Discotic liquid crystals with aggregation-induced emission properties based on tetraphenylethylene and triphenylene derivatives

Article abstract of DOI:10.1080/15421406.2021.1905139

A novel aggregation-induced emission active molecules (TP-Cn-PETPE, n = 4 and 10) were synthesized, which contain a tetraphenylethene derivative as the emission active moiety, a pentahexyloxytriphenylene core as the mesogenic unit and an alkoxy spacer. Ex

Full text of DOI:10.1080/15421406.2021.1905139

Molecular Crystals and Liquid Crystals
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
Discotic liquid crystals with aggregation-induced
emission properties based on tetraphenylethylene
and triphenylene derivatives
Xiangfei Kong, Ronggen Luo, Hongkang Gong, Dong Chen, Shijun Yang,
Shiqing Li, Guixia Wang & Zhiqun He
To cite this article: Xiangfei Kong, Ronggen Luo, Hongkang Gong, Dong Chen, Shijun Yang,
Shiqing Li, Guixia Wang & Zhiqun He (2021): Discotic liquid crystals with aggregation-induced
emission properties based on tetraphenylethylene and triphenylene derivatives, Molecular Crystals
and Liquid Crystals, DOI: 10.1080/15421406.2021.1905139
To link to this article: https://doi.org/10.1080/15421406.2021.1905139
Published online: 29 Jun 2021.
Submit your article to this journal
Article views: 40
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=gmcl20

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
https://doi.org/10.1080/15421406.2021.1905139
Discotic liquid crystals with aggregation-induced emission
properties based on tetraphenylethylene and triphenylene
derivatives
Xiangfei Konga, Ronggen Luoa, Hongkang Gongb, Dong Chena, Shijun Yanga,
Shiqing Lia, Guixia Wanga, and Zhiqun Heb
aCollege of Chemistry and Bioengineering, Guangxi Key Laboratory of Electrochemical and
b
Magnetochemical Functional Materials, Guilin University of Technology, Guilin, China; Key Laboratory
of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology,
Beijing Jiaotong University, Beijing, China
KEYWORDS
ABSTRACT
Aggregation-induced emis-
sion; discotic molecule;
liquid crystal;
tetraphenylethylene;
triphenylene
A novel aggregation-induced emission active molecules (TP-Cn-
PETPE, n ¼ 4 and 10) were synthesized, which contain a tetrapheny-
lethene derivative as the emission active moiety, a pentahexyloxytri-
phenylene core as the mesogenic unit and an alkoxy spacer.
Experimental results revealed that these two compounds both had
AIE properties, even in the liquid state at room temperature. While
only TP-C4-PETPE showed a monotropic liquid crystal phase upon
heating. In addition, these two compounds were fully characterized
1
by H and 13C NMR, IR, EA and MS.
Introduction
Luminescent liquid crystals (LCs) are catching increasing attention for their promising
applications, such as organic light-emitting diodes (OLEDs) [1], organic lasers [2], sen-
sors [3] and so on. Especially, they can emit linear or circular polarized light when the
molecules aligned [4], and used to fabricate more efficient emissive liquid crystal dis-
plays [5].
Despite the unique advantage of luminescent LCs, getting these materials is still chal-
lenging at present. For most LCs, especially the discotic LCs, are weak luminophors in
the solid-state when aggregates are formed, for typical aggregation caused quenching
(ACQ) effects. However, the effect of aggregation-induced emission (AIE), discovered
by Tang and coworkers in 2001 [6], offers a promising way to solve this problem. The
AIE fluorogens give faint emission in solution but exhibit intense emission in the con-
densed state, attributed to the restriction of intramolecular rotations (RIR), aggregation-
induced planarization, and the formation of J-aggregates in some cases [7].
Tetraphenylethylene (TPE), a prototypical AIE-active dye, has been under extensive and
CONTACT Guixia Wang
Bioengineering, Guangxi Key Laboratory of Electrochemical and Magnetochemical Functional Materials, Guilin University
of Technology, Guilin, 541004 China; Zhiqun He zhqhe@bjtu.edu.cn Key Laboratory of Luminescence and
2010033@glut.edu.cn; Shiqing Li
lisq@glut.edu.cn
College of Chemistry and
Optical Information, Ministry of Education, Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing,
100044 China
ß 2021 Taylor & Francis Group, LLC

2
K. XIANGFEI ET AL.
intensive investigations because of its facile synthesis, high solid-sate efficiency, versatile
functionalization approaches and constructing heterogeneous inorganic materials [8].
Discotic LC molecule is normally composed of a planar rigid core and several flexible
alkyl chains as substitutes peripherally connected to the former, most of which tend to
self-organize into columnar phase because of p–p interactions between the neighboring
cores, as well the van der Waals attraction involving alkyl chains [9]. Thus discotic LCs
exhibit excellent electron and/or hole transporting properties along the column in col-
umnar mesophases [10]. These materials are therefore considered as quasi one-dimen-
sional semiconductors [11]. Triphenylene (TP)-based discotic LCs, a typical discotic
liquid crystal, have been synthesized and extensively studied in the past decades. For its
derivatives are thermally and chemically stable, their chemistry is fairly accessible, and
they show a variety of mesophases [9b].
Herein, we designed and synthesized a new class of AIE-LCs using TP derivatives as
the mesogenic core, (phenylethylnyl)tetraphenylethene (PETPE) as the emission active
moiety, and the flexible alkoxy chain as the bridge. Of which the AIE properties and
mesophases were investigated.
Experimental
Materials and methods
The target compounds TP-C4-PETPE and TP-C10-PETPE were synthesized according
to Scheme 1. The 2-(hydroxyl)-3,6,7,10,11-penta(hexyloxy)triphenylene (1) [12] and 2-
(10-bromodecyloxy)-3,6,7,10,11-penta(hexyloxy)triphenylene (3) [13] were readily
obtained according to the procedures reported previously. Compound 4-bromophenyl-
tri-phenylethene (9) was prepared according to the reported procedures [8b, 14]. They
matched the spectral data with the literature’s values. 2-(4-Bromobutyloxy)-3,6,7,10,11-
penta(hexyloxy)triphenylene (2) can be synthesized via alkylation of 1 with 1, 4-dibro-
mobutane under phase transfer conditions in high yield [13]. Then using Williamson
ether synthesis method, 2 and 3 reacted with 4-iodophenol in DMF to yield the iodo-
benzene derivative (4 and 5, respectively) [15]. Diphenylmethane (6) reacted with n-
butyllithium in THF at 0 ꢀC to afford diphenylmethyllithium, which further reacted
with 4-bromobenzophenone (7) at 0 ꢀC to room temperature (rt) affording the corre-
sponding alcohol (8). Compound 9 was obtained by acid-catalyzed dehydration of 8
[14]. Protective acetylene (10) was obtained by the Sonogashira coupling of 9 with 2-
methyl-3-butyn-2-ol [16]. In the presence of potassium hydroxide, 10 was refluxed in
toluene to give 4-ethylnylphenyltriphenylethene (11) by eliminating one molecule of
acetone. Finally, 11 further coupled with 4 and 5, catalyzed by the copper-palladium
system, to afford the target compounds TP-C4-PETPE and TP-C10-PETPE, respect-
ively [17]. Since these two molecules had similar polarity with 4 and 5, they require
repeated purification by flash column chromatography.
All chemicals and solvents were from Aladdin Industrial Corporation, XiLong
Chemical, and FuYu Chemical. All were analytical-grade reagents and used as received
unless otherwise noted.
1H and 13C NMR spectra were recorded on a Bruker spectrometer (500 MHz). Mass
spectra were obtained using an Agilent 6495 in the ESI mode. IR spectra was performed

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
3
Scheme 1. Synthetic route of TP-C4-PETPE and TP-C10-PETPE. Reagents and conditions: (i) KOH, tet-
rabutylammonium bromide, DCM/H2O ¼ 2/1, rt, 12 h, 92%; (ii) 4-iodophenol, KI, K2CO3, DMF, 80 ꢀC,
24 h, 88%; (iii) n-BuLi, THF, 0 ꢀC–rt, 5 h; (iv) TsOH, toluene, 80 ꢀC, 6 h, 53% (two steps); (v) 2-methyl-3-
butyn-2-ol, PdCl2(PPh3)4, Et3N, H2O, 90 ꢀC, 5 h, 53%; (vi) KOH, toluene, 110 ꢀC, 0.5 h, 90%; (vii)
PdCl2(PPh3)4, CuI, PPh3, Et3N, THF, 65 ꢀC, 12 h, about 40%
on a VECTOR 22 FT-IR spectrometer (KBr tablet). Elemental analyses were performed
on a Thermo Flash EA-1112 instrument. UV/Vis spectra were recorded on a Shimadzu
UV-2450 spectrometer. Fluorescent emissions were performed on a HITACHI F-4600
instrument. DSC experiments were carried out on a Thermal Analysis DSC-Q100
instrument. The liquid crystal properties were evaluated by a POM (Olympus
THMS600) instrument provided with a heating stage (Linkam THMSE 600). All theor-
etical calculations were carried out using the Gaussian16 (revision A.03) suite of

4
K. XIANGFEI ET AL.
programs. Full geometry optimization of the target compounds at the density functional
theory (DFT) level using Becke’s three-parameter B3LYP exchange functional and the
3-21 G basis set. The geometries were fully optimized in the gas phase, and the side
alkyl chains were all replaced by methyl groups to reduce the computational load, for
the side chains have little effect on the HOMO and LUMO values of discotic liquid
crystals [18].
Synthesis of 2-(4-bromobutyloxy)-3,6,7,10,11-penta(hexyloxy)triphenylene (2)
Compound 1 (0.74 g, 1.00 mmol), 1,4-dibromobutane (1.28 g, 6 mmol), potassium
hydroxide (0.20 g, 3.38 mmol), tetrabutylammonium bromide (0.15 g, 0.36 mmol), DCM
(10 mL) and water (5 mL) were added to a flask (50 mL). The reaction was carried out
at room temperature for 12 h, and monitored by TLC. After the reaction was completed,
water (10 mL) was added to the reaction mixture, and extracted with DCM (3 ꢁ 10 mL)
and purified by flash column chromatography (silica gel, PE/EA ¼ 30/1) to afford com-
1
pound 2 (0.89 g, 92%) as a brown solid. H NMR (400 MHz, CDCl3) d 7.83 (s, 6H),
4.23 (t, J ¼ 6.5 Hz, 12H), 3.38 (t, J ¼ 6.5 Hz, 2H), 1.95–1.90 (m, 14H), 1.60–1.51 (m,
10H), 1.45–1.35 (m, 20H), 0.93 (t, J ¼ 6.5 Hz, 15H).
Synthesis of 2,3,6,7,10-penta(hexyloxy)-11-(4-(4-iodophenoxy)butyloxy)-tripheny-
lene (4)
Under nitrogen, compound 2 (0.94 g, 1.07 mmol), 4-iodophenol (0.46 g, 2.12 mmol),
potassium iodide (0.16 g, 1.04 mmol), potassium carbonate (0.28 g, 2.12 mmol), catalytic
amount of polyethylene glycol 1000, and DMF (4 mL) were added to a flask. The reac-
tion was refluxed at 80 ꢀC for 24 h and monitored by TLC. After the reaction was com-
pleted, water (40 mL) was added. The mixture was extracted with DCM (3 ꢁ 10 mL).
The combined organic layers were washed with brine (10 mL). Then the organic phase
was dried (Na2SO4) and concentrated in vacuo. The crude product was purified by flash
column chromatography (silica gel, PE/DCM ¼ 3/1) to give 4 (0.95 g, 88%) as a brown
1
solid. H NMR (500 MHz, CDCl3) d 7.96 (s, 1H), 7.84 (s, 1H), 7.83 (s, 3H), 7.81 (s,
1H), 7.57 (d, J ¼ 9.0 Hz, 2H), 6.78 (d, J ¼ 9.0 Hz, 2H), 4.62–4.53 (t, J ¼ 4.5 Hz, 2H),
4.44–4.38 ((t, J ¼ 4.5 Hz, 2H), 4.25–4.18 (m, 10H), 1.95–1.80 (m, 10H), 1.67–1.58 (m,
4H), 1.56–1.55 (m, 10H), 1.43–1.35 (m, 20H), 0.93 (t, J ¼ 7.0 Hz, 15H).
Synthesis of 2,3,6,7,10-pentat(hexyloxy)-11-(10-(4-iodophenoxy)decyloxy)-tripheny-
lene (5)
5 was synthesized and purified according to the procedure of 4, and a brown solid
1
(0.92 g, 90%). H NMR (500 MHz, CDCl3) d 7.84 (s, 6H), 7.52 (d, J ¼ 9.0 Hz, 2H), 6.65
(d, J ¼ 9.0 Hz, 2H), 4.23 (t, J ¼ 6.5 Hz, 12H), 3.89 (t, J ¼ 6.5 Hz, 2H), 1.99–1.90 (m,
12H), 1.81–1.71 (m, 2H), 1.65–1.49 (m, 14H), 1.46–1.34 (m, 28H), 0.93 (t,
J ¼ 7.0 Hz, 15H).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
5
Synthesis of (2-(4-bromophenyl)ethene-1,1,2-triyl)-tribenzene (9) [14]
Under nitrogen, diphenylmethane (1.01 g, 6.03 mmol) was dissolved in THF (20 mL) in
a three-necked-flask (100 mL). The solution was cooled to 0 ꢀC, and n-butyllithium
(2.4 M, 2.3 mL) was added slowly with a syringe. Then the reaction was stirred at 0 ꢀC
for one more hour. The THF (10 mL) solution of 4-bromobenzophenone (1.30 g,
5 mmol) was slowly added into the flask at 0 ꢀC. The reaction was warmed to room
temperature and then stirred for 5 h. After the reaction completed, ammonium chloride
aqueous solution (5%, 30 mL) was added to quench the reaction. The mixture was
extracted with DCM (3 ꢁ 10 mL) to afford the crude product of 8 as a white solid.
The crude product of 8 and p-toluenesulfonic acid (0.15 g, 0.88 mmol) were added to
toluene (40 mL) and then the solution was refluxed for 6 h. After completion, toluene
was removed in vacuo. The crude product was purified by flash column chromatog-
1
raphy (silica gel, PE) to obtain 9 (1.01 g, 53%) as a white solid. H NMR (500 MHz,
CDCl3) d 7.22 (d, J ¼ 8.5 Hz, 2H), 7.16–7.10 (m, 9H), 7.09–6.95 (m, 6H), 6.89 (d,
J ¼ 8.5 Hz, 2H).
Synthesis of 2-methyl-4-(4-(1,2,2-triphenylvinyl)phenyl)but-3-yn-2-ol (10)
Under nitrogen,
9 (0.2 g, 0.49 mmol), 2-methyl-3-ynyl-2-ol (0.1 g, 0.98 mmol),
bis(triphenylphosphine)palladium(II) dichloride (0.034 g, 0.049 mmol), triethylamine
(0.5 mL) and water (3 mL) were added to a flask (50 mL). The reaction was carried out
for 5 h at 90 ꢀC. After the reaction was completed, water (10 mL) was added. The mix-
ture was extracted with DCM (3 ꢁ 10 mL). The combined organic layers were washed
with brine (10 mL). Then the organic phase was dried (Na2SO4) and concentrated in
vacuo. The crude product was purified by flash column chromatography (silica gel, PE/
DCM ¼ 3/1)to obtain compound 10 (0.11 g, 53%) as a yellow solid. 1H NMR
(500 MHz, CDCl3) d 7.15 (d, J ¼ 8.5 Hz, 2H), 7.12–7.10 (m, 9H), 7.05–6.98 (m, 8H),
1.98 (s, 1H), 1.58 (d, J ¼ 4.5 Hz, 6H).
Synthesis of (2-(4-ethynylphenyl)ethene-1,1,2-triyl)-tribenzene (11)
10 (0.11 g, 0.24 mmol) and potassium hydroxide (0.067 g, 1.2 mmol) were added to tolu-
ene (20 mL). The reaction was carried out for 0.5 h at 110 ꢀC. After the reaction was
completed, the toluene was removed in vacuo. The crude product was purified by flash
column chromatography (silica gel, PE/DCM ¼ 50/1) to obtain 11 (0.08 g, 90%) as a
1
yellow solid. H NMR (500 MHz, CDCl3) d 7.22 (d, J ¼ 8.5 Hz, 2H), 7.13–7.08 (m, 9H),
7.04–6.97 (m, 8H), 3.03 (s, 1H).
Synthesis of TP-C4-PETPE
Under nitrogen, compound 4 (0.36 g, 0.35 mmol), compound 11 (0.12 g, 0.34 mmol),
bis(triphenylphosphine)palladium(II) dichloride (0.041 g, 0.034 mmol), cuprous iodide
(0.0032 g, 0.017 mmol), triethylamine (5 ml) and THF (5 ml) were added to a flask
(50 mL). The reaction was carried out overnight at 65 ꢀC. After the reaction was com-
pleted, water (100 mL) was added. The mixture was extracted with DCM (3 ꢁ 10 mL).
The combined organic layers were washed with brine (10 mL). Then the organic phase
was dried (Na2SO4) and concentrated in vacuo. The crude product was purified by flash

6
K. XIANGFEI ET AL.
column chromatography (silica gel, PE/EA ¼ 10/1) to obtain the titled compound
1
(0.16 g, 38%) as a yellow liquid. H NMR (500 MHz, CDCl3) d 7.85 (s, 1H), 7.84 (s,
4H), 7.83 (s, 1H),7.41 (d, J ¼ 8.5 Hz, 2H), 7.24 (d, J ¼ 8.5 Hz, 2H), 7.17–7.08 (m, 9H),
7.02–6.92 (m, 8H), 6.87 (d, J ¼ 8.5 Hz, 2H), 4.30 (s, 2H), 4.23–4.18 (m, 10H), 4.12 (s,
2H), 2.11 (s, 4H), 1.93–1.83 (m, 10H), 1.59 (s, 10H), 1.40–1.30 (m, 20H), 0.95–0.90 (m,
15H). 13C NMR (125 MHz, CDCl3) d 159.2, 149.1, 149.0, 143.55, 143.48, 143.4, 141.51,
140.4, 132.9, 131.4,131.3, 130.8, 127.8, 127.7, 127.6, 126.6, 126.5, 123.7, 121.5, 115.2,
114.5, 107.5, 107.3, 89.7, 88.2, 69.8, 69.7, 68.1, 31.7, 29.6, 29.5, 29.2, 26.2, 26.0, 25.9,
22.7, 14.1, 14.0. IR (KBr) ꢀmax (cmꢂ1): 2921, 2854, 1612, 1515, 1438, 1386, 1259, 1168,
1039, 836, 698. Elemental analysis calcd for C86H102O7 (M ¼ 1247.75): C, 82.78; H, 8.24;
þ
found: C, 82. 80; H, 8.20. MS (ESI): m/z (%) ¼ 1269.8 [M þ Na]
Synthesis of TP-C10-PETPE
Compound TP-C10-PETPE was synthesized and purified according to the procedure of
1
TP-C4-PETPE, and was a yellow solid (0.12 g, 40%). H NMR (500 MHz, CDCl3) d
7.84 (s, 6H), 7.40 (d, J ¼ 8.5 Hz, 2H), 7.24 (d, J ¼ 8.5 Hz, 2H), 7.16–7.07 (m, 9H),
7.02–6.92 (m, 8H), 6.83 (d, J ¼ 8.5 Hz, 2H), 4.23 (t, J ¼ 6.5 Hz, 12H), 3.94 (t, J ¼ 6.5 Hz,
2H), 1.97–1.90 (m, 12H), 1.81–1.74 (m, 2H), 1.65–1.50 (m, 14H), 1.47–1.36 (m, 28H),
0.93 (t, J ¼ 6.5 Hz, 15H). 13C NMR (125 MHz, CDCl3) d 159.2, 149.1, 149.0, 143.6,
143.4, 141.5, 140.4, 132.9, 131.4, 131.3, 130.8, 127.8, 127.7, 127.6, 126.6, 126.5, 123.7,
121.5, 115.2, 114.5, 107.5, 107.3, 89.7, 88.2, 69.8, 69.7, 68.1, 31.7, 29.6, 29.5, 29.2, 26.2,
26.0, 25.9, 22.7, 14.1, 14.0. IR (KBr) ꢀmax (cmꢂ1): 2927, 2860, 1627, 1511, 1430, 1259,
1166, 1033, 837, 698. Elemental analysis calcd for C92H114O7 (M ¼ 1330.85): C, 82.96;
H, 8.63; found: C, 82.96; H, 8.68. MS (ESI): m/z (%) ¼ 1353.9 [M þ Na]þ.
Results and discussion
Phase behaviors
Mesomorphic properties of TP-C4-PETPE and TP-C10-PETPE were investigated by
polarizing optical microscopy (POM) and differential scanning calorimeter (DSC). Peak
transition temperatures along with the associated enthalpy changes (DH) are listed in
Table 1. As shown in Fig. 1a, TP-C4-PETPE showed one broad endothermic peak at
48 ꢀC and another clear one at 74 ꢀC during the first heating process, and a broad exo-
thermic peak was observed at 10 ꢀC in the first cooling process. POM observation
showed that the TP-C4-PETPE had clear birefringence pattern at rt. When heated, it
melted at 45 ꢀC, and the birefringent fluid was maintained up to 75 ꢀC, then the
birefringent phenomenon disappeared. During the cooling process to rt, the birefringent
phenomenon was not observed. In the end a sticky liquid was obtained. However, when
it was lay aside for five days at rt, the birefringent phenomenon was resorted partially.
Encouraged by this, we heated a new sample to 55 ꢀC and then cooled it to 50 ꢀC at the
rate of 0.5 ꢀC minꢂ1, then the birefringent phenomenon was maintained and the optical
texture observed at 50 ꢀC can be seen clearly (see Fig. 1b). It can be seen that TP-C4-
PETPE showed a monotropic liquid crystal phase.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
7
Table 1. Phase behaviors of TP-Cn-PETPE (n ¼ 4 and 10). Phase transition temperatures (peak, ꢀC)
and associated enthalpy changes (J gꢂ1, in parentheses) determined by DSC at a scan rate of
10 ꢀC minꢂ1
.
First heating scan
T/ꢀC
First cooling scan
T/ꢀC
Compounds
(DH/J g-1)
(DH/J g-1)
TP-C4-PETPE
TP-C10-PETPE
Cr 49 (0.027) LC 74 (20.95) I
Cr 5 (0.45) I
I 11 (0.69) Cr
I 2 (0.77) Cr
Cr: crystalline, I: isotropic liquid.
Figure 1. (A) The DSC traces for TP-Cn-PETPE (n ¼ 4 and 10) under a nitrogen atmosphere (10ꢀC
minꢂ1, the first heating-cooling cycle, peak temperatures labelled); (B) Optical texture of TP-C4-PETPE
(at 50 ꢀC upon heating).
As shown in Fig. 1a, TP-C10-PETPE showed one broad endothermic peak at 5 ꢀC
and a broad exothermic one at 2 ꢀC during the first heating and cooling process,
respectively. Under microscopic observation, it was a sticky liquid without birefringent
phenomenon at rt., and there was no birefringent pattern when heated up to 90 ꢀC or
cooled down to rt. From the above we knew TP-C10-PETPE show no liquid crystal-
line behavior.
Photophysical properties
To test the optical properties of TP-C4-PETPE and TP-C10-PETPE, their UV/Vis
absorption spectra in THF/water mixtures with different H2O fractions (fw) were meas-
ured firstly. Five sets of solution (concentration 1 ꢁ 10ꢂ5 mol Lꢂ1) at water fractions
(fw) 0%, 30%, 60%, 90% and 99% were measured. Fig. 2 shows the absorption spectra of
TP-C4-PETPE. In pure THF solution, the absorption range was in the ultraviolet
region, between 240 and 400 nm. Its absorption maximum was at 280 nm, and the peak
optical density corresponding to an extinction coefficient (e) was 1.5 ꢁ 105
L
molꢂ1 cmꢂ1. The absorption spectrum was the sum spectra of TP and PETPE units,
ꢃ
which were independent of each other and attributed to the p-p electron transition of
TP and PETPE moieties, respectively [8c, 13, 17]. The spectrum at fw 30% was almost
identical with that in pure THF solution. However, when fw exceeded 60%, the solution

8
K. XIANGFEI ET AL.
Figure 2. UV/Vis absorption spectra of TP-C4-PETPE in THF/H2O mixtures at fw ¼ 0, 30, 60, 90 and
99%. Solution concentration: 1 ꢁ 10ꢂ5 mol Lꢂ1
.
decreased in absorption intensity and were red shifted. A level-off tail was seen in the
visible spectral region; which are commonly observed in nanoparticle suspensions [6],
confirming the existence of nanoaggregates of TP-C4-PETPE in these solvent mixtures.
The similar experimental phenomena was also observed from the absorption spectra of
TP-C10-PETPE in THF/water mixtures. This suggested that the length of the alkoxy
spacers had negligible influence on the optical properties in the dispersed and aggre-
gated states, owing to their similar electronic structure. And this was further confirmed
by the calculated HOMO frontier molecular orbitals of these two molecules in the
ground states (see Fig. 3). The HOMO and LUMO frontier molecular orbitals of TP-
C4-PETPE and TP-C10-PETPE are both located on PETPE moieties and the values
were ꢂ1.43 eV and ꢂ5.04 eV, respectively (see Fig. 3). The calculated optical band gaps
(denoted as Eg) was 3.61 eV, which corresponded to a wavelength of 343 nm. This value
was matched the absorption range of the moiety of (phenylethylnyl)tetraphenylethene of
TP-C4-PETPE in solution (see Fig. 2), and that of the phenyltetraphenylethene group
in a polymeric film [19].
Since water is a poor solvent for TP-C4-PETPE and TP-C10-PETPE, their AIE char-
acteristics were investigated in THF/H2O mixtures. The fluorescence spectra of TP-C4-
PETPE in THF/H2O mixtures (concentration 1 ꢁ 10ꢂ5 mol Lꢂ1) at fw 0–99% showed in
Fig. 4A. In pure THF solution, a strong emission peak at 389 nm was observed, which
was attributed to the emission of the TP unit [13]. The PETPE unit showed no emission
at this moment, and the emission at about 500 nm was negligible. After the addition of
water into the THF solution, the emission intensity of TP unit decreased slightly, but
that of PETPE unit increased a little and red-shifted subtly at fw 30% (Fig. 4B). At fw
60%, the emission intensity of PETPE slightly increased and red-shifted (Fig. 4B). While
the emission intensity of TP unit decreased drastically for the ACQ effect, for the form-
ing of the aggregation state can be seen clearly from the UV/Vis spectra at fw from 30%
to 60% (Fig. 2). When fw exceeded 90%, the emission of the TP unit decreased and
reached a minimum due to the ACQ effect. However, the fluorescence of PETPE unit

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
9
Figure 3. Optimized geometric structure of TP-C4-PETPE and TP-C10-PETPE in gas phase and their
frontier orbitals calculated by density functional theory (DFT) at the B3LYP/3-21G level.
Figure 4. Fluorescence spectra of TP-C4-PETPE (A) and TP-C10-PETPE (C) in THF/water mixtures with
different water fractions (fw 0–99%); Plots of wavelengths and the ratio of maximum fluorescence
intensity of PETPE unit of TP-C4-PETPE (B) and TP-C10-PETPE (D) vs. fw, I0: emission intensity of
PETPE unit of TP-C4-PETPE and TP-C10-PETPE in pure THF solution, respectively. Excitation wave-
length: 280 nm, Solution concentration: 1 ꢁ 10ꢂ5 mol Lꢂ1
.
was significantly enhanced and red-shifted due to the AIE effect. At fw 99%, the emis-
sion intensity was enhanced nearly 36-fold compared to the pure THF solution, and the
fluorescence maximum was shifted to 525 nm (Fig. 4B). These results indicated that the

10
K. XIANGFEI ET AL.
Figure 5. Photographs of TP-C4-PETPE coating on the glass substrate at 90 ꢀC (A) and cooling to rt
(C), TP-C10-PETPE coating at 90 ꢀC (B) and cooling to rt (D) irradiated with a 365 nm UV light.
Figure 6. PL spectra of TP-C4-PETPE and TP-C10-PETPE in liquid state at rt. Excitation wave-
length: 380 nm.
PETPE and TP unit of TP-C4-PETPE possessed AIE and ACQ characteristics,
respectively.
The fluorescence spectra of TP-C10-PETPE in THF/H2O mixtures at fw 0–99% are
shown in Fig. 4C. When fw increased from 0 to 99%, the PETPE unit and TP unit of
TP-C10-PETPE respectively possessed AIE and ACQ characteristics, just like that of
TP-C4-PETPE. At fw 99%, the emission intensity was enhanced nearly 81-fold com-
pared to that of the pure THF solution, and the fluorescence maximum was shifted to
495 nm (Fig. 4D).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
11
Based on the results above, TP-C4-PETPE could form tighter aggregates in aqueous
media, owing to it forms a solid precipitate in solution at rt. In contrast, TP-C10-
PETPE formed comparatively looser aggregates because it is stick fluid at rt, that could
not restrict the intramolecular rotation and yielded a smaller red shift.
To further investigate the fluorescent properties in a pristine state, we observed tem-
perature-dependent fluorescence emission of TP-C4-PETPE and TP-C10-PETPE. These
two compounds both were liquid at 90 ꢀC and emitted faintly (Fig. 5A,B). When they
are cooled naturally to room temperature, they both became thickened and can not
flow freely, and emitted stronger light as expected (Fig. 5C,D). For the intramolecular
rotation was more restricted at room temperature. Furthermore, the PL spectra of these
two sticky liquid at rt were measured (Fig. 6). Their maximum emission is about at
540 nm, which is longer than that of the two compounds in THF/H2O mixture at fw
99%. This is attributed to the tighter aggregates of them in the pristine states. In add-
ition, TP-C4-PETPE showed AIE effect in the solid state at rt, too.
Conclusions
In summary, two AIE active compounds were prepared and characterized. These com-
pounds are characterized by TPE derivatives linked to pentahexyloxytriphenylene via an
alkoxy bridge, and they all showed typical AIE effects. In addition, they had intense
fluorescence emission when they were in the liquid state at room temperature. At 90 ꢀC,
they were still fluorescent liquids, but their intensity decreased. TP-C4-PETPE, with a
shorter bridge, showed a monotropic liquid crystal phase. While TP-C10-PETPE, shows
no mesophase in heating or cooling processes.
Disclosure statement
The authors declare no competing financial interest.
Acknowledgments
We thank Guangxi key laboratory of hidden metallic ore deposits exploration for providing sup-
port with the POM measurements.
Funding
This work was supported by the National Natural Science Foundation of China under Grant
No.11364013, Guangxi Natural Science Foundation under Grant No. 2018GXNSFAA281115, and
Opening Foundation of Guangxi Key Laboratory of Electrochemical and Magnetochemical
Functional Materials under Grant No. EMFM20162202.
References
[1] (a) Y. Wang et al., J. Mater. Chem. C, 5, 3999 (2017). doi:10.1039/C7TC00034K; (b) S.
Jiang et al., Dyes Pigments, 159, 533 (2018). doi:10.1016/j.dyepig.2018.07.018; (c) J. De
et al., ACS Appl. Mater. Interfaces, 11, 8291 (2019). doi:10.1039/C7TC00034K

12
K. XIANGFEI ET AL.
[2] N. Wang et al., Opt. Express. 23 (26), 33938 (2015). doi:10.1364/OE.23.033938
[3] (a) Y. Dong et al., Appl. Phys. Lett. 91, 011111 (2007). doi:10.1063/1.2753723; (b) X. Zhou
et al., Chem. Rev. 115, 7944 (2015).
[4] (a) J. Sha et al., Org. Electron. 50, 177 (2017). (b) C. Yu, C. Hsu, and H. Weng, RSC Adv.
8, 12619 (2018). doi:10.1016/j.orgel.2017.07.044
[5] D. Zhao et al., Adv. Opt. Mater. 4 (4), 534 (2016). doi:10.1002/adom.201500646
[6] J. Luo et al., Chem. Commun. (18), 1740 (2001). doi:10.1039/b105159h
[7] (a) Y. Hong, J. W. Y. Lam, and B. Z. Tang, Chem. Soc. Rev. 40, 5361 (2011). (b) J. Mei
et al., Chem. Rev. 115, 11718 (2015). (c) T. Wu, J. Huang, and Y. Yan, Chem. Asian J. 14,
730 (2019). doi:10.1039/c1cs15113d
[8] (a) W. Z. Yuan et al., Adv. Mater. 22, 2159 (2010). (b) J. Mei et al., Adv. Mater. 26, 5429
(2014). doi:10.1002/adma.201401356; (c) N. Li et al., ACS Appl. Mater. Interfaces 10,
24249 (2018). doi:10.1021/acsami.8b04113; (d) J. Knelles et al., Chemphyschem 20, 2210
(2019). doi:10.1002/adma.200904056
[9] (a) R. J. Bushby and O. R. Lozman, Curr. Opin. Colloid Interface Sci. 7, 343 (2002). (b) S.
Kumar, Liq. Cryst. 31, 1037 (2004). doi:10.1080/02678290410001724746; (c) S. Laschat
et al., Angew. Chem., Int. Ed 46, 4832 (2007). doi:10.1016/S1359-0294(02)00085-7
[10] E. O. Arikainen et al., J. Mater. Chem. 5 (12), 2161 (1995). doi:10.1039/jm9950502161
[11] N. Boden, R. J. Bushby, and J. Clements, J. Chem. Phys. 98 (7), 5920 (1993). doi:10.1063/
1.464886
[12] X. Kong et al., Tetrahedron. Lett. 52 (1), 77 (2011). doi:10.1016/j.tetlet.2010.10.152
[13] X. Kong et al., RSC Adv. 7 (28), 17030 (2017). doi:10.1039/C7RA01320E
[14] M. Banerjee et al., J. Org. Chem. 72 (21), 8054 (2007). doi:10.1021/jo701474y
[15] X. Kong et al., Mol. Cryst. Liq. Cryst. 650 (1), 56 (2017). doi:10.1080/15421406.2017.
1328218
[16] J. T. Guan et al., Tetrahedron. Lett. 48 (40), 7129 (2007). doi:10.1016/j.tetlet.2007.07.207
[17] X. Kong et al., New J. Chem. 42 (5), 3211 (2018). doi:10.1039/C7NJ04328G
[18] Y. Zhang et al., ACS Appl. Mater. Interfaces. 9 (23), 20010 (2017). doi:10.1021/acsami.
7b03795
[19] J. Zhu et al., Polym. Chem. 10 (46), 6342 (2019). doi:10.1039/C9PY01290G