(N-H), 2946 cm-1
(-CH2-), 2857 cm-1 (-CH3), 1732 cm-1 (C=O at COOR), 1698 cm-1 (C=O at
RCONHR’), 1670 cm-1 (C=C), 1597, 1525, 1492 cm-1 (phenyl); 1H NMR (400 MHz,
CDCl3) δ 7.65 (s, 1H), 7.27 (s, 1H), 7.18 – 6.95 (m,16H), 5.39 (d, J = 3.9 Hz, 1H),
4.73 – 4.59 (m, 1H), 2.73 (t, J = 6.2 Hz, 2H), 2.62 (t, J = 6.3 Hz, 2H), 2.33 (d, J = 7.7
Hz, 2H), 2.01 (t, J = 16.0 Hz, 2H), 1.85 (t, J = 15.8 Hz, 3H), 1.55 – 0.84 (m, 33H),
13
0.70 (s, 3H); C-NMR (CDCl3, 75MHz) δ (ppm):172.8, 169.5, 143.9, 140.6, 140.1,
139.7, 132.1, 131.1, 127.8, 126.2, 122.7, 118.8, 74.5, 56.6, 56.3, 49.8, 42.5, 39.7, 37.8,
36.9, 36.4, 36.1, 35.9, 32.6, 31.6, 29.0, 28.0, 24.3, 23.7, 22.4, 20.9, 19.4, 18.4, 12.1;
6

ACCEPTED MANUSCRIPT
MALDI-TOF MS (ES+): m/z 816.53 ([M+H]+, calcd for C57H69NO3, 815.53).
3. Result and discussion
3.1 Synthesis
The target compound was synthesized according to the routes depicted in Scheme 1.
The molecular structure of the target compound with the structural character of ALS
(aromatic group A, linker L, steroidal group), in which a tetraphenylethylene (TPE)
unit was used as aromatic group A and cholesterol was used as steroidal group S. The
TPE core, a propeller-like luminogen, as a prototypical AIEgen, is expected to make
the molecule display aggregation-induced emission.[2, 6, 13, 38, 39] Cholesterol is
favorable for facilitating gelation of solvents and thus been widely used for designing
new LMOGs.[18, 19] The TPE group and cholesterol group were linked by an alkyl
chain with an acyl amino linkage. Therefore, it can be expected that three kinds of
intermolecular interactions, including hydrogen bonding, π-π interactions, and
hydrophobic interactions, would be involved in the formation of the gelation process.
1
13
Their molecular structures were confirmed by H and C NMR spectroscopy, mass
spectrometry (MS) and Fourier-transform infrared spectroscopy (FT-IR).
3.2 AIE properties
The UV-Vis absorption and PL emission behaviors of the diluted mixtures of the
compound were studied in a mixture of THF/water with different water fractions to
determine their AIE properties. The PL spectra of 2.5 × 10-5M compound TPE-Ch in
THF/water mixtures with different water contents was shown in Figure 1. The figure
shows that the PL intensity was very weak and essentially did not change as the water
7

ACCEPTED MANUSCRIPT
fraction of the THF/water mixture increased from 0% to 80%.Very interesting, a
dramatic enhancement in luminescence was observed when the water fraction reached
90%, which was approximately 180 times higher than that in the pure THF. This result
indicated that this compound exhibited strong AIE activity. The AIE activity may be
attributed to the restriction of intramolecular rotations (RIR) of the
tetraphenylethylene (TPE) when in aggregation state.[9]
Figure 1
The UV-vis absorption spectra of compound TPE-Ch in the THF/water mixtures
(2.5 × 10-5M) are shown in Figure S1. The spectra displayed absorption tails
extending well into the long wavelength region, indicating that the molecules
aggregated into nanoparticles in the mixtures. The Mie effect of the nanoparticles has
been considered to cause such leveling-off of tails in the absorption spectra. [12, 39,
40]Therefore, the increase in PL intensity can be attributed to an AIE effect caused by
the formation of molecular aggregates, in which the restriction of intramolecular
rotations increased the fluorescent emission.
Quantum mechanical computations were conducted using the Materials Studio 7.0
software to study the lowest energy spatial conformation of the compound.[6] The
energy of the molecule with different conformation was calculated by GGA/PW91
method. The highest occupied molecular orbitals (HOMOs) and the lowest
unoccupied molecular orbitals (LUMOs) of the compound were obtained (Figure 2)
after structural optimization. As shown in Figure 2, the electron cloud distributions in
HOMO and LUMO of TPE-Ch was mainly localized on the tetraphenylethylene and
8

ACCEPTED MANUSCRIPT
the amide moieties with the energy gap between the HOMO and LUMO of 0.79 ev.
Figure 2
3.3 Gelation property
The gelation tests on TPE-Ch were carried out in various solvents with 3.0% (w/v)
as a standard concentration by using a test-tube-inversion method[29]. (Table 1) A
mixture TPE-Ch and solvent was heated until the solid was dissolved. A
thermodynamic gel (T-gel) was obtained after the hot solution had been cooled to
room temperature and aged for at least 30 min. A sonication gel (S-gel) was identified
when the hot solution was allowed to cool to room temperature (25oC) and was
treated immediately with ultrasound (200 W, 53 kHz, 25oC).[28, 29] The gelation was
then checked visually at about 25oC (Figure 3).
Table 1
Figure 3
It is interesting to note that gelation occurred in cyclohexane solution of TPE-Ch
by ultrasonic treatment (200 W, 53 kHz) for 5 minutes (designated as S-gel). To our
surprise, TPE-Ch could also form gel by directly cooling the hot solution (above 75
oC) to room temperature and aging for about 30 min (designated as T-gel). The critical
gelation concentration (CGC) (tested by using the “stable to inversion of a test tube”
method[41] ) was significantly decreased from 60 mg mL-1 in the cooling process to
17 mg mL-1 in the ultrasonic process, and the gel–sol transition temperature (Tg)
(determined by the“falling drop” method[20] ) of S-gel was higher than that of the
T-gel for the same concentration. (Table 2) In addition, the power and the
9

ACCEPTED MANUSCRIPT
concentration can influence the time to form the S-gel. The stronger the power was,
the shorter the time needed to form the S-gel. The higher the concentration was, the
shorter the time needed to form the S-gel, too.(Figure 4) At the same time, after
undergoing sonication, a reversed gel (R-gel) was obtained by heating the S-gel to a
sol and then cooling it to room temperature.
Table 2
Figure 4
The gelator was found to be initially insoluble in these solvents at room
temperature, but the mixtures became clear after heating. Upon cooling or ultrasonic
process of these solutions to room temperature, the formation of immobile gels was
observed. This thermo-reversible gelation process, which is characteristically
accompanied by enhanced fluorescence emission, can easily be distinguished even by
naked eyes from the photographic images (in Figure 5A).
To investigate the interrelationship between the emission and aggregation modes
along with the sol-gel transition, the temperature dependent fluorescence spectra in
o
the cyclohexane (60 mg mL-1) was measured from 70 to 25 C. As shown in Figure
5B, the initial solution exhibited almost non-fluorescence, but the fluorescence
intensity increased along with the decrease in temperature. The remarkable
fluorescence enhancement from the gels was possibly due to the formation of
self-assembly aggregates belonged to gelation-induced fluorescence enhanced
emission.[42]
Figure 5
10

ACCEPTED MANUSCRIPT
In order to gain better insight into the molecular organization in the gel specimens,
the morphologies of xerogels obtained from TPE-Ch were investigated by scanning
electron microscopy (SEM), Atomic Force Microscope (AFM) and Transmission
electron microscope (TEM) (Figure 6, Figure S2). Interestingly, we found that the
morphologies of TPE-Ch xerogels strongly depend on external stimuli. The T-gel
xerogel of cyclohexane generated the formation of sheets consisting of porous
aggregates, while tightly arranged three-dimensional branch-like fibers of
approximate width 100 nm to form entangled networks were obtained from the S-gel.
Furthermore, the morphology of such a gel from sonication showed rod-like structure
of several micrometres and curled sheets changed by a sol–gel process(R-gel). The
results strongly suggest that the sonication has changed the aggregation action in the
process of gelation. The morphology of the gel observed by AFM and TEM was in
agreement with the SEM analysis.
Figure 6
The compound TPE-Ch exhibited similar absorption spectra for the S-gel, T-gel
and R-gel, particularly, the maximum absorption in TPE-Ch in THF solution (2.5 ×
10-5 mol L-1 was located at 318 nm and 253 nm in the gel (6.8 × 10-2 mol L-1),
irrespective of sonication or cooling (Figure S3), The blueshifted absorption indicated
an H aggregation of TPE-Ch molecules in the gel.[28] The emission of S-gel
occurred at 477 nm was shifted to 470 nm for the T-gel and R-gel, respectively
(Figure 7). The redshift of the emission in the S-gel with respect to that in T-gel and
R-gel suggested the sonication treatment may strengthen the π-π interaction.[29]
11

ACCEPTED MANUSCRIPT
Figure 7
To check the contribution of hydrogen bonds in the amide and ester groups to the
gelation process, the infrared spectra of TPE-Ch before and after gelation were
measured, and the NH stretching bands (ʋNH) and C=O stretching bands (ʋC=O) were
carefully examined(Figure 8). The results were summarized in Table 3. The sample
before gel showed a relatively weak NH stretching band at 3413 cm-1 and a weak
C=O stretching band at 1733 cm-1.However, the gel samples of T-gel and R-gel
showed a strong NH stretching band at 3331 cm-1 and a strong C=O stretching band at
1733 cm-1 for intermolecular hydrogen bonding. Moreover, in the S-gel sample of
TPE-Ch, the NH stretching bands at 3433 and 3343cm-1 also indicates the existence
of hydrogen bonding in the S-gel.[43] The NH stretching bands were obviously
blueshifted compared with the T-gel and the R-gel, which suggests that the sonication
may releases the self-lock and induces the formation of semistable initial aggregates,
leading to accelerated gelation rates and formation of higher-order nanostructures.[28,
29, 32, 34]
Table 3
Figure 8
The molecular packing of the TPE-Ch xerogels under different external stimuli
was further investigated by powder X-ray diffraction spectra (Figure 9). For SAXD,
the neat solid of TPE-Ch showed peak at 2.52 corresponding to d spacing of 3.50 nm,
and the T-gel xerogel and S-gel xerogel of TPE-Ch displayed similar X-ray
diffraction profiles, with two peaks corresponding to d spacings of 5.58 nm, 2.68 nm
12

ACCEPTED MANUSCRIPT
and 5.25 nm, 3.11 nm, respectively, these values indicate that T-gel may form a
lamellar structure.[28, 43, 44] The two peaks for the R-gel xerogel correspond to 5.48
nm and 2.74 nm, similar to those of the T-gel xerogel. From WAXD, T-gel and R-gel
displayed similar X-ray diffraction profiles at the peak about 0.52 nm, but the neat
solid and S-gel showed another peak corresponding to d spacing of 0.45 and 0.43 nm,
respectively. It is suggested that the aggregation depends on the gelling stimuli and
can be recovered without noticeable changes.[28]
Figure 9
On the basis of the spectral study and XRD results, combined with the CPK model
of TPE-Ch, the molecular packing of the xerogels was conjectured as shown in
Figure 10. In the thermal process, the gradual formation of the intermolecular H
bonds takes place at amide group and the tetraphenylethylene (TPE) units are packing
by face-to-face. The molecules are further connected in the direction perpendicular to
the intermolecular H bonds through van der Waals forces between the cholesterol
groups with a resulting layer distance of 5.58 nm (structure B in Figure 10). However,
in the sonication process, the TPE-Ch molecule unwind, as a result, the
intermolecular H bonds takes place between NH(amide) and C=O(ester) groups, and
the tetraphenylethylene (TPE) units are packing by side-by-side (structure C in Figure
10). It may be the reason that sonication provides heat and pressure on the
nanosecond scale and extreme cooling rates, leading to rapid and spontaneous
aggregation through interpenetrating H-bond interactions.[28]
Figure 10
13

ACCEPTED MANUSCRIPT
3.4 Mesomorphic behavior
The mesomorphic behavior of TPE-Ch was evaluated using differential scanning
calorimetry (DSC) and hot-stage polarized optical microscopy (POM). Figure 11
shows the first heating, cooling and second heating DSC curves of TPE-Ch. For the
o
first heating curve, the lower peak temperature at 126 C was the transition between
crystalline solid phase and liquid crystalline (LC) phase, and the other transition at
o
184 C belonged to liquid crystalline phase to isotropic phase transition, while a
o
significant cold crystallization at 154 C was possibly one liquid crystalline phase to
the other crystalline phase transition. The POM observations showed that by heating
o
the temperature above 126 C, the sample began to flow with color birefringence,
suggestive of a liquid, indicating the sample really turned into the liquid crystalline
state. According to the textures obtained during cooling from the isotropic melt and
observed by POM (Figure 12), the fingerprint texture formed from TPE-Ch may
belong to the cholesteryl liquid crystal. The results of DSC and POM studies showed
that the characteristics of the phase transitions observed in the DSC curves for
TPE-Ch are consistent with those found by POM observations
Figure 11
Figure 12
3.5 Thermal property
The thermal property of TPE-Ch was investigated by thermogravimetric analysis
(TGA). TPE-Ch exhibited high thermal stability. The decomposition temperature with
5% weight loss under a N2 atmosphere (5% Td ) was 286.5 oC.
14

ACCEPTED MANUSCRIPT
Figure 13
4. Conclusion
In summary, a novel gelation-induced enhanced emission compound TPE-Ch
based on tetraphenylethylene and cholesterol derivative has been designed and
synthesized. The compound exhibits AIE behavior, as indicated by the significant
fluorescence enhancement in the aggregated state and gel state. Moreover, the
fluorescence intensity can be reversibly changed with gel-solution transition by
alternate cooling and heating. Furthermore, it is surprising that the self-assembly of
the compound can be controlled by ultrasound stimuli and restored by a thermal
process through intermolecular H bonds, π-π interaction and van der Waals forces.
The POM and DSC studies revealed that TPE-Ch can form cholesteryl liquid crystal
by cooling from the isotropic melt. The self-assembly controlled by the sonication or
thermal process may have potential applications in biodelivery systems, responsive
materials and etc.
Acknowledgements
This work was financially supported by NSFC (2187080411, 21372194, 21722603
and 21773103). M. Luo also acknowledge the Research Funds of Lingnan Normal
University (QL1515) and Zhanjiang Science and Technology Tackling
Project(2016B01040).
15

ACCEPTED MANUSCRIPT
Reference
[1] Xu F, Yuan M-S, Wang W, Du X, Wang H, Li N, et al. Symmetric and
unsymmetric thienyl-substituted fluorenone dyes: static excimer-induced emission
enhancement. RSC Adv 2016;6(80):76401-8.
[2] Zhang Y, Mao H, Kong L, Tian Y, Tian Z, Zeng X, et al. Effect of E/Z
isomerization on the aggregation-induced emission features and mechanochromic
performance of dialdehyde-substituted hexaphenyl-1,3-butadiene. Dyes and Pigments.
2016;133:354-62.
[3] Ren YY, Wu NW, Huang J, Xu Z, Sun DD, Wang CH, et al. A neutral branched
platinum-acetylide complex possessing a tetraphenylethylene core: preparation of a
luminescent organometallic gelator and its unexpected spectroscopic behaviour during
sol-to-gel transition. Chemical communications 2015;51(82):15153-6.
[4] Shanmugasundaram M, Joseph J, Ramaiah D. Tuning of photoluminescence
properties of functional phthalides for OLED applications. Journal of Photochemistry
and Photobiology A: Chemistry 2016;330:156-62.
[5] Luo J, Xie Z, Lam JWY, Cheng L, Tang BZ, Chen H, et al. Aggregation-induced
emission of 1-methyl-1,2,3,4,5-pentaphenylsilole. Chem Commun 2001(18):1740-1.
[6] He Z, Shan L, Mei J, et al. Aggregation-induced emission and
aggregation-promoted photochromism of bis(diphenylmethylene)dihydroacenes.
Chem Sci 2015;6:3538–43.
[7] Mei J, Leung NLC, Kwok RTK, Lam JWY, Tang BZ. Aggregation-Induced
Emission: Together We Shine, United We Soar! Chem Rev 2015;115(21):11718-940.
16

ACCEPTED MANUSCRIPT
[8] Liu G, Wu D, Liang J, Han X, Liu SH, Yin J. Tetraphenylethene modified
[n]rotaxanes: synthesis, characterization and aggregation-induced emission behavior.
Organic & biomolecular chemistry 2015;13(13):4090-100.
[9] Qin A, Tang B. Aggregation-Induced Emission: Fundamentals. Wiley
2014:1-414.
[10] Qin A, Tang B. Aggregation-Induced Emission:Applications. Wiley
2013:1-275.
[11] Yan N, He G, Zhang H, Ding L, Fang Y. Glucose-based fluorescent
low-molecular mass compounds: creation of simple and versatile supramolecular
gelators. Langmuir 2010;26(8):5909-17.
[12] Luo M, Zhou X, Chi Z, Liu S, Zhang Y, Xu J. Fluorescence-enhanced
organogelators with mesomorphic and piezofluorochromic properties based on
tetraphenylethylene and gallic acid derivatives. Dyes and Pigments 2014;101:74-84.
[13] Luo M, Wang S, Wang M, Huang S, Li C, Chen L, et al. Novel organogel
harnessing Excited-State Intramolecular Proton Transfer process with aggregation
induced emission and photochromism. Dyes and Pigments 2016;132:48-57.
[14] Zhang C, Li Y, Xue X, Chu P, Liu C, Yang K, et al. A smart pH-switchable
luminescent hydrogel. Chemical communications 2015;51(20):4168-71.
[15] Babu SS, Praveen VK, Ajayaghosh A. Functional pi-gelators and their
applications. Chem Rev 2014;114(4):1973-2129.
[16] Zhang Q, Qu DH, Ma X, Tian H. Sol-gel conversion based on photoswitching
between noncovalently and covalently linked netlike supramolecular polymers.
17

ACCEPTED MANUSCRIPT
Chemical communications 2013;49(84):9800-2.
[17] Luo M, Zhou X, Chi Z, Ma C, Zhang Y, Liu S, et al. Synthesis and Properties of
Gelators Derived from Tetraphenylethylene and Gallic Acid with
Aggregation-Induced Emission. Journal of Molecular and Engineering Materials
2013;01(03):1340007.
[18] Yang X, Zhang G, Zhang D. Stimuli responsive gels based on low molecular
weight gelators. J Mater Chem 2012;22(1):38-50.
[19] Sun F, Zhang G, Zhang D. A new gelator based on tetraphenylethylene and
diphenylalanine: Gel formation and reversible fluorescence tuning. Chin Sci Bull
2012;57(33):4284-8.
[20] Zhang P, Wang H, Liu H, Li M. Fluorescence-enhanced organogels and
mesomorphic superstructure based on hydrazine derivatives. Langmuir
2010;26(12):10183-90.
[21] Nayak MK, Kim B-H, Kwon JE, Park S, Seo J, Chung JW, et al.
Gelation-Induced Enhanced Fluorescence Emission from Organogels of
Salicylanilide-Containing Compounds Exhibiting Excited-State Intramolecular Proton
Transfer: Synthesis and Self-Assembly. Chemistry - A European Journal
2010;16(25):7437-47.
[22] Chen Q, Zhang D, Zhang G, Yang X, Feng Y, Fan Q, et al. Multicolor Tunable
Emission from Organogels Containing Tetraphenylethene, Perylenediimide, and
Spiropyran Derivatives. Adv Funct Mater 2010;20(19):3244-51.
[23] Simalou O, Zhao X, Lu R, Xue P, Yang X, Zhang X. Strategy to control the
18

ACCEPTED MANUSCRIPT
chromism and fluorescence emission of a perylene dye in composite organogel
phases. Langmuir 2009;25(19):11255-60.
[24] Chen P, Lu R, Xue P, Xu T, Chen G, Zhao Y. Emission enhancement and
chromism in a salen-based gel system. Langmuir 2009;25(15):8395-9.
[25] An B-K, Lee D-S, Lee J-S, Park Y-S, Song H-S, Park SY. Strongly Fluorescent
Organogel System Comprising Fibrillar Self-Assembly of a Trifluoromethyl-Based
Cyanostilbene Derivative. J Am Chem Soc 2004;126:10232-3.
[26] Xue P, Lu R, Lu R, Zhang Y, Nomoto H, Takafuji M, et al. Functional
organogel based on a salicylideneaniline derivative with enhanced fluorescence
emission and photochromism. Chem Eur J 2007;13(29):8231-9.
[27] Arumugaperumal R, Raghunath P, Lin M, Chung W. Distinct Nanostructures and
Organogel
Driven
by
Reversible
Molecular
Switching
of
a
Tetraphenylethene-Involved Calix[4]arene-Based Amphiphilic [2]Rotaxane. Chem
Mater 2018;30:7221-33.
[28] Wu J, Yi T, Shu T, Yu M, Zhou Z, Xu M, et al. Ultrasound Switch and Thermal
Self-Repair of Morphology and Surface Wettability in a Cholesterol-Based
Self-Assembly System. Angew Chem 2008;120(6):1079-83.
[29] Wu J, Yi T, Xia Q, Zou Y, Liu F, Dong J, et al. Tunable gel formation by both
sonication and thermal processing in a cholesterol-based self-assembly system. Chem
Eur J 2009;15(25):6234-43.
[30] Yang XL, Liu YJ, Li JH, Wang Q, Yang M, Li C. A novel
aggregation-induced-emission-active supramolecular organogel for the detection of
19

ACCEPTED MANUSCRIPT
volatile acid vapors. New J Chem 2018;42(21):17524-32.
[31] Wang H LQ, Hu Y, Liu M, Huang X, Gao W, Wu H,. A Multiple
Stimuli-Sensitive Low-Molecular-Weight Gel with an Aggregate-Induced Emission
Effect for Sol–Gel Transition Detection. ChemistryOpen 2018;7:457-62.
[32] Bardelang D. Ultrasound induced gelation: a paradigm shift. Soft Matter
2009;5(10):1969.
[33] Naito M, Inoue R, Iida M, Kuwajima Y, Kawamorita S, Komiya N, et al. Control
of Metal Arrays Based on Heterometallics Masquerading in Heterochiral
Aggregations
of
Chiral
Clothespin-Shaped
Complexes.
Chemistry
2015;21(37):12927-39.
[34] Isozaki K, Takaya H, Naota T. Ultrasound-induced gelation of organic fluids
with metalated peptides. Angew Chem Int Ed Engl 2007;46(16):2855-7.
[35] Nuthanakanti A, Srivatsan SG. Hierarchical self-assembly of switchable
nucleolipid supramolecular gels based on environmentally-sensitive fluorescent
nucleoside analogs. Nanoscale 2016;8(6):3607-19.
[36] Shen J, Ding P, Gao L, Gao Y, Zhang Q, Yuan S, Xin X. Formation of
organogels with aggregation-induced emission characteristics triggered by thermal
and ultrasound. Colloid Polym Sci 2017;295:1765-72.
[37] Yan D, Tang Y, Lin H, Wang D. Tunable two-color luminescence and
host-guest energy transfer of fluorescent chromophores encapsulated in metal-organic
frameworks. Scientific reports 2014;4:4337.
[38] Xu B, Chi Z, Zhang J, Zhang X, Li H, Li X, et al. Piezofluorochromic and
20

ACCEPTED MANUSCRIPT
aggregation-induced-emission compounds containing triphenylethylene and
tetraphenylethylene moieties. Chem Asian J 2011;6(6):1470-8.
[39] Zhang X, Chi Z, Li H, Xu B, Li X, Liu S, et al. Synthesis and properties of
novel aggregation-induced emission compounds with combined tetraphenylethylene
and dicarbazolyl triphenylethylene moieties. J Mater Chem 2011;21(6):1788-96.
[40] Xu B, Chi Z, Li H, Zhang X, Li X, Liu S, et al. Synthesis and Properties of
Aggregation-Induced Emission Compounds Containing Triphenylethene and
Tetraphenylethene Moieties. The Journal of Physical Chemistry
2011;115(35):17574-81.
C
[41] Chung JW, An B-K, Park SY. A Thermoreversible and Proton-Induced Gel-Sol
Phase Transition with Remarkable Fluorescence Variation. Chem Mater
2008;20:6750–5.
[42] Zhu L, Ma X, Ji F, Wang Q, Tian H. Effective enhancement of fluorescence
signals in rotaxane-doped reversible hydrosol-gel systems. Chemistry
2007;13(33):9216-22.
[43] Hanabusa K, Matsumoto M, Kimura M, Kakehi A, Shirai H. Low Molecular
Weight Gelators for Organic Fluids: Gelation Using a Family of Cyclo(dipeptide)s. J
Colloid Interface Sci 2000;224(2):231-44.
[44] Estroff L, Leiserowitz L, Addadi L, Weiner S, Hamilton A. Characterization of
an organic hydrogel: a cryo ‐ transmission electron microscopy and X ‐ ray
diffraction study. Adv Mater 2003;15:38-42.
21

ACCEPTED MANUSCRIPT
Table 1 Gelation properties in various solvents
Solvents
Phase
Solvents
Phase
Cyclohexane
DMF
G
S
Toluene
S
S
I
Chloroform
Hexane
DMSO
S
p-Xylele
S
Petroleum ether
Ethanol
I
1,4-Dioxane
Actonitrile
Ethyl acetate
Actone
S
I
PG
S
THF
S
S
S
I
Dichloromethane
Ethylene glycol
Methyl alcohol
S
Diethyl ether
S
G: stable gel formed at room temperature; PG: partial gel; S: soluble; I: insoluble; P:
precipitate.
22

ACCEPTED MANUSCRIPT
Table 2. the CGC and Tg of S-gel and T-gel in cyclohexane solvent
CGC(mg mL-1)
Tg (o C)
65~68
62~66
S-gel
T-gel
17
60
23

ACCEPTED MANUSCRIPT
Table 3 The wavelengths of the IR band related to amide and ester groups of TPE-Ch
before gel and after gel.
ʋNH (cm-1)
3413
ʋC=O (cm-1)
1733
Before gel
S-gel
3433,3343,1670
3331,1671
3331,1671
1733
T-gel
1733
R-gel
1733
24

ACCEPTED MANUSCRIPT
Figure captions
Figure 1 (A) PL spectra of TPE-Ch in THF/water mixtures with different water
fractions (Inset: Change in PL peak intensities with different water fractions in
THF/water mixtures, concentration 2.5 × 10-5M, λem = 474 nm), (B) the images in
THF/water mixtures with different water fractions were taken under room light (top)
and 300 nm UV light (bottom).
Figure 2 Molecular orbital amplitude plots of HOMO and LUMO energy levels of
TPE-Ch.
Figure 3 Pictures of S-gel (55.8 mg mL-1, ultrasonic treatment: 200 W, 53 kHz, 5
minutes); T-gel (133.4 mg mL-1); and R-gel (55.8 mg mL-1) in cyclohexane: under
room light (left) and 365 nm UV light (right).
Figure 4 the relationship between the power and the time needed to form S-gel in
different concentration.
Figure 5 (A) the emission images in sol (left) and gel (right) state under room light
(top) and 365 nm UV light (bottom), (B) Temperature-dependent fluorescence spectra
in cyclohexane (60 mg/ml, λex = 365 nm).
Figure 6 （A）SEM images of the xerogels from the TPE-Ch in S-gel (55.8 mg mL-1,
ultrasonic treatment: 200 W, 53 kHz, 5 minutes); T-gel (133.4 mg mL-1); and R- gel
(55.8 mg mL-1).（B）AFM image of xerogel in S-gel (55.8 mg mL-1), (C) TEM image
of xerogel in T-gel (114 mg mL-1).
Figure 7 Normalized fluorescent spectra of TPE-Ch in S-gel (55.8 mg mL-1,
ultrasonic treatment: 200 W, 53 kHz, 5 minutes); T-gel (133.4 mg mL-1); and R- gel
25

ACCEPTED MANUSCRIPT
(55.8 mg mL-1).
Figure 8 IR spectra for xerogel of TPE-Ch in S-gel (55.8 mg mL-1, ultrasonic
treatment: 200 W, 53 kHz, 5 minutes); T-gel (133.4 mg mL-1); and R- gel (55.8 mg
mL-1).
Figure 9 Powder XRD profile of the neat solid and xerogel of TPE-Ch at room
temperature: (A) Small angle X-ray diffraction (SAXD), (B) Wide angle X-ray
diffraction (WAXD).
Figure 10 Perspective structures of TPE-Ch; structure A: isolated TPE-Ch; structure
B: aggregation in the T-gel; structure C: aggregation in the S-gel; White C, red O,
blue N.
Figure 11 DSC curves of compound TPE-Ch.
Figure 12 Optical micrographs of compound TPE-Ch between crossed polarizers:
liquid crystalline texture at 140 oC.
Figure 13 TGA thermograms of TPE-Ch.
26

ACCEPTED MANUSCRIPT
Scheme 1
Scheme 1 Synthetic routes for TPE-Ch
27

ACCEPTED MANUSCRIPT
600
500
400
300
200
100
0
(A)
600
500
400
300
200
100
0
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
0
20
40
60
80
100
V (H20) / %
350
400
450
500
550
600
650
700
Wavelength / nm
Figure 1
28