Methyl-restricted rotor rotation on the stator produces high-efficiency fluorescence emission: A new strategy to achieve aggregation-induced emission

Article abstract of DOI:10.1039/c9ra01636h

At present, we have realized that the aggregation-induced emission (AIE) achieves the purpose of fluorescence enhancement by restricting rotations to reduce intermolecular or intramolecular energy loss. Based on this idea, we synthesized a novel fluorene-

Full text of DOI:10.1039/c9ra01636h

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Methyl-restricted rotor rotation on the stator
produces high-efficiency fluorescence emission:
a new strategy to achieve aggregation-induced
emission†
Cite this: RSC Adv., 2019, 9, 12078
Haicheng Yang,
Xinyue Zhou, Tianqi Hui, Yingying Han, Xiaonan Jiang and Jie Yan*
At present, we have realized that the aggregation-induced emission (AIE) achieves the purpose of
fluorescence enhancement by restricting rotations to reduce intermolecular or intramolecular energy
loss. Based on this idea, we synthesized a novel fluorene-based fluorescent compound with a restricted
rotor rotation on the stator through the Suzuki coupling reaction. The luminescence effect was
evaluated by comparing its fluorescence intensity with that of the control compound. Finally, theoretical
calculations showed that the presence of methyl groups hindered the thermal rotation of the fluorenyl
groups. Thus, the results indicated that the fluorescence of this compound was better than that of the
control compound. A new synthetic pathway for high-efficiency AIE-based fluorescent luminogens has
been developed.
Received 4th March 2019
Accepted 3rd April 2019
DOI: 10.1039/c9ra01636h
rsc.li/rsc-advances
wavelengths covering the visible and NIR regions for cell
imaging. The emission colors were tuned by simple alteration of
Introduction
1
Aggregation-induced emission (AIE) is a new phenomenon that the HOMO–LUMO energy levels by the introduction of electron
26
is contrary to the commonly observed aggregation-caused donor (D)–acceptor (A) substituents.
2
quenching (ACQ). Because of its important academic value
A large amount of research has been devoted to the basic
biop- understanding of the mechanism behind the AIE phenom-
3
–5
and diversied applications in uorescent sensors,
6–8
9–11
27–31
robes,
changing smart materials,
research interest. Novel AIE nano-uorescent probes have have suggested that the restriction of intramolecular rotation
optoelectronic devices,
and mechanical color- enon,
both to solve ACQ and develop efficient solid state
12–14
it has stimulated extensive luminogens. Theoretical calculations and experimental results
15
32,33
excellent water solubility, biocompatibility and optical prop- (RIR)
is the main cause of the AIE effect. In the solution
16,17
erties,
mental detection, cell imaging and chemical sensors.
and can be applied in disease diagnosis, environ- state, the aromatic rotor typically annihilates the excitons in
1
8,19
The a nonradiative transition mode. However, in the aggregated
most important one among these is the application in cell state, the rotation of the rotor is restricted, resulting in the
imaging. Fluorescent probes that are used to enter cells and predominant radiative transition of the excited state, thus
3
4
image require a simple designs and surface functionaliza- successfully producing luminogens.
Therefore, aromatic
20
tions, biodegradability and good biocompatibility. In order to rotors are very important in the design of AIE active lumi-
achieve these functions, Wei et al. developed a series of small nogens. It has been reported that the volume of the aromatic
3
5
36

uorescent molecules with the AIE effect, and also developed rotor, the number of restricted benzene rings, and the
37
AIE uorescent mesoporous silica nanoparticles for intracel- connection between the stator and the rotor all affect the
21–23
lular imaging.
Some functionalized uorescent nano- luminous efficiency of the AIE light-emitting device. However,
particles have demonstrated specic targeting ability towards there are few reports of groups on the stator that restrict the
cancer cells, which is used for therapeutic diagnosis, and rotation of the uorescent rotor. The benecial outcome of the
24,25
signicant progress has been made.
Recently, Tang et al. AIE effect would be to restrict the rotation of the rotor in the
reported a series of triphenylamine (TPA)–thiophene building aggregated state, reduce the non-radiative annihilation process,
block-based AIEgens having tunable maximum emission and promote the radiative quenching pathway. Therefore, the
rotation of the rotor is restricted, and the plane p-conjugate is
better generated between the rotor and the stator, which can
College of Chemistry and Chemical Engineering, Liaoning Normal University, Huanghe increase the luminogens emission efficiency to some extent. In
Road 850#, Dalian City, 116029, PR China. E-mail: yhc1994@live.cn
order to gain a deeper understanding of the relationship
between the structure of AIE luminescent materials and the
1
13
†
Electronic supplementary information (ESI) available: H and C NMR spectra
and additional gures. See DOI: 10.1039/c9ra01636h
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intensity of luminescence, we have focused on uorene- mmol), and H
substituted methylbenzene, an AIE luminescent agent with was stirred at 90 C for 10 h. The reaction mixture was diluted
2
SO
4
ꢀ
(3 mL) in acetic acid (50 mL)–water (10 mL)
a twisted propeller conformation with a large sterically with water (125 mL), and the resulting precipitate was ltered,
hindered stator.
washed with water to remove the acid, and washed with acetone
We want to know if the uorescence of the AIE luminogens can to give 1,3,5-triiodo-2,4,6-trimethylbenzene, a white solid
1
be enhanced to some extent when a large sterically hindered group (21.0 g, 84.5%). H NMR (500 MHz, CDCl
3
), d (TMS, ppm): 3.01
1
3
blocks the aromatic rotor. For this, we prepared a new large (s 9H). C NMR (125 MHz, CDCl
3
), d (TMS, ppm): 144.15,
sterically hindered uorene-substituted methylbenzene (1,3,5- 101.16, 39.56.
tris(9,9-dimethyluoren-2-yl)-2,4,6-trimethylbenzene) (TFTB) and
compared its luminescence properties with uorene-substituted 2,4,6-trimethylbenzene (3.0 g, 6.03 mmol), 4,4,4 ,4 ,5,5,5 ,5 -
Procedure for the synthesis of 2. A mixture of 1,3,5-triiodo-
0
0
0
0
0
benzene without large sterically hindered groups (1,3,5-tris(9,9- octamethyl-2,2 -bi(1,3,2-dioxaborolane) (6.3 g, 25.86 mmol),
38,39
dimethyluoren-2-yl)benzene)
(TFB) (Chart 1).
PdCl (dppf) (0.2 g), and KOAc (4.0 g, 29.5 mmol) was added to
2
a ask. The ask was connected to a Schlenk line, which evac-
uated the air and relled the ask with nitrogen. Then, 50 mL of
DMF was degassed and added through a cannula. The ask was
Experimental
Chemicals and instruments
ꢀ
equipped with a water condenser and stirred at 90 C under
Mesitylene, 2-bromo-9,9-dimethyluorene and all other chem- nitrogen for 24 h. Aer cooling to room temperature, 25 mL of
icals and reagents were purchased from Aladdin Industrial water was added and then extracted with CH Cl (3 ꢂ 50 mL);
2
2
Corporation. THF was distilled under dry nitrogen immediately the combined organic layer was washed with saturated saline
1
13
prior to use. H and C NMR spectra were measured on and dried over anhydrous MgSO . The solvent was evaporated
4
a Bruker AV 500 spectrometer in deuterated chloroform or and the residue was puried by column chromatography over
dichloromethane using tetramethylsilane (TMS; d ¼ 0) as the silica gel using ethyl acetate/petroleum ether (1 : 4, v/v); then, it
internal reference. UV-Vis spectra were measured on a JASCO V- was recrystallized from hexane to give 1,3,5-tris(4,4,5,5-
5
70 spectrophotometer. Photoluminescence was recorded on tetramethyl-1,3,2-dioxaborolan-2-yl)-2,4,6-trimethylbenzene,
1
a JASCO FP-6500 spectrophotometer. Thermal transitions were which was a colorless transparent solid (2.40 g, 80%). H NMR
investigated by differential scanning calorimetry using a STA (500 MHz, CDCl ), d (TMS, ppm): 2.39 (s, 9H), 1.34 (s, 36H).
1
3
C
3
ꢀ
ꢁ1
449 F3 under dry nitrogen at a heating rate of 10 C min . High NMR (125 MHz, CDCl ), d (TMS, ppm): 147.02, 84.71, 26.38,
3
+
resolution mass spectrometry was measured on a LTQ-Orbitrap 23.99. HRMS: m/z 498.3495 (M , calcd 498.0756).
XL high resolution mass spectrometer. X-ray diffraction
Procedure for the synthesis of 3 (TFTB) (pathway c). A
patterns were recorded on a D8 Advance powder diffractometer mixture of 1,3,5-tris(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
using the monochromatized X-ray beam from a nickel-ltered
˚
Cu Ka radiation (l ¼ 1.54183 A).
Aggregation-induced emission investigation
Stock THF solutions of the luminogens with a concentration of
100 mM were prepared. Aliquots of the stock solution were
transferred to 10 mL volumetric asks. Aer appropriate
amounts of THF were added, water was added dropwise under
vigorous stirring to furnish 10 mM solutions with different water
contents. The PL measurements of the resultant solutions were
then performed immediately.
Synthetic details
Procedure for the synthesis of 1. A mixture of mesitylene
2 4 2
(6.0 g, 50 mmol), I (15.5 g, 60 mmol), HIO $2H O (7.0 g, 32.5
Scheme 1 Reactions and conditions: (a) HIO
acid, water; (b) 4,4,4 ,4 ,5,5,5 ,5 -octamethyl-2,2 -bi(1,3,2-dioxabor-
4
$2H
2
0
O, I
2
, H
2
SO
4
, acetic
0
0
0
0
olane), PdCl
Pd(PPh , K
,4,5,5-tetramethyl-1,3,2-dioxaborolane, Pd(PPh
2
(dppf), KOAc, DMF; (c) 2-bromo-9,9-dimethylfluorene,
PO , DMSO, water; (d) 2-(9,9-dimethylfluoren-2-yl)-
, K PO , dioxane,
water; (e) 4,4,4 ,4 ,5,5,5 ,5 -octamethyl-2,2 -bi(1,3,2-dioxaborolane),
PdCl (dppf), KOAc, DMF; (f) 1,3,5-tribromobenzene, Pd(PPh , K PO
dioxane, water.
)
3 4
3
4
4
)
3 4
3
4
0
0
0
0
0
2
3
)
4
3
4
,
Chart 1 AIE luminogen TFTB and its control example.
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1
3
yl)-2,4,6-trimethylbenzene (1.0 g, 2.0 mmol), 2-bromo-9,9- transparent solid (4.40 g, 75%). H NMR (500 MHz, CDCl ),
dimethyluorene (1.9 g, 6.96 mmol), Pd(PPh3)4 (0.2 g, 17 d (TMS, ppm): 7.88 (s, 1H), 7.81 (d, J ¼ 7.5 Hz, 1H), 7.74 (dd, J ¼
mmol), and K PO (3.0 g, 14.17 mmol) was added to a ask. The 12.1, 5.7 Hz, 2H), 7.45–7.41 (m, 1H), 7.35–7.30 (m, 2H), 1.50 (s,
3
4
1
3

ask was connected to a Schlenk line, which evacuated the air 6H), 1.38 (s, 12H). C NMR (125 MHz, CDCl ), d (TMS, ppm):
3
and relled the ask with nitrogen. A solution of 30 mL of 154.32, 154.12, 153.70, 152.77, 142.21, 141.27, 140.39, 139.20,
DMSO and 2 mL of water was degassed and added through 138.99, 137.48, 133.49, 128.77, 128.08, 127.75, 126.97, 123.82,
a cannula. The ask was equipped with a water condenser and 122.64, 120.44, 119.88, 119.34, 83.75, 46.87, 27.08, 24.93, 19.62.
ꢀ
stirred at 95 C under nitrogen for 48 h. Aer cooling to room
Procedure for the synthesis of 5. A mixture of 1,3,5-tri-
temperature, 25 mL of water was added and then extracted with bromobenzene (1.0 g, 3.18 mmol), 2-(9,9-dimethyluoren-2-yl)-
CH Cl (3 ꢂ 50 mL); the combined organic layer was washed 4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3.1 g, 9.68 mmol),
2
2
with saturated saline and dried over anhydrous MgSO . The Pd(PPh ) (0.2 g), and K PO (3.0 g, 14.17 mmol) was added to
4
3 4
3
4
solvent was evaporated and the residue was puried by column a ask. The ask was connected to a Schlenk line, which evac-
chromatography over silica gel using CH Cl /petroleum ether uated the air and relled the ask with nitrogen. A solution of
1 : 5, v/v); then, the solvent was removed to give 1,3,5-tris(9,9- 30 mL of dioxane and 2 mL of water was degassed and added
2
2
(
dimethyluoren-2-yl)-2,4,6-trimethylbenzene (TFTB), a white through a cannula. The ask was equipped with a water
ꢀ
solid (0.21 g, 14%).
condenser and stirred at 85 C under nitrogen for 24 h. Aer
Procedure for the synthesis of 3 (TFTB) (pathway d). A cooling to room temperature, 25 mL of water was added and
mixture of 1,3,5-triiodo-2,4,6-trimethylbenzene (1.0 g, 2.01 then extracted with CH Cl (3 ꢂ 50 mL); the combined organic
2
2
mmol), 2-(9,9-dimethyluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2- layer was washed with saturated saline and dried over anhy-
dioxaborolane (2.56 g, 8.0 mmol), Pd(PPh ) (0.2 g, 17 mmol), drous MgSO . The solvent was evaporated and the residue was
3
4
4
and K
was connected to a Schlenk line, which evacuated the air and CH
relled the ask with nitrogen. A solution of 30 mL of dioxane removed to give 1,3,5-tris(9,9-dimethyluoren-2-yl)benzene
3
PO
4
(3.0 g, 14.17 mmol) was added to a ask. The ask puried by column chromatography over silica gel using
2
2
Cl /petroleum ether (1 : 5, v/v); then, the solvent was
1
3
and 2 mL water was degassed and added through a cannula. (TFB), a white solid (1.52 g, 73%). H NMR (500 MHz, CDCl ),
The ask was equipped with a water condenser and stirred at d (TMS, ppm): 7.89 (s, 3H), 7.85 (d, J ¼ 7.8 Hz, 3H), 7.78 (dd, J ¼
ꢀ
8
5 C under nitrogen for 24 h. Aer cooling to room tempera- 6.3, 1.2 Hz, 6H), 7.73 (dd, J ¼ 7.8, 1.6 Hz, 3H), 7.47 (dd, J ¼ 6.3,
1
3
ture, 25 mL of water was added and then extracted with CH Cl
1.2 Hz, 3H), 7.39–7.32 (m, 6H), 1.57 (s, 18H). C NMR (125
2
2
(
3 ꢂ 50 mL); the combined organic layer was washed with MHz, CDCl ), d (TMS, ppm): 154.42, 153.97, 142.97, 140.55,
3
4
saturated saline and dried over anhydrous MgSO . The solvent 138.84, 127.37, 127.08, 126.54, 125.37, 122.66, 121.78, 120.38,
was evaporated and the residue was puried by column chro- 120.15, 47.07, 27.29. HRMS: m/z 654.3287 (M , calcd 654.8792).
matography over silica gel using CH Cl /petroleum ether (1 : 5,
+
2
2
v/v); then, the solvent was removed to give 1,3,5-tris(9,9-
Results and discussion
dimethyluoren-2-yl)-2,4,6-trimethylbenzene (TFTB), a white
1
solid (0.71 g, 51%). H NMR (500 MHz, CDCl ), d (TMS, ppm): Synthetic strategy
3
7
1
3
.79 (d, J ¼ 7.8 Hz, 3H), 7.75 (d, J ¼ 6.7 Hz, 3H), 7.69 (d, J ¼
The compound TFTB was prepared by a Suzuki coupling reac-
tion, which was carried out using an aryl boronate in the
presence of a base and a Pd (0) catalyst (Scheme 1). The rst
synthesized 1,3,5-tris(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
.4 Hz, 3H), 7.63 (dd, J ¼ 7.8, 1.7 Hz, 3H), 7.45 (d, J ¼ 6.3 Hz,
40
1
3
H), 7.37–7.30 (m, 6H), 3.00 (s, 9H), 1.56 (s, 18H). C NMR (125
MHz, CDCl
3
), d (TMS, ppm): 155.73, 155.35, 145.57, 142.28,
1
1
40.35, 139.82, 128.66, 128.46, 127.73, 124.04, 122.84, 121.71,
21.49, 102.60, 48.42, 40.98, 28.72. HRMS: m/z 696.3756 (M ,
yl)-2,4,6-trimethylbenzene and 2-bromo-9,9-dimethyluorene
+
41–43
can be used as the substrate.
use
It is also possible to
and 2-(9,9-
calcd 696.9589).
1,3,5-triiodo-2,4,6-trimethylbenzene
Procedure for the synthesis of 4. A mixture of 2-bromo-9,9-
dimethyluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
as substrates, and the target compounds can be obtained by
both methods. However, the second method resulted in
a higher yield (51%) due to the steric hindrance of the reaction.
Their spectra can be found in the ESI.† Its powder was crystal-
line, as revealed by the X-ray diffractogram (Fig. S1†). All lumi-
nescent agents are soluble in common organic solvents such as
tetrahydrofuran (THF), but insoluble in water.
0
0
0
0
dimethyluorene (5.0 g, 18.31 mmol), 4,4,4 ,4 ,5,5,5 ,5 -octa-
methyl-2,2 -bi(1,3,2-dioxaborolane) (4.8 g, 19 mmol), PdCl (-
dppf) (0.2 g), and KOAc (4.0 g, 29.5 mmol) was added to a ask.
The ask was connected to a Schlenk line, which evacuated the
air and relled the ask with nitrogen. 50 mL of DMF was
degassed and added through a cannula. The ask was equipped
0
2
ꢀ
with a water condenser and stirred at 100 C under nitrogen for
24 h. Aer cooling to room temperature, 25 mL of water was
added and then extracted with CH Cl (3 ꢂ 50 mL); the
2
2
Aggregation-induced emission (AIE) property
combined organic layer was washed with saturated saline and
dried over anhydrous MgSO
the residue was puried by column chromatography over silica and recorded its PL spectrum in the water-THF mixture (Fig. 1).
gel using CH Cl /petroleum ether (1 : 20, v/v); then, it was When the water fraction (f , vol%) in the water–THF mixture
recrystallized from hexane to give 2-(9,9-dimethyluoren-2-yl)- was less than 50%, its PL emission remained in a very weak
4
. The solvent was evaporated and To test if TFTB is AIE active, we added water to its THF solution
2
2
w
4,4,5,5-tetramethyl-1,3,2-dioxaborolane,
a
colorless state with only a slight change. When a large amount of water
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Fig. 1 (A) Photograph of TFTB in a water–THF mixed solution (f
water–THF mixed solution. (C) Fluorescence change pattern of TFTB in a water–THF mixed solution. (I is the PL intensity in a pure THF solution.)
0
w
¼ 0–99%) under a UV lamp. (B) PL spectrum of TFTB in different fractions of
w
(f $ 60%) was added, a long-wavelength emission with a peak arranged in a star-shaped propeller shape. The highly twisted
at 394 nm appeared, and the intensity was greatly enhanced. conformation of the TFTB results in a poor electronic commu-
The emission peak red-shied compared to that of its THF nication between the rotor and the stator and little orbital
solution and the frequency-doubled peak appeared at 561 nm. overlap. Molecular orbital amplitude maps of the LUMO and
TFTB is insoluble in water, and an increase in water content HOMO levels of the two molecules (Fig. S3†) show that they were
causes the TFTB molecules to assume an aggregated state. The clearly dominated by the orbits of the uorene rings of the
formation of aggregates greatly weakens the intramolecular surrounding rotors. This indicates that the emission of TFTB is
rotation (IMR) process, causing the luminogens to emit intense derived from the excited state of the rotor uorene ring around

uorescence. A similar emission behavior of TFB was also it. Among them, the three uorene rings of TFTB contribute to
observed in the water–THF mixture (Fig. S2†), conrming that it the LUMO and HOMO energy levels. However, there is a ring
is also AIE active.
that does not contribute to its HOMO level at all in TFB.
TFTB shows the maximum absorption at 328 nm (Fig. S4†),
and its energy band gap is calculated to be 4.77 eV (Fig. S5†).
TFB shows the maximum absorption at 336 nm, and its energy
band gap is calculated to be 4.32 eV. Since there is a uorene
ring in TFB that does not contribute to its HOMO level, this is
also the reason why the energy band gap of TFTB is wider than
that of TFB. This is in good agreement with the blue-shi of the
absorption spectrum of TFTB in the THF solution. The struc-
tural difference between TFTB and TFB is that the former has
three methyl groups on the stator. Following our hypothesis, it
is clear that the hindrance of these three methyl groups restricts
the rotation of the rotor, so that TFTB emits in the solution
state, while TFB has only weak luminescence in the solution
state. The gradually thickened TFTB and TFB in the THF solu-
tion (from 1 mM to 100 mM) only increase their emission
intensities, and hardly affect their spectral distribution and
peak position. TFTB has two peaks at 362 nm and 380 nm, while
TFB has only one peak, which appears at 368 nm (Fig. 3). This is
because the methyl group inside the TFTB molecule in the
solution state hinders the IMR process of its luminescent rotor,
causing its various portions to emit characteristic peaks.
However, due to the IMR process, TFB loses energy between the
rotor and the stator; the exciton radiation is attenuated, and the
emission peaks of each part are mixed.
Computational research, photophysical properties
The molecular conformation was optimized by the semi-
empirical PM3 method (Fig. 2). The uorene unit was
Fig. 2 Optimized molecular structures of TFTB and TFB calculated by
a semi-empirical PM3 method. (The blue line represents the benzene
ring plane; the red line represents the fluorene ring plane.)
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plane, as shown in the potential energy surface scan (Fig. 5).
When the angle between the uorene ring plane and the
ꢀ
benzene ring plane of TFTB was 99.76 , the total energy of the
entire molecular system was the lowest. When the angle was
ꢀ
1
89.76 , the uorene ring was closest to the methyl group, and
the total energy of the entire molecular system was the highest.
ꢀ
When the TFB's uorene-benzene dihedral angle was ꢁ38.03 ,
the total energy of the system was the lowest. When the angle
ꢀ
was 81.97 , the total energy of the system was the highest. When
both energies were highest, the energy of TFTB was much larger
than that of TFB. However, aer one revolution, the total energy
Fig. 3 (A) PL spectra of different concentrations of TFTB in THF
solution. (B) PL spectra of different concentrations of TFB in THF
solution. (Intermediate panel) photograph of TFTB and TFB at the same of the TFTB system was not the same as the initial energy
concentration (1000 mM) in a THF solution under a UV lamp.
because the uorene ring itself did not have a symmetrical
structure. The methyl group was not evenly extruded on the

uorene ring. This is not the case with TFB. Collectively, these
TFTB and TFB can also uoresce in the solid state (Fig. 4A results veried that the methyl group on the stator could restrict
and C). Their solids show PL emission characteristics. The PL the rotation of the rotor.
spectrum of the TFTB solid exhibits a peak at 424 nm (Fig. 4B).
Its quantum yield is 37.44%. Its solid has very good uorescence
under UV light. The PL spectrum of the TFB solid exhibits
a peak at 380 nm. Its quantum yield is 21.36%. However, the

uorescence of the solid under UV light is inferior to that of
TFTB because the twisted conformation of TFTB makes it less
prone to p-stacking. The TFB's uorene rings can partially
overlap in the solid state, resulting in strong intermolecular
interactions, thereby reducing the emission efficiency. This is
ꢀ
also conrmed from the T
g
¼ 328 C of TFB, which is greater
ꢀ
than the T
g
¼ 282 C of TFTB (Fig. S6†), indicating that the TFB
intermolecular interaction is stronger than TFTB. The above
evidence demonstrates that restricting the intramolecular
rotation can produce strong uorescence emissions.
Potential energy surface scan
To further verify that the presence of methyl groups on the
stator does hinder the rotation of the rotor, we calculated the
total energy of the two molecular systems as a function of the
Fig. 5 The total energy of the system varies with the angle between
angle between the uorene ring plane and the benzene ring the fluorene ring plane and the benzene ring plane.
Fig. 4 (A) Photos of the solid under UV light. (B) Solid PL spectra of TFTB and TFB. (C) Photomicrograph of the TFTB solid.
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1
4 X. Zhang, X. Zhang, L. Tao, Z. Chi, J. Xu and Y. Wei, J. Mater.
Chem. B, 2014, 2, 4398.
Conclusions
In summary, a new AIE-active large sterically hindered uorene- 15 J. Z. Liu, J. W. Y. Lam and B. Z. Tang, Chem. Rev., 2009, 109,
benzene copolymer TFTB and a new phenyl boronate interme-
5799.
diate were synthesized. By comparing the uorescence proper- 16 Q. Wan, Q. Huang, M. Y. Liu, D. Z. Xu, H. Y. Huang,
ties of TFTB with those of the control compound TFB and from
X. Y. Zhang and Y. Wei, Appl. Mater. Today, 2019, 9, 145.
the theoretical calculation data, it was conrmed that the 17 X. Y. Zhang, K. Wang, M. Y. Liu, X. Q. Zhang, L. Tao,
groups present on the stator could hinder the rotation of the
Y. W. Chen and Y. Wei, Nanoscale, 2015, 7, 11486.
uorescent rotor and deactivate the IMR process, enhancing the 18 X. Y. Zhang, X. Q. Zhang, B. Yang, M. Y. Liu, W. Y. Liu,
uorescence emission in solids and solutions. The properties of
Y. W. Chen and Y. Wei, Polym. Chem., 2014, 5, 356.


TFTB examined in this work provide a new strategy for 19 X. Y. Zhang, X. Q. Zhang, B. Yang, M. Y. Liu, W. Y. Liu,
synthesizing AIE luminogens with a distorted conformation.
Y. W. Chen and Y. Wei, Polym. Chem., 2014, 5, 399.
0 Z. Long, M. Y. Liu, R. M. Jiang, Q. Wan, L. C. Mao, Y. Q. Wan,
F. J. Deng, X. Y. Zhang and Y. Wei, Chem. Eng. J., 2016, 308,
2
Conflicts of interest
527.
There are no conicts to declare.
21 Z. Long, L. C. Mao, M. Y. Liu, Q. Wan, Y. Q. Wan, X. Y. Zhang
and Y. Wei, Polym. Chem., 2017, 8, 5644.
2
2 Z. Long, M. Y. Liu, K. Wang, F. J. Deng, D. Z. Xu, L. J. Liu,
Y. Q. Wan, X. Y. Zhang and Y. Wei, Mater. Sci. Eng. C,
2016, 66, 215.
Acknowledgements
We thank the State Key Laboratory of Fine Chemicals of Dalian
University of Technology for providing us with support on high- 23 L. Huang, S. J. Yang, J. Y. Chen, J. W. Tian, Q. Huang,
resolution mass spectrometer.
H. Y. Huang, Y. Q. Wen, F. J. Deng, X. Y. Zhang and
Y. Wei, Mater. Sci. Eng., C, 2018, 94, 270.
2
4 R. M. Jiang, M. Y. Liu, H. Y. Huang, L. C. Mao, Q. Huang,
Y. Q. Wen, Q. Y. Cao, J. W. Tian, X. Y. Zhang and Y. Wei, J.
Colloid Interface Sci., 2018, 519, 137.
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