Stimuli-Responsive Properties of Aggregation-Induced-Emission Compounds Containing a 9,10-Distyrylanthracene Moiety

Article abstract of DOI:10.1002/chem.201804315

Two 9,10-distyrylanthracene-based luminophores exhibiting aggregation-induced emission and stimuli-responsive properties were synthesized. Seven- or five-color luminescence switching based on a single organic molecule was achieved for the first time. Thes

Full text of DOI:10.1002/chem.201804315

A Journal of
Accepted Article
Title: Stimuli-Responsive Properties of Aggregation-Induced-Emission
Compounds Containing 9,10-Distyrylanthracene Moiety
Authors: Guang Shao, Xiang-Rui Jia, Hui-Juan Yu, Jian Chen, Wei-Jie
Gao, Jing-kun Fang, Yuan-Shou Qin, and Xiao-Kai Hu
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201804315
Link to VoR: http://dx.doi.org/10.1002/chem.201804315
Supported by

10.1002/chem.201804315
Chemistry - A European Journal
FULL PAPER
Stimuli-Responsive Properties of Aggregation-Induced-Emission
Compounds Containing 9,10-Distyrylanthracene Moiety
Xiang-Rui Jia,‡ [a] Hui-Juan Yu,‡ [a, b] Jian Chen, [a, b] Wei-Jie Gao, [a, b] Jing-kun Fang, *[c] Yuan-Shou Qin,
[d] Xiao-Kai Hu, [e] and Guang Shao*[a, b]
Abstract:
Two
aggregation-induced-emission
active
effects of aggregation-caused emission quenching, completely
or partially. In most cases, aggregation-caused emission
quenching limits the practical applications of organic materials
which often require materials to be solid and films, particularly in
optoelectronic devices. [1a,1c] Aggregation-induced-emission (AIE)
is an intriguing photophysical phenomenon associated with
chromophore aggregation.[9] AIE materials can enhance
emission from aggregate or solid state in comparison to their
diluted solutions, which have been found in several systems,
such as silole, tetraphenylethylene (TPE), triphenylethylene,
cyano distyrylbenzene, distyrylanthracene and their derivatives.
luminophores based on 9,10-distyrylanthracene with stimuli-
responsive properties are successfully synthesized. A distinct
seven- or five-colour luminescence switching built upon a single
organic molecule is firstly achieved. These phase transitions can
be interconverted by physical stimuli such as grinding by mortar
and pestle, heating and exposing to the vapor of organic
solvents. Moreover, an applicable strategy for the design of new
mechano-responsive materials with π-conjugated luminophores
is proposed.
[1,10-12]
In the case of 9,10-distyrylanthracene derivatives, the
9,10-divinylanthracene segment can undergo an active rotation
process in a diluted solution which quenches the emission from
luminophores. But in aggregate state, the intramolecular rotation,
in other words, the non-radiative decay channel is blocked which
leads to the enhanced emission of molecules. [12-15]
Introduction
Functional materials that change their some properties in
response to a single stimulus or multiple stimuli are called smart
materials.[1] Piezochromism refers to a phenomenon that the
luminescence properties of materials can change with
mechanical force, in which the presence of more than two
different pressure-dependent stable or metastable states is
essential. [2-4] Piezochromic luminescent materials have received
considerable interest in recent years in view of their potential
applications in sensors, memory chips, camouflage,
optoelectronic devices, and so forth. [5-8] However, the studies of
piezochromic materials remain inadequate due to the absence
of an effective mechanism to illustrate the close correlation
between the changes of molecular packing and their
corresponding luminescence properties. Therefore, the ability to
dynamically control the molecular aggregation state and the
consequent fluorescence colour and/or intensity is very
important to develop new piezochromic luminescent materials.
Many conventional luminophores often experience some
In fact, a luminescent material sensitive to pressure stimuli
with an AIE property was first reported by Park in 2010, which is
a CN-substituted distyrylbenzene derivative.[10] Subsequently,
quite a few AIE-based piezochromismic compounds and a
relationship between AIE nature and piezochromism were
reported by Chi.[16] AIE compounds with amorphous forms or
strong crystallinity are found to be not suitable as piezochromic
materials. The proper crystallinity is a prerequisite for AIE-based
piezochromism.[16] As AIE materials can enhance emission in
the solid state, it is highly expected to develop high sensitive
piezochromic materials based on AIE properties. However, most
of AIE-based piezochromismic materials are TPE systems, and
moreover, only a dual-color luminescence switching. AIE-based
piezochromismic materials with more than two different
pressure-dependent stable or metastable states have rarely
been reported.[1,16,17]
To obtain multi-colored switching luminophores with enhanced
emission in the solid state,[18-23] we report the design and
synthesis of two new 9,10-distyrylanthracene derivatives
[a] X.-R. Jia, Dr. H.-J. Yu, J. Chen, W.-J. Gao, Prof. Dr. G. Shao
School of Chemistry
Sun Yat-sen University
Guangzhou, 510275, PR China
E-mail: shaog@mail.sysu.edu.cn
[b] Dr. H.-J. Yu, J. Chen, W.-J. Gao, Prof. Dr. G. Shao
Shenzhen Research Institute
Sun Yat-sen University
Shenzhen, 518057, PR China
[c] Prof. Dr. Jing-kun Fang
School of Chemical Engineering
Nanjing University of Science and Technology
Nanjing, 210094, PR China
E-mail: fjk_003@163.com
[d] Yuan-Shou Qin
Zeloq (Shenzhen) Technology Co. Ltd.
Shenzhen, 518104, PR China
[e] Dr. X.-K. Hu
Institute of Frontier Materials
Deakin University
Geelong 3216, Australia
Scheme 1. Synthesis of compounds JX01 and JX02.
‡ These authors contributed equally to this work.
Supporting information (SI) for this article is given via a link at the end of the
document.
This article is protected by copyright. All rights reserved.

10.1002/chem.201804315
Chemistry - A European Journal
FULL PAPER
denoted as JX01 and JX02 (Scheme 1) and explore their AIE
and stimuli-responsive properties. The introduction of planar 3,
6-dimethoxy-carbazole group into JX02 is used to adjust the
related properties and for comparison. AIE properties, molecular
packing
in
crystals,
quantum-chemical
calculations,
electrochemical properties, stimuli-responsive properties,
thermal stabilities, differential scanning calorimetry (DSC), and
X-ray diffraction based on these two compounds were
extensively investigated and compared with each other for
understanding the structure-property relationships.
Figure 1
.
Six π-π stacking molecules of JX01. (Hydrogen atoms were
omitted for clarity.)
Results and Discussion
Synthesis
The synthetic procedures of two fluorescent compounds (JX01
and JX02) are shown in Scheme 1. The detailed synthetic
procedures of key intermediates (2, 4 and 7) were described in
SI, which were prepared according to the reported methods.[8,24-
26]
The double bonds were introduced by Wittig-Horner reaction.
The reaction of aldehyde (4 or 7) with stabilized phosphorus
ylide led to olefin with excellent E-selectivity. The molecular
structures of new compounds (JX01 and JX02) were
Figure 2. Nine stacking molecules of JX02.
conjugation effect, in the same H2O contents, JX02 shows
remarkably higher quantum yields than JX01 (Table S2, SI
1
characterized by H/13CNMR spectroscopy (Figure S5, S6 and
)
.
S8, SI), high-resolution mass spectrometry (HRMS) (Figures S7
and S9, SI), and X-ray diffraction (Figures 1 and 2; Figures S10–
S13, SI). All these analytical data are consistent with the
proposed structures.
Their UV-vis absorption spectra and the corresponding molar
absorption coefficients in the mixed solvents (H2O/THF,
1.0×10-5 mol/L) were reported. For JX01 and JX02, the spectra
profiles almost remain unchanged with H2O contents below 60%
and 50%, respectively. The spectral region starts to increase at
a H2O content of 70% or 60%, which could be attributed to the
light-scattering or Mie effect of nano-aggregate suspension in
solvent mixtures, as the organic molecules begin to aggregate in
AIE properties
The fluorescence behavior of JX01 and JX02 was studied in
diluted solutions of H2O/THF with different H2O fractions (Figure
3; Figures S15
,
S17 and S18, SI). The 9,10-
this solvent composition.[27]
(Figures S14 and S16, Table S3,
divinylanthracene segment can undergo an active rotation
process in pure THF solution that deactivates the
corresponding excited states, thus making them non-
emissive in solution. As H2O is non-solvent for JX01 and
JX02, these organic molecules have to aggregate when a
large amount of H2O is added. When the volume fraction of
H2O exceeds a critical value (60% for JX01 and 50% for
JX02), the intramolecular rotations of aryl rotors are greatly
restricted owing to the physical constraint. This restriction of
intramolecular rotations blocks the non-radiative pathway
and opens up the radiative channel. As a result, these
organic molecules become emissive in the aggregate
state.[12-14] Plot of photoluminescence intensity versus different
H2O fractions in H2O/THF mixtures shows the fluorescence
behavior of JX01 and JX02 while changing the H2O portion
SI). Both fluorescence and UV-vis absorption spectra confirm
that JX01 and JX02 have a significant AIE effect caused by
molecular aggregates with an addition of H2O to H2O/THF
mixtures.
H
O fraction
(a)
250
200
150
100
50
2
240
210
180
150
120
90
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
95%
0
0
20
40
60
80
100
H2O fraction/%
(b)
60
0% 60% 70% 95%
30
(
Figure 3; Figure S15, SI). Notably, the fluorescence intensity
of JX02 decreases in H2O/THF mixtures containing 80% of H2O,
which is often observed in some AIE compounds, but its intrinsic
mechanism still remains enigmatic.[13] Just as expected,
quantum yields of JX01 and JX02 in pure THF are very low
(0.018 and 0.093, respectively). When the volume fraction
of H2O exceeds a critical value (60% for JX01 and 50% for
JX02), they both exhibit higher quantum yields. As the
planar carbazole group of JX02 can induce an enhanced π-
0
480
510
540
570
600
630
660
690
720
750
Wavelength (nm)
Figure 3. Fluorescence spectra of JX01 (10.0 μM) in H2O/THF mixtures
with different H2O contents at 25 C. Inset (a): Plot of fluorescence peak

intensity versus different H2O fractions. Inset (b): Fluorescence emission
in different H2O fractions under UV-light (365 nm).
This article is protected by copyright. All rights reserved.

10.1002/chem.201804315
Chemistry - A European Journal
FULL PAPER
HOMO
LUMO
more robust. Of course, the interfaces are easy to be destroyed
through slip deformation by external stimuli.
JX01
Calculation
To gain insight into the molecular structure and electron
distribution, the optimized geometries of JX01 and JX02 were
calculated by using density functional theory (DFT) at B3LYP/6-
31G (d, p) level based on
a
Gaussian09 software
JX02
package with the isodensity surface values fixed at 0.02 (Figure
4). For JX01 and JX02, the distribution of frontier molecular
orbitals is similar and both LUMOs are mainly located on the
9,10-divinylanthracene segment. In contrast, their HOMOs
delocalize throughout the entire molecules and the HOMO
distribution of JX02 is more uniform due to the introduction of
planar carbazole groups. The results indicate that the electrons
could transfer from triphenyl amine or carbazole group to 9,10-
divinylanthracene core in excited state. The calculated energy
levels of molecular orbital are displayed in Table 1, which show
that the molecular conformations affect the HOMO and LUMO
energy levels. The HOMO levels of JX01 and JX02 are –4.38
and –4.75 eV, respectively. Although the HOMO of JX01 is 0.37
eV higher than that of JX02, the values of excitation transition
energy (Eg) are very close.
Figure 4. Calculated frontier molecular orbitals of JX01 and JX02.
Table 1. Energy levels and band gaps of molecular orbital of JX01 and JX02.
λonset
(nm)[c]
–
Eg
HOMO
(eV)
LUMO
(eV)[d]
–1.71
–3.05
–2.06
–3.17
Compound
(eV) [c]
2.67
2.40
2.69
2.56
JX01[a]
JX01[b]
JX02[a]
JX02[b]
–4.38
–5.45
–4.75
–5.73
515
–
483
[a] Obtained from calculation. [b] Obtained from CV. [c] Estimated according to
the onset wavelength of UV absorption. [d] LUMO = Eg + HOMO.
The morphology of aggregated molecules in H2O/THF
mixtures with different H2O fractions was observed by ultra-high
resolution scanning electron microscope (SEM). The SEM
images evidently show their different aggregated forms:
nanostructure units (Figures S19 and S20, SI).
Cyclic voltammetry (CV)
CV was recorded to determine the ground-state oxidation
potential (Figures S21–S23, SI). On the basis of the reported
HOMO level of spiro-OMeTAD (–5.22 eV),[29] the HOMO levels
of JX01 and JX02 are –5.45 and –5.73 eV, respectively. Eg
was calculated from the onset wavelength of UV absorption (515
nm, 2.40 eV for JX01 and 483 nm, 2.56 eV for JX02; Figures
S24 and S25, SI).[30] LUMO energy levels were obtained from
HOMO energy and Eg and calculated to be –3.05 and –3.17 eV,
respectively (Table 1). Both calculation and experiment results
suggest that the HOMO and LUMO levels of JX01 are up-shifted.
Thus, the introduction of triphenyl amine group on primary ligand
can increase the HOMO energy because of its stronger electron-
donating effect.
Crystal structure elucidations
As shown in Figures 1, 2 and Figures S10–S13, SI, X-ray
diffraction analyses unambiguously clarify the molecular
structures of JX01 and JX02, revealing that all molecules adopt
highly twisted conformations in the crystal state. Such twist
stress is believed to be released when triggered by external
pressure or heating, which leads to the planarization of
molecular conformation resulting in a red shift of fluorescence
spectra. For triarylamine-based JX01, the central nitrogen atom
is bounded with three carbon atoms via sp2-hybridization (planar
configuration), and the three phenyl groups assume a propeller-
like structure relative to the plane defined by three C-N bonds. In
crystal, there is a strong intermolecular interaction between the
benzene ring of triphenyl amine and the benzene ring of
anthracene through π–π stacking interactions. Due to the
nonplanar structure of triarylamine, the molecular configuration
of JX01 is beneficial to restrain complex intermolecular
aggregation (Figure 1; Figure S11, SI).[28] For JX02, the planar
carbazole group can induce a stronger intermolecular interaction
and the two adjacent molecules are bound together by hydrogen
bonds (C-H⋯O) to form molecular layers (ca. 2.46 and 2.60 Å,
Figure S13, SI). Furthermore, there are many multiple hydrogen
bonds (C-H⋯O) between molecular layer with a distance of ca.
2.66
Å (Figure 2), which help to rigidify the molecular
conformation, so that these molecular layers become clearly
evident and distinct in crystal (Video S1, SI). As a result, the
close-stacked arrangements of JX02 molecules should be much
Figure 5. Seven phase transition sequences for compound JX01.
This article is protected by copyright. All rights reserved.

10.1002/chem.201804315
Chemistry - A European Journal
FULL PAPER
from CH2Cl2/hexane mixtures (Figure 6). When JX02-1, JX02-2,
JX02-4 and JX02-5 were ground with a mortar and pestle, they
were all transformed to an orange powder bearing an
amorphous form (JX02-3, λem = 604 nm, Figures S54–S57, S62,
S63, S68 and S69, SI). The 67 nm red shift of fluorescence
emission upon grinding (JX02-1→JX02-3) is a very significant
pizeochromica effect.[6] When JX02-3 on a glass plate was
exposed to CH2Cl2 vapor at 25 C, the color also quickly (ca. 30
s) changed from orange to yellow-green (JX02-5, λem = 565 nm,
Figures S66 and S67, SI). As these stimuli were nondestructive
in chemical structure, JX02-3 and JX02-5 could be
interconverted by application of grinding-fuming process for
many times without fatigue (Figure S70, SI). After heating at 160
C for 60 s, the orange ground powder (JX02-3) turned into a
yellow-green form (JX02-2, λem = 569 nm, Figures S58 and S59,
SI). When JX02-2 andJX02-3 were heated at 260 C for 3 min,
Figure 6. Five phase transition sequences for compound JX02
.
Stimuli-responsive properties
Interestingly, in the solid state, multi-colored switching
luminophores which were different in molecular packing mode
under an external stimulus were observed (Figures 5 and 6,
seven colors for JX01 and five colors for JX02). When
compound JX01 was subjected to reprecipitation or
recrystallization, two different forms were obtained: yellow
powder (JX01-1, λem = 569 nm) by reprecipitation from CH2Cl2
they were both transformed into a green powder (JX02-4, λem
=
534 nm, Figures S60, S61, S64 and S65, SI).
To gain further insight into the mechanofluorochromism,
the influence of different applied pressure on luminescence
of compounds JX01 and JX02 was investigated. The
powder (JX01-1 or JX02-1) was placed in a hole (diameter:
7 mm) of a steel mould and the hydrostatic pressure was
controlled by a display meter of press (Figure S81c, SI).
During the compression process, the fluorescence
maximum of pellets (JX01-1) gradually red-shifted to 619
nm (orange) at 0.1 GPa and eventually to 645 nm (red) at
0.5 GPa (Figure 7). The fluorescence spectrum (λem = 645
nm) under a pressure of 0.5 GPa is very similar to that of
the ground powder (JX01-3). Similarly, for JX02-1 sample,
the fluorescence maximum of pellets gradually red-shifted
to 574 nm (yellow-green) at 0.1 GPa and eventually to 601
nm (orange) at 0.5 GPa (Figure S81, SI). The fluorescence
spectrum (λem = 601 nm) under a pressure of 0.5 GPa is
also very similar to that of the ground powder (JX02-3). As
the applied pressure increased, the fluorescence emission
of pellets (JX01-1 or JX02-1) showed a gradual red shift.
For JX01 and JX02, multiple phenyl peripheries are linked
to 9,10-divinylanthracene core via a rotatable carbon-
carbon single bond to form an AIE moiety. The steric effects
among these phenyl rings force the molecules to adopt a
highly twisted conformation. The twisted conformations,
weak π–π stacking interactions and/or hydrogen bonds
make molecular packing relatively loose and generate
many cavities with a low lattice energy. These loose
molecular packing and labile cavities render the crystal to
be easily destroyed by conformational planarization or slip
deformation under external stimuli, which might be
responsible for the dramatic color change of
luminescence.[12-14]
with a slow addition of hexane and orange crystal (JX01-2, λem
=
592 nm) by recrystallization from CH2Cl2/hexane mixtures
(Figure 5). When JX01-1 and JX01-2 were ground with a mortar
and pestle, they were transformed to a red powder bearing an
amorphous form (JX01-3, λem = 643 nm, Figures S26–S30, SI).
The 74 nm red shift of fluorescence emission upon grinding
(JX01-1→JX01-3) is a very significant pizeochromica effect.[6]
After heating at 160 C for 60 s, the red ground powder (JX01-3)
turned into an orange amorphous form (JX01-5, λem = 600 nm,
Figures S31 and S32, SI). Moreover, when JX01-3 was put into
a sealed beaker containing a small amount of CH2Cl2 at 25 C
for 30 s, the color changed from red to orange due to the
morphological transition from amorphous phase to crystalline
(JX01-4, λem = 615 nm, Figures S35, S36 and Video S2, SI).
This material with a fast response speed can be applied for in
situ measuring device. Similarly, after being ground with a
mortar and pestle, JX01-4 and JX01-5 can also be transformed
into a red powder (JX01-3, Figures S33, S34, S37 and S38, SI).
Moreover, the switching processes between JX01-3 and JX01-4
could be repeated several times without any fatigue (Figure S39,
SI). These reversible emission spectra without any obvious
reduction of emission intensity make JX-01
a promising
candidate for pressure or solvent detector. At last, when JX01-
1and JX01-2 were placed on a thin glass plate and heated by a
hot plate at 160 C for 60 s, two similar orange powder states
(JX01-6, λem = 602 nm, and JX01-7, λem = 606 nm, Figures S40–
S43, SI) were observed, respectively. Although JX01-6 exhibits
an emission spectrum similar to that of JX01-7, their X-ray
diffraction (XRD) patterns are different (Figures S52 and S53,
SI). Further, the DSC analysis of JX01-1 and JX01-2 indicates
the morphological difference between JX01-6 and JX01-7, and
more details about this difference will be discussed in the
subsequent DSC thermograms.
Thermogravimetric analysis (TGA) and DSC thermograms
Similarly, when compound JX02 was subjected to
reprecipitation or recrystallization, two different forms were
TGA measurements show that JX01-1 and JX02-1 have
high decomposition temperatures (415 and 420
respectively) (Figures S82 and S83, SI). The three forms
JX01-1 JX01-2 and JX01-3) of JX01 were analyzed by
DSC from 25 to 280 C (Figures S84–S89, SI). An obvious
C,
obtained: green powder (JX02-1, λem
=
537 nm) by
reprecipitation from CH2Cl2 with a slow addition of hexane and
(
,
yellow-green crystal (JX02-2, λem = 574 nm) by recrystallization

This article is protected by copyright. All rights reserved.

10.1002/chem.201804315
Chemistry - A European Journal
FULL PAPER
(a)
heating DSC profile (162, 235 and 336 C, Figure S94, SI). The
exothermic peak at 162 C coincides with the transformation of
JX02-3 into JX02-2 at 160 C (Figures S58 and S59, SI).
Similarly, the amorphous ground sample (JX02-3) undergoes an
exothermic recrystallization process at about 160 C, and JX02-
2 is thermodynamically more stable than JX02-3. The second
peak at 235 C means when the heating temperature is further
increased, JX02-3 can be further transformed, which
substantiates the phase transition sequences: JX02-3→JX02-
2→JX02-4 (Figure 6).
1.0
Pressure
0.9
0 GPa, 569 nm, a
0.10 GPa, 619 nm, b
0.20 GPa, 628 nm, c
0.38 GPa, 638 nm, d
0.50 GPa, 645 nm, e
JX01-1
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
c
d
e
Wide-angle X-ray diffraction (WAXD) spectra
500
550
600
650
700
750
800
WAXD spectra unequivocally reveal stimuli-induced changes
between different forms (Figures S44–S53 and S71–S80, SI).
Sharp and intense reflections of JX01-1, JX01-2, JX01-4, JX01-
6 and JX01-7 can be observed, indicating their crystalline
structures. After being ground, the XRD pattern of JX01-3
(Figures S46–S48, SI) indicates a phase conversion of crystal to
amorphousness (JX01-1, JX01-2 and JX01-4 to JX01-3). When
JX01-3 was fuming with CH2Cl2 vapor for 30 s, an amorphous
form to a crystalline phase transition occurred (JX01-3→JX01-4),
and some reflection peaks were observed (Figures S35, S36
and S50, SI). In contrast, when JX01-3 was heated at 160 C for
60 s, the amorphous form remained intact during phase
conversion (JX01-3 to JX01-5, Figures S31, S32 and S51, SI).
Similarly, the XRD patterns of JX02-3 (Figures S74–S77, SI)
reveal that JX02-1, JX02-2, JX02-4 and JX02-5 are all
transformed into an amorphous form with grinding. But, when
JX02-3 was fuming with CH2Cl2 vapor, the amorphous form
remained intact during phase conversion (JX02-3 to JX02-5,
Figures S66, S67 and S80, SI). In contrast, when JX02-3 was
heated at 160 C for 60 s, an amorphous form to a crystalline
phase transition occurred (JX02-3 to JX02-2, Figures S58, S59
and S73, SI). The above results suggest that the compounds
(JX01 and JX02) under investigation represent enantiotropic
systems and their metastable states can readily be influenced by
crystallization conditions or external stimuli.
Wavelength (nm)
(b)
Figure 7. (a) Fluorescence spectra of JX01-1 powder under external pressure.
(b) The observed color changes from light yellow (λem = 569 nm) to red (λem
=
645 nm) due to different applied pressure.
endothermic peak is observed at 162 C in the first heating DSC
profile of JX01-1 (Figure S84, SI), which means that heating
could convert the thermodynamically stable crystalline sample
into a metastable state via an endothermic process at about 162
C. This result is consistent with the transformation of JX01-1
into JX01-6 at 160 C (Figures S40 and S41, SI). For JX01-2,
there are three endothermic peaks in the first heating DSC
profile (167, 218 and 240 C, Figure S86, SI). Although the first
endothermic peaks of JX01-1 and JX01-2 are close (162 vs. 167
C), their melting points have a big difference (218 vs. 240 C).
This result further proves the morphological difference between
JX01-6 and JX01-7. In the DSC profile of JX01-2, the peak at
218 C may originate from JX01-1. A possible reason is that a
small amount of JX01-1 was also formed when the orange
crystal (JX01-2) was recrystallized from CH2Cl2/hexane mixtures.
In the DSC profile of JX01-3, a broad exothermic peak is
observed at 162 C in the first run, which coincides with the
conversion processes from JX01-3 to JX01-5 (Figures S31, S32
and S88, SI). This result demonstrates that the amorphous
ground sample (JX01-3) can undergo an exothermic
recrystallization process at about 162 C, and JX01-5 is
thermodynamically more stable than JX01-3.
pH response
JX01-1 can exhibit a prominent Lewis base character because
of the electron-donating triphenyl amine group, which can
undergo repeatable protonation and deprotonation. The
evaluation of pH responsiveness was conducted in the solid
state. Trifluoroacetic acid (TFA) and aqueous ammonia (NH3)
vapor were employed as stimuli. JX01-1 on a glass plate
appears orange in daylight and emits bright yellow light under
UV illumination. Its color visually changed from orange to jasper
when exposed to TFA gas. After fumed with NH3 vapor, its
original color was recovered. The orange-jasper color switching
process is reversible and repeatable (Figure 8). This pH-
The three forms (JX02-1, JX02-2 and JX02-3) of JX02 were
analyzed by DSC from 50 to 350 C (Figures S90–S95, SI). In
the DSC profile of JX02-2, a short and broad peak at 259 C is
observed in the first run, which is consistent with the
transformation of JX02-2 into JX02-4 at 260 C (Figures S60,
S61 and S92, SI). For JX02-3, there are three peaks in the first
Figure 8. Color changes of a TFA or NH3 fumed sample (JX01-1).
This article is protected by copyright. All rights reserved.

10.1002/chem.201804315
Chemistry - A European Journal
FULL PAPER
responsive behavior is attributed to the protonation of triphenyl
amine group, which effectively eliminates the intrinsic
intramolecular charge transfer (ICT) effect of donor–acceptor
molecules.[1,31] But such pH-induced fluorescence switching
cannot be reproduced by using the following acids: HCl, HNO3,
HCOOH, CH3COOH, H3PO4, HClO4 and H2SO4. For JX02-1, its
pH-responsive color change is indistinct, which might be
ascribable to the weak basicity of carbazole group (Figure S96,
SI).
with compound 2 (492 mg, 1.03 mmol, 1.0 equiv.), compound 7
(663 mg, 2.00 mmol, 1.94 equiv.), NaH (1.0 g, 41.7 mmol, 40.4
equiv.) and THF (15 mL). The reaction mixture was heated at 45
C for 24.0 h and cooled to room temperature. The reaction was
quenched with H2O and extracted with ethyl acetate five times.
The extract was then dried over magnesium sulfate and filtered.
After evaporation at a reduced pressure, the residue was
subjected to column chromatography on silica gel (petroleum
ether/dichloromethane = 1/1, V/V), affording compound JX02 as
solids (630 mg, 73.5%). The product was further purified by
recrystallization
(hexane/dichloromethane)
for
property
1
Conclusions
measurements. H NMR (400 MHz, CDCl3): δ (ppm) 8.49-8.47
(m, 4H), 8.05 (d, J = 16.0 Hz, 2H), 7.91 (d, J = 8.0 Hz, 4H), 7.66
(d, J = 8.0 Hz, 4H), 7.59 (d, 4.0 Hz, 4H), 7.56-7.52 (m, 4H), 7.45
(d, J = 8.0 Hz, 4H), 7.11-7.00 (m, 6H), 3.98 (s, 12H). HRMS
(ESI/Q-TOF) m/z: [M]+ Calcd for C58H44N2O4: 832.3296;
Found:832.3314.
In summary, AIE-based piezochromism with a reversible
seven- or five-color luminescence switching built upon a single
organic molecule has been firstly achieved. The fluorescence
switching process can be smoothly triggered through disrupting
the ordered molecular packing (mechanical grinding) and
repacking (heating or solvent annealing). These phase
transitions were confirmed by color changes, fluorescence
spectra, WAXD patterns and DSC thermograms. The loose
molecular packing and labile cavities in crystal might be
responsible for the dramatic color change of luminescence. In
addition, a pH-responsive AIE system (JX-01) displays a
reversible fluorescent “ON/OFF” response when fumed with
volatile TFA/NH3 vapors. These design principles appear to be
readily applicable to new mechano-responsive materials with π-
Acknowledgements
This work was financially supported by the Science and
Technology
Planning
Project
of
Guangzhou
City
(201607010349), the Science and Technology Planning Project
of Shenzhen City (20180205162723338), the Science and
Technology Planning Project of Guangdong Province
(2015A010105013) and the National Natural Science
Foundation of China (21102187).
conjugated
luminophores.
Further
investigation
of
distyrylanthracene derivatives with expanded π systems and
their applications for organic devices are underway.
Conflict of interest
Experimental Section
The authors declare no conflict of interest.
Synthesis of compound JX01. Under an Ar atmosphere, a
two-necked flask equipped with a magnetic stirrer was charged
with compound 2 (182 mg, 0.38 mmol, 1.0 equiv.), compound 4
(280 mg, 0.84 mmol, 2.2 equiv.), NaH (500 mg, 20.8 mmol, 54.8
equiv.) and THF (6 mL). The reaction mixture was heated at 40
C for 48.0 h and cooled to room temperature. The reaction was
quenched with H2O and extracted with ethyl acetate five times.
The extract was then dried over magnesium sulfate and filtered.
After evaporation at a reduced pressure, the residue was
subjected to column chromatography on silica gel (petroleum
ether/ethyl acetate = 15/1, V/V), affording compound JX01 as
solids (200 mg, 62.9%). The product was further purified by
Keywords: chromophores
•
fluorescence
•
sensors
•
piezochromism • aggregation-induced-emission
[1] a) J. Mei, N. L. C. Leung, R. T. K. Kwok, J. W. Y. Lam, B. Z. Tang, Chem.
Rev. 2015, 115, 11718-11940; b) Y. Sagara, T. Kato, Nat. Chem. 2009, 1,
605-610; c) F. Y. Song, Z. Xu, Q. S. Zhang, Z. Zhao, H. K. Zhang, W. J.
Zhao, Z. J. Qiu, C. X. Qi, H. Zhang, H. H. Y. Sung, I. D. Williams, J. W. Y.
Lam, Z. J. Zhao, A. J. Qin, D. G. Ma, B. Z. Tang, Adv. Funct. Mater. 2018,
28, 1800051.
[2] a) Z. X. Chen, J. A. M. Mercer, X. L. Zhu, J. A. H. Romaniuk, R. Pfattner, L.
Cegelski, T. J. Martinez, N. Z. Burns, Y. Xia, Science 2017, 357, 475-479;
b) M. Chen, R. Chen, Y. Shi, J. G. Wang, Y. H. Cheng, Y. Li, X. D. Gao, Y.
Yan, J. Z. Sun, A. J. Qin, R. T. K. Kwok, J. W. Y. Lam, B. Z. Tang, Adv.
Funct. Mater. 2018, 28, 1704689.
[3] F. Xu, T. Nishida, K. Shinohara, L. F. Peng, M. Takezaki, T. Kamada, H.
Akashi, H. Nakamura, K. Sugiyama, K. Ohta, A. Orita, J. Otera,
Organometallics 2017, 36, 556-563.
recrystallization
(hexane/dichloromethane)
for
property
measurements. 1H NMR (400 MHz, CDCl3) δ (TMS, ppm): 8.41–
8.39 (m, 4H), 7.76 (d, J = 16.0 Hz, 2H), 7.49 (d, J = 8.0 Hz, 4H),
7.46–7.43 (m, 4H), 7.12 (d, J = 8.0 Hz, 8H), 7.00 (d, J = 8.0 Hz,
4H), 6.87–6.82 (m, 10H), 3.81 (s, 12H). 13C NMR (100 MHz,
CDCl3) δ (TMS, ppm):155.99, 148.66, 140.79, 137.00, 132.85,
129.66, 127.29, 126.73, 126.65, 126.58, 125.02, 122.35, 120.64,
114.77, 55.53. HRMS (ESI/Q-TOF) m/z: [M]+ Calcd for
C58H48N2O4 836.3609; Found 836.3631.
[4] H. X. Wu, Y. Jiang, Y. Ding, Y. Y. Meng, Z. Zeng, C. Cabanetos, G. F.
Zhou, J. W. Gao, J. M. Liu, J. Roncali, Dyes Pigm. 2017, 146, 323-330.
[5] J. Kunzelman, M. Kinami, B. R. Crenshaw, J. D. Protasiewicz, C. Weder,
Adv. Mater. 2008, 20, 119-122.
[6] Y. J. Dong, B. Xu, J. B. Zhang, X. Tan, L. J. Wang, J. L. Chen, H. G. Lv, S.
P. Wen, B. Li, L. Ye, B. Zou, W. J. Tian, Angew. Chem. Int. Ed. 2012, 51,
10782-10785.
[7] Y. Sagara, T. Mutai, I. Yoshikawa, K. Araki, J. Am. Chem. Soc. 2007, 129,
1520-1521.
Synthesis of compound JX02. Under an Ar atmosphere, a
two-necked flask equipped with a magnetic stirrer was charged
[8] L. Y. Bai, P. Bose, Q. Gao, Y. X. Li, R. Ganguly, Y. L. Zhao, J. Am. Chem.
Soc. 2017, 139, 436-441.
This article is protected by copyright. All rights reserved.

10.1002/chem.201804315
Chemistry - A European Journal
FULL PAPER
[9] B. K. An, S. K. Kwon, S. D. Jung, S. Y. Park, J. Am. Chem. Soc. 2002, 124,
14410-14415.
[10] S. J. Yoon, J. W. Chung, J. Gierschner, K. S. Kim, M. G. Choi, D. H. Kim,
S. Y. Park, J. Am. Chem. Soc. 2010, 132, 13675-13683.
[11] F. S. Zhang, J. Fan, H. J. Yu, Z. F. Ke, C. M. Nie, D. B. Kuang, G. Shao,
C. Y. Su, J. Org. Chem. 2015, 80, 9034-9040.
[12] B. Xu, J. T. He, Y. J. Dong, F. P. Chen, W. L. Yu, W. J. Tian, Chem.
Commun. 2011, 47, 6602-6604.
[13] X. Q. Zhang, Z. G. Chi, B. J. Xu, L. Jiang, X. Zhou, Y. Zhang, S. W. Liu, J.
R. Xu, Chem. Commun. 2012, 48, 10895-10897.
[14] X. Q. Zhang, Z. G. Chi, J. Y. Zhang, H. Y. Li, B. J. Xu, X. F. Li, S. W. Liu,
Y. Zhang, J. R. Xu, J. Phys. Chem. B 2011, 115, 7606-7611.
[15] X. Cheng, Z. Y. Zhang, H. Y. Zhang, S. H. Han, K. Q. Ye, L. Wang, H. Y.
Zhang, Y. Wang, J. Mater. Chem. C 2014, 2, 7385-7391.
[16] Z. G. Chi, X. Q. Zhang, B. J. Xu, X. Zhou, C. P. Ma, Y. Zhang, S. W. Liu, J.
R. Xu, Chem. Soc. Rev. 2012, 41, 3878-3896.
[17] H. S. Yuan, K. Wang, K. Yang, B. B. Liu, B. Zou, J. Phys. Chem. Lett.
2014, 5, 2968-2973.
[18] Y. Sagara, T. Kato, Angew. Chem. Int. Ed. 2011, 50, 9128-9132.
[19] K. K. Neena, P. Thilagar, Organometallics 2017, 36, 2692-2701.
[20] K. K. Neena, P. Sudhakar, K. Dipak, P. Thilagar, Chem. Commun. 2017,
53, 3641-3644.
[21] Z. Y. Ma, M. J. Teng, Z. J. Wang, S. Yang, X. R. Jia, Angew. Chem. Int.
Ed. 2013, 52, 12268-12272.
[22] Y. G. Shi, J. W. Wang, H. J. Li, G. F. Hu, X. Li, S. K. Mellerup, N. Wang, T.
Peng, S. N. Wang, Chem. Sci. 2018, 9, 1902-1911.
[23] S. Yagai, S. Okamura, Y. Nakano, M. Yamauchi, K. Kishikawa, T. Karatsu,
A. Kitamura, A. Ueno, D. Kuzuhara, H. Yamada, T. Seki, H. Ito, Nat.
Commun. 2014, 5, 4013.
[24] Z. He, W. Y. Wong, X. M. Yu, H. S. Kwok, Z. Y. Lin, Inorg. Chem. 2006,
45, 10922-10937.
[25] M. L. Louillat, F. W. Patureau, Org. Lett. 2013, 15, 164-167.
[26] International patent, Novel oligothiophene derivatives, their process of
preparation and their uses, International publication number: WO
2012/049167.
[27] H. Tong, Y. Q. Dong, M. Häußler, J. W. Y. Lam, H. H.-Y. Sung, I. D.
Williams, J. Z. Sun, B. Z. Tang, Chem. Commun. 2006, 1133-1135.
[28] J. Y. Wang, K. Liu, L. C. Ma, X. W. Zhan, Chem. Rev. 2016, 116, 14675-
14725.
[29] J. Chen, B. X. Chen, F. S. Zhang, H. J. Yu, S. Ma, D. B. Kuang, G. Shao,
C. Y. Su, Chem. Asian J. 2016, 11, 1043-1049.
[30] G. Shao, H. J. Yu, N. Zhang, Y. J. He, K. J. Feng, X. Yang, R. H. Cao, M.
L. Gong, Phys. Chem. Chem. Phys. 2014, 16, 695-702.
[31] X. Cheng, D. Li, Z. Y. Zhang, H. Y. Zhang, Y. Wang, Org. Lett. 2014, 16,
880-883.
This article is protected by copyright. All rights reserved.

10.1002/chem.201804315
Chemistry - A European Journal
FULL PAPER
FULL PAPER
AIE-based piezochromism with
Xiang-Rui Jia, Hui-Juan Yu, Jian
Chen, Wei-Jie Gao, Jing-kun
Fang*, Yuan-Shou Qin, Xiao-Kai
Hu, and Guang Shao*
a
distinct
seven-color
luminescence switching built
upon a single organic molecule
is firstly achieved.
Page No. – Page No.
Stimuli-Responsive Properties of
Aggregation-Induced-Emission
Compounds Containing 9,10-
Distyrylanthracene Moiety
This article is protected by copyright. All rights reserved.