π-Stacking Conversion and Enhanced Force-Stimuli Response of a Divinylanthracene Derivative in a Hydrogen-Bonded Framework

Article abstract of DOI:10.1021/acs.cgd.0c01637

Hydrogen bond-induced π-stacking conversion was used to achieve an enhanced force-stimuli response of 9,10-bis(2-(pyridin-4-yl)vinyl)anthracene (BP4VA). In BP4VA crystals, the molecules adopted a J-aggregate pattern, and no overlap between the central anthracene planes was observed. Trimesic acid (TA) as a hydrogen bond donor could promote the transformation of the π-stacking type of BP4VA as a hydrogen bond acceptor. It was found that TA and BP4VA molecules formed two-dimensional lamellar hydrogen-bonded frameworks with large windows, which were filled by BP4VA molecules belonging to other layers. Within such three-dimensional packing, J-aggregate stacking type of BP4VA converted into a mixture of J-type and H-type dimers. Moreover, BP4VA adopted a highly twisted conformation, and π-πinteraction between them was very weak. So, the hydrogen-bonded complex emitted a short wavelength fluorescence. More importantly, the yellow hydrogen-bonded complex turned into red solids under force stimuli, and its fluorescence had a fairly large shift of more than 110 nm. This is in contrast with a spectral shift of 43 nm from the sheared neat BP4VA crystals. Quantum chemical calculation and spectral observations implied that the planarization, shortened π-distance, and large overlap between anthracence units should be responsible for the large spectral shift. The results imply that the appropriate acid as a hydrogen bond donor might help distyrylanthracene derivatives possess outstanding functions.

Full text of DOI:10.1021/acs.cgd.0c01637

pubs.acs.org/crystal
Article
π‑Stacking Conversion and Enhanced Force-Stimuli Response of a
Divinylanthracene Derivative in a Hydrogen-Bonded Framework
Yanning Han, Tong Zhang, Qiao Chen, Xinyu Chen, and Pengchong Xue*
Cite This: Cryst. Growth Des. 2021, 21, 1342−1350
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: Hydrogen bond-induced π-stacking conversion was used to achieve an enhanced force-stimuli response of 9,10-bis(2-
(pyridin-4-yl)vinyl)anthracene (BP4VA). In BP4VA crystals, the molecules adopted a J-aggregate pattern, and no overlap between
the central anthracene planes was observed. Trimesic acid (TA) as a hydrogen bond donor could promote the transformation of the
π-stacking type of BP4VA as a hydrogen bond acceptor. It was found that TA and BP4VA molecules formed two-dimensional
lamellar hydrogen-bonded frameworks with large windows, which were filled by BP4VA molecules belonging to other layers. Within
such three-dimensional packing, J-aggregate stacking type of BP4VA converted into a mixture of J-type and H-type dimers.
Moreover, BP4VA adopted a highly twisted conformation, and π−π interaction between them was very weak. So, the hydrogen-
bonded complex emitted a short wavelength fluorescence. More importantly, the yellow hydrogen-bonded complex turned into red
solids under force stimuli, and its fluorescence had a fairly large shift of more than 110 nm. This is in contrast with a spectral shift of
43 nm from the sheared neat BP4VA crystals. Quantum chemical calculation and spectral observations implied that the
planarization, shortened π-distance, and large overlap between anthracence units should be responsible for the large spectral shift.
The results imply that the appropriate acid as a hydrogen bond donor might help distyrylanthracene derivatives possess outstanding
functions.
mic property of the hydrogen-bonded eutectic system is still
rather rare33,34 and is worth studying.
INTRODUCTION
■
It is well-known that the hydrogen bond (H-bond) as strong
intermolecular interaction is also a powerful means to
construct functional supramolecular systems by offering
multiple weak secondary interactions to control molecular
arrangement or stabilize special conformation.1−4 The H-bond
has been utilized to construct cocrystals with excellent and
controllable luminescent properties.5−9 Moreover, intermolec-
ular hydrogen bonds could convert the π-stacking model to
enhance or improve the specific functions of the self-assembled
system.10−12 Recently, organic materials in response to
mechanical forces have attracted widespread attention because
of their wide applications in electronic devices, optical data
storage, pressure sensors, and security.13−23 These materials
can change their charge, luminescence, conductivity, and shape
under force stimuli. Specifically, those organic molecules may
change their color or luminescent properties through a process
called mechanochromism (MC), because their molecular
structures or aggregate types are different before and after
mechanical force stimuli.24−32 However, the research on how
the intermolecular hydrogen bond regulates the mechanochro-
Distyrylanthracene derivatives have been proven to exhibit
excellent responses to force stimuli. For example, 9,10-bis(2-
(pyridin-2-yl)vinyl)anthracene (BP2VA) was found to shift its
emission from green (528 nm) to red (652 nm) under an
applied pressure of 8 GPa.35 However, mechanical grinding led
to an emission shift of only 31 nm. Its analogues, 9,10-bis(2-
(pyridin-4-yl)vinyl)anthracene (BP4VA), also possessed a
small bathochromic shift after grinding.36 Their crystal
structures show that both kinds of molecules stacked to form
J-aggregates, in which the distance between anthracene
moieties is long, and no effective overlap between anthracene
Received: December 2, 2020
Revised: January 5, 2021
Published: January 12, 2021
https://dx.doi.org/10.1021/acs.cgd.0c01637
Cryst. Growth Des. 2021, 21, 1342−1350
© 2021 American Chemical Society
1342

Crystal Growth & Design
pubs.acs.org/crystal
Article
moieties exists. Such intermolecular packing prevents anthra-
cene moieties from being close to each other and forming
sufficient overlap under a shearing force, resulting in small
spectral shifts induced by planarization of the molecular
conformation.37 Recently, Xu, Tian, and Zhao et al. found that
halogen bonding could regulate stacking models of BP2VA,
9,10-bis(2-(pyridin-3-yl)vinyl)anthracene (BP3VA), and
BP4VA in the cocrystals of them and 1,3,5-trifluoro-2,4,6-
triiodobenzene or 1,2,4,5-tetrafluoro-3,6-diiodobenzene. Coc-
rystals exhibited distinct luminescence properties, and they also
responded to force stimuli in different ways.38−40 However,
spectral shifts of such cocrystals after grinding were not
amplified. Therefore, it still remains a challenge in promoting
them with poor MC to possess outstanding force-induced
spectral shifts without applying ultrahigh pressure.
In this case, the intermolecular H-bond as an efficient means
was used to regulate molecular stacking and its mechano-
chromism. An aromatic acid, trimesic acid, was selected as a H-
bond donor to construct cocrystals (HBC-1) with BP4VA as a
H-bond acceptor. Single-crystal analysis indicated that H-
bonds promoted two-dimensional (2D) lamellar frameworks,
which were arranged to form three-dimensional (3D) multi-
layer self-assemblies, in which two new π-stacking types of H-
dimers and J-dimers within BP4VA moieties emerged in
addition to the original J-type stacking (Scheme 1). Gratify-
Figure 1. Photos of HBC-1 crystals in natural (left) and 365 nm
(right) light.
parsed, and the molar ratio was found to be 1:1 as well.
Moreover, the simulated powder XRD pattern of single crystal
was the same as that of ethanol-washed solids (Figure S4),
suggesting that the molecules in washed solids, called HBC-1,
were arranged together in the same manner as that in the single
crystal.41
Thereafter, packing details in the single crystal of HBC-1
were investigated. Crystals belonged to a triclinic system with
̅
P1 space group, and detailed data are listed in Table S1. As
shown in Figure 2a, BP4VA in HBC-1 adopted a cis-form, in
which two vinylpyridine moieties arrayed along the same
direction (Figure S5b). A previous report confirmed that
BP4VA in the crystals are in trans-conformation.36 This is also
verified in our experiment by cultivating the single crystal of
pristine BP4VA (Figure S5a). Therefore, TA promoted BP4VA
to adopt a cis-form. Owing to the stronger acidity of TA (pKa1
= 2.12), intermolecular proton transfer from TA to alkaline
molecules may happen.42 However, it did not happen in the
current case, as confirmed by IR spectra (Figure S6). A strong
peak appeared at 1720 cm−1, which was attributed to the
carboxyl, while the vibrational peak at 1620 cm−1, which
belongs to the carboxylate anion of Na2TA, was not observed
in the IR spectrum of pristine HBC-1. Therefore, TA did not
lose its proton. Yellow color and green fluorescence of HBC-1
also proved that BP4VA in HBC-1 was not protonated because
protonated BP4VA is red with a longer emission wavelength.43
In the BP4VA crystal, BP4VA adopted a twisted
conformation (Figure S5a), and one 1D J-aggregate stacking
was observed, in which the overlap between adjacent
anthracenes did not exist (Figure S7), implying weak π−π
interaction. In HBC-1 crystal, terminal pyridine moieties were
involved in the formation of two kinds of intermolecular H-
bonds with two carboxyl groups, and a 1D chain was formed.
Many 1D chains were interconnected with H-bonds between
carbonyl and hydroxyl of the carboxyl unit. The O1···N1, O4···
N2, and O5···O3 distances of the H-bonds were 2.55, 2.65, and
2.65 Å, respectively. The corresponding angles of H-bonds
were 167.47°, 158.48°, and 148.28° (Table S2), suggesting the
existence of strong H-bonds.44 As a result, a 2D lamellar H-
bonded framework with an irregular rhombic window was
constructed (Figure. 2a).12 The window size was about 7.9 Å ×
20.3 Å. The distance between two anthracene moieties reached
9.2 Å. Another 2D network stacked on it with a short
interplanar distance (ca. 3.0 Å) of TA units in an antiparallel
model (Figure 2b). Within such stacking, there was not
efficient overlap between TA moieties, but dipole−dipole
interactions between carbonyl units existed (Figure S8a).
Moreover, two adjacent BP4VA molecules formed face-to-face
dimers (H-type), in which the adjacent anthracene planes
overlapped by about 40%, the vertical π-stacking distance
Scheme 1. Conversion of π-Stacking of BP4VA with the
a
Help of TA
a
For clarity, TA molecules and hydrogen atoms are not shown.
ingly, such multilayer self-assemblies endowed HBC-1 with an
amplified spectral shift, while shearing force was applied.
Yellow HBC-1 crystals changed into red powders accompany-
ing by a fluorescent shift of over 110 nm after grinding.
RESULTS AND DISCUSSION
■
BP4VA was synthesized from 9,10-dibromoanthracene and 4-
vinylpyridine in a Heck reaction condition. It was soluble in
common solvents, such as chloroform, THF, CH2Cl2, DMF,
and toluene, and emitted a slightly red-shifted fluorescence in
the polar solvents (Figure S1). For example, the maximal
emission wavelength located at 542 nm in cyclohexane and its
DMC solution emitted orange fluorescence with a maximum
shift at 560 nm. Because BP4VA consisted of two pyridine
units and TA had three carboxyl moieties, our original
assumption was to construct their H-bonded complex with a
molar ratio of 3:2. However, the as-synthesized yellow solid
contained excess TA (Figure S2). This excess TA could be
removed by washing with ethanol, and the molar ratio of the
two compounds was 1:1 in washed solids. The obtained light-
yellow solids emitted strong green fluorescence (ΦF = 0.53,
Figure S3). In addition, when the methanol solution of TA was
diffused in the BP4VA solution in dichloromethane (molar
ratio of 2:3), large yellow crystals with green fluorescence were
achieved (Figure 1). Its single-crystal structure was successfully
1343
https://dx.doi.org/10.1021/acs.cgd.0c01637
Cryst. Growth Des. 2021, 21, 1342−1350

Crystal Growth & Design
pubs.acs.org/crystal
Article
Figure 2. (a) Two-dimensional H-bonded framework with windows (7.9 Å × 20.3 Å) and their stacking, (b) stacking between first and second
layers, (c) stacking between second and third layers, (d) H-type dimer and (e) J-type dimer, and (f) stacking between three BP4VA molecules
within the window of a 2D lamellar framework.
reached 3.91 Å, and the shortest distance between carbon
atoms in adjacent pyridine units was about 3.42 Å (Figure 2d).
In fact, the stacking model between along its long axis is J-type
in such stacking (Figure 2d, top view). There are only two
additional weak C−H···π interactions between BP4VA
molecules (Figure S8b) to stabilize the molecular conforma-
tion. BP4VA molecules of the third 2D layer filled in the void
of two layers (Figure 2c). The interplanar distance between
TA molecules is 3.48 Å and head-to-tail packing between
BP4VA molecules of second and third layers (J-type, Figure
2e). A long distance of 6.7 Å between two anthracenes
illustrates no overlap between them. Two C−H···π interactions
between them exist.
In addition, there are many C−H···O interactions between
carboxyl and BP4VA (Figure S8c). As a result, one stable
three-dimensional (3D) structure forms with the help of
multiple weak interactions, including dipole−dipole interac-
tions, C−H···π and C−H···O weak H-bonds (Figure S8c), in
which the window of the 2D framework is completely filled by
three BP4VA molecules assigned to three layers (Figure 2f).
Overall, the H-bond not only changed the molecular
conformation, but also has ability to adjust the π-stacking
type of BP4VA in crystals.45 Therefore, changed luminescence
and response to force stimuli can be expected.
A very small amount of HBC-1 could dissolve in
cyclohexane (CH) through ultrasonic treatment, and the
solution was yellowish and emitted strong yellow fluorescence.
Its absorption and emission spectra were the same as those of
neat BP4VA (Figure S1), and the maxima located at 407 and
542 nm, respectively. Moreover, the BP4VA and HBC-1
possessed almost the same fluorescence decay curved (Figure
S9a). The lifetime is 10.79 ns. These results suggest that the H-
bond did not impact the photophysical properties of BP4VA in
solutions. As-synthesized HBC-1 emitted strong green
fluorescence and the maximal emission peak located at 504
nm. The fluorescence decay curve consists of two components.
Their lifetimes are 2.69 and 5.8 ns (Table S3, Figure S9b).
Two shorter lifetimes are consistent with the existence of two
kinds of J-type dimers in HBC-1 because J-stacking always
results in allowed transition from the lowest excited state to the
ground state and then a shorter fluorescence lifetime.
Moreover, the maximal absorption peak was at 410 nm and
1344
https://dx.doi.org/10.1021/acs.cgd.0c01637
Cryst. Growth Des. 2021, 21, 1342−1350

Crystal Growth & Design
pubs.acs.org/crystal
Article
had a slightly bathochromic shift relative to that in cyclo-
hexane. To further understand the spectral result in solution
and crystals, the quantum chemical calculations were
performed. The conformation of an isolated BP4VA molecule
was optimized by DFT calculation, and torsion and dihedral
angles of optimized molecule are shown in Figure S5 and
Table S4. Two torsion angles between central anthracene and
adjacent vinyl groups are almost the same and are as large as
about 52.6° owing to steric hindrance between hydrogen
atoms. In the HBC-1 crystal, BP4VA possesses an asymmetric
conformation, and the torsion angles reach 57.5° and 77.1°.
Moreover, the dihedral angles between pyridine and
anthracene moieties are larger than those in the isolate
molecule. The results indicate that BP4VA has a poor π-
conjugation in the HBC-1 crystal, being a possible reason for
the short emission wavelength.35,46−48
between anthracenes will strongly influence the HOMO−
LUMO band gap as well as the luminescence of the molecular
crystalline state.49−51 So, the electron transitions of H-type and
J-type dimers in HBC-1 crystal were simulated. The frontier
orbitals of two dimers distribute in both molecules, as shown in
Figure 4c,d. Both dimers possess red-shifted absorption bands
Figure 4. Frontier orbitals of (a) optimized BP4VA, J-type dimers
from (b) PB4VA and (d) HBC-1 crystal, H-type dimer from (c)
original HBC-1 crystal, (e) face-to-face H-type dimer with a short
distance (3.40 Å) and small torsion angle (52°), and (f) back-to-back
H-type dimer with distance (3.55 Å) and torsion angle (52°).
relative to that of the isolated molecule. The peak of H-type
was mainly originated from HOMO to LUMO and located at
403.82 nm. A transition from HOMO to LUMO+1 in J-type
dimer is attributed to a peak at 397.62 nm. Small shifts
illustrated weak π-stacking between BP4VA molecules in the
BC-1 crystal. In addition, compared to in solution, the close
packing in the crystal provides a rigid environment, reduces the
large conformation changes of excited molecules, and then
prevents large Stokes shifts. So, poor π-conjugation, weak π-
stacking, and rigid microenvironment together led to a shorter
emission wavelength of HBC-1 crystals relative to that in
cyclohexane. On the other hand, the BP4VA crystal possessed
short absorption (408 nm) and emission (505 nm) wave-
lengths too (Figure S10). Its crystal structure indicates that the
torsion angles are large too (Figure S5a). On the basis of this
conformation, a short absorption wavelength of 409.48 nm for
isolated BP4VA was obtained from TD/DFT calculations. The
J-type dimer possessed a slight red-shift of ca. 3 nm (Table
S5), implying poor π-conjugation and weak π-stacking in
BP4VA crystals too.
Subsequently, their responses to force stimuli were
investigated and compared. After yellow BP4VA was ground,
the obtained solids were still yellow, but the fluorescence
turned from green to yellow (Figure 5, left). The maximal
emission wavelength shifted from 504 to 547 nm, indicating a
bathochromic shift of 43 nm (Figure 4a). When the ground
solid was fumed by THF, CH2Cl2, or chloroform, the
fluorescence color recovered to green, and the fluorescence
spectrum was also restored. Moreover, such color conversion
Figure 3. (a) Normalized absorption and (b) emission spectra of
HBC-1 in cyclohexane and crystal.
Electron transition simulations of single molecule and
dimers in crystals were performed to disclose the π-stacking
effect on the spectra. The results are listed in Table S5.
Optimized BP4VA in a vacuum has an absorption peak at
446.63 from the transition of HOMO to LUMO. A shorter
absorption wavelength of 391.95 nm was obtained for isolated
BP4VA with a conformation in HBC-1 crystal, confirming a
weak π-conjugated degree. Moreover, HOMO and LUMO
mainly distribute at anthracene, indicating that π-packing
1345
https://dx.doi.org/10.1021/acs.cgd.0c01637
Cryst. Growth Des. 2021, 21, 1342−1350

Crystal Growth & Design
pubs.acs.org/crystal
Article
of emission intensity at 500 nm. After 4 min, the pristine peak
at 500 nm almost disappeared.
We found that a wide absorption band with a maximum at
470 nm emerged after BP4VA solids were exposed to HCl
vapor (Figure S12), and HCl-fumed solids had a emission peak
(λem = 620 nm) similar to that of ground HBC-1 (Figure S15).
Moreover, Tian et al. also implied that the protonated BP4VA
in the solid state might emit red fluorescence,36 so we initially
thought that the red shift of the spectrum was caused by
proton transfer from TA to BP4VA during grinding. However,
the FT-IR spectrum had a subtle change after shearing (Figure
S6). The vibrational peak at 1720 cm−1 ascribed to the
carboxyl moieties of TA slightly became weak and wide,
suggesting mechanical force mildly destroys intermolecular H-
bonds.56 Furthermore, the solid 13C NMR spectrum of ground
HBC-1 did not have obvious alternation relative to that of
pristine one (Figure S16). Signals from protonated pyridine
were not found. Therefore, force-induced proton transfer
should not be responsible for a large spectral shift of more than
100 nm. Then, the unique intermolecular π-packing pattern in
HBC-1 may be a possible cause of enhanced mechanochromic
behavior.
Figure 5. Photos of BP4VA (left) and HBC-1 (right) under 365 nm
light.
could be repeated many times, suggesting a reversible
process.52−54 Interestingly, yellow HBC-1 solids were sheared;
the color changed into orange red, and the sheared section
emitted weak red fluorescence under 365 nm light. After
shearing for 4 min, almost all the solids emitted an orange-red
fluorescence (Figure 5, right). The fluorescence quantum yield
of ground red solid is about 8.0%. The fluorescence recovered
to green, and the red color also changed into yellow, while the
sheared solid was exposed to THF vapor for 10 min or heated
at 200 °C for 2 min. Fumed or heated yellow solids turned into
red ones with orange-red fluorescence again after grinding,
suggesting a reversible force response. Thus, TA can help
BP4VA obtain enhanced mechanochromism with a higher
color contrast. XRD patterns were measured to further
understand the reversible color conversion. Pristine HBC-1
solids possessed strong diffraction peaks, which weakened
under force stimuli. After thermal and fuming treatment, the
intensity of diffraction peaks increased again (Figure S11).
This result indicates that mechanical force may destroy the
molecular ordered arrangement in the crystal phase and
promote the formation of an amorphous state.55 In addition,
thermal and fuming treatment could result in the recovery of
the original crystal phase because solvent fuming and thermal
treatment could accelerate the movement of molecules and
promote the transformation of thermodynamically unstable
amorphous powder into stable crystals. Thus, the reappearance
of green fluorescence should be attributed to the recovery of
the original crystal phase.
On account of the large torsion angles in HBC-1 crystal and
the small torsion angle in the optimized structure, BP4VA
molecules would have a planarization process, while the
The next question is how TA promotes large color contrast
after force stimuli. UV−vis absorption and emission were
measured to disclose the mechanochromic process. The
absorption peak of pristine HBC-1 solid was located at 408
nm. After grinding, the absorption band widened, the maximal
absorption peak shifted to 440 nm, and the absorption band
extended to above 550 nm (Figure S12), which resulted in the
red color of sheared solid. After grinding for 4 min, ground
solid had a wide emission band with a maximum at 622 nm
and a weak peak at about 500 nm, indicating a shift of 118 nm
compared with that of pristine HBC-1 solids. While the ground
solid was heated at 200 °C for 2 min, the fluorescence was
recovered. Moreover, heated solid was ground again for 4 min,
and red fluorescence with a maximum at 622 nm emerged
again. Such a process could be repeated many times (Figure
S13), meaning reversible mechanofluorochromism. In addi-
tion, we found that the emission spectra were strongly
dependent on grinding times. As shown in Figure S 14, the
emission band only become wide after grinding for 0.5 min,
and a new shoulder peak at 600 nm appeared after 1 min;
moreover, increasing in grinding time led to gradual weakening
Figure 6. Normalized fluorescence spectra of (a) BP4VA and (b)
HBC-1 solids in different states. Excitation wavelengths are 400 nm,
and the grinding time is 4 min.
1346
https://dx.doi.org/10.1021/acs.cgd.0c01637
Cryst. Growth Des. 2021, 21, 1342−1350

Crystal Growth & Design
pubs.acs.org/crystal
Article
multiple intermolecular weak interactions (C−H···π and C−
H···O) that stabilize the molecular highly twisted conformation
were destroyed and the twist stress was released.57 As a result,
the torsion angles became small, and then the molecular
conjugation was increased. In addition, Dong et al. obtained
another crystal phase of BP4VA with a torsion angle of 64.1°
by vacuum sublimation and found that it emitted yellow
fluorescence (552 nm).36 An H-type stacking and partial
overlap between anthracenes, being similar to H-type in HBC-
1 crystal, existed in this crystal (Figure S17). The interplanar
distance (3.61 Å) between anthracene moieties was shorter
than that in HBC-1 crystal, implying that a short interplanar
distance might lead to longer wavelength fluorescence.58,59
They also found a BP2VA crystal, which emitted red
fluorescence (618 nm).35 The adjacent anthracene planes
overlapped almost in a face-to-face stack with a interplanar
distance of 3.52 Å, and the molecule had an asymmetric
conformation with two small torsion angles (53.44° and
51.66°) (Figure S18). This result indicated that a significant
overlap of anthracene moieties and small torsion angle indeed
might contribute to a long emission wavelength because of a
strong exciton couple. Furthermore, as suggested by IR and
solid NMR spectra, 2D H-bonded lamellar frameworks still
existed under force stimuli. So, it is rational to assume that 2D
sheets would slide while the external pressure was applied.60
As shown in Figure 7, while green layer slipped along the α
direction, the interplanar distance between anthracene units
with a maximum at 440 nm, both new dimers may exist in the
ground solid. So, the enhanced fluorescence response of the
HBC-1 crystal to force stimulation is the result of three factors,
including planarization, reduction of interplanar spacing, and
large overlap between anthracenes after 2D H-bonded layers
slide. To further confirm this assumption, time-resolved
fluorescence spectra of pristine and ground solids were
measured and are shown in Figure S9b. The fluorescence
decay of ground solid at 610 nm is double exponential. The
lifetimes are 1.35 and 17.98 ns. The lifetime of 1.35 ns is
shorter than those of pristine solid and may be from the face-
to-face J-type dimer with a short interplanar distance. Back-to-
back H-type dimers should be responsible for the component
with a longer lifetime of 17.98 ns because the transition from
the lowest excited state to the ground is forbidden in the H-
dimer.
CONCLUSIONS
■
In summary, a hydrogen-bonded complex of trimesic acid and
anthracene derivatives with vinylpyridine moieties was
prepared, and its self-assembly and the response to mechanical
force stimuli were investigated. TA and BP4VA self-assembled
into a 2D lamellar H-bonded framework with large windows,
and then these windows were filled by BP4VA molecules of
other layers. In such cocrystals, TA assisted BP4VA to transfer
π-stacking from J-aggregate to a mixture of J-type and H-type
dimers with highly distorted conformations and weak π−π
interactions, which resulted in a short emission wavelength.
After mechanical force stimuli, 2D H-bonded layers slid and
promoted the molecular planarization, the proximity to each
other, and increased overlap between anthracene moieties,
which induced an enhanced mechanochromism. The shift
value of fluorescence spectrum increased from 43 nm of
BP4VA to 110 nm of HBC-1. Therefore, H-bond-induced π-
stacking conversion is a positive approach to adjust and control
molecular photophysical and stimuli-responsive properties.
More excellent or regulated stimuli-responsive materials will be
expected to be developed on the basis of this strategy.
Figure 7. Schematic of enhanced mechanochromic behavior for
HBC-1. The same color BP4VA molecules are in the same 2D H-
bonded layer. TA and hydrogen atoms are not shown for clarity.
EXPERIMENTAL SECTION
■
1H and 13C NMR spectrum in solution was recorded using a Bruker
Avance 400 MHz spectrometer at 400 and 100 MHz in CDCl3. Solid
13C NMR spectra were measured on a JEOL JNM-ECZ600R
spectrometer. UV−Vis spectra were obtained on a Mapada UV-
1800pc spectrophotometer. Fluorescence emission spectra were
obtained on FL-3 and Hitachi F-4700 fluorescence spectrophotom-
eter. Lifetime and fluorescence quantum yields of solids were
measured on an FL-3 fluorescence spectrophotometer. C, H, and N
elemental analyses were performed on a PerkinElmer 240C elemental
analyzer. XRD patterns were obtained on a Bruker D8 Advance X-ray
diffraction instrument equipped with graphite-monochromatized
CuKα radiation (λ = 1.5418 Å), by employing a scanning rate of
0.0261° s−1 in the 2θ range from 5° to 30°. Heating recovery of
ground solids was employed using a temperature-controlled heating
board. Geometrical optimization was performed by density functional
theory (DFT) calculations at the B3LYP/6-31G(d) level with the
Gaussian 09W program package. Electronic transition data were
obtained by the TD/DFT-mpw1pw91/6-31G(d) calculation based
on the conformation at the ground state or in crystals. For isolated
molecules and dimers in crystals, non-hydrogen atom coordinates
were fixed, and only hydrogen atoms are optimized to obtain the
conformation for TD/DFT calculation.
within green and orange layers shortened to form a dense face-
to-face J-type dimer, accompanying by a planarization process.
The theory calculation gave a red-shifted absorption band,
while the interplanar distance and torsion angle were set to 3.4
Å and 52° (Figure S19a), respectively. The frontier orbitals
mainly distributed in anthracenes (Figure 4e), and the red-
shifted absorption peak at ca. 434 nm mostly was ascribed to
the transition from HOMO to LUMO. So, force-induced
sliding along the α direction might lead to strengthened π−π
interactions or exciton couple. A red-shifted emission band
with a longer wavelength was expected while such a dimer was
excited. If the yellow-green layer moved along the β direction,
a back-to-face H-type dimer between yellow-green and orange
layers formed with the help of intermolecular π−π attraction. If
two anthracene moieties were arranged based on the BP2VA
crystal with red fluorescence, and the interplanar distance and
torsion angle were set to 3.55 Å and 52° (Figure S19b),
respectively, theoretical calculations gave two adjacent bath-
ochromic absorption peaks at 446.13 and 443.40 nm. Because
the ground HBC-1 has a bathochromic shift absorption band
Single crystals of BP4VA were obtained by slowing solvent
evaporation (CH2Cl2 and n-hexane mixture). Single crystals of
HBC-1 were achieved by solvent diffusion and then evaporation. The
1347
https://dx.doi.org/10.1021/acs.cgd.0c01637
Cryst. Growth Des. 2021, 21, 1342−1350

Crystal Growth & Design
pubs.acs.org/crystal
Article
detailed process: BP4VA and TA with a molar ratio of 3:2 were
dissolved in THF and methanol, respectively, and then methanol
solution was carefully added on the surface of the THF solution. The
mixture was placed for 2 weeks to obtain yellow crystals. Good
crystals were selected for X-ray diffraction analysis on in a Bruker
SMART APEX II CCD-based diffractometer with graphite mono-
chromatized Mo Kα radiation (λ = 0.71073 Å) using the φ−ω scan
technique. The crystals were kept at 296 K during data collection. The
structure was solved by the direct methods and refined on F2 by full-
matrix least-squares using the SHELXTL-2013 program. The C, N, O,
and H atoms were easily placed from the subsequent Fourier-
difference maps and refined anisotropically. CCDC 1973460 and
1973465 contain the supplementary crystallographic data for HBC-1
and BP4VA.
orcid.org/0000-0002-8335-6138;
Email: xuepengchong@126.com, hxxyxpc@tjnu.edu.cn
Authors
Yanning Han − Tianjin Key Laboratory of Structure and
Performance for Functional Molecules, College of Chemistry,
Tianjin Normal University, Tianjin, P. R. China
Tong Zhang − Tianjin Key Laboratory of Structure and
Performance for Functional Molecules, College of Chemistry,
Tianjin Normal University, Tianjin, P. R. China
Qiao Chen − Tianjin Key Laboratory of Structure and
Performance for Functional Molecules, College of Chemistry,
Tianjin Normal University, Tianjin, P. R. China
Xinyu Chen − Tianjin Key Laboratory of Structure and
Performance for Functional Molecules, College of Chemistry,
Tianjin Normal University, Tianjin, P. R. China
Scheme 2. Synthesis Route of BP4VA
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.cgd.0c01637
Notes
The authors declare no competing financial interest.
9,10-Bis(2-(pyridin-4-yl)vinyl)anthracene (BP4VA). 4-Vinyl-
pyridine (1.5 g, 14.27 mmol) and 9,10-dibromoanthracene (2.0 g,
5.95 mmol) were dissolved in 50 mL of dry DMF, and K2CO3 (3.0 g,
21.7 mmol) and PdCl2 (2.0 mg) were added. N2 was bubbled into the
mixture for 5 min, and the mixture was refluxed under N2. After 12 h,
the mixture was poured into 100 mL of water. The crude solid was
obtained by suction filtration. The yellow product was gained by
column chromatography (silica, CH2Cl2/petroleum ether = 4/1).
ACKNOWLEDGMENTS
■
This work was supported by the Scientific Research
Foundation of Tianjin Normal University (Grant No.
5RL151), the Foundation of Development Program of Future
Expert in Tianjin Normal University (WLQR201804), and the
Science &Technology Development Fund of Tianjin Educa-
tion Commission for Higher Education (2018ZD12).
1
Yield = 78%. H NMR (400 MHz, CDCl3) δ 8.74−8.68 (m, 4H),
8.33 (dd, J = 6.8, 3.3 Hz, 4H), 8.18 (d, J = 16.4 Hz, 2H), 7.60−7.55
(m, 4H), 7.53 (dd, J = 6.9, 3.2 Hz, 4H), 6.91 (d, J = 16.5 Hz, 2H)
(Figure S20). 13C NMR (101 MHz, CDCl3) δ 150.44, 144.27, 135.27,
132.07, 129.95, 129.39, 126.14, 125.81, 120.98 (Figure S21).
Synthesis of Hydrogen-Bonded Complex. BP4VA (0.500 g,
1.30 mmol) and TA (0.182 g, 0.87 mmol) were added into 100 mL of
THF, and the mixture was refluxed for 24 h. After cooling to room
temperature, light yellow solids were obtained by suction filtration. 1H
NMR spectrum in DMSO-d6 indicated that the ratio of BP4VA to TA
was 1:4. Excess TA was washed by ethanol, and their molar ratio was
confirmed to be 1:1 by NMR spectrum. The obtained yellow solids
emitted strong green fluorescence.
REFERENCES
■
(1) Hirschberg, J. H. K. K.; Brunsveld, L.; Ramzi, A.; Vekemans, J. A.
J. M.; Sijbesma, R. P.; Meijer, E. W. Helical Self-Assembled Polymers
from Cooperative Stacking of Hydrogen-Bonded Pairs. Nature 2000,
407, 167−170.
(2) Lin, R. B.; He, Y.; Li, P.; Wang, H.; Zhou, W.; Chen, B.
Multifunctional Porous Hydrogen-Bonded Organic Framework
Materials. Chem. Soc. Rev. 2019, 48, 1362−1389.
(3) Mote, N. R.; Chikkali, S. H. Hydrogen-Bonding-Assisted
Supramolecular Metal Catalysis. Chem. - Asian J. 2018, 13, 3623−
3646.
(4) Zhao, J.; Yang, D.; Yang, X.-J.; Wu, B. Anion Coordination
Chemistry: From Recognition to Supramolecular Assembly. Coord.
Chem. Rev. 2019, 378, 415−444.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.cgd.0c01637.
■
sı
(5) Yan, D.; Evans, D. G. Molecular Crystalline Materials with
Tunable Luminescent Properties: From Polymorphs to Multi-
Component Solids. Mater. Horiz. 2014, 1, 46−57.
IR, UV, NMR, fluorescence spectra, crystal data,
quantum chemical calculation results, molecular stacking
in different crystals (PDF)
(6) Liu, J.; Ye, K.; Shen, Y.; Peng, J.; Sun, J.; Lu, R. Photoactuators
Based on the Dynamic Molecular Crystals of Naphthalene Acrylic
Acids Driven by Stereospecific [2 + 2] Cycloaddition Reactions. J.
Mater. Chem. C 2020, 8, 3165−3175.
(7) Grove, R. C.; Malehorn, S. H.; Breen, M. E.; Wheeler, K. A. A
Photoreactive Crystalline Quasiracemate. Chem. Commun. 2010, 46,
7322−7324.
(8) Koner, R.; Goldberg, I. Crystal Engineering of Molecular
Networks. Hydrogen Bonding Driven Two-Dimensional Assemblies
of Tetrapyridylporphyrin with Benzene Tri- and Tetra-Carboxylic
Acids. CrystEngComm 2009, 11, 1217−1219.
̈
(9) Lu, J.; Perez-Krap, C.; Suyetin, M.; Alsmail, N. H.; Yan, Y.; Yang,
S.; Lewis, W.; Bichoutskaia, E.; Tang, C. C.; Blake, A. J.; Cao, R.;
Accession Codes
CCDC 1973460 and 1973465 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
Pengchong Xue − Tianjin Key Laboratory of Structure and
Performance for Functional Molecules, College of Chemistry,
Tianjin Normal University, Tianjin, P. R. China;
■
̈
Schroder, M. A Robust Binary Supramolecular Organic Framework
(SOF) with High CO2 adsorption and Selectivity. J. Am. Chem. Soc.
2014, 136, 12828−12831.
(10) Ono, T.; Hisaeda, Y. Flexible-Color Tuning and White-Light
Emission in Three-, Four-, and Five-Component Host/Guest Co-
1348
https://dx.doi.org/10.1021/acs.cgd.0c01637
Cryst. Growth Des. 2021, 21, 1342−1350

Crystal Growth & Design
pubs.acs.org/crystal
Article
Crystals by Charge-Transfer Emissions as Well as Effective Energy
Transfers. J. Mater. Chem. C 2019, 7, 2829−2842.
(28) Fang, M.; Yang, J.; Liao, Q.; Gong, Y.; Xie, Z.; Chi, Z.; Peng,
Q.; Li, Q.; Li, Z. Triphenylamine Derivatives: Different Molecular
Packing and the Corresponding Mechanoluminescent or Mechano-
chromism Property. J. Mater. Chem. C 2017, 5, 9879−9885.
(29) Zhang, X.; Zhang, L.-Y.; Wang, J.-Y.; Dai, F.-R.; Chen, Z.-N.
Two-Step Phosphorescent Mechanochromism Due to Intramolecular
Deformation. J. Mater. Chem. C 2020, 8, 715−720.
(11) Xue, P.; Wang, P.; Yao, B.; Sun, J.; Gong, P.; Zhang, Z.; Qian,
C.; Lu, R. Nanofibers of Hydrogen-Bonded Two-Component Gel
with Closely Connected p- and n-Channels and Photoinduced
Electron Transfer. ACS Appl. Mater. Interfaces 2014, 6, 21426−21434.
(12) Huang, Y.; Shiota, Y.; Su, S.; Wu, S.; Yao, Z.; Li, G.; Kanegawa,
S.; Kang, S.; Kamachi, T.; Yoshizawa, K.; Ariga, K.; Sato, O. Molecular
Machines Thermally Induced Intra-Carboxyl Proton Shuttle in a
Molecular Rack- and-Pinion Cascade Achieving Macroscopic Crystal
Deformation. Angew. Chem., Int. Ed. 2016, 55, 14628−14632.
(13) Yuan, Y.; Chen, W.; Ma, Z.; Deng, Y.; Chen, Y.; Chen, Y.; Hu,
W. Enhanced Optomechanical Properties of Mechanochemilumines-
cent Poly(Methyl Acrylate) Composites with Granulated Fluorescent
Conjugated Microporous Polymer Fillers. Chem. Sci. 2019, 10, 2206−
2211.
(30) Yuan, W.; Cheng, J.; Li, X.; Wu, M.; Han, Y.; Yan, C.; Zou, G.;
Mullen, K.; Chen, Y. 5,6,12,13-Tetraazaperopyrenes as Unique
̈
Photonic and Mechanochromic Fluorophores. Angew. Chem., Int.
Ed. 2020, 59, 9940−9945.
(31) Toma, O.; Mercier, N.; Allain, M.; Meinardi, F.; Forni, A.;
Botta, C. Mechanochromic Luminescence of N, N′ -Dioxide-4,4′
-Bipyridine Bismuth Coordination Polymers. Cryst. Growth Des. 2020,
20, 7658−7666.
(32) Xiong, J.; Wang, K.; Yao, Z.; Zou, B.; Xu, J.; Bu, X.-H. Multi-
Stimuli-Responsive Fluorescence Switching from a Pyridine-Function-
alized Tetraphenylethene AIEgen. ACS Appl. Mater. Interfaces 2018,
10, 5819−5827.
(33) Lu, B.; Zhang, Y.; Yang, X.; Wang, K.; Zou, B.; Yan, D.
Piezochromic Luminescence of AIE-Active Molecular Co-Crystals:
Tunable Multiple Hydrogen Bonding and Molecular Packing. J.
Mater. Chem. C 2018, 6, 9660−9666.
(34) Yan, D.; Yang, H.; Meng, Q.; Lin, H.; Wei, M. Two-
Component Molecular Materials of 2,5-Diphenyloxazole Exhibiting
Tunable Ultraviolet/Blue Polarized Emission, Pump-Enhanced
Luminescence, and Mechanochromic Response. Adv. Funct. Mater.
2014, 24, 587−594.
(35) Dong, Y.; Xu, B.; Zhang, J.; Tan, X.; Wang, L.; Chen, J.; Lv, H.;
Wen, S.; Li, B.; Ye, L.; Zou, B.; Tian, W. Piezochromic Luminescence
Based on the Molecular Aggregation of 9,10-Bis((E)-2-(Pyrid-2-
Yl)Vinyl)Anthracene. Angew. Chem., Int. Ed. 2012, 51, 10782−10785.
(36) Dong, Y.; Zhang, J.; Tan, X.; Wang, L.; Chen, J.; Li, B.; Ye, L.;
Xu, B.; Zou, B.; Tian, W. Multi-Stimuli Responsive Fluorescence
Switching: The Reversible Piezochromism and Protonation Effect of a
Divinylanthracene Derivative. J. Mater. Chem. C 2013, 1, 7554−7559.
(37) Zhang, X.; Chi, Z.; Li, H.; Xu, B.; Li, X.; Zhou, W.; Liu, S.;
Zhang, Y.; Xu, J. Piezofluorochromism of an Aggregation-Induced
Emission Compound Derived from Tetraphenylethylene. Chem. -
Asian J. 2011, 6, 808−811.
(38) Liu, Y.; Li, A.; Xu, S.; Xu, W.; Liu, Y.; Tian, W.; Xu, B.
Reversible Luminescent Switching in an Organic Cocrystal: Multi-
Stimuli-Induced Crystal-to-Crystal Phase Transformation. Angew.
Chem., Int. Ed. 2020, 59, 15098−15103.
(39) Bai, L.; Bose, P.; Gao, Q.; Li, Y.; Ganguly, R.; Zhao, Y.
Halogen-Assisted Piezochromic Supramolecular Assemblies for
Versatile Haptic Memory. J. Am. Chem. Soc. 2017, 139, 436−441.
(40) Liu, Y.; Ma, S.; Xu, B.; Tian, W. Construction and Function of a
Highly Efficient Supramolecular Luminescent System. Faraday
Discuss. 2017, 196, 219−229.
(41) Li, C.; Zhou, H.; Ju, Y.; Du, M. Water-Mediated Structural
Transformations of Cu(II) 5-Halonicotinates Coordination Networks
with Distinct Mechanisms. Chem. - Eur. J. 2017, 23, 12985−12990.
(14) Chi, Z.; Zhang, X.; Xu, B.; Zhou, X.; Ma, C.; Zhang, Y.; Liu, S.;
Xu, J. Recent Advances in Organic Mechanofluorochromic Materials.
Chem. Soc. Rev. 2012, 41, 3878−3896.
(15) Wang, J.; Chai, Z.; Wang, J.; Wang, C.; Han, M.; Liao, Q.;
Huang, A.; Lin, P.; Li, C.; Li, Q.; Li, Z. Mechanoluminescence or
Room-Temperature Phosphorescence: Molecular Packing-Dependent
Emission Response. Angew. Chem., Int. Ed. 2019, 58, 17297−17302.
(16) Theato, P.; Sumerlin, B. S.; O’Reilly, R. K.; Epps, T. H., III
Stimuli Responsive Materials. Chem. Soc. Rev. 2013, 42, 7055.
(17) Sagara, Y.; Yamane, S.; Mitani, M.; Weder, C.; Kato, T.
Mechanoresponsive Luminescent Molecular Assemblies: An Emerg-
ing Class of Materials. Adv. Mater. 2016, 28, 1073−1095.
(18) Xue, P.; Ding, J.; Wang, P.; Lu, R. Recent Progress in
Mechanochromism of Phosphorescent Organic Molecules and Metal
Complexes. J. Mater. Chem. C 2016, 4, 6688−6706.
(19) Zhang, X.; Shi, J.; Shen, G.; Gou, F.; Cheng, J.; Zhou, X.; Xiang,
H. Non-Conjugated Fluorescent Molecular Cages of Salicylaldehyde-
Based Tri-Schiff Bases: AIE, Enantiomers, Mechanochromism, Anion
Hosts/Probes, and Cell Imaging Properties. Mater. Chem. Front. 2017,
1, 1041−1050.
(20) Zhao, J.; Chi, Z.; Yang, Z.; Mao, Z.; Zhang, Y.; Ubba, E.; Chi,
Z. Recent Progress in the Mechanofluorochromism of Distyrylan-
thracene Derivatives with Aggregation-Induced Emission. Mater.
Chem. Front. 2018, 2, 1595−1608.
(21) Fu, Z.; Wang, K.; Zou, B. Recent Advances in Organic
Pressure-Responsive Luminescent Materials. Chin. Chem. Lett. 2019,
30, 1883−1894.
(22) Xie, Y.; Li, Z. Triboluminescence: Recalling Interest and New
Aspects. Chem. 2018, 4, 943−971.
(23) Zhan, L.; Chen, Z.; Gong, S.; Xiang, Y.; Ni, F.; Zeng, X.; Xie,
G.; Yang, C. Fluorescence A Simple Organic Molecule Realizing
Simultaneous TADF,RTP,AIE, and Mechanoluminescence: Under-
standing the Mechanism Behind the Multifunctional Emitter. Angew.
Chem., Int. Ed. 2019, 58, 17651−17655.
(24) Yang, M.; Park, I. S.; Miyashita, Y.; Tanaka, K.; Yasuda, T.
Mechanochromic Delayed Fluorescence Switching in Propeller-
Shaped Carbazole−Isophthalonitrile Luminogens with Stimuli-
Responsive Intramolecular Charge-Transfer Excited States. Angew.
Chem., Int. Ed. 2020, 59, 13955−13961.
(25) Zhao, Z.; Chen, T.; Jiang, S.; Liu, Z.; Fang, D.; Dong, Y. Q. The
Construction of a Multicolored Mechanochromic Luminogen with
High Contrast through the Combination of a Large Conjugation Core
and Peripheral Phenyl Rings. J. Mater. Chem. C 2016, 4, 4800−4804.
(26) Li, N.; Gu, Y.; Chen, Y.; Zhang, L.; Zeng, Q.; Geng, T.; Wu, L.;
Jiang, L.; Xiao, G.; Wang, K.; Zou, B. Pressure-Induced Emission
Enhancement and Piezochromism of Triphenylethylene. J. Phys.
Chem. C 2019, 123, 6763−6767.
(27) Sun, J.; Sun, J.; Mi, W.; Xue, P.; Zhao, J.; Zhai, L.; Lu, R.
Carbazole Modified Salicylaldimines and Their Difluoroboron
Complexes: Effect of the Tert-Butyl and Trifluoromethyl Terminal
Groups on Organogelation and Piezofluorochromism. New J. Chem.
2017, 41, 763−772.
́
(42) Campos-Gaxiola, J. J.; García-Grajeda, B. A.; Hernandez-
́
̈
Ahuactzi, I. F.; Guerrero-Alvarez, J. A.; Hopfl, H.; Cruz-Enríquez, A.
Supramolecular Networks in Molecular Complexes of Pyridine
Boronic Acids and Polycarboxylic Acids: Synthesis, Structural
Characterization and Fluorescence Properties. CrystEngComm 2017,
19, 3760−3775.
(43) Ma, S.; Zhang, J.; Liu, Y.; Qian, J.; Xu, B.; Tian, W. Direct
Observation of the Symmetrical and Asymmetrical Protonation States
in Molecular Crystals. J. Phys. Chem. Lett. 2017, 8, 3068−3072.
(44) Arunan, E.; Desiraju, G. R.; Klein, R. A.; Sadlej, J.; Scheiner, S.;
Alkorta, I.; Clary, D. C.; Crabtree, R. H.; Dannenberg, J. J.; Hobza, P.;
Kjaergaard, H. G.; Legon, A. C.; Mennucci, B.; Nesbitt, D. J.
Definition of the Hydrogen Bond (IUPAC Recommendations 2011).
Pure Appl. Chem. 2011, 83, 1637−1641.
(45) Sokolov, A. N.; Friscic, T.; MacGillivray, L. R. Enforced Face-
to-Face Stacking of Organic Semiconductor Building Blocks within
1349
https://dx.doi.org/10.1021/acs.cgd.0c01637
Cryst. Growth Des. 2021, 21, 1342−1350

Crystal Growth & Design
pubs.acs.org/crystal
Article
Hydrogen-Bonded Molecular Cocrystals. J. Am. Chem. Soc. 2006, 128,
2806−2807.
(46) Xue, P.; Sun, J.; Chen, P.; Gong, P.; Yao, B.; Zhang, Z.; Qian,
C.; Lu, R. Strong Solid Emission and Mechanofluorochromism of
Carbazole-Based Terephthalate Derivatives Adjusted by Alkyl Chains.
J. Mater. Chem. C 2015, 3, 4086−4092.
(47) Zhang, T.; Zhang, C.; Li, X.; Liang, M.; Bian, W.; Zhang, Y.;
Wang, K.; Xue, P. Fluorescence Response of Cruciform D−π−A−π−
D Phenothiazine Derivatives to Mechanical Force. CrystEngComm
2019, 21, 4192−4199.
(48) Links, D. A. Multifunctional Organic Fluorescent Materials
Derived from 9, 10-Distyrylanthracene with Alkoxyl Endgroups of
Various Lengths W. Chem. Commun. 2012, 11, 10895−10897.
(49) Hayes, C. O.; Bell, W. K.; Cassidy, B. R.; Willson, C. G.
Synthesis and Characterization of a Two Stage, Nonlinear Photobase
Generator. J. Org. Chem. 2015, 80, 7530−7535.
(50) Shao, B.; Jin, R.; Li, A.; Liu, Y.; Li, B.; Xu, S.; Xu, W.; Xu, B.;
Tian, W. Luminescent Switching and Structural Transition Organic
Molecular Polymorphs. J. Mater. Chem. C 2019, 7, 3263−3268.
(51) He, Z.; Zhang, L.; Mei, J.; Zhang, T.; Lam, J. W. Y.; Shuai, Z.;
Dong, Y. Q.; Tang, B. Z. Polymorphism-Dependent and Switchable
Emission of Butterfly-Like Bis(Diarylmethylene)Dihydroanthracenes.
Chem. Mater. 2015, 27, 6601−6607.
(52) Yuan, W.; Ren, X.-K.; Li, M.; Guo, H.; Han, Y.; Wu, M.; Wang,
Q.; Li, M.; Chen, Y. From S,N-Heteroacene to Large Discotic
Polycyclic Aromatic Hydrocarbons (PAHs): Liquid Crystal versus
Plastic Crystalline Materials with Tunable Mechanochromic Fluo-
rescence. Angew. Chem., Int. Ed. 2018, 57, 6161−6165.
(53) Yang, X.; Wang, Q.; Hu, P.; Xu, C.; Guo, W.; Wang, Z.; Mao,
Z.; Yang, Z.; Liu, C.; Shi, G.; Chen, L.; Xu, B.; Chi, Z. Achieving
Remarkable and Reversible Mechanochromism from a Bright Ionic
AIEgen with High Specificity for Mitochondrial Imaging and
Secondary Aggregation Emission Enhancement for Long-Term
Tracking of Tumors. Mater. Chem. Front. 2020, 4, 941−949.
(54) Deng, X.; Guo, H.; Meng, X.; Wang, K.; Zou, B.; Ma, Y. Visible
Responses under High Pressure in Crystals: Phenolphthalein and Its
Analogues with Adjustable Ring-Opening Threshold Pressures. Chem.
Commun. 2019, 55, 4663−4666.
(55) Wang, Y.; Xu, D.; Gao, H.; Wang, Y.; Liu, X.; Han, A.; Zhang,
C.; Zang, L. Twisted Donor−Acceptor Cruciform Luminophores
Possessing Substituent-Dependent Properties of Aggregation-Induced
Emission and Mechanofluorochromism. J. Phys. Chem. C 2018, 122,
2297−2306.
(56) Xue, P.; Yang, Z.; Chen, P. Hiding and Revealing Information
Using the Mechanochromic System of a 2,5-Dicarbazole-Substituted
Terephthalate Derivative. J. Mater. Chem. C 2018, 6, 4994−5000.
(57) Liu, W.; Wang, Y.; Sun, M.; Zhang, D.; Zheng, M.; Yang, W.
Alkoxy-Position Effects on Piezofluorochromism and Aggregation-
Induced Emission of 9,10-Bis(Alkoxystyryl)Anthracenes. Chem.
Commun. 2013, 49, 6042−6044.
(58) Shao, B.; Jin, R.; Li, A.; Liu, Y.; Li, B.; Xu, S.; Xu, W.; Xu, B.;
Tian, W. Luminescent Switching and Structural Transition through
Multiple External Stimuli Based on Organic Molecular Polymorphs. J.
Mater. Chem. C 2019, 7, 3263−3268.
(59) Zhang, T.; Han, Y.; Liang, M.; Bian, W.; Zhang, Y.; Li, X.;
Zhang, C.; Xue, P. Substituent Effect on Photophysical Properties,
Crystal Structures and Mechanochromism of D-π-A Phenothiazine
Derivatives. Dyes Pigm. 2019, 171, 107692.
(60) Niu, C.; You, Y.; Zhao, L.; He, D.; Na, N.; Ouyang, J.
Solvatochromism, Reversible Chromism and Self-Assembly Effects of
Heteroatom-Assisted Aggregation-Induced Enhanced Emission
(AIEE) Compounds. Chem. - Eur. J. 2015, 21, 13983−13990.
1350
https://dx.doi.org/10.1021/acs.cgd.0c01637
Cryst. Growth Des. 2021, 21, 1342−1350