Aggregation-induced ratiometric emission and mechanochromic luminescence in a pyrene-benzohydrazonate conjugate

Article abstract of DOI:10.1039/c8nj01379a

Luminogenic materials with aggregation-induced emission (AIE) have recently aroused great attention due to their potential application in many fields. However, aggregation induced ratiometric luminescence in addition to emission turn-on has been scarcely studied. Here, a structure tunable pyrene benzohydrazonate-based molecular platform exhibits a drastic aggregation-induced color change (Δλ_em,max ～ 130 nm) and a high solid-state quantum yield (QY_max ～ 54.5%). The exciting switch behaviour is triggered by intermolecular hydrogen-bonding through the carbohydrozone bridge, which leads to fixation of the molecular conformations. In addition, by virtue of the multiple excimer state of the pyrenyl unit, a broad range of carbohydrozone-based materials with high contrast mechanochromic luminescence have been developed. These systems represent stimuli-responsive optoelectronic switching devices leading toward multistate dynamic molecular systems in both solution and the solid state.

Full text of DOI:10.1039/c8nj01379a

View Article Online
View Journal
NJC
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: D. Wu, Y. Li, J.
Yong, S. Huang, Y. Li, Y. Liu and W. Huang, New J. Chem., 2018, DOI: 10.1039/C8NJ01379A.
This is an Accepted Manuscript, which has been through the
Volume 40 Number
1 January 2016 Pages 1–846
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
Accepted Manuscripts are published online shortly after
New Journal of Chemistry
www.rsc.org/njc
A journal for new directions in chemistry
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

Please do not adjust margins
New Journal of Chemistry
Page 1 of 5
View Article Online
DOI: 10.1039/C8NJ01379A
Aggregation-induced ratiometric emission and mechanochromic
luminescence in pyrene-benzohydrazonate conjugate
Received 00th January 20xx,
Accepted 00th January 20xx
Yao Li, Wei Huang, Juan Yong, Shuaidan Huang, Yujie Li, Yang Liu and Dayu Wu*
DOI: 10.1039/x0xx00000x
www.rsc.org/
intramolecular motion. The intramolecular rotation can be blocked
when aggregation state of these molecules forms, giving rise to
strong emission. A well-known AIE fluorogen is tetraphenylethene
(TPE), in which the restriction of intramolecular motion (RIM) of its
multiple phenyl rotors against its ethylene stator has been
proposed to account for its strong fluorescence in the aggregation
state.3,4 It was also recognized that formation of hydrogen bonds
between luminogens can rigidify their molecular structures,5-10
which helps reduce the nonradiative decay of their excitons and
maximize the probability of radiative transitions. To our best
knowledge, most of the AIE systems have been identified on the
basis of intensity turn-on at a specific wavelength, however, AIE
sensors with fluorescence colour change are desirable, as they
endow a dimension with the discriminative power and allow
visualization by naked-eye.11
Luminogenic materials with aggregation-induced emission (AIE)
have recently aroused great attention due to the potential
application in many fields. However, the aggregation induced
ratiometric luminescence in addition to emission turn-on has been
scarcely studied. Here,
a
structure tunable pyrene
benzohydrazonate-based molecule platform exhibits drastic
aggregation-induced color change (Δλem,max ~ 130 nm) and high
solid-state quantum yield (Q.Ymax ~ 54.5%). The exciting switch
behaviour is triggered by intermolecular hydrogen-bonding
through the carbohydrozone bridge giving rise to fixation of the
molecular conformations. In addition, by virture of multiple
excimer state of pyrenyl unit, a broad range of carbohydrozone-
based materials with high contrast mechanochromic luminescence
have been developed. These systems represent stimuli-responsive
optoelectronic switching devices leading toward multistate
dynamic molecular systems in both solution and solid.
(c)
(a)
O
N
N
The development of efficient organic luminogenic materials in
the solid and aggregate states are crucial for the potential
application in the field of advanced OLED and biosensor.1
Traditional investigations on luminescence have been generally
performed in the diluted state, where the emitting molecule can be
approximately treated as isolated one without being perturbed by
intermolecular interaction.2 The studies of dilution solution could
provide the fundamental information on luminescence processes at
molecular level. The conclusion for concentrated solution can not
be simply duplicated from the diluted solution, which frequently
exhibit the different emitting behaviour. The emission of a
luminophore is typically weakened when molecules are aggregated
due to energy transfer and the formation of excimers and
exciplexes, namely aggregation-caused quenching (ACQ). Recently,
a reversal phenomenon called aggregation-induced emission (AIE)
has been put forward. In this case, the isolated fluorogens show the
Ph-Ph
H
O
N
R= -H (1)
-Cl (2)
N
H
-OMe (3)
R
R1
R1
R1
N
N
N
N
N
N
H
H
H
O
O
O
R2
R2
R2
Fig. 1. (a) The chemical structure of model complex ph-ph and pyrene-containing
benzohydrazonate derivatives . (b) Proposed 1-D hydrogen bonding chain of
the carbohydrozone unit. (c) Mercury representation of hydrogen bonding
structure along the crystallographic a axis in model complex ph-ph from X-ray
diffraction data.
1-3
In the previous studies, we and other groups have developed
carbohydrozone derivatives for metal coordination and sensing
platform in which the proton attached on the imine N atom is
released upon metal coordination or acid-base neutralization giving
rise to more π-conjugation system.12-15 To further test the active
hydrogen hypothesis, the model complex ph-ph was synthesized,
Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology,
Collaborative Innovation Center of Advanced Catalysis & Green Manufacturing,
School of Petrochemical Engineering, Changzhou University, Changzhou, Jiangsu
213164, China. E-mail: wudy@cczu.edu.cn
†Electronic supplementary informaꢀon (ESI) available: Synthesis details, additional
spectroscopic data CV plot and etc. CCDC 1826737 contains the crystallographic
data.
negligible emission due to the nonradiative decay through
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 2 of 5
View Article Online
DOI: 10.1039/C8NJ01379A
COMMUNICATION
Journal Name
Fig. 2 (A) PL spectra of
H2O. (B) Cyclic voltammograms of
0.05 mol L-1 of tetrabutylammonium hexafluorophosphate (TBAPF6) (C) PL
spectra of in DMF/H2O mixtures with different volume fractions of H2O. Inset:
Emission color change from blue to yellow in aqueous DMF with fw = 0 - 90%
2
in DMF/H2O mixtures with different volume fractions of
2
in DMF and aqueous DMF (20%) containing
3
Fig. 3 (A) Plots of relative PL intensity (I/I0) and (B) change of emission maximum
3 =
. Concentration = 10−5 M, λex = 365 nm, I0
(
intensity at fs = 0%.
ꢀλ) versus solvent fraction (fs) of
under 365 nm UV light. (D) Plots of normalized PL intensity of
different emission wavelengths. λex = 365 nm, C = 10 μM.
3 versus fw at
peak collapsed in the emission spectra and a new peak obtained
its intensity at ca. 550 nm for compound 2 (Fig. 2A). The ratiometric
fluorochromism could be readily detected by the naked-eye from
blue to yellow (inset in Fig 2A). The CV as well as DPV
measurements of all the compounds were also carried out in dry
DMF and wet DMF (fw. 20%) solutions, respectively (Fig. S5-S7,
ESI).23 The electrochemical behavior of 2 as representative was
plotted by cyclic voltammetry (CV) under a N2 atmosphere (Fig. 2B).
The quasireversible potentials (E = (Epox+ Epred)/2) are −500 mV
versus Ag+/Ag for complex 2, which are attributed to the one-
electron reduction of a carbohydrozone group. However, the redox
process was switched off in a wet DMF solution with fw of 20%,
which reflect the difference in conductivity in the presence of bulk
water.
Likewise, the transition from fluid phase to aggregation state
occurs at the water fraction of ca. 80% for compound 3.(Fig. 2C).
Upon further increasing water fraction, the new emission with
larger stokes shift develops and finally obtain its 5-fold
enhancement in emission intensity compared to the molecularly
dispersed state (Fig. 2D), demonstrating that the longer-wavelength
emission is an AIE phenomenon. The ratiometric AIE is uncommon
in that the large emission maximum shift (above 100 nm) was due
to the formation of hydrogen-bonding aggregate state.
The PL analysis of all molecules indicated that their photophysical
properties behave in the similar manner, and the longer-
wavelength emission showed unusual AIE effect. The shorter-
wavelength emission at ca. 440 nm increased as the humidity in
DMF aqueous media rose and then decreased upon forming
aggregate. The similar phenomenon has been recently observed in
some simple molecules with nonconjugation structure, which is
ascribed to intramolecular through-space conjugation between the
“isolated” phenyl rings.24 In this case, the shift of emission
maximum should be associated with the solvent polarity. To further
check this point, the PL spectra of 3 as representative in the
presence of other nonsolvent with relatively weak polarity, such as
CH3OH, CH2Cl2 and CH3CN, were measured and compared (Fig. S8,
ESI). Fig. 3A and 3B showed the relationship between the relative
and its crystal structure was determined.(For details, see Table S1,
ESI) X-ray diffraction analysis revealed that the trans-NH proton in
ph-ph would be accessible for intermolecular hydrogen bonding
(Fig. S2, ESI). Fig. 1c shows that, indeed, this type of complex adopts
the anticipated trans conformation and consequently forms
hydrogen-bonded chains in the crystalline state. The hydrogen
bonding parameters is as following: d(N···O)=2.854(3) Å;
d(H···O)=1.875Å; <NH···O=169.2o. The C-N and N-N bond distances
of being 1.350(2) Å and 1.389(2) Å, respectively, fall within the
intermediate one between the normal single and double bond
within carbohydrozone block, which is indicative of the conjugate
structure along the carbohydrozone bridge. The feasible
modulation of self-assembled hydrogen bonding structure from
benzohydrazonate inspired us to creat a molecule with simple
structure but controllable assembly property to show a novel mode
of AIE luminescence.16-21 Here, our effective strategy is to introduce
a multiple excimer state of pyrene into benzohydrazonate platform.
The multistable emitting states can be manipulated in the manner
of aggregation-induced ratiometric luminescence and high-contrast
mechanochromism, which distinguished from traditional turn-on
mode in the AIE systems.22
Compounds 1-3 were prepared in the similar manner to that of
ph-ph through using pyrene-1-carbaldehyde instead of
benzaldehyde. (for details, see ESI). They have the poor solubility in
most of organic solvents and water but is completely soluble in
polar solvents, such as DMF and DMSO. The strongest absorption
was located at ca. 370 nm (λmax) in solution with shoulder peaks at
380 nm and 400 nm (Fig. S3, ESI) Upon increasing amount of water
in DMF solution, the absorption didn’t significantly change until the
water fraction (fw) reaches ca 90% for 1 and 80% for 2 and 3, at
which they began to aggregate. All the compounds display a distinct
and well-known fluorescent spectra of pyrene moieties centered at
ca. 410 nm in DMF solution, which can be attributed to the
monomeric emission of pyrenyl group. The monomeric emission
exhibits small red shift under the low water fraction (fw). When the
water fraction went higher, it is interesting to observe the original
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 3 of 5
View Article Online
DOI: 10.1039/C8NJ01379A
Journal Name
COMMUNICATION
emission intensity (I/I0) and change of emission maximum (Δλ) and
the nonsolvent fraction. Upon increasing the water fraction (fw) in
DMF/water mixture from 0 to 98 %, the FL intensity increased 8.9
times accompanying with an Δλ value to 130 nm. Under the same fs
(solvent fraction) change, neither I/I0 nor Δλ showed the noticeable
change.
To confirm the formation of luminogen aggregated in DMF/water
mixtures, dynamic light scattering (DLS) measurement of 2 was
conducted. According to the DLS results as shown in Fig. 4, the
average diameters of the particles are about 955 nm with 90%
water content in DMF/H2O mixture. It was suggested that the
aggregation driven growth is one of the reasons for the ratiometric
AIE. We thus used the scanning electron microscope (SEM) to
examine the morphological structure of the white precipitates. As
can be seen from Figure 4(b), the precipitates are one-dimensional
microsticks with diameters down to a few hundred nanometers and
lengths up to several micrometers.
Fig. 5 Partial 1H NMR titration with D2O in DMSO-d6.
(a)
35
It is well known the luminescence from an organic emitter can be
modulated in solid through substituent effect.25 Since the molecule
of benzohydrazonate terminal can be easily modified with the
different substituents, the resulting fluorescent is expected to be
chromically tunable. Compounds 1-3 are strongly emissive under
UV light in the solid state (Fig. S10, ESI). Upon excitation at 365 nm,
compound 1 shows the strongest emission band with the peak
maximum at 502 nm and quantum yield of 54.5% (Table S1).
Although the monomer emission position is insensitive to the
substituent effect, the compounds 2 and 3 show the obvious blue-
shift relative to 1. Furthermore, the absolute luminescence
quantum yield of 1 (54.5%) is significantly high relative to the values
observed for the others (3.79 – 4.81%), indicative of the substituent
effect on the solid emitting.
30
dm = 955 nm
25
20
15
10
5
0
0
1000
2000
3000
4000
5000
6000
7000
Size / nm
(b)
The strong solid-state emission and the possibility of multiple
excimer-like emission behavior of pyrenyl unit encouraged us to
study the mechanochromic properties.26-31 The emission spectra of
pyrenyl-benzohydrazonate 2–3 pristine and ground solid are
studied and shown in Fig. 6 together with the spectra in diluted
solution in the manner of multistable emtting state(For 1, see
Fig.S11, ESI). The pristine solid compound 2 and 3 shows 54 nm and
42 nm red-shift compared to the spectra of monomer state.
Furthermore, upon grinding using a mortar and a pestle, the blue-
emitting pristine solids were converted to yellowish green emitting
solids and the emission peaks exhibit varying degree of red-shift,
i.e., 16, 64 and 80 nm for 1, 2 and 3, respectively. Such the
remarkable multistable luminochromism may be associated with
the different excimer-like states, excimer 1 (E1) and excimer 2 (E2),
for pyrenyl-base compounds. Furthermore, the emission of excimer
2 could be converted to excimer 1 after heating treatment at
approximately 120 oC for several minutes. Beside the emission
response to the force and heat stimuli, all compounds also
displayed a response to solvent vapor. After exposure to the
dichloromethane vapor, the yellowish-green emission could be
recovered to the initial emission of the pristine sample, and the
reversible switching between emission of the two different states
could be repeated after many cycles.
Fig. 4. (a) Dynamic light scattering (DLS) results showing the particle size diameter at fw
= 90% and (b) SEM image showing size of aggregates.
In order to disclose whether the potential structure change occurs
in the presence of water, compound
3 was chosen as
1
representative and H NMR spectra was monitored through D2O
1
titration experiment. From the H NMR titration spectroscopy data
in Fig. 5, the resonance at 11.95 ppm continued to become weak
upon increasing the water fraction to 20%, suggesting that proton
on imine site is active toward the potential proton exchange and/or
intermolecular hydrogen bonding. The presence of water also
causes significant upfield shifts of the Ha signals and downfield
shifts of hydrogen atom on the phenyl ring, indicative of the tiny
change of the conjugation in the presence of bulk water.
In order to establish the origin and mechanism of the reversible
piezochromic behavior, the UV−vis spectra in the solid state of the
pristine and ground state of the selected complexes were obtained.
The results show complete consistency of the absorption bands for
all of the complexes (Fig. S12, ESI). The significant change in
emission spectra upon grinding are, therefore, not attributed to the
structure change. Powder XRD was carried out to investigate the
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 4 of 5
View Article Online
DOI: 10.1039/C8NJ01379A
COMMUNICATION
Journal Name
possible phase transformation. The sharp peaks in the XRD pattern
(Fig. S13, ESI) unambiguously indicate that the pristine sample has a
well-ordered crystalline structure. The ground sample exhibits
identical diffraction signals, which indicates that the grinding cannot
form the amorphous phase. Because the crystalline phase is
unresponsive to mechanical grinding, the distinct luminescence
response to force implies that the solid packing involving π···π and
N-H···O intermolecular interactions are strong enough for
stabilization of crystalline phase under mechanical grinding. Such a
red shift frequently arises from the conformational planarization
induced by the high pressure.33
media to strengthen the π-conjugation structure. The weak
emission in DMF solution is stemmed from the pyreny
monomer. The strong emission in the presence of water was
dominantly attributed to the formation of the intermolecular
H-bonding system, thus preventing the rotation of
carbohydrozone groups. The excimer structure showed slight
disorder upon mechanical grinding, which could be restored by
fuming or heating. As an important application, the
spectroscopic properties and luminescence color change in the
solid state were reversible upon grinding and fuming or
heating. We believe that these studies can arrive in a deeper
insight into the atypical AIE mechanism and develop rewritable
media, pressure sensors and security inks in the future.
This work was supported by NSFC programs (Grants 21471023
& 21671027). We are thankful for financial support by the
PAPD of Jiangsu Higher Education Institutions.
Notes and references
1
2
3
M. Schwoerer and H. C. Wolf, Organic Molecular Solids,
Wiley-VCH, Weinheim, Germany, 2007.
S. Srinivasan, P. A. Babu, S. Mahesh and A. Ajayaghosh, J. Am.
Chem. Soc., 2009, 131, 15122.
J. Luo, Z. Xie, J. W. Y. Lam, L. Cheng, H. Chen, C. Qiu, H. S.
Kwok, X. Zhan, Y. Liu, D. Zhu and B. Z. Tang, Chem. Commun.,
2001, 1740.
4
5
6
7
8
9
B. Z. Tang, X. Zhan, G. Yu, P. P. S. Lee, Y. Liu and D. Zhu, J.
Mater. Chem., 2001, 11, 2974.
Yuning Hong, Jacky W. Y. Lam and B. Z. Tang. Chem. Soc.
Rev., 2011, 40, 5361.
W. X. Tang, Y. Xiang and A. J. Tong, J. Org. Chem., 2009, 74
2163.
,
Y. Qian, S. Y. Li, G. Q. Zhang, Q. Wang, S. Q. Wang, H. J. Xu, C.
Z. Li, Y. Li and G. Q. Yang, J. Phys. Chem. B, 2007, 111, 5861.
T. Mutai, H. Tomoda, T. Ohkawa, Y. Yabe and K. Araki,
Angew. Chem., Int. Ed., 2008, 47, 9522.
S. Y. Ryu, S. Kim, J. Seo, Y. W. Kim, O. H. Kwon, D. J. Jang and
S. Y. Park, Chem. Commun., 2004, 70.
10 R. T. K. Kwok, C.W. T. Leung, J. W. Y. Lam and B. Z. Tang.
Chem. Soc. Rev., 2015, 44, 4228.
11 Q. Chai, J. Wei, B. Bai, H. Wang and M. Li, Dyes and Pigments,
2018, 152, 93.
12 W. Huang, F.-X. Shen, S.-Q. Wu, L. Liu, D. Wu, Z. Zheng, J. Xu,
M. Zhang, X.-C. Huang, J. Jiang, F. Pan, Y. Li, K. Zhu, and O.
Sato. Inorg. Chem. 2016, 55, 5476.
Fig. 6 Multistate emission spectra of compound 2 and 3 in diluted solution, pristine,
ground and annealed solids and the photographs taken under 365 nm UV illumination.
13 D. Wu, X. Zhang, P. Huang, W. Huang, M. Ruan and Z. W.
Ouyang. Inorg. Chem. 2013, 52, 10976.
14 D. Wu, O. Sato, Y. Einaga and C.-Y. Duan. Angew. Chem. Int.
Ed. 2009, 48, 1475.
15 D. Wu, W. Huang, C. Duan, Z. Lin and Q. Meng. Inorg. Chem.
2007, 46 , 1538.
Fourier transform infrared spectroscopy (FTIR) measurement
was implemented under vacuum to further confirm H-bonding
self-assembled structures at molecular level. For the pristine
solid, the broad vibrational bands were observed at around
3200 and 3000 cm–1 (Fig. S14, ESI), the former of which can be
assigned to the NH stretching vibration, remarkably lower than 16 Z. Chi, X. Zhang, B. Xu, X. Zhou, C. Ma, Y. Zhang, S. Liu and J.
that of the free N–H group (ca. 3400 cm-1), whereas the latter
Xu, Chem. Soc. Rev., 2012, 41, 3878.
17 J. Wang, J. Mei, R. Hu, J. Z. Sun, A. Qin and B. Z. Tang, J. Am.
Chem. Soc., 2012, 134, 9956.
18 M. Irie, T. Fukaminato, T. Sasaki, N. Tamai and T. Kawai,
Nature, 2002, 420, 759.
is characteristic of an NH deformation vibration of
carbohydrozone units.34 This is in accord with a previous
report on strong H-bonded urea units.35 Upon a certain
pressure, the vibration cannot show obvious change and the
resultant H-bonded arrays are less disordered.
19 M. Teng, X. Jia, X. Chen, Z. Ma and Y. Wei. Chem. Commun.,
2011, 47, 6078.
To conclude, a pyrenyl-benzohydrazonate molecular platform
was prepared and photophysical properties were investigated,
which showed unusual ratiometric aggregation-induced
emission and mechanochromic luminescence. We proposed a
novel strategy for developing pyrenyl-based AIEgens by
introducing intermolecular hydrogen bonding in aqueous
20 Q. Fang, J.Li, S. Li, R. Duan, S. Wang, Y. Yi, X. Guo, Y. Qian, W.
Huang and G. Yang. Chem. Commun., 2017, 53, 5702.
21 R. Hu, N. L. C. Leung and B. Z. Tang. Chem. Soc. Rev., 2014,
43, 4494.
22 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.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
New Journal of Chemistry
Page 5 of 5
View Article Online
DOI: 10.1039/C8NJ01379A
Journal Name
COMMUNICATION
23 L. Ji, R. M. Edkins, A. Lorbach, I. Krummenacher, C. Brückner,
A. Eichhorn, H. Braunschweig, B. Engels, P. J. Low, and T. B.
Marder. J. Am. Chem. Soc. 2015, 137, 6750.
24 H. Zhang, X. Zheng, N. Xie, Z. He, J. Liu, N. L. C. Leung, Y. Niu,
X. Huang, K. S. Wong, R. T. K. Kwok, H. H. Y. Sung, I. D.
Williams, A. Qin, J. W. Y. Lam and B. Z. Tang. J. Am. Chem.
Soc. 2017, 139, 16264.
25 J. Wang, X. Gu, P. Zhang, X. Huang, X. Zheng, M. Chen, H.
Feng, R. T. K. Kwok, J. W. Y. Lam and B. Z. Tang. J. Am. Chem.
Soc. 2017, 139, 16974.
26 X. Meng, G. Qi, X. Li, Z. Wang, K. Wang, B. Zou and Y. Ma. J.
Mater. Chem. C, 2016, 4, 7584.
27 S.-S. Zhao, L. Chen, L. Wang and Z. Xie. Chem Commu, 2017,
53, 7048.
28 J. N. Zhang, H. Kang, N. Li, S. M. Zhou, H. M. Sun, S. W. Yin, N.
Zhao and B. Z. Tang. Chem. Sci., 2017, 8, 577.
29 K. K. Neena, P. Sudhakar, K. Dipak and P. Thilagar. Chem.
Commun., 2017, 53, 3641.
30 H. Yu, W. Ren, H. Lu, Y. Liang and Q. Wang. Chem. Commun.,
2016, 52, 7387.
31 Y. Sagara, Y. C. Simon, N. Tamaoki and C. Weder. Chem.
Commun., 2016, 52, 5694.
32 X. Sun, X. Zhang, X. Li, S. Liu and G. Zhang, J. Mater. Chem.,
2012, 22, 17332.
33 C. Wang and Z. Li. Mater. Chem. Front., 2017, 1, 2174.
34 Y. Yanagisawa, Y. Nan, K. Okuro and T. Aida. Science, 2018,
359, 72–76.
35 R. Custelcean, M. G. Gorbunova and P. V. Bonnesen. Chem.
Eur. J. 2005, 11, 1459–1466.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins