The influence of intermolecular interactions and molecular packings on mechanochromism and mechanoluminescence-a tetraphenylethylene derivative case

Article abstract of DOI:10.1039/c9tc04501e

Four tetraphenylethylene (TPE) derivatives 1-4 were synthesized to explore the influence of intermolecular interaction and molecular packing modes on their mechanochromism (MC) and mechanoluminescence (ML) performances. Compounds 1 and 2 modified with carboxyl groups had strong intermolecular interactions and were MC-active and ML-inactive, while compound 3 functionalized with a carboxyl ester had self-reversible MC and ML. Single crystal study of these molecules suggested that besides intermolecular interaction, molecular packing was also important for MC and ML properties. The carboxyl ester-modified 3c had weaker intermolecular interactions than 1c/2c, but it formed an intact three-dimensional hydrogen-bonded network and moderate packing density, which can efficiently block non-radiative relaxation and lead to ML. While 1c and 2c had strong molecular interactions, the molecular packing density in 1c was rather low due to its porous structure and 2c had a defective hydrogen-bonded network. These defective packings allowed non-radiative energy loss and inactivated the ML property of these two molecules.

Full text of DOI:10.1039/c9tc04501e

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Materials Chemistry C
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PAPER
The influence of intermolecular interactions and
molecular packings on mechanochromism and
mechanoluminescence – a tetraphenylethylene
derivative case†
Cite this: J. Mater. Chem. C, 2019,
, 12709
7
a
a
b
c
a
Guangxi Huang,
Yuqing Jiang, Jianguo Wang,
Zhen Li,
Bing Shi Li
*
d
and Ben Zhong Tang
Four tetraphenylethylene (TPE) derivatives 1–4 were synthesized to explore the influence of intermole-
cular interaction and molecular packing modes on their mechanochromism (MC) and mechanolumines-
cence (ML) performances. Compounds 1 and 2 modified with carboxyl groups had strong intermolecular
interactions and were MC-active and ML-inactive, while compound 3 functionalized with a carboxyl
ester had self-reversible MC and ML. Single crystal study of these molecules suggested that besides
intermolecular interaction, molecular packing was also important for MC and ML properties. The
carboxyl ester-modified 3c had weaker intermolecular interactions than 1c/2c, but it formed an intact
three-dimensional hydrogen-bonded network and moderate packing density, which can efficiently block
non-radiative relaxation and lead to ML. While 1c and 2c had strong molecular interactions, the
molecular packing density in 1c was rather low due to its porous structure and 2c had a defective
hydrogen-bonded network. These defective packings allowed non-radiative energy loss and inactivated
the ML property of these two molecules.
Received 13th August 2019,
Accepted 17th September 2019
DOI: 10.1039/c9tc04501e
rsc.li/materials-c
original luminescence states, a majority of MC molecules require
thermal annealing or solvent vapor fuming, while the remaining
1
. Introduction
In recent years, mechanical-responsive organic luminogens have minority spontaneously recover at room temperature without using
2
gained more and more scientific and technological interest by any external stimuli. Another important type of mechanical-
virtue of their wide application potentiality in the fields of responsive luminescent materials is mechanoluminescence (ML)
security papers, optical storage, pressure sensors, new light or triboluminescence (TL) materials, which can emit light in
1
sources etc. Upon external mechanical forces such as grinding, the crushing process of crystal or microcrystal powder upon
3
crushing or pressing, these materials can show corresponding mechanical stimuli without UV irradiation.
luminescence responses. One of the most common types of
mechanical-responsive luminescent materials is molecules induced emission (AIE) skeletons have been explored. The
with mechanochromism (MC), whose emission color/strength AIE molecules are more prone to show MC than conventional
To date, a number of MC luminogens with aggregation
4
5
can be altered upon mechanical stimuli. To recover to their luminescent ones, because the twisted structures of the AIE
skeletons have flexibility to become a planar or even more
a
twisted conformation upon external stimuli. Accompanied with
the easily made conformation adjustments are the dramatic
changes in their conjugation states, which lead to the MC
activity. Molecules with AIE skeletons also have the advantage
of showing intensive luminescent emission in the solid state,
which facilitates the observation of fluorescence variation in
the powder or crystalline state. In comparison, the research of
organic ML materials is developing slowly, though the first
Key Laboratory of New Lithium-Ion Battery and Mesoporous Material, College of
Chemistry and Environmental Engineering, Shenzhen University, 1066 Xueyuan
Avenue, Nanshan, Shenzhen 518055, China. E-mail: phbingsl@szu.edu.cn
Department of Chemistry and Chemical Engineering, Inner Mongolia University,
Hohhot, 010021, China
b
c
Hubei Key Lab on Organic and Polymeric Opto-Electronic Materials, Department of
Chemistry, Wuhan University, Wuhan 430072, China
d
Hong Kong Branch of Chinese National Engineering Research, Center for Tissue
Restoration and Reconstruction, Department of Chemistry, The Hong Kong
University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong,
China
6
example can be traced back to 1605 by Francis Bacon. The
introduction of AIE characteristics by Chi and Li et al. has
†
Electronic supplementary information (ESI) available. CCDC 1904514 for 3,
provided some novel ML luminogens since 2015. Nevertheless,
1
904515 for 1 and 1904516 for 2. For ESI and crystallographic data in CIF or other
1
h,7
electronic format see DOI: 10.1039/c9tc04501e
the family of ML molecules still needs expanding,
and the
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w
structure–property relationship of ML molecules also needs emission wavelength in the aggregation state ( f = 99%) was
to be clarified. The most recent research reported by Li’s group also related to the position of substituents: it was 487 nm for 1,
pointed out that the strong intermolecular interactions in ML 484 nm for 3, 469 nm for 2 and 468 nm for 4, showing the
crystals contributed to their ML activity by reducing energy loss same trend as their absorption spectra. To better understand
through non-radiative relaxation channels during the crushing the photophysical properties of 1–4, density functional
8
process. However, too strong intermolecular interactions from theory (DFT) calculations were carried out (Fig. S3, ESI†). The
tight molecular packing in the crystal are also found to hinder meta-position of the substituent probably interrupted the intra-
conformation changes and weaken the ML performance. There- molecular p-conjugation in 2 and 4, leading to the hypsochro-
fore, thoroughly understanding the structure–property relation- mic absorption spectra. This agreed well with their larger
ship of ML molecules still remains a challenging task.
g
energy gap (DE ) values than those of 1 and 3. In molecules 3
To further probe the underlying mechanism of MC/ML and 4, none of the electron cloud was located on the methyl
phenomena, we screened ML molecules with AIE skeletons to group on both the highest occupied molecular orbitals (HOMOs)
select proper model molecular systems. TPE derivatives are and the lowest unoccupied molecular orbitals (LUMOs). The
easily synthesized and some of them have demonstrated MC above results illustrated that the additional methyl group
4
b,9
or ML activity.
carboxyl group to enhance strong intermolecular interactions impact on the electron distribution, so 3 and 4 displayed similar
and with methyl ester to decrease intermolecular interactions. DE and dipole moments with their hydrolysis products 1 and 2,
We therefore modify TPE skeletons with a (mainly due to its weak electron-donating property) had little
g
Unexpectedly, the TPE moiety with methyl ester rather than respectively. Therefore, these molecules can be systematically
carboxyl group emitted bright ML. Single crystal analysis compared together.
showed that intact three-dimensional hydrogen-bonded net-
works and a high packing density should provide guarantees slowly evaporating their mixture solvent (dichloromethane/
for ML activity through the restriction of non-radiative relaxa- hexane for 1 and 2, and acetone/H O for 3 and 4). Three
Single crystals of the four compounds were cultured by
2
tion during the crushing process of crystals. The relationship compounds 1c, 2c and 3c were obtained as single crystals and
between intermolecular interactions and self-reversible MC their single crystal data are summarized in Table S1 (ESI†).
property was also systematically demonstrated. This work helps However, the obtained solid of 4 (4pc) was polycrystal, whose
to thoroughly understand the influence of molecular interaction structure could not be deciphered. The photos and photo-
and packing on the ML property of molecules and also enlarges physical properties of the as-prepared powder and single crystal
the ML family. It provides beneficial experience for designing (polycrystal) of 1–4 were measured and are listed in Table 1 and
new bright ML materials towards practical applications.
Fig. S6 (ESI†). The para-position substituted compounds have
obviously higher fluorescence efficiency than the meta-position
ones. The as-prepared powders of 2–4 (2p, 3p and 4p) displayed
similar blue fluorescence, quantum yield and fluorescence
lifetimes to their single crystals (2c and 3c) or polycrystal
2. Results and discussion
2.1. Molecular synthesis
(4pc), respectively. In contrast, the as-prepared powder of 1
Compounds 3 and 4 were synthesized through classic Suzuki
coupling reactions. Hydrolysis of 3 and 4 quantitatively afforded
compound 1 and 2, respectively. 1 and 3 have been widely used
as synthetic intermediates for AIE derivatives. 2 and 4 were
characterized by H and C NMR, high resolution mass spectro-
scopy (HRMS) and elemental analysis (Experimental section and
(
1p) emitted green fluorescence (lem = 469 nm, F = 30.7%, and
f
t = 2.23 ns), which was different from the blue fluorescence
of yellowish single crystal 1c (lem = 458 nm, F = 23.4%, and
t = 1.95 ns). The distinct fluorescence in different states might
imply the MC activity of compound 1.
f
1
13
Fig. S13–S18, ESI†). 1–4 were very stable up to 260 1C, verified by 2.3. MC/ML experiments
thermogravimetric analysis (Fig. S1, ESI†).
MC and ML of 4 were not further explored and discussed due to
the lack of single crystal structures. MC and ML activity of 1–3
were then explored in detail. As shown in Fig. 1, 1 and 2 had
2.2. Photophysical properties
The absorption spectra of the four compounds were measured apparent MC properties. The ground state 1g exhibited green
in THF solution (10 mM) (Fig. S2, ESI†). Their absorption fluorescence (lem = 482 nm) under irradiation of UV light
bands ranged from 308 to 330 nm, which were attributed to (Fig. 1a). Upon fuming (1f) with dichloromethane or heating
the p–p* transitions of the TPE moiety. It could be found that (1h) to 140 1C on a heating board, the maximum emission peak
the existence of the methyl group had a minor effect on the blue-shifted to 447 nm and 449 nm, respectively (Fig. 1b). The
absorption spectra. The meta-position substituents (2 and 4) PXRD pattern revealed that 1g was in an amorphous state due
blueshifted the maximum absorption wavelength compared to to the absence of diffraction peaks (Fig. 1c). After fuming or
the para-position ones (1 and 3), which might be ascribed to the heating, the amorphous state of 1g transformed into a crystal-
decrease of conjugated degree. Compounds 1–4 all displayed line state (1f and 1h were the same state), as revealed by many
typical AIE features: they were non-emissive in dilute THF sharp and intense diffraction peaks. The PXRD pattern of 1f/1h
w
solution and their fluorescence was turned on at the f (the was different to that of 1c; their emission wavelengths had about
volume fraction of water) higher than 90%. The maximum 10 nm distinction. Differential scanning calorimetry (DSC)
12710 | J. Mater. Chem. C, 2019, 7, 12709--12716
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Table 1 Molecular structures, optical properties and photos of 1–4
Photos
a
b
b
f
b
Molecluar structure
State
l
abs [nm]
Under daylight
Under UV light
l
em [nm]
F
[%]
t [ns]
c
1
1
2
2
3
3
4
4
p
469
458
436
436
447
448
439
438
30.7
23.4
11.3
11.1
36.8
34.2
1.5
2.23
3
21
d
c
1.95
1.13
1.07
1.93
1.96
0.66
0.67
p
c
3
3
3
08
23
11
p
c
p
pc
e
1.4
a
b
The maximum absorption wavelength (labs) in THF solution (10 mM). The maximum emission wavelength (lem), fluorescence lifetime (t) and
c
d
e
f
fluorescence quantum yield (F ) in solid state. p depicted as-prepared powder. c depicted single crystal. pc depicted polycrystal.
Fig. 1 Photos of (a) 1 and (d) 2 in g (ground), f (fumed) and h (heated) powder states, respectively. Photos were respectively taken under natural light
upper) and UV illumination (lower). Conditions: I, grinding; II, fuming with dichloromethane vapor for 1 min; III, heating at 140 1C for 1 min. Normalized
(
photoluminescence (PL) intensity of (b) 1 and (e) 2 in p (as-prepared), g, f and h powder states and single crystal c, respectively. PXRD patterns of all
powder states and single crystal of (c) 1 and (f) 2.
thermograms of all states of 1 showed the same endothermic (lem = 450 nm) had about 20 nm wavelength shift relative to
peak at about 208 1C (Fig. S7, ESI†), which is assigned to the the fumed powder 2f (lem = 432 nm) or the heated powder 2h
melting peak. A cold crystallization peak was observed for 1p (lem = 426 nm) (Fig. 1d and e). Molecule 2g had a similar PXRD
(134 1C) and 1g (138 1C), respectively. It corresponds to their pattern to that of 2f and 2h and also 2c except for a sharp peak
transformation into a more stable crystal structure 1f/1h, as at 2y = 33.11, revealing 2g was still in an ordered packing state
verified by their almost flat DSC curves prior to the occurrence (Fig. 1f). According to the Bragg equation, a higher 2y angle
of the melting peak. For compound 2, the ground powder 2g implied a shorter distance between molecules. Thus, the peak
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Fig. 2 (a) Photos of 3 in 3r (self-recovered) and 3g (ground) powder state. Photos were respectively taken under natural light (upper) and UV illumination
lower). Conditions: I, grinding; IV, self-recovered within 1 h. (b) ML images of single crystal 3c at room temperature. (c) Normalized PL intensity of 3p (as-
(
prepared powder), 3g, 3r and 3c, and ML intensity of 3c. (d) PXRD patterns of all states of 3. (e) DSC curves of powder states of 3. The inset shows the
magnification of the curve of 3g.
at 2y = 33.11 demonstrated the compressing of crystalline crystal and as-prepared powder of 1 or 2, even in the dark.
powder after grinding. However, no cold crystallization peak Though 3p was in the same crystalline state as 3c as indicated
was observed in the DSC curves of 2 in different states (Fig. S8, by their similar PXRD patterns, the crystalline grain size of 3p
ESI†), which might derive from the relatively intact crystalline and 3c should have significant differences due to their different
state of 2p/2g compared to that of 1p/1g. MC reversibility of growth conditions. ML intensity decreased gradually after
compound 1 and 2 was further confirmed. The switching of their repeatedly grinding, suggesting that the absence of ML for 3p
fluorescence could be repeated many times by repeated fuming/ might be caused by its finer size. The ML spectrum of 3c was
grinding without any deterioration (Fig. S9a and b, ESI†).
redshifted relative to its fluorescence spectrum and resembled
Unlike 1 and 2, the MC property of compound 3 was found the fluorescence of its ground state 3g before self-recovery.
to be self-reversible. The cyan emission of the ground sample It was probable that ML originated from the excited state of
(3g, lem = 468 nm) could self-recover to the original blue molecules on the fractured surface of the crystal, where the
fluorescence (3r, lem = 447 nm) without applying any other molecules were semi-crystalline, similar to that of 3g.
stimuli within 1 h (Fig. 2a and c). This self-reversible MC
phenomenon could be repeated many times between blue
2.4. Crystal structures
and cyan emissions as well (Fig. S9c, ESI†). In addition, fuming According to the above results, 1 and 2 were MC-active and
with solvent or heating could effectively shorten the recovery ML-inactive, while 3 was both self-reversible MC- and ML-active.
process to about 1 min. After grinding, compound 3 did not In order to disclose the relationship between the molecular
completely transform into an amorphous state, as shown arrangement/packing and MC/ML properties, single crystal
from the remaining diffraction peaks (Fig. 2d), revealing only structures of 1–3 were analyzed. Crystal 3c belonged to a mono-
a considerable decrease of crystallinity during the grinding clinic system with P21 space group, whereas 1c and 2c belonged
process. Diffraction peaks of 3r were more intense than those to a monoclinic system with P21/c space group. In the unit cell of
of 3g, demonstrating its self-reversible feature. The DSC 1c and 3c, molecules showed two conformations (blue one and
thermogram of 3g showed a weak cold crystallization peak grey one), while 2c had only one conformation (Fig. S10, ESI†).
ranging from 50 to 70 1C (Fig. 2e), which was not observed in The molecules in the three crystals were arranged in a layer
that of 3p or 3r. The relatively low temperature (compared to by layer manner (Fig. S11, ESI†), which greatly facilitates
138 1C of 1g) of the phase transition peak should be just molecular slippage and collapse upon grinding, resulting in
responsible for the self-reversible MC property of compound 3. their MC feature. No p–p stackings but multiple intermolecular
Bright blue ML was observed for 3c when it was ground or interactions were found among adjacent molecules in these
scraped at room temperature by a spatula, as verified by the three single crystals due to the existence of oxygen atoms and
photo in Fig. 2b. However, no ML was found for the single the highly twisted TPE moiety. The intermolecular hydrogen
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Table 2 Summary of the intermolecular interactions in three single (1.787 and 1.849 Å) with the blue conformation one via their
crystals
carboxyl groups. There also existed two C–HÁ Á ÁO interactions
(
2.449 and 2.641 Å) and eight C–HÁÁÁp interactions (2.797–3.026 Å)
Crystal
1
for the grey conformation in crystal 1, while its blue conformation
had four C–HÁÁÁO interactions (2.449–2.645 Å) and six C–HÁÁÁp
interactions (2.878–3.026 Å) (Fig. 3b and Fig. S12a, ESI†). Isomer-
ization can induce different intermolecular interactions and
2
3
Grey
Blue
Grey
d/Å
Grey
d/Å
Blue
Conformation d/Å
d/Å
d/Å
10
a
d
O–H. . .O
1.787(1)
.849(1)
2.449(1)
.641(1)
1.787(1) 1.805(2)
1.849(1)
2.449(1) 2.576(2) 2.683(1) 2.683(1)
2.641(1) 2.615(2) 2.690(1) 2.690(1)
molecular packing in the solid state. In crystal 2c, besides two
strong hydrogen bonds (1.805 Å) between carboxyl groups, there
are also eight weak C–HÁÁÁO hydrogen bonds with distances
ranging from 2.576 Å to 3.187 Å (Fig. 3d). In particular,
1
b
[
Ph]C–H. . .O
2
2
.645(2) 2.946(2) 3.156(1) 2.760(2)
3
.187(2)
2.883(2) the distribution of intermolecular interactions in 2c was not
balanced: two of the four phenyl rings only had very weak
2.869(1) 2.869(1) C–HÁ Á Áp interactions ranging from 3.173 Å to 3.182 Å (Fig. S12b,
3
3
.107(2)
.156(1)
c
[
[
CH3]
C–H. . .O
Ph]C–H. . .p
b
2.797(2)
2.878(1) 3.173(2) 2.827(1) 2.827(1) ESI†). Due to the ineffective restriction of weak intermolecular
2
2
2
2
3
.878(1)
.894(1)
.920(2)
.975(1)
.026(1)
2.894(1) 3.182(2) 2.942(2) 2.958(1)
interactions, the intramolecular motions of these two phenyl
2.978(1) 3.027(1) rings would increase the non-radiative transitions to deactivate
2.922(2)
2.975(1)
3.026(1)
2.958(1) 2.978(1)
2.992(2) 3.110(2)
the excited state, in accordance with its lower fluorescence
3.027(1)
c
efficiency compared to compound 1c. Crystal 3c had the max-
imum number of intermolecular interactions among the three
[
CH3]C–H. . .p
3.104(2)
a
b
O–H of carboxyl group and O of another carboxyl group. C–H of
crystals, including four C–HÁ Á ÁO interactions (2.683–3.156 Å)
and eight C–HÁ Á Áp interactions (2.827–3.027 Å) for the grey
conformation (Fig. 3f and Fig. S12c, ESI†); and ten C–HÁ Á ÁO
interactions (2.683–3.156 Å) and eight C–HÁ Á Áp interactions
c
d
benzene ring. C–H of methyl group. The number of hydrogen
bonds. Bond length of C–HÁ Á Áp interaction is the distance between
hydrogen atom and the plane of the benzene ring.
(2.827–3.110 Å) for the blue conformation (Fig. 3g and Fig. S12c,
bonds shorter than 3.2 Å in these single crystals were analyzed ESI†). The above results showed that 3c possessed a higher
and are shown in Fig. S12 (ESI†) and listed in Table 2. As shown number of interactions but most of the interactions had longer
in Fig. 3a and Fig. S12a (ESI†), each molecule 1 with grey distances than those in 1c/2c, while molecules 1c/2c had much
conformation had two strong O–HÁ Á ÁO hydrogen bondings stronger intermolecular interactions than 3c. The relatively
Fig. 3 The intermolecular interactions of (a) grey and (b) blue conformations in 1c; (d) grey conformation in 2c; (f) grey and (g) blue conformations in 3c.
The detailed molecular packing modes in (c) 1c, (e) 2c and (h) 3c viewed along the b-axis.
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Table 3 Summary of single crystal information and ML property of 1c–3c
Intermolecular interactions
Strong
Three-dimensional hydrogen-bonded network
Packing density
Low (porous)
Schematic diagram
ML
1c
2c
3c
Intact
Inactive
Strong
Defective
Intact
High
Inactive
Active
Relatively weak
Moderate
weak intermolecular interactions in 3c favor conformation an intact three-dimensional hydrogen-bonded network and a
changes and the reconstruction of higher crystallinity 3r from moderate packing density, which should contribute to its ML
lower crystallinity 3p needed only a small amount of energy. activity. Unlike the source of energy, the resultant emission of ML
This resulted in its low cold crystallization temperature, easily and photoluminescence should coincide and the non-radiative
restoring its original state at room temperature, showing the relaxation channels of photoluminescence were also applicable to
self-reversible MC property.
ML. For porous 1c, plenty of space for intramolecular motions
dissipated the energy of the excited state during the crushing
process of crystals, causing the inactivation of ML. In 2c, the rows
of unsubstituted phenyl rings were vulnerable to mechanical
stimulations and easily became fractured while the rest stabilized
by strong intermolecular interactions still remained intact. The
dislocation or squeezing probably drew phenyl rings with weak
interactions closer to form new/strong interactions and thus
consumed the energy that would have otherwise excited the
ground state molecules, resulting in the inactivation of ML. Only
the moderate compact packing with intact three-dimensional
hydrogen-bonded network in crystal 3c could effectively reduce
energy loss under the aforementioned situations during the
fracturing process of the crystal so as to realize bright ML.
2.5. Structure–property relationship
Strong interaction is an important factor for the ML property;
however it cannot explain why only 3c exhibited the ML property,
therefore molecular packing modes should also be considered.
As revealed from the crystal structures, 1c–3c adopted a similar
packing mode viewed along the b-axis (Fig. 3c, e and h): the
benzoic acid or methyl benzoate groups were inclined to interact
with each other to form a row of substituted and a row of
unsubstituted phenyl rings alternately. In 1c, each pair of
benzoic acid substituents coalesced with two O–HÁ Á ÁO bonds
and other parts of TPE cores further connected with other
hydrogen bonds to form a three-dimensional porous structure
along the b-axis (Fig. 3c). In contrast, methyl benzoate group of 3
staggered due to the lack of hydrogen bonding, fulfilling the void
in between and forming compact stacking (Fig. 3h). Molecular
3
. Conclusion
stacking can be simply evaluated by the ratio of density (r ) to In conclusion, we deliberately synthesized a series of TPE
c
molecular weight (M ). Apparently, the packing density of 3c derivatives to explore the influence of intermolecular inter-
w
À3
À1
(
rc = 1.187 g cm , and Mw = 390.46 g mol ) was higher than action and molecular packing modes on their MC and ML
that of 1c (r = 1.061 g cm , and M
c w
= 376.43 g mol ). The performances. The results revealed that the carboxyl modified 1
À3
À1
multiple intermolecular interactions in 3c efficiently stabilized and 2 were MC-active, but ML-inactive, while the carboxyl ester
its intact three-dimensional hydrogen-bonded network (Fig. 3h modified compound 3 was self-reversible MC-active and ML-
and Fig. S12c, ESI†). Crystal 2c had the most compact stacking active. Single crystals of 1c–3c suggested that the porous
À3
À1
c w
(r = 1.208 g cm , and M
= 376.43 g mol ) among the three structure of 1c and defective hydrogen-bonded network of 2c
crystals; however, the distribution of intermolecular interactions inhibited their ML activity through dissipating the energy of the
in 2c was unbalanced. The rows of unsubstituted phenyl excited state; while 3c with both an intact three-dimensional
rings had very weak intermolecular interactions, causing the hydrogen-bonded network and moderate packing density can
formation of a defective three-dimensional hydrogen-bonded efficiently avoid non-radiative energy loss during the crushing
network (Fig. 3e and Fig. S12b, ESI†).
process of crystals, showing self-reversible MC and ML as well.
The characteristic information of the three single crystals is This work has provided a new view and offered solid proof for
summarized in Table 3 for better understanding the internal understanding MC and ML mechanisms, and can help to better
mechanism of ML. Due to the isomerization of the carboxyl design bright ML materials towards practical applications.
group, 1c and 2c displayed different characteristics. Crystal 1c
has an integral three-dimensional hydrogen-bonded network
accompanied with a porous structure (low packing density).
4
4
. Experimental section
.1. Reagents and materials
, 4-methoxycarbonylphenylboronic acid, 3-methoxy-
weaker intermolecular interactions than 1c/2c, it achieved both carbonylphenylboronic acid, bromotriphenylethylene and other
Molecules in 2c were stacked tightly but form a discontinuous
3 4
hydrogen-bonded network in one dimension. Although 3c had Pd(PPh )
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chemicals were all purchased from Energy Chemical Company. compact fluorescence lifetime spectrometer (C11367-11,
CO , KOH and solvents were all purchased from Xilong Hamamatsu, Japan). DSC measurements were carried out on
K
2
3
Chemical Co., Ltd. All the chemicals were used as received a NETZSCH DSC 200F3 instrument at a heating rate and a
À1
without further purification. Compounds 1 and 3 were prepared cooling rate of 10 1C min in nitrogen. TGA analysis was
1
1
according to a previous paper.
performed on a NETZSCH SA409PC thermogravimeter. Powder
X-ray diffraction (PXRD) patterns were obtained in the reflec-
tion mode at room temperature using a 2.2 kW Empyrean X-ray
4.2. Synthesis
Synthesis of compound 4. Bromotriphenylethylene (1.111 g, Diffraction System (PANalytical, Netherland). The ML spectra
3
5
.3 mmol), 3-(methoxycarbonyl)phenyl boronic acid (900 mg, were collected using a spectrometer of Acton SP2750 with a
.0 mmol), and Pd(PPh ) (70 mg, 61 mmol) were placed in a liquid-nitrogen-cooled CCD (SPEC-10, Princeton) as a power
3 4
Schlenk flask and the flask was evacuated and recharged with detector (data-collection time is 1s and the diameter of optical
N gas. 35 mL of THF and 5 mL of K CO aqueous solution fiber is 600 mm). The theoretical ground-state geometry and
2
2
3
À1
(
3.0 mol L ) were degassed for 30 min and then added. The electronic structure of the molecule were optimized using the
resulting mixture was refluxed for 18 h. After cooling to room density functional theory (DFT) with B3LYP hybrid functional
temperature, the reaction mixture was diluted with CH Cl at the basis set level of 6-31+G(d). All the theoretical calcula-
washed with water and brine, dried over Na SO , filtered, and tions were performed using the Gaussian 03 package.
2
2
,
1
2
2
4
evaporated. The resulting residue was purified by chromato-
graphy on a silica gel column (dichloromethane/petroleum
4.4. Crystal structural analysis
ether, v/v, 1/3), affording compound 4 (1.10 g, 85.6%) as a faint Single crystals of 1 and 2 were obtained by slow evaporation of
1
yellow solid. M.p. 156–158 1C; H NMR (500 MHz, CDCl3): their CH Cl /hexane solutions at room temperature. Single
2
2
d = 7.77 (dt, J = 7.8, 1.5 Hz, 1H), 7.71 (t, J = 1.5 Hz, 1H), 7.23 crystals of 3 were obtained by slow evaporation of its acetone/
(
(
(
1
1
dt, J = 7.8, 1.5 Hz, 1H), 7.16 (t, J = 8.0 Hz, 1H), 7.12–7.08 H O solution at room temperature. The single-crystal structure
2
1
3
m, 9H), 7.05–7.00 (m, 6H), 3.81 (s, 3H) ppm; C NMR was measured using a Bruker D8 Venture X-ray diffraction system
125 MHz, CDCl ): d = 167.2, 144.3, 143.5, 143.3, 143.2, 142.1, equipped with a CCD detector using graphite-monochromated Cu
40.0, 136.0, 132.5, 131.4, 131.4, 131.4, 129.9, 128.0, 127.9, Ka radiation. All calculations were performed using SHELXL97
27.9, 127.8, 127.8, 126.8, 126.8, 126.8, 52.1 ppm; HRMS and crystal structure crystallographic software packages. Crystallo-
3
+
(
ESI): m/z calcd for C H NaO : 413.1517 [M + Na] , found: graphic data for the structures reported in this paper have been
2
8
22
2
4
13.1514; element analysis calcd (%) for C H O : C, 86.13; deposited with the Cambridge Crystallographic Data Centre as
2
8
22 2
H, 5.68; found: C, 85.68; H, 5.79.
supplementary publication no. CCDC: 1904514 for 3, 1904515 for
Synthesis of compound 2. To a solution of compound 4 1 and 1904516 for 2.†
(1.20 g, 3.08 mmol) in a mixture of 20 mL of THF and 20 mL of
2
H O was added KOH (3.00 g, 53.6 mmol). The resulting solution
was refluxed for 1 d. After cooling to room temperature, the pH
value of the mixture was adjusted to 1.0 by 1 M HCl solution,
Conflicts of interest
The authors declare no conflict of interest.
then the reaction mixture was filtered to afford compound 2
1
(
(
1
1
(
1.12 g, 97.0%) as an off-white solid. M.p. 265–267 1C; H NMR
6
500 MHz, d -DMSO): d = 12.85 (br, 1H), 7.67 (dt, J = 7.5, 1.5 Hz, Acknowledgements
H), 7.56 (s, 1H), 7.24 (t, J = 8.0 Hz, 1H), 7.20 (dt, J = 7.8, 1.5 Hz,
1
3
This work was supported by the National Natural Science
Foundation of China (21574085) and the National Natural
Science Foundation of Guangdong Province (2016A030312002
and 2017A030313067).
H), 7.17–7.09 (m, 9H), 7.00–6.97 (m, 6H) ppm; C NMR
6
100 MHz, d -DMSO): d = 167.0, 143.5, 142.9, 142.8, 142.7,
1
1
41.4, 139.6, 135.0, 131.4, 130.7, 130.6, 130.6, 130.4, 128.1,
28.0, 127.9, 127.8, 127.5, 126.7, 126.7 ppm; HRMS (ESI): m/z
+
calcd for C H NaO : 399.1361 [M + Na] , found: 399.1360;
2
7
20
2
element analysis calcd (%) for C H O : C, 86.14; H, 5.36;
found: C, 85.97; H, 5.45.
2
7
20 2
References
1
(a) S.-J. Yoon, J. W. Chung, J. Gierschner, K. S. Kim,
M.-G. Choi, D. Kim and S. Y. Park, J. Am. Chem. Soc., 2010,
132, 13675–13683; (b) S. M. Jeong, S. Song, K.-I. Joo, J. Kim,
S.-H. Hwang, J. Jeong and H. Kim, Energy Environ. Sci., 2014,
7, 3338–3346; (c) H. Sun, S. Liu, W. Lin, K. Y. Zhang, W. Lv,
X. Huang, F. Huo, H. Yang, G. Jenkins, Q. Zhao and
W. Huang, Nat. Commun., 2014, 5, 3601; (d) X. Wang,
H. Zhang, R. Yu, L. Dong, D. Peng, A. Zhang, Y. Zhang,
H. Liu, C. Pan and Z. L. Wang, Adv. Mater., 2015, 27,
2324–2331; (e) H. Zhang, F. Gao, X. Cao, Y. Li, Y. Xu,
W. Weng and R. Boulatov, Angew. Chem., Int. Ed., 2016,
4
1
.3. Characterization
13
H and C NMR spectra were recorded on a VNMRS 400 NMR
spectrometer (Varian, USA). High resolution mass spectroscopy
(HR-MS) was performed using an Autoflex III mass spectro-
meter (MALDI-TOF-MS, Bruker, Germany). Element analysis
was performed using a vario EL cube elemental analyzer
(Elementar, Germany). UV-Vis spectra were recorded using a
UV-2600 spectrometer (Shimadzu, Japan). Absolute quantum
efficiency was measured on an integrating sphere (C11347-11,
Hamamatsu, Japan). Fluorescence lifetime was measured on a
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View Article Online
Paper
Journal of Materials Chemistry C
5
5, 3040–3044; ( f ) Y. Sagara, S. Yamane, M. Mitani,
T. Jiang, Q. Dang, Y. Li, Q. Li and Z. Li, Angew. Chem., Int. Ed.,
2018, 57, 16821–16826; (i) J. Yang, J. Qin, P. Geng, J. Wang,
M. Fang and Z. Li, Angew. Chem., Int. Ed., 2018, 57, 14174–14178;
( j) Q. Sun, L. Tang, Z. Zhang, K. Zhang, Z. Xie, Z. Chi, H. Zhang
and W. Yang, Chem. Commun., 2018, 54, 94–97; (k) Q. Sun,
K. Zhang, Z. Zhang, L. Tang, Z. Xie, Z. Chi, S. Xue, H. Zhang and
W. Yang, Chem. Commun., 2018, 54, 8206–8209; (l) K. Zhang,
Q. Sun, Z. Zhang, L. Tang, Z. Xie, Z. Chi, S. Xue, H. Zhang and
W. Yang, Chem. Commun., 2018, 54, 5225–5228; (m) J.-A. Li,
J. Zhou, Z. Mao, Z. Xie, Z. Yang, B. Xu, C. Liu, X. Chen, D. Ren,
H. Pan, G. Shi, Y. Zhang and Z. Chi, Angew. Chem., Int. Ed., 2018,
57, 6449–6453; (n) Z. Xie, T. Yu, J. Chen, E. Ubba, L. Wang,
Z. Mao, T. Su, Y. Zhang, M. P. Aldred and Z. Chi, Chem. Sci.,
2018, 9, 5787–5794; (o) K. Zhang, Q. Sun, L. Tang, Y. Wang,
X. Fan, L. Liu, S. Xue and W. Yang, J. Mater. Chem. C, 2018, 6,
8733–8737; (p) Q. Huang, X. Mei, Z. Xie, D. Wu, S. Yang,
W. Gong, Z. Chi, Z. Lin and Q. Ling, J. Mater. Chem. C, 2019,
7, 2530–2534.
C. Weder and T. Kato, Adv. Mater., 2016, 28, 1073–1095;
(
g) Z. Qiu, W. Zhao, M. Cao, Y. Wang, J. W. Y. Lam, Z. Zhang,
X. Chen and B. Z. Tang, Adv. Mater., 2018, 30, 1803924;
h) W. Li, Q. Huang, Z. Mao, Q. Li, L. Jiang, Z. Xie, R. Xu,
(
Z. Yang, J. Zhao, T. Yu, Y. Zhang, M. P. Aldred and Z. Chi,
Angew. Chem., Int. Ed., 2018, 57, 12727–12732.
(a) P. S. Hariharan, N. S. Venkataramanan, D. Moon and
S. P. Anthony, J. Phys. Chem. C, 2015, 119, 9460–9469;
2
(b) F. Zhao, C. Fan, Z. Chen, G. Liu and S. Pu, RSC Adv.,
2
017, 7, 43845–43848; (c) Z. Chen, G. Liu, R. Wang and S. Pu,
RSC Adv., 2017, 7, 15112–15115; (d) P. S. Hariharan,
V. K. Prasad, S. Nandi, A. Anoop, D. Moon and S. P. Anthony,
Cryst. Growth Des., 2017, 17, 146–155; (e) T. Butler, A. S. Mathew,
M. Sabat and C. L. Fraser, ACS Appl. Mater. Interfaces, 2017, 9,
1
7603–17612; ( f ) K. K. Kartha, V. S. Nair, V. K. Praveen,
M. Takeuchi and A. Ajayaghosh, J. Mater. Chem. C, 2019, 7,
292–1297.
1
3
4
Y. Xie and Z. Li, Chem, 2018, 4, 943–971.
8 (a) Y.-B. Gong, P. Zhang, Y.-R. Gu, J.-Q. Wang, M.-M. Han,
C. Chen, X.-J. Zhan, Z.-L. Xie, B. Zou, Q. Peng, Z.-G. Chi and
Z. Li, Adv. Opt. Mater., 2018, 6, 1800198; (b) Y. Yu, C. Wang,
Y. Wei, Y. Fan, J. Yang, J. Wang, M. Han, Q. Li and Z. Li, Adv.
Opt. Mater., 2019, 0, 1900505.
(a) J. Zhao, Z. Chi, Y. Zhang, Z. Mao, Z. Yang, E. Ubba and
Z. Chi, J. Mater. Chem. C, 2018, 6, 6327–6353; (b) Z. Yang,
Z. Chi, Z. Mao, Y. Zhang, S. Liu, J. Zhao, M. P. Aldred and
Z. Chi, Mater. Chem. Front., 2018, 2, 861–890; (c) J. Zhao,
Z. Chi, Z. Yang, Z. Mao, Y. Zhang, E. Ubba and Z. Chi, Mater.
Chem. Front., 2018, 2, 1595–1608.
C. Wang and Z. Li, Mater. Chem. Front., 2017, 1, 2174–2194.
(a) L. M. Sweeting, A. L. Rheingold, J. M. Gingerich,
A. W. Rutter, R. A. Spence, C. D. Cox and T. J. Kim, Chem.
Mater., 1997, 9, 1103–1115; (b) H. Nakayama, J.-i. Nishida,
N. Takada, H. Sato and Y. Yamashita, Chem. Mater., 2012,
9 (a) H. Yuan, K. Wang, K. Yang, B. Liu and B. Zou, J. Phys.
Chem. Lett., 2014, 5, 2968–2973; (b) B. Xu, J. He, Y. Mu,
Q. Zhu, S. Wu, Y. Wang, Y. Zhang, C. Jin, C. Lo, Z. Chi,
A. Lien, S. Liu and J. Xu, Chem. Sci., 2015, 6, 3236–3241;
(c) B. Xu, W. Li, J. He, S. Wu, Q. Zhu, Z. Yang, Y.-C. Wu,
Y. Zhang, C. Jin, P.-Y. Lu, Z. Chi, S. Liu, J. Xu and
M. R. Bryce, Chem. Sci., 2016, 7, 5307–5312; (d) C. Wang,
B. Xu, M. Li, Z. Chi, Y. Xie, Q. Li and Z. Li, Mater. Horiz.,
2016, 3, 220–225; (e) Y. Xie, J. Tu, T. Zhang, J. Wang, Z. Xie,
Z. Chi, Q. Peng and Z. Li, Chem. Commun., 2017, 53,
11330–11333; ( f ) F. Liu, J. Tu, X. Wang, J. Wang, Y. Gong,
M. Han, X. Dang, Q. Liao, Q. Peng, Q. Li and Z. Li, Chem.
Commun., 2018, 54, 5598–5601; (g) N. Li, Y. Gu, Y. Chen,
L. Zhang, Q. Zeng, T. Geng, L. Wu, L. Jiang, G. Xiao, K. Wang
and B. Zou, J. Phys. Chem. C, 2019, 123, 6763–6767.
5
6
24, 671–676; (c) P. Jha and B. P. Chandra, Luminescence,
2014, 29, 977–993.
7
(a) S. Xu, T. Liu, Y. Mu, Y.-F. Wang, Z. Chi, C.-C. Lo, S. Liu,
Y. Zhang, A. Lien and J. Xu, Angew. Chem., Int. Ed., 2015, 54,
8
74–878; (b) J. Yang, X. Gao, Z. Xie, Y. Gong, M. Fang,
Q. Peng, Z. Chi and Z. Li, Angew. Chem., Int. Ed., 2017, 56,
5299–15303; (c) K. K. Neena, P. Sudhakar, K. Dipak and
P. Thilagar, Chem. Commun., 2017, 53, 3641–3644;
1
(d) J. Yang, Z. Ren, Z. Xie, Y. Liu, C. Wang, Y. Xie, 10 H. Jiang, P. Hu, J. Ye, A. Chaturvedi, K. K. Zhang, Y. Li,
Q. Peng, B. Xu, W. Tian, F. Zhang, Z. Chi, Q. Li and Z. Li,
Angew. Chem., Int. Ed., 2017, 56, 880–884; (e) M. Fang,
Y. Long, D. Fichou, C. Kloc and W. Hu, Angew. Chem., Int.
Ed., 2018, 57, 8875–8880.
J. Yang, Q. Liao, Y. Gong, Z. Xie, Z. Chi, Q. Peng, Q. Li 11 H. Zhou, Q. Ye, X. Wu, J. Song, C. M. Cho, Y. Zong,
and Z. Li, J. Mater. Chem. C, 2017, 5, 9879–9885; ( f ) J. Guo,
X.-L. Li, H. Nie, W. Luo, S. Gan, S. Hu, R. Hu, A. Qin, Z. Zhao,
B. Z. Tang, T. S. A. Hor, E. K. L. Yeow and J. Xu, J. Mater.
Chem. C, 2015, 3, 11874–11880.
S.-J. Su and B. Z. Tang, Adv. Funct. Mater., 2017, 27, 1606458; 12 M. J. Frisch, G. Trucks, H. Schlegel, G. Scuseria, M. Robb,
(
g) C. Arivazhagan, A. Maity, K. Bakthavachalam, A. Jana, S. K.
Panigrahi, E. Suresh, A. Das and S. Ghosh, Chem. – Eur. J., 2017,
3, 7046–7051; (h) J. Wang, C. Wang, Y. Gong, Q. Liao, M. Han,
J. Cheeseman, G. Scalmani, V. Barone, B. Mennucci and
G. Petersson, Gaussian 09, Revision D. 01, Gaussian, Inc.,
Wallingford, CT, 2009.
2
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