A Structurally Variable Porous Organic Salt Based on a Multidirectional Supramolecular Cluster

Article abstract of DOI:10.1002/chem.201602233

A porous organic salt (POS) composed of 2-sulfophenyl anthracene (2-SPA) and triphenylmetylamine (TPMA) forms five types of porous crystals, POS-a–e, by recognizing subtle differences in the molecular structure of incorporated guest molecules. This struct

Full text of DOI:10.1002/chem.201602233

DOI: 10.1002/chem.201602233
Full Paper
&
Crystal Engineering
A Structurally Variable Porous Organic Salt Based on
a Multidirectional Supramolecular Cluster
Tetsuya Miyano, Naoki Okada, Ryunosuke Nishida, Atsushi Yamamoto, Ichiro Hisaki, and
Norimitsu Tohnai*[a]
Abstract: A porous organic salt (POS) composed of 2-sulfo-
phenyl anthracene (2-SPA) and triphenylmetylamine (TPMA)
forms five types of porous crystals, POS-a–e, by recognizing
subtle differences in the molecular structure of incorporated
guest molecules. This structurally variable POS was hierarchi-
cally designed on the basis of a supramolecular cluster with
a directionally flexible linker formed by the organic salt. X-
ray crystallographic analysis reveals that the salt forms six
conformers attributable to rocking and rotational motions of
the phenylene group in 2-SPA. The clusters form POS crystals
through different porous networks according to the con-
formers. The POS crystals show a wide range of fluorescence
spectra that are responsive to differences in the molecular
and electronic structure of the guest molecule. This remark-
able behavior has potential application in sensitive chemical
sensors that are responsive to slight differences in molecular
structures.
Introduction
structural conversion, and so on. Cooper and Mastalerz de-
signed porous crystals by using the self-assembly of perma-
nent porous organic cages with large surface area.[12] Mean-
while, Ward utilized salts composed of guanidinium and sulfo-
nate groups to yield large supramolecular cages containing
a large guest and flexible hydrogen-bonded frameworks show-
ing single-crystal–single-crystal transformation through guest
exchange.[13] The groups of Credi and Comotti reported stimu-
li-sensitive porous materials that show adsorption and release
of gas upon photoirradiation.[14] In this way, organic porous
frameworks assembled by noncovalent interactions become
suitable for constructing robust and flexible porous structures
with dynamic structural behavior and solvent-induced adapta-
tion that is reminiscent of a living system. Especially, porous
materials composed of hydrogen-bonding organic frameworks
were investigated because the robust or flexible porous struc-
tures keeping permanent porosity.[8]
Nanometer-sized porous materials have attracted much atten-
tion because of their potential for many applications.[1] Over
the past couple of decades, metal organic frameworks
(MOFs)[2] have been studied and advanced because of their
permanent porosity. Moreover, there are many types of porous
networks in MOFs because of the diverse range of secondary
building units that act as building blocks of porous structures,
which provides high designability. As a result, a variety of func-
tional materials have been reported that can be used, for ex-
ample, for storage and separation of gasses,[3] chemical and
gas sensors,[4] catalysts,[5] and platforms for polymerization.[6]
Meanwhile, the number of reported covalent organic frame-
works (COFs)[7] have grown rapidly because they can offer the
same advantages. Porous networks of MOFs and COFs have
been constructed by using strong bonds such as coordination
bonds or covalent bonds, to yield permanent porosity with
open channels in crystalline materials. However, these methods
have limitations in terms of processability, because of the
strong interactions. On the other hand, noncovalent organic
frameworks (NCOFs) or supramolecular frameworks that are
constructed through hydrogen bonds,[8] halogen bonds,[9] and
the others[10] have gained interest because of their easy solu-
tion-based fabrication and reassembly, recyclability, dynamic
Previously, our group reported that various sulfonic acids
and triphenylmethylamine (TPMA) specifically formed [4+4]
supramolecular clusters through charge-assisted hydrogen-
bonded networks.[14] Subsequently, these clusters were con-
nected by CH-p interactions, p-p interactions, or neutral hydro-
gen bonds to yield porous structures through the formation
and interpenetration of diamondoid networks.[15] The hierarchi-
cal method used to construct these crystals, which we termed
diamondoid porous organic salts (d-POSs), are illustrated in
Figure 1a. By using this approach, we designed porous crystals
with dynamic structural behavior that were responsive to
guest absorption–desorption processes and moisture.[16] How-
ever, the clusters only form diamondoid networks irrespective
of the guest molecules used as template. Having a directionally
diverse in-cluster linker is important for constructing structural-
ly variable porous materials with various functions. In previous
[a] T. Miyano, N. Okada, R. Nishida, Dr. A. Yamamoto, Dr. I. Hisaki,
Prof. Dr. N. Tohnai
Department of Material and Life Science
Graduate School of Engineering, Osaka University
2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)
E-mail: tohnai@mls.eng.osaka-u.ac.jp
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201602233.
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Figure 1. a) Previous method of construction for a diamondoid porous network based on a rigid tetrahedral supramolecular cluster. b) New design of multidir-
ectional supramolecular cluster forming various types of porous networks.
studies, a sulfo group was directly bonded to polyaromatic
groups, acting as a linker that connected the clusters. In these
cases, the directions of polyaromatic groups were limited to
tetrahedral because of the steric hindrance of TPMA, which
prevents the clusters from forming other networks. Therefore,
some of their organic salts form only one porous structure, ir-
respective of the molecular structure of the template. In other
words, these organic salts have low molecular recognition. Re-
solving the problem of limited networks opens up the possibil-
ity of using POS crystals as novel functional organic materials.
In this work, we designed a multidirectional supramolecular
cluster composed of TPMA and 2-sulfophenyl anthracene (2-
SPA) having a phenylene group between anthracene and sul-
fonic acid, as shown in Figure 1b. The phenylene group ena-
bles the cluster to be connected in a multidirection manner.
Then, the cluster forms various types of porous networks, in
addition to the diamondoid network noted in the previous
work, according to the direction of the linkers. As a result, the
salt forms appropriate porous crystals in accordance with the
molecular structure of the template. In other words, the salt
precisely recognizes differences in the molecular structures of
the template. Moreover, the fluorescence spectra were highly
sensitive to the structure of the template, because of the flexi-
ble dihedral angle between the phenylene group and anthra-
cene moiety as well as the interactions between fluorophores.
These results strongly suggest that introduction of directional
flexibility in the linker plays a very important role in forming
structurally variable porous crystals with fluorescence modula-
tion. To our knowledge, this POS constitutes the first report of
a multicomponent porous material formed by noncovalent in-
teractions that forms various porous crystals with fluorescence
modulations.
Results and Discussion
Preparation and crystallization of a salt composed of 2-SPA
and TPMA
The synthetic route used to prepare 2-SPA is shown in
Scheme 1. According to an established procedure,[17] 2-SPA was
synthesized by Suzuki coupling of 2-anthraceneboronic acid
and neopentyl 4-bromobenzenesulfonate followed by hydroly-
sis of the 2-SPA precursor. Then 2-SPA was mixed with TPMA at
a ratio of 1:1 in methanol and evaporated to yield an organic
salt. Subsequently, single crystals suited to various measure-
ments were prepared by recrystallization from chloroform
mixed with various guest molecules used as template, as de-
scribed in Scheme 2.
Single-crystal X-ray structural analysis revealed that the or-
ganic salt composed of 2-SPA and TPMA molecules formed
five types of porous structures, POS-a–e, depending on the
template molecules and recrystallization conditions, as shown
Scheme 1. Synthesis of 2-SPA.
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in Table 1. Recrystallization from chloroform with vari-
ous template molecules by slow evaporation at room
temperature yielded POS-a–d crystals. In addition, re-
crystallization from chloroform with benzene at low
temperature yielded POS-b and POS-e crystals,
whereas a POS-a crystal was obtained from the same
solvent mixture at room temperature.
Conformers and porous networks of supramolec-
ular clusters
Surprisingly, four 2-SPA molecules and TPMA mole-
cules always formed a [4+4] supramolecular cluster
in all POS crystals. On the other hand, conformations
of the cluster differed (Figure 2), owing to the intro-
duction of a phenylene group between the sulfonic
acid and anthracene. There are several factors that
determine the conformers, which are attributable to
not only rotational motion but also rocking motion
of the 2-SPA molecules in the cluster (Figure 2a).
These conformers affect the directions of the anthra-
cene moieties acting as a linker. As a result, the clus-
ter formed various porous networks as shown in
Figure 3. The precise network structures are com-
pletely different, whereas the structures of the con-
formers are similar. For example, conformations Cc
and Cd-i are similar from the viewpoint of linker direction, how-
ever, networks formed by these conformers are clearly different
(Figure 3-c,d). Subsequently, the networks of the various clus-
ters interpenetrated each other to yield POS crystals. According
to authoritative topological descriptions of porous networks,[18]
interpenetrated networks of Ca, Cb, Cc, Cd-i, Cd-ii, and Ce were
described by dia-c4, sql, dia-c4, dia-c4, dia-c, and dia-c4, re-
spectively. These findings show that slight differences in the
connection direction and dihedral angle strongly affect the
structure of the porous networks. In other words, increasing
the flexibility of the direction of the cluster linker enhances the
diversity of the porous networks.
Scheme 2. Chemical structures of organic salt and template molecules.
Table 1. Recrystallization conditions for preparing POS crystals.
Crystal
Template
Recrystallization
method[a]
T
[8C]
POS-a (Ben)
POS-b (Ben)
POS-b (m-Xy)
POS-b (Ani)
POS-c (p-Xy)
POS-c
benzene
benzene
m-xylene
N,N-dimethylaniline
p-xylene
solvent evaporation
vapor diffusion
solvent evaporation
solvent evaporation
solvent evaporation
solvent evaporation
RT
0
RT
RT
RT
RT
benzene/decane
(Ben/Dec)
POS-d (Mes)
POS-d (EtAc)
POS-e (Ben)
mesitylene
ethyl acetate
benzene
solvent evaporation
solvent evaporation
solvent evaporation
RT
RT
0
[a] Recrystallized from mixture of chloroform and template molecule.
Figure 2. [4+4] Supramolecular clusters composed of 2-SPA and TPMA. a) Hydrogen-bonding networks of the clusters and an example of 2-SPA conformation-
al isomers. Conformers of supramolecular clusters formed in b) POS-a: Ca; c) POS-b: Cb; d) POS-c: Cc; e,f) POS-d: CdÀi and CdÀii, and g) POS-e: Ce.
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Figure 3. Porous networks composed of supramolecular clusters in each POS crystals a) network of Ca in POS-a; b) network of Cb in POS-b; c) network of Cc in
POS-c; d) network of Cd-i in POS-d; e) network of Cd-ii in POS-d; f) network of Ce in POS-e.
The structures of POS-a–e crystals
Correlation between POS crystals and template molecules
In the POS-a crystal, which belongs to the space group C2/c, Ca
clusters were connected by p-p interaction to form the net-
work (Figure 3a) as in previous studies. Subsequently, the net-
works interpenetrated each other to yield the POS-a crystal
with 0D closed voids (Figure 4a). In the POS-b crystal (space
group: Pban), Cb clusters were connected by CH-p interactions
to form the network shown in Figure 3b. The two networks
then interpenetrated and laminated to yield POS-b with two
types of voids: 0D closed and 1D bottle-neck voids (Figure 4b).
In POS-c (space group: C2/c), Cc clusters were connected by
CH-p and p-p interactions to form the network (Figure 3-c).
The networks then interpenetrated to yield POS-c with chan-
nels (Figure 4-c). In POS-d (space group: C2/c), two conforma-
tionally different clusters, Cd-i and Cd-ii, were constructed, each
of which formed a different network. Cd-i clusters were ar-
ranged to form the network shown in Figure 2d, whereas Cd-ii
clusters were connected by CH-p interactions to form a similar
network to that seen in POS-b. Subsequently, two different
networks interpenetrated in an intricate manner to yield POS-d
with 0D closed and 1D channel voids (Figure 4d). POS-e (space
group: Pc) was obtained by recrystallization at low tempera-
ture. In this crystal, Ce clusters were connected by CH-p and p-
p interactions to form a network (Figure 2 f) that was distinct
from the other networks of POSs. The network then interpene-
trated to yield POS-e with 0D closed and 1D void spaces (Fig-
ure 4e).
Different types of POS crystals were obtained by recrystalliza-
tion at room temperature depending on differences in the mo-
lecular size and shape of the template. For example, when
benzene molecules were used as template, the salt yields POS-
a. On the other hand, use of slightly larger template molecules
such as toluene, m-xylene, and N,N-dimethylaniline yielded
POS-b. In POS-a, benzene occupied the 0D void spaces (Fig-
ure S1), but larger template molecules could not do so. Thus,
recrystallization with such template molecules yielded POS-
b with larger 0D and 1D bottle-neck void spaces. In POS-b, the
template molecules occupied the 0D and 1D channel void
spaces (Figure S2). POS-c with 1D channels was obtained by
using the longer template molecule p-xylene (Figure S3). The
inclusion of benzene with decane also yielded POS-c. However,
bulky template molecules such as mesitylene could not be in-
corporated into the narrow channels in POS-c. Thus, larger
template molecules yielded POS-d with large 0D and 1D chan-
nel voids (Figure S4). These results indicate that the salt forms
different types of POS crystals by recognizing subtle differen-
ces in template molecular structure; for example, the presence
and position of a methyl group. That is, the salt had high mo-
lecular recognition ability, yielding different POS structures de-
pending on the template molecule. It is very likely that the
clusters with directionally flexible linker increased the diversity
of the porous crystal structure.
To summarize, in the crystal structures of POSs composed of
2-SPA and TPMA, the salt assembled into conformers of supra-
molecular clusters with different connecting directions to form
various types of porous networks classifiable into four types.
These networks then interpenetrated to yield porous crystals
in response to differences in template molecular structures.
Fluorescence modulation depending on the template mole-
cules
POS crystals displayed a wide range of emission from blue to
yellow-green, depending on the template molecule (Fig-
ure 5a). Figure 5-c shows fluorescence spectra of these crystals
excited at 365 nm. The spectra of POS-a,c,d were observed in
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Figure 5. (a) Photographs of POSs crystals containing various template mole-
cules under UV irradiation (l=365 nm). Normalized b) excitation and c) fluo-
rescence spectra of each POS crystal excited at 365 nm.
template molecular structure, even though all crystal structures
were nearly the same. However, it is difficult to determine the
precise correlation between fluorescence modulations and the
interactions or dihedral angles of fluorophores because of the
many factors affecting the fluorescence spectra. The maximum
wavelength of the fluorescence emission spectra shifted from
429 to 515 nm in POS-b(m-Xy) and POS-b(Ani), whereas their
excitation spectra were not redshifted at all (Figure 5b). This
suggests that there are no interactions in the ground state be-
tween template molecules and fluorophores. The fluorescence
lifetime of POS-b(Ani) (67 ns (Figure S7)) was clearly longer
than that of POS-b(m-Xy) (0.34 nm (Figure S6)). These results
suggest that interactions between the template molecules and
the fluorophores occurred to provide redshifted exciplex fluo-
rescence. Consequently, fluorescence spectra of the organic
salt depended sensitively on differences in electronic structures
as well as molecular structures of the template molecule.
These results indicate that the introduction of a phenylene
group between the sulfonic acid and anthracene increases the
sensitivity for template molecules, leading to the emission of
different fluorescence for different template molecules.
Figure 4. Crystal structures and void spaces. a) POS-a; b) POS-b; c) POS-c;
d) POS-d; e) POS-e. Guest molecules included in the void spaces are omitted
for clarity.
a longer wavelength region (from 436 to 477 nm) than those
of POS-b(m-Xy) (429 nm). In POS-a,c,d, porous networks were
formed by p-p or CH-p interactions between anthracene moi-
eties or between anthracene and a phenylene group. On the
other hand, the sheet network in POS-b was formed by only
CH-p interactions between anthracene moieties. The type of
interaction has an influence on the fluorescence modulations.
In addition, the dihedral angle between the anthracene moiety
and phenylene group significantly alters the fluorescence. In
the present POSs, there were some conformers of 2-SPA and
different interactions between fluorophores, even in the iso-
structures. Thus, POS crystals with templates displayed differ-
ent fluorescence spectra in response to slight differences in
Finally, we performed guest exchange experiments for POS-
b(m-Xy) by vapor exposure to benzene or N,N-dimethylaniline
for one day at 508C. Fluorescence spectra were drastically
changed by vapor exposure (Figure S9), whereas their PXRD
patterns were not shifted (Figure S8). In the fluorescence spec-
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0.562 mmol) under N2 atmosphere. The reaction mixture was
heated at 1158C and stirred for 6 h. The mixture was then concen-
trated in vacuo, extracted with chloroform, washed with water and
brine, and dried over anhydrous Na2SO4. The product was purified
with column chromatography (silica gel; chloroform/hexane=4:1
v/v) to give 2-sulfophenyl anthracene precursor (6.68 g, 91%) as
trum of POS-b(m-Xy) exposed to benzene (Figure S9b), the
peak around 490 nm increased and it corresponded to excimer
emission of anthracene reported in a previous study.[19] In this
case, anthracene moieties became rotatable because the size
of benzene is smaller than m-xylene. As a result, anthracene
moieties tend to interact with each other in the excited state
to increase excimer emission. In addition, the fluorescence
spectrum of POS-b(m-Xy) exposed to N,N-dimethylaniline (Fig-
ure S9c) corresponded to POS-b(Ani) (Figure 5-c). These results
strongly suggest that m-xylene molecules were exchanged to
other volatile solvents by vapor exposure while maintaining
the porous crystal structure.
1
a pale-yellow solid. H NMR (400 MHz, CDCl3): d=8.52 (s, 1H; Ar-H),
8.48 (s, 1H; Ar-H), 8.27 (s, 1H; Ar-H), 8.13 (d, J=8.8 Hz, 1H; Ar-H),
8.04 (m, 4H; Ar-H), 7.94 (d, J=8.0 Hz, 2H; Ar-H), 7.74 (dd, J1 =
9.2 Hz, J2 =1.2 Hz, 1H; Ar-H), 7.51 (m, 2H; Ar-H), 3.76 (s, 2H; CH2),
0.95 ppm (s, 9H; CH3).
Preparation of the organic salt composed of 2-SPA and TPMA:
2-SPA was obtained by hydrolysis of 2-SPA precursor. 2-SPA precur-
sor, dioxane, ethanol, and 0.5m HCl was added to a pressure bottle
and stirred at 1608C for 18 h. The reaction mixture was concentrat-
ed in vacuo and dissolved in methanol. This operation was repeat-
ed several times to remove HCl. Subsequently, 2-SPA and TPMA
were mixed in methanol in a 1:1 molar ratio. The solution was
evaporated to give a pale-yellow powder of the crude salt.
Conclusion
We have prepared multidirectional supramolecular clusters
composed of triphenylmethylamine (TPMA) and 2-sulfophenyl
anthracene (2-SPA) having a phenylene group between the sul-
fonate and anthracene. The organic salt formed [4+4] supra-
molecular clusters with various conformers, and these clusters
formed different porous networks according to their conforma-
tion. Subsequently, the clusters interpenetrated each other to
yield porous crystals with different void spaces, POS-a–e, by
recognizing the different template molecular structures. The
salt also showed a wide range of fluorescence from 429 to
515 nm in response to the molecular shapes and chemical
properties of the template molecules, because of the different
interactions between fluorophores or fluorophores and tem-
plate molecules. The present study demonstrates that the in-
troduction of flexibility to the building blocks of porous net-
works yields guest-sensitive porous materials based on supra-
molecular clusters. We believe that these results may lead to
useful new approaches to constructing statically flexible and
dynamically transformable porous materials with fluorescent
modulations. Such materials may be applied as sensitive chem-
ical sensors that are responsive to slight differences in molecu-
lar structures.
Preparation of single crystals: The crude salt was dissolved in
chloroform and various template solvents were added to the solu-
tion. Slow evaporation of the solvent at RT gave each single crystal
with template except for POS-b-Ben and POS-e-Ben. POS-b-Ben
crystal was obtained by vapor diffusion method with benzene at
08C and POS-e-Ben crystal was obtained by slow evaporation at
08C.
Fluorescence spectroscopy measurements: Fluorescence spectra
were measured with a FP-6500 spectrofluorometer (Jasco). Samples
for the measurements in the solid state were encapsulated in
a quartz cell (30ꢁ30ꢁ0.3). The excitation wavelength was 365 nm.
Fluorescence lifetime measurements: Fluorescence lifetime meas-
urements for the crystals were undertaken with a TemPro Fluores-
cence Lifetime System (Horiba Jobin Yvon) equipped with an LED
excitation source of 352 nm with a pulse-duration full width at half
maximum (FWHM) of approximately 1 ns.
Molecular graphics and calculations: The inclusion space volumes
filled by the solvent molecules in the crystal structures were calcu-
lated from the atomic coordinates by using the PLATON program.
The atomic radii (ꢂ) were adopted as follows: H 1.20, C 1.70, O
1.60, N 1.65, and S 1.80. The probe radius was fixed at 0.7 ꢂ.
Experimental Section
Crystallographic analysis of single crystals: X-ray diffraction data
of POS-a(Ben) and POS-d(Mes) were collected with a Rigaku R-AXIS
RAPID diffractometer with a 2D area detector by using graphite-
monochromatized CuKa radiation (l=1.54187 ꢂ). The data of
POS-b(Ben) were recorded with a Rigaku XtaLAB P-200 system by
using graphite monochromatic CuKa radiation (l=1.54187 ꢂ). The
other X-ray diffraction data were collected with a CCD with syn-
chrotron radiation (l=0.8000 ꢂ) monochromated by the fixed exit
Si (111) double crystal. The cell refinements were performed with
HKL2000 software.[20] Direct methods (SIR-2004,[21] SIR-2008,[22] She-
lexlS[23] and Superflip[24]) were used for the structure solution. All
calculations were performed with the observed reflections [I>
2s(I)] by using the CrystalStructure crystallographic software pack-
age[23] except for refinement, which was performed using
SHELXL.[25] All non-hydrogen atoms were refined with anisotropic
displacement parameters, placed in idealized positions, and refined
as rigid atoms with the relative isotropic displacement parameters.
The data were also refined by using the SQUEEZE routine function
in PLATON to solve the structures without the influence of the dis-
ordered guest molecules.[26]
All chemicals and solvents were commercially available and used
without any purification.
Synthesis of neopentyl 4-bromobenzenesulfonate: Neopentyl al-
cohol dissolved in chloroform (10 mL) was added to solution of 4-
bromobenzenesulfonyl chloride (10.2 g, 40.0 mmol) in chloroform
(20 mL) and pyridine (11.7 mL, 40.0 mmol) at À58C for 1 h. The so-
lution was then stirred overnight at RT. Chloroform (100 mL) was
added and the mixture was washed with 0.1m HCl, water, brine,
dried over anhydrous NaSO4 and concentrated. Recrystallization
from hexane gave the product (10.1 g, 98%) as colorless crystals.
1H NMR (400 MHz, CDCl3): d=7.78 (d, J=8.8 Hz, 2H; Ar-H), 7.71 (d,
J=8.8 Hz, 2H; Ar-H), 3.69 (s, 2H; CH2), 0.93 ppm (s, 9H; CH3).
Synthesis of 2-sulfophenyl anthracene precursor: 2-Sulfophenyl
anthracene precursor was synthesized according to an established
procedure. Toluene (200 mL), ethanol (50 mL), and 2mK2CO3 solu-
tion (50 mL) were added to a mixture of neopentyl 4-bromobenze-
nesulfonate (5.53 g, 18.1 mmol), 2-anthraceneboronic acid (4.02 g,
18.1 mmol) and tetrakis(triphenylphosphane)palladium (0) (0.65 g,
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Acknowledgements
This work was supported by JSPS KAKENHI Grant Number
JP25288036 and JSPS KAKENHI Grant Number JP16H01027 in
“Precisely Designed Catalysts with Customized Scaffolding”. We
thank Dr. K. Aburaya and Dr. H. Sato (Rigaku Corporation) for
crystal structure analysis. We also thank Professor Dr. M.Miyata
(Osaka University) for his support. T. M. thanks the Interactive
Materials Science Cadet Program in Osaka University. The syn-
chrotron radiation experiments were performed at BL38B1 in
the SPring-8 with the approval of the Japan Synchrotron Radia-
tion Research Institute (JASRI) (Proposal nos. 2014A1648 and
2015A1776). We deeply appreciate the referee’s constructive
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Keywords: cluster compounds
·
crystal engineering
·
fluorescence · host–guest systems · supramolecular chemistry
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Received: May 11, 2016
Published online on && &&, 0000
Chem. Eur. J. 2016, 22, 1 – 8
www.chemeurj.org
7
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
FULL PAPER
&
Crystal Engineering
T. Miyano, N. Okada, R. Nishida,
A. Yamamoto, I. Hisaki, N. Tohnai*
&& – &&
A Structurally Variable Porous Organic
Salt Based on a Multidirectional
Supramolecular Cluster
Flexible crystals: A flexible supramolec-
ular cluster composed of an organic salt
provides structurally variable porous
crystals with high molecular recognition
ability. The structures and fluorescence
properties of the porous crystals differ
in response to differences in the molec-
ular structures of incorporated mole-
cules (see scheme).
&
&
Chem. Eur. J. 2016, 22, 1 – 8
www.chemeurj.org
8
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!