Luminescent liquid crystals bearing an aggregation-induced emission active tetraphenylthiophene fluorophore

Article abstract of DOI:10.1039/c9tc00448c

The newly emerging aggregation-induced emission (AIE) theory provides a striking perspective to synthesize luminescent liquid crystal (LLC) materials with outstanding solid-state luminescence properties which have showed potential applications as semicond

Full text of DOI:10.1039/c9tc00448c

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ISSN 2050-7526
PAPER
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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
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Luminescent liquid crystals bearing aggregation-induced emission
active tetraphenylthiophene fluorophore
Ling-Xiang Guo, Yi-Bo Xing, Meng Wang, Sun Ying, Xue-Qin Zhang, Bao-Ping Lin and Hong Yang*
Received 00th January 20xx,
Accepted 00th January 20xx
The newly emerging aggregation-induced emission (AIE) theory provides a striking perspective to synthesize luminescent
liquid crystal (LLC) materials with outstanding solid-state luminescence properties which have exhibited prosperous
applications in semiconductor materials, liquid crystal displays and organic light-emitting diodes. However, to date, all the
known AIE-active LLC molecules are based on very limited AIE fluorophores including cyanostilbene, tolane,
tetraphenylethene and metallomesogen cores, which greatly impede the wide application of these materials, while on the
other hand leave us plenty of opportunities to develop novel AIE-based LLC materials. In this work, we design and synthesize
two categories of tetraphenylthiophene-core disk-like molecules, TPTn bearing one tetraphenylthiophene-core and eight
peripheral alkoxyl chains, and TPTEn bearing one tetraphenylthiophene-core and four 3,4,5-trialoxybenzoate groups, which
can form the square, rectangular or hexagonal columnar phases depending on the mesogenic core structures and the chain
length of the aliphatic tails. Meanwhile, these tetraphenylthiophene-core LLC molecules exhibit obvious AIE characteristics,
the fluorescence emission intensity values measured in aggregated state were hundred times higher than those values
presented in benign solvents. Furthermore, these AIE-active tetraphenylthiophene core LLC materials showed narrow band
gap energies and excellent gelation ability in appropriate solvents, which might have potential applications as organic
semiconductor materials and sensors.
DOI: 10.1039/x0xx00000x
www.rsc.org/
materials with unique solid-state luminescence properties.21-27
Introduction
Briefly,
scientists
introduced
AIE
active
fluorophores/chromophores as mesogenic cores and decorated
them with peripheral flexible long chains to synthesize AIE-
based discotic or calamitic LC molecules,28-60 whose light
emissions could be dramatically enhanced by molecular
aggregations and self-organizations in their mesophases.
Thanks to this outstanding solid-state luminescence
advantage, AIE-based LLC materials have exhibited potential
applications in one-dimensional semiconductor materials32,35
and organic light-emitting diodes (OLEDs).34,39 Nevertheless
according to the literatures, to date, all the known AIE-active
LLC molecules were based on very limited AIE fluorophores
Luminescent liquid crystals (LLCs) have gained a great deal of
attention and considerable interest from both scientific and
industrial organizations,1-4 because of their outstanding
technique advantages such as supramolecular self-assembly,
anisotropic fluid property and intrinsic light-emitting ability.5-8
Most importantly, LLCs have shown a promising prospect in
liquid crystal displays (LCDs), since LLC molecules can emit linear
or circular polarized light when aligned,9 which can not only
simplify the device design, reduce manufacturing costs and
increase power efficiency of LCDs, but also improve brightness,
color contrast ratio and viewing angle of LCDs.10-15
However, there still exist huge challenges in molecular
design of highly efficient LLCs. In particular, when LLC molecules
aggregate into liquid crystal (LC) phases, the ordered stacking
and strong intermolecular interactions of π-π bonds often
induce aggregation-caused quenching (ACQ) problem,16-20
which severely limits the practical application of LLC materials.
Fortunately, the newly emerging aggregation-induced emission
(AIE) theory provides a striking perspective to synthesize LLC
including
cyanostilbene,37,40-47
-
tolane,28,36,38
tetraphenylethene9,29 31,33,34,39,48-58 and metallomesogen59 cores
(Fig. 1A), which greatly impede the wide applications of these
materials, while on the other hand leave us plenty of
opportunities to develop novel AIE-based LLC materials.
Thiophene-based mesogenic compounds have recently
attracted wide scientific attention because thiophene unit
possesses several extraordinary technique advantages. For
example, thiophene mesogens usually have low phase
transition temperature, large dielectric anisotropy and high
charge-carrier mobility. Moreover, the intramolecular or
intermolecular interactions between sulfur atoms markedly
influence on both the polarization of emitted light and the
mesomorphic properties.1,60-62 On the other hand, tetraphenyl-
functionalized thiophene as a representative AIE function unit,
have been intensively investigated and widely used in OLED and
School of Chemistry and Chemical Engineering, Jiangsu Province Hi-Tech Key
Laboratory for Bio-medical Research, Jiangsu Key Laboratory for Science and
Application of Molecular Ferroelectrics, Southeast University, Nanjing, Jiangsu
Province 211189, China
*E-mail: yangh@seu.edu.cn
Electronic Supplementary Information (ESI) available: Synthetic procedures, NMR
spectra, and DSC, POM, XRD data. See DOI: 10.1039/x0xx00000x
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fluorogenic sensors.22,63-67 However, to our surprise, there was applying tetraphenylthiophene as a new mesogenic core (Fig.1
View Article Online
no any previous report using tetraphenylthiophene as the B). The mesomorphic propertieDs,OI: 10A.1I0E39/Cb9TeCh0a0v4io48rsC,
mesogenic unit of luminescent LC materials.
electrochemical performances and gelation properties of the
Inspired by all the pioneering works, herein we design and corresponding compounds are thoroughly investigated.
synthesize a series of AIE-active discotic LLC materials by
Fig. 1 (A) Some representative molecular structures of AIE-active LLCs reported in literature. (B) Two series of novel AIE-active LLC molecules reported in this work.
and eight peripheral alkoxyl chains, and TPTEn bearing one
tetraphenylthiophene-core and four 3,4,5-trialoxybenzoate
groups, here n represents the carbon number of alkoxyl tails.
Results and discussion
The synthetic protocols of six AIE-active tetraphenylthiophene-
core LC molecules TPTn and TPTEn (n = 8, 10, 12) are
Design and Synthesis
We designed two categories of tetraphenylthiophene-core disk-
schematically illustrated in Scheme 1.
like molecules, TPTn bearing one tetraphenylthiophene-core
Scheme 1. Synthetic routes of the tetraphenylthiophene-core discotic LC molecules TPTn and TPTEn (n = 8, 10, 12).
A Suzuki coupling reaction of 2,3,4,5-tetrabromothiophene tetrakis(3,4- dimethoxyphenyl)thiophene (1), which was then
and (3,4-dimethoxyphenyl)boronic acid gave 2,3,4,5- subjected to a BBr3-activated demethylation reaction and a
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following etherification reaction to provide TPT12
TPT8
reaction
methoxyphenyl)boronic acid, the resulting compound
treated with BBr3 and converted to
hydroxylphenyl)thiophene (
, TPT10 and relatively higher viscosities compared with those of calamitic
View Article Online
DOI: 10.1039/C9TC00448C
.
TPTEn series started with an alternative Suzuki coupling LCs.68,69 Based on POM observation, TPT12 showed a typical
of
2,3,4,5-tetrabromothiophene
and
(4- broken focal-conic fan-shaped texture (Fig. 2c). The
5
was representative WAXS patterns of TPT12 were shown in Fig. 2d-
tetra(4- f, which consisted of a sharp and intense scattering peak at d-
6
), which was further DCC-coupled spacing of 35.3 Å, along with two weak reflections at d-spacing
o
with 3,4,5-trialoxybenzoic acids to give the desired molecules of 25.0 Å and 17.6 Å recorded at 40 C. These peaks were
TPTE12
,
TPTE10 and TPTE8 respectively.
indexed as 100, 110 and 020, with a reciprocal d-spacing ratio
of 1 : √2 : 2.0, which were characteristic reflections of square
columnar (Cols) phase, with a lattice constant of a = 35.3 Å.
Mesomorphic Properties
The mesomorphic properties of compounds TPTn and TPTEn Similar to TPT12, TPT10 exhibited a broken focal-conic texture
were investigated by using a combination of polarized optical and possessed the characteristic reflections of square columnar
microscopy (POM), differential scanning calorimetry (DSC) and (Cols) phase (Figure. S26).
wide-angle X-ray scattering (WAXS) experiments. The thermal
In contrast to TPT12 and TPT10, TPT8 with a shorter alkyl
properties of compounds TPTn and TPTEn were investigated by tail presented a focal-conic fan-shaped texture at room-
thermogravimetric analysis (TGA) under nitrogen atmosphere. temperature (Fig. 3c). The WAXS pattern of TPT8 on cooling
The initial thermal decomposition temperatures (Td, at 5% displayed three reflections in the small-angle region, which
weight loss) of all the six compounds were above 350 oC, which consisted of a sharp and intense scattering peak at d-spacing of
were respectively estimated at around 380 oC for TPTn (Fig. 2a, 26.2 Å (Fig. 3d), along with two weak reflections at d-spacing of
o
Fig. 3a) and 369 oC for TPTEn (Fig. 4a). It indicated that 17.3 Å and 14.8 Å at 22 C as shown in Fig. 3e. All the above
compounds TPT and TPTE had good thermal stabilities and peaks were indexed as 100, 110 and 300 with a reciprocal d-
could meet most of application requirements.
As illustrated in Fig. 2b, TPT12 possessed two enantiotropic rectangular columnar (Colr) phase with lattice constants of a =
phase transitions in DSC diagrams. The two distinct peaks 26.2 Å, b = 22.7 Å. Furthermore, the WAXS patterns of TPT12
spacing ratio of 1 : 1.5 : 1.8, which implied the existence of
,
corresponded to the crystal-to-LC and LC-to-isotropic phase TPT10 and TPT8 showed a broad halo at 4.3~4.7 Å (Fig. 2d,
transitions respectively. The large LC-to-isotropic transition Figure S26d, Fig. 3d) in the wide-angle region, which confirmed
temperature hysteresis (48 oC on heating and 30 oC on cooling) the liquid-like order of the peripheral aliphatic tails.
was often observed in many discotic LC molecules due to their
Fig. 2 (a) TGA curve of TPT12. (b) DSC thermogram of TPT12 with a heating/cooling rate of 10 oC /min. (c) POM image of TPT12 recorded at 24 oC. (d) WAXS patterns of
TPT12 recorded on heating process. (e) Partial enlarged small-angle region of WAXS pattern of TPT12 recorded at 40 oC on heating process. (f) WAXS patterns of TPT12
recorded on cooling process.
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DOI: 10.1039/C9TC00448C
Fig. 3 (a) TGA curve of TPT8. (b) DSC thermogram of TPT8 with a heating/cooling rate of 10 oC /min. (c) POM image of TPT8 recorded at room temperature. (d) WAXS
patterns of TPT8 recorded on cooling process. (e) Partial enlarged small-angle region of WAXS pattern of TPT8 recorded at 22 oC on cooling process. (f) WAXS patterns
of TPT8 recorded on heating process.
As illustrated in Fig. 4b, the DSC curve of TPTE12 showed detailed phase transitions and lattice parameters of all the
two enantiotropic phase transitions, with a melting point above compounds TPTn and TPTEn determined by DSC, POM
o
o
around 6 C and a clearing point temperature around 55 C and WAXS, were listed in Table 1 and Table 2.
respectively. Under POM observation, the POM image of
Table 1. Phase transition temperatures (oC) of TPTn and TPTEn (n = 8, 10, 12).a
TPTE12 was attributed to a broken focal-conic fan-shaped
texture (Fig. 4c). Based on Fig. 4d,e, the WAXS patterns of
TPTE12 recorded at 40 C displayed three reflections at d-
spacing of 39.7 Å, 22.9 Å and 19.9 Å in the small-angle region
Compound
TPT12
TPT10
Heating
K 27 → Cols 48 → I
K 6 → Cols 37 → I
Colr 32 → I
Cooling
I 30 → Cols 21 → K
I 9 → Cols -7 → K
I 24 → Colr
o
TPT8
(Fig. 4d), with a reciprocal d-spacing ratio of 1 :
√3 : 2. The three
TPTE12
TPTE10
TPTE8
K 6 → Colh 55 → I
Colh 61 → I
I 49 → Colh -4 → K
I 58 → Colh
peaks were indexed as 100, 110 and 200 reflections, indicating
a hexagonal columnar (Colh) phase.70 Moreover, TPTE12
presented a broad diffused scattering peak at ca. 4.7 Å in the
wide-angle region, which was in compliance with liquid-like
orders of the peripheral alkoxy tails. In addition, its analogues
TPTE10 and TPTE8 also showed Colh microstructure,
demonstrated by DSC (Fig. S27a and Fig. S28a), POM (Fig. S27b
and Fig. S28b) and WAXS (Fig. S27c and Fig. S28c) data. The
Colh 63 → I
I 59 → Colh
aK = crystal phase; Colh = hexagonal columnar phase; Colr = rectangular
columnar phase; Cols = square columnar phase; I = isotropic phase.
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DOI: 10.1039/C9TC00448C
Fig. 4 (a) TGA curve of TPTE12. (b) DSC thermogram of TPTE12 with a heating/cooling rate of 10 oC /min. (c) POM image of TPTE12 recorded at 40 oC. (d) WAXS patterns
of TPTE12 recorded on heating process. (e) Partial enlarged small-angle region of WAXS pattern of TPTE12 recorded at 40 oC on heating process. (f) WAXS patterns of
TPTE12 recorded on cooling process.
around 290 nm and 330 nm. The fluorescence emission
intensity of TPT12 was measured by using the above three
absorption wavelengths as excitation wavelengths respectively.
It was found that the strongest fluorescence intensity was
achieved when 330 nm was chosen as the excitation
wavelength. UV-vis absorption spectra of TPT10 (Figure. S29a)
and TPT8 (Figure. S29b) are similar to that of TPT12. Compared
with TPTn, the intense absorption maximum band and the
fluorescence excitation wavelength of TPTEn appeared at 280
nm with a blue-shift of 50 nm (Fig. 5b, Figure. S30a,b), which
indicated that compared with flexible alkoxyl tails, 3,4,5-
trialoxybenzoate as a more bulky group, could further restrict
to a deeper extent the intramolecular rotation of the phenyl
rotors against the central thiophene core.
Table 2. X-ray scattering data of the mesophases of TPTn and TPTEn (n = 8, 10,
12)
.
Lattice
spacing (Å)
d-spacing
(Å)
35.3
Miller
indices
100
Compound
TPT12
Mesophase
Cols at 40 oC
a = 35.3
a = 27.0
25
110
020
100
110
020
100
110
300
100
110
200
17.6
27.3
19.5
13.1
26.2
17.3
14.8
39.7
22.9
19.9
TPT10
TPT8
Cols at 20 oC
Colr at 22 oC
a = 6.2
b = 22.7
TPTE12
TPTE10
TPTE8
Colh at 40 oC
Colh at 50 oC
Colh at 50 oC
a = 45.8
a = 39.3
a = 38.0
34.0
19.6
17.0
100
110
200
32.9
18.9
16.4
100
110
200
Fig. 5 UV-vis spectra of (a) TPT12 and (b) TPTE12 dissolved in pure THF at room
temperature (conc. = ca. 10-5 mol/L).
Photophysical Properties
UV-vis absorption spectra of compounds TPTn and TPTEn were
measured in THF (ca. 10-5 mol/L) at room temperature. As
illustrated in Fig. 5a, the absorption maximum of TPT12 in
solution appeared at ca. 235 nm with two shoulder peaks
In order to investigate the AIE properties of the two
tetraphenylthiophene LC molecular systems, TPT12 and TPTE12
were chosen as two representative examples. Tetrahydrofuran
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(THF) was applied as a good solvent, to dissolve TPT12 and photoluminescence (PL) properties of TPT12 and VTiePwTAEr1tic2lewOnelirnee
DOI: 10.1039/C9TC00448C
TPTE12, while water was used as a poor solvent to induce TPT12 examined in pure THF and THF/water mixtures with different
and TPTE12 to aggregate. In such
a condition, the water fraction (0～90 %) at room temperature (Fig. 6a-d).
Fig. 6 Fluorescence spectra of (a) TPT12 (conc. = 0.17 mM, λexc = 330 nm) and (b) TPTE12 (conc. = 0.17 mM, λexc = 280 nm) in THF/water mixture with different water
fractions. Diagram of fluorescence intensity of (c) TPT12 and (d) TPTE12 plotted against water fraction of THF/water mixture. The insets depict the fluorescence images
of TPT12 and TPTE12 solid samples exposed under 365 nm UV light. Fluorescence spectra of (e) TPT12 and (f) TPTE12 neat samples in comparison with their THF/water
solutions. Fluorescence spectra of (g) TPT12
(v/v = 10/90) mixture.
, TPT10, TPT8 (conc. = 0.17 mM, λexc = 330 nm) and (h) TPTE12, TPTE10, TPTE8 (conc. = 0.17 mM, λexc = 330 nm) in THF/water
As shown in Fig. 6a, in pure THF, TPT12 could hardly emit absolute fluorescence quantum yields (ΦF) of TPT12 dispersed
light under UV illumination with 330 nm excitation in THF with 0 % and 90 % water fractions were examined as 0.06
wavelength. After the addition of water into the THF solution, %and 6.32 %respectively.
a
the AIE phenomenon of TPT12 could be clearly observed and
The AIE effect of TPTE12 was also investigated by using the
evidenced by the plot of the fluorescence intensity (Fig. 6c) and same method described above. As illustrated in Fig. 6b, TPTE12
the photograph (Fig. 6c inset) of the sample dissolved in hardly emitted light in THF/H2O cosolvent with a low water
THF/water cosolvent with different water fraction (0
～90 %). As fraction (no more than 10%), while the fluorescence intensity of
illustrated in Fig. 6a, the fluorescence intensity of TPT12 was TPTE12 gradually increased along with the water fraction of
very weak and had a negligible change in the range of water THF/H2O cosolvent increasing from 10 % to 90 %. The
fraction from 0 % to 50 %, because TPT12 molecules were fully fluorescence emission intensity of TPTE12 in the THF/H2O
dissolved in these THF/water cosolvents and could not cosolvent with 90 % water fraction, reached a maximum value
effectively form nanoparticles. However when more water was which was approximately 105-fold higher than that in pure THF,
added into the solution, the fluorescence intensity of TPT12 accompanied by a weak bathochromic-shift (406-409 nm) of
would have a sharp jump along with the water fraction emission peak (Fig. 6d). In addition, the absolute fluorescence
increasing from 50 % to 70 %. The maximum emission quantum yields (ΦF) of TPTE12 dispersed in THF with 0 % and 90
wavelength peak (λem) of TPT12 appeared at ca. 436 nm. The % water fractions were examined as 0.05 % and 9.35 %
solution became opaque since TPT12 formed hydrophobic respectively.
nanoaggregates in the aqueous solution, and the opaque
All the experimental results indicated that the originally
suspension solution was macroscopically homogeneous non-luminescent solutions of TPT12 and TPTE12 with
without visible precipitates even after stored for 30 days. tetraphenylthiophene cores could be induced to emit light
Further increasing the water fraction in the THF/water intensively once the corresponding nanoaggregates were
cosolvent would just raise the fluorescence emission intensity formed by the addition of water into THF, which confirmed the
of TPT12 faintly. The fluorescence intensity of TPT12 in AIE property of TPT12 and TPTE12. Due to the space
THF/water cosolvent with 90 % water fraction was about 180- constraints, the intramolecular rotations of TPT12 and TPTE12
fold higher than that dissolved in pure THF, accompanied by a were greatly hindered, which suppressed the non-radiative
bathochromic-shift of the maximum emission peak about 11 nm transition. Accordingly, the excited molecules could only radiate
at the same time. The possible reason is due to the restricted into the ground state through radiative decay, resulting in
intramolecular rotation of the phenyl rotors against the central strong fluorescence. Meanwhile, the planarization caused by
tetraphenylthiophene core, which consumed the excited state the aggregation would increase the effective conjugate length
energy and reduced the nonradiative pathways.71-75 The
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Fig.7 Cyclic voltammetry curves (ten times of redox processes) of (a) TPT12 and
of the molecules and cause a bathochromic-shift of the
emission wavelength 76,77
(b) TPTE12 measured in anhydrous dichloromethane (conc. = 10 mg/mL) with a
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scanning rate of 0.1 V/s at room temperature.
DOI: 10.1039/C9TC00448C
.
Moreover, upon excitation at 365 nm UV light, TPT12 was
found to be dark blue emissive in solid state, while TPTE12 was
pale blue-light emissive in solid state. As demonstrated in Fig.
6e,f, compared with their optical performances in THF/water
(v/v = 10/90) mixture, the maximum emission wavelengths of
TPT12 and TPTE12 neat samples were 443 nm and 417 nm with
a significant red shift (ca. 7 nm and 8 nm) respectively,
Cyclic voltammetry curves of TPT12 and TPTE12 measured
in ten times of redox processes, were shown in Fig. 7. TPT12 and
TPTE12 had good cycle stability and exhibited reversible
oxidation/ reduction potentials in the range of -2.0~2.2 V, which
were around 0.67 V/-1.04 V and 0.66 V/-1.32 V respectively. The
HOMO/LUMO energy levels were calculated according to the
following formula:39,79
o
measured at 28 C which was in in the temperature range of
EHOMO = -(Eox - E Fc/Fc+ + 4.8) eV
ELUMO = -(Ered - E Fc/Fc+ + 4.8) eV
ΔEg = ELUMO - EHOMO
(1)
(2)
(3)
their LC phases. Their absolute fluorescence quantum yields
(ΦF) were further enhanced to 9.61 % and 14.80 % respectively.
The relationship between the luminescent behaviours and
the chemical structures of the LLCs, in particular, the chain
length of the aliphatic tails in TPTn and TPTEn compounds, were
further investigated. We measured the fluorescence emission
intensities of TPTn and TPTEn with different aliphatic chain
length in THF/water (v/v = 10/90) mixture, as illustrated in Fig.
S31 and Fig. 6g,h. It showed that the emission intensities of
TPTn and TPTEn (n = 12, 10, 8) increased gradually with the
increase of the peripheral flexible chain length. It may be due to
the fact that the longer peripheral flexible chain would increase
the steric hindrance, enhance the limitation of intramolecular
rotation, and cause an increase in fluorescence emission
intensity.
As shown in Table 3, the HOMO/LUMO energy levels of
TPT12 were calculated to be around -5.36 eV/-3.65 eV, and ΔEg
value was around 1.71 eV, while HOMO/LUMO energy levels of
TPTE12 were found to be around -5.35 eV/-3.37 eV, and ΔEg
value was around 1.98 eV. The experimental results indicated
that both TPT12 and TPTE12 possessed narrow energy gaps.
Compared with TPT12, TPTE12 exhibited a similar HOMO
energy level, an enhanced LUMO energy level, and a broader
energy band gap, which might derive from the fact that the
conjugation system of TPTE12 was larger than that of TPT12
.
Being solid-state emitters with low band gap energies, TPT12
and TPTE12 would have a broad prospect of application in the
field of optoelectronics.80
Electrochemical Property
Table 3. Electrochemical properties of TPT12 and TPTE12.
To further investigate the electrochemical properties and
estimate the energy levels of the highest occupied molecular
orbital (HOMO) and the lowest unoccupied molecular orbital
Compound
TPT12
TPTE12
Eox/V Ered/V
EHOMO/eV
-5.36
-5.35
ELUMO/eV
-3.65
-3.37
ΔEg/eV
1.71
1.98
0.67
0.66
-1.04
-1.32
(LUMO) of TPT12 and TPTE12
, we carried out cyclic
voltammetry (CV) studies by using the classical three-electrode
method. Following the literature protocol,78,79 TPT12 and
TPTE12 were completely dissolved in anhydrous
dichloromethane (conc. = 10 mg/mL) respectively, which were
sonicated at room temperature for 10 min. The two uniform
solutions were spin-coated on clean ITO substrates to form two
films of TPT12 and TPTE12, which were allowed to evaporate
dichloromethane completely to give dry TPT12 and TPTE12
films. The CV system used the sample-coated ITO film as a
working electrode, platinum plate as a counter electrode and
Ag/Ag+ as a reference electrode. Meanwhile, an acetonitrile
Gelation Property
In order to investigate the gelation property of
tetraphenylthiophene-core discotic LLC molecules, the gelation
behaviours of TPT12 and TPTE12 were examined by gelation
test, which was described as follows: a solution of TPT12 in any
specific solvent with a concentration of ca. 60 mg/mL was
heated in a sealed glass vial until forming a clear solution, and
was then cooled down to room temperature. The gel states
formed in 8 different solvents of TPT12 and TPTE12 were
measured by the ‘‘stable to inversion of a test tube’’
method.48,80 The experimental results of TPT12 and TPTE12
were shown in Table S1 (ESI) and Fig. 8a. Gel formation of TPT12
could not be observed in protic solvents (DMF, methanol and
ethanol) or aprotic polar solvents (acetone or THF). However,
TPT12 could form gels in ethyl acetate (EA) or the mixed solvent
of dichloromethane (DCM) and ethyl acetate (v:v, 1:2), while
TPTE12 could form a white gel only in ethyl acetate.
solution
of
tetrabutylammonium
hexfluorophosphate
(Bu4N+[PF6]-, 0.1 M) was used as an electrolyte solution, and
ferrocenium/ferrocene (Fc/Fc+) was used as an internal
standard compound (EFc/Fc+ = 0.11 V).
The gel morphologies of TPT12 and TPTE12 were further
observed by using a scanning electron microscope (SEM), as
shown in Fig. 8b-d. The gel of TPT12 in ethyl acetate presented
helical thread-like structures (Fig. 8b), while the gel of TPT12 in
the mixed solvent of dichloromethane and ethyl acetate (v:v,
1:2) showed microporous structures (Fig. 8c). Furthermore, the
gel of TPTE12 in ethyl acetate appeared the microporous
structures (Fig. 8d). These gel states of liquid crystals which
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Journal of Materials Chemistry C
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Journal Name
were commonly thought of as a metastable state between solid tails, while TPTEn bearing one tetraphenylthiophene-core and
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and liquid, might have potential applications in sensors48 and four 3,4,5-trialoxybenzoate groups would all generate the
DOI: 10.1039/C9TC00448C
conductive materials.81
hexagonal columnar phase. Meanwhile, the representative
TPT12 and TPTE12 molecules both exhibited obvious AIE
characteristics. The fluorescence emission intensity values of
TPT12 and TPTE12 measured in aggregated state were 180 and
105 times higher than those values presented in benign
solvents, respectively. Furthermore, these AIE-active
tetraphenylthiophene core LLC materials showed narrow
energy gaps and excellent gelation ability in appropriate
solvents, which might have potential applications as organic
semiconductor materials and sensors. We hope this work would
bring a new perspective for developing luminescent liquid
crystal materials and devices.
Acknowledgements
This research was supported by Jiangsu Provincial Natural
Science Foundation of China (No. BK20170024, BK20180406),
the Fundamental Research Funds for the Central Universities
(No. 2242018K41026, 2242018K40048, 2242017K3DN12) and
the Priority Academic Program Development of Jiangsu Higher
Education Institutions.
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DOI: 10.1039/C9TC00448C
Table of Contents Graphic
Luminescent liquid crystals bearing aggregation-induced emission
active tetraphenylthiophene fluorophore
Ling-Xiang Guo, Yi-Bo Xing, Meng Wang, Sun Ying, Xue-Qin Zhang, Bao-Ping Lin and Hong Yang*
In this work, six novel luminescent liquid crystal materials bearing an
aggregation-induced emission active tetraphenylthiophene fluorophore are described.