Diamondoid porous organic salts toward applicable strategy for construction of versatile porous structures

Article abstract of DOI:10.1021/cg300796u

To achieve efficient construction of organic porous materials with versatile properties, we propose a widely applicable novel strategy using organic salts comprising triphenylmethylamine (TPMA) and sulfonic acids. We demonstrate that TPMA and sulfonic acids having polyaromatic moieties give a new class of porous structures consisting of diamond networks, named as diamondoid porous organic salts (d-POSs). In the d-POSs, TPMA and the sulfonic acids are assembled into stable tetrahedral supramolecular clusters via charge-assisted hydrogen bonding as primary building blocks. Subsequently, the clusters are accumulated by π-π interactions between the polyaromatic moieties to yield the d-POSs through formation of the diamond networks. Large steric hindrance of the clusters prevents the diamond networks from constructing highly interpenetrated structures, giving continuous open channels. It should be noted that the interpenetration degree of the diamond networks is controlled by tuning the bulkiness of the cluster with alteration of sulfonic acids. Anthracene-2-sulfonic acid (2-AS) constructs a 3-fold structure with one-dimensional channels, whereas pyrene-1-sulfonic acid (1-PyS) yields a 2-fold structure having two-dimensional channels. Furthermore, the organic salt of TPMA and 2-AS also give polymorphic structures in response to host-guest ratio and guest species, indicating not only their stability but the flexibility of the d-POSs.

Full text of DOI:10.1021/cg300796u

Article
pubs.acs.org/crystal
Diamondoid Porous Organic Salts toward Applicable Strategy for
Construction of Versatile Porous Structures
Atsushi Yamamoto,† Shinji Uehara,† Tomoya Hamada,† Mikiji Miyata,† Ichiro Hisaki,†
and Norimitsu Tohnai*,†,‡
†Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871,
Japan
‡PRESTO, Japan Science and Technology Agency (JST), Japan
S
* Supporting Information
ABSTRACT: To achieve efficient construction of organic
porous materials with versatile properties, we propose a widely
applicable novel strategy using organic salts comprising
triphenylmethylamine (TPMA) and sulfonic acids. We
demonstrate that TPMA and sulfonic acids having poly-
aromatic moieties give a new class of porous structures
consisting of diamond networks, named as diamondoid porous
organic salts (d-POSs). In the d-POSs, TPMA and the sulfonic
acids are assembled into stable tetrahedral supramolecular
clusters via charge-assisted hydrogen bonding as primary building blocks. Subsequently, the clusters are accumulated by π−π
interactions between the polyaromatic moieties to yield the d-POSs through formation of the diamond networks. Large steric
hindrance of the clusters prevents the diamond networks from constructing highly interpenetrated structures, giving continuous
open channels. It should be noted that the interpenetration degree of the diamond networks is controlled by tuning the bulkiness
of the cluster with alteration of sulfonic acids. Anthracene-2-sulfonic acid (2-AS) constructs a 3-fold structure with one-
dimensional channels, whereas pyrene-1-sulfonic acid (1-PyS) yields a 2-fold structure having two-dimensional channels.
Furthermore, the organic salt of TPMA and 2-AS also give polymorphic structures in response to host−guest ratio and guest
species, indicating not only their stability but the flexibility of the d-POSs.
ions and the sulfonate ions are connected by disulfonate pillars
to yield grid-like structures with one-dimensional open
channels. On the other hand, we previously reported the
preparation of organic structures, called porous organic salts
(POSs), consisting of sulfonic acids and aliphatic amines.8 For
example, biphenyl-4,4′-disulfonic acid and aliphatic primary
amines construct POSs with layer networks via charge-assisted
hydrogen bonding.8a The size and shape of the void space can
be readily modulated by alteration of the amine used. We
expect that the POS system is also a suitable system for
producing a variety of organic porous structures with versatile
functionalities, by combinatorial diversity of sulfonic acids and
amines.
In this Article, we propose a novel efficient strategy for
constructing porous structures having diamond networks by the
POS system. The construction of such structures is fascinating
due to not only their highly symmetrical and shapely networks
but also their stiffness, stability, and large void space. Since the
first report of stable organic diamond networks of tetrahedral
tetracarboxylic acid derivatives by Ermer in 1988,9 some porous
structures have been prepared utilizing similar single tetrahedral
INTRODUCTION
■
The construction of porous structures using small organic
compounds has been attracting a great deal of interest due to
the wide variety of applications in not only gas and molecular
storage1 but also guest-responsive materials such as chemical
sensors.2 Recently, strategic construction of porous structures
such as metal−organic frameworks (MOFs)3 and covalent−
organic frameworks (COFs)4 has been receiving attention
because of their concise strategy and molecular compatibility.
These structures are strongly constructed by either coordina-
tion bonding or covalent bonding. In comparison with these
materials, organic porous structures formed by weak non-
covalent bonding are also attractive due to their processing
advantage and good workability.5 In this context, we focus on
organic salts comprising ammonium sulfonates to design
porous structures.6 The organic salt systems in which two
components are combined enable systematic design of resultant
structures by changing the combination. Furthermore, the ion
pairs of ammonium sulfonates produce strong intermolecular
interactions such as hydrogen bonds and electrostatic
interactions. The strong interactions make possible formation
of the pairs invariably. In the past two decades, Ward et al. have
best investigated a variety of nanoporous structures based on
guanidine and disulfonic acids.7 In these structures, two-
dimensional hydrogen-bonding sheets comprising guanidinium
Received: June 12, 2012
Revised: July 11, 2012
Published: July 12, 2012
© 2012 American Chemical Society
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molecules as building blocks.10 However, it still remains
difficult to achieve the desired variety in such structures using
this conventional strategy. This is because the structural design
of diamond networks often restricts the molecular config-
uration to a tetrahedral shape, which prevents any further
modification. Moreover, these diamond networks tend to form
highly interpenetrating structures,11 resulting in small or absent
void space, because of the “less-bulkiness” building blocks. To
overcome these problems, we conceive a supramolecular-based
strategy, where tetrahedral supramolecules formed by simple
molecules serve as building blocks to construct diamond
networks (Figure 1a). The tetrahedral supramolecule is
jutting out in the tetrahedral direction would also serve as
supramolecular glue to connect the clusters through π−π
interactions,13 forming not only rigid but also flexible
(amphoteric) diamond networks and porous structures.
These amphoteric structures are expected to show more static
and dynamic responses to external stimuli than those observed
in some flexible MOFs.2b,c,3c In addition, the size, shape, and
functionalities of the cluster should be easily tuned by arranging
the sulfonic acid derivatives. We combined different three
sulfonic acid derivatives with TPMA: napthalene-2-sulfonic acid
(2-NS), anthracene-2-sulfonic acid (2-AS), and pyrene-1-
sulfonic acid (1-PyS) (Figure 1b,ii). The organic salts produced
from 2-AS or 1-PyS yield diamond networks and porous
interpenetrated structures including the aromatic molecules.
Interestingly, the degree of interpenetration of the diamond
networks is controlled by tuning the bulkiness of the cluster,
which resulted in the formation of different size and
dimensional void space. Furthermore, the diamond networks
of 2-AS also alter their structures in response to host−guest
ratio and guest species.
RESULTS AND DISCUSSION
■
Hierarchical Construction of d-POS. The organic salt
comprising 2-AS and TPMA yielded yellow crystals by
recrystallization from a mixture of ethanol and a nonpolar
solvent such as an aromatic hydrocarbon. Single crystals
suitable for X-ray crystallographic analysis were obtained by
recrystallization from a mixed solvent of ethanol and 1,2,4-
trichlorobenzene (TCB). The X-ray analysis revealed that the
crystal has a porous structure based on a diamond network,
named diamondoid porous organic salt (d-POS) (d-POS 1a,
Figure 2a). The crystallographic parameter is also shown in
Table 1. d-POS 1a is hierarchically constructed starting from 2-
AS and TPMA (Figure 2c). First, 2-AS and TPMA are
assembled into [4 + 4] supramolecular clusters by charge-
assisted hydrogen bonding. The hydrogen-bonding distances
between oxygen atoms of 2-AS and nitrogen atoms of TPMA
range from 2.735 to 2.863 Å (Figure S1). Although the
hydrogen bonding constructs a cubic-like network, the clusters
have a tetrahedral shape because the anthracenyl groups are
sufficiently longer than the triphenylmethyl groups (the longest
distance between the sulfur atom and any carbon atoms is 9.1
Å) (Figures 1b, 2c). The longest distance between neighboring
sides of the tetrahedral cluster is approximately 26 Å. Next, the
anthracenyl groups form π−π stacking, acting as linkers to
arrange the clusters into the resulting diamond network (Figure
2c). The mean plane distance between the aromatic moieties is
3.384 Å (Figure S2). The diamond network contains a very
large void space with 35 × 36 Å hexagonal windows. Hence,
three independent diamond networks are interpenetrated to fill
the void space. Nevertheless, the interpenetrated structure still
has one-dimensional (1D) void space including TCB molecules
used for recrystallization solvent as guest molecules (Figure 2c
and a, right). The bulkiness of the supramolecular cluster at the
tetrahedral nodes plays a key role in generating such void space.
The sphere-like core covered with triphenylmethyl groups in
the cluster is approximately 16 Å in diameter. This bulkiness
causes a large steric hindrance between the nodes, preventing
the formation of highly interpenetrating structure and complete
filling of the void space. The volume of the void space is 30%
(calculated by PLATON/VOID15), with the largest space of
10.7 × 10.7 Å and the smallest space of 6.1 × 6.1 Å (Figure 2a,
right). In the void space, four TCB molecules are included per
Figure 1. (a) Proposed supramolecular-based strategy. (b) [4 + 4]
supramolecular cluster constructed of TPMA and sulfonic acid
derivatives (i) and chemical structures of sulfonic acid derivatives
and guest molecules (ii). The distances are defined between a carbon
or sulfur atom and any carbon atoms.
expected to work as a “sterically bulky” node to inhibit the
diamond networks from constructing highly interpenetrating
structures. Previously, we reported specific supramolecules
named [4 + 4] supramolecular clusters, which are constructed
from organic salts comprising triphenylmethylamines (TPMA)
and monosulfonic acid derivatives (Figure 1b,i).12 Within the
clusters, the sulfonic acid derivatives are always arranged
tetrahedrally via cubic-like charge-assisted hydrogen bonding.
In this respect, we designed tetrahedral supramolecular clusters
as building blocks for the diamond networks that combine
TPMA with monosulfonic acid derivatives having polycyclic
aromatic moieties. We expect that the long aromatic moieties
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Figure 2. Crystal structures of d-POSs. Top view and void space of d-POSs composed of 2-AS and TPMA including TCB (d-POS 1a) (a) and 1-PyS
and TPMA including TMB (d-POS 2) (b). In the top view, guest molecules are omitted for clarity. In the sky-blue-colored void space, guest
molecules are represented by green balls and sticks. Hydrogen atoms are omitted for clarity except in the space-filling model of a cluster. Hierarchical
interpretation of d-POS 1a (c) and 2 (d). In the diamond networks and interpenetrated structures, triphenylmethyl groups are omitted for clarity.
The independent diamond networks are indicated by orange, green, and blue.
cluster. Interestingly, these guest molecules are arranged almost
parallel to each other (Figure 2a, right and Figure S3). The
distance between centroids of neighboring molecules is 3.930
Å. The guest molecules also adjust their alignment to the void
space through CH−Cl contacts with the void surface, which is
covered by aromatic rings. The effective CH−Cl contacts
between the guest molecules and the walls well contribute to
the specific parallel alignment. Highly interpenetrated struc-
tures are generally regarded as unfavorable structures due to
compression of the void space. However, the characteristic
arrangement of the guest molecules is confined by the 1D void
space formed by the interpenetration of the diamond networks.
Such 1D arrays of molecules may give rise to unique properties
such as polarization performance and anisotropic conductivity
of charge.16
Structural Diversification of d-POS Depending on
Sulfonic Acids. As well as the organic salt containing 2-AS, the
organic salt composed of 1-PyS and TPMA also forms a type of
d-POS 2 by a similar hierarchical process (Figure 2b,d). Single
crystals for X-ray crystallographic analysis were obtained by
recrystallization from a mixed solvent of ethanol and 1,3,5-
trimethylbenzene (TMB). According to the X-ray analysis, 1-
PyS and TPMA also form tetrahedral supramolecular clusters
by charge-assisted hydrogen bonding in the structure (Figure
2d). The longest distance between neighboring sides of the
cluster is approximately 25 Å. The clusters are arranged in a
diamond network by π−π stacking between the pyrenyl groups.
The diamond network also has large void space with 29 × 32 Å
hexagonal windows and constructs an interpenetrated structure.
However, it is noteworthy that only two independent diamond
networks are interpenetrated, unlike the 3-fold interpenetrated
structure of d-POS 1a. Accordingly, the structure has 2D void
space (Figure 2b, right). The 1D void space with the largest
space of 7.1 × 5.1 Å and the smallest space of 5.7 × 5.7 Å are
connected by small orthogonal channels (calculated volume of
the void space is 29%). TMB molecules used for recrystalliza-
tion solvent are included in the main 1D void space as guest
molecules. The differences in these void spaces arise from the
shape and size variations of the substituents of the sulfonic acid
derivatives. The longest distance between the sulfur atom and
any carbon atoms in 1-PyS is 7.8 Å, which is slightly shorter
than that of 2-AS (Figure 1b,ii). Therefore, the hexagonal
window in the diamond network of d-POS 2 is smaller than
that of 1a. In contrast, the width of 1-PyS is larger than that of
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Table 1. Crystallographic Parameters of d-POSs
2AS-TPMA TCB (d-POS 1a)
1-PyS-TPMA TMB (d-POS 2)
2AS-TPMA TMB (d-POS 1b)
2-AS-TPMA TMB (d-POS 1c)
formula
fw
C39H30NO3SCl3
711.10
tetragonal
I41/a
C79H66N2O6S2
1203.52
tetragonal
I41/a
C264H216O24N8S8
4141.13
monoclinic
P21/n
C396H322O36N12S12
6209.68
monoclinic
P21/c
crystal system
space group
a [Å]
30.5283(2)
30.5283(2)
14.09420(10)
90
27.0647(6)
27.0647(6)
35.4072(9)
90
26.1730
31.95700(10)
32.73900(10)
90
31.2919(6)
41.6841(8)
31.9775(13)
90
b [Å]
c [Å]
α [deg]
β [deg]
γ [deg]
V [Å3]
Z
90
90
111.6200
90
90.7570(8)
90
90
90
13 135.47(15)
16
25 935.7(11)
16
25 456.78(11)
4
41 707.1(13)
4
dcalcd [g m−3
]
1.438
1.257
1.080
0.989
T [K]
93
103
93
123
reflns observed
reflns unique
5509
124 789
11 853
0.1172
0.3712
880741
62 437
323 245
72 781
5509
56 289
R1 (I > 2.0σ(I))
Rw (all data)
0.0684
0.1769
880742
0.0841
0.1047
0.2642
0.2678
a
CCDC no.
881390
881391
a
See ref 14.
Figure 3. Crystal structures of d-POSs composed of 2-AS and TPMA including TMB. Top view of d-POS 1b (a) and 1c (b). In the top view, guest
molecules and hydrogen atoms are omitted for clarity except for in the space-filling model of one supramolecular cluster. Visualization of the void
space in d-POS 1b (c) and 1c (d). Void spaces are indicated in sky blue, and guest molecules are represented by green sticks. Hydrogen atoms of the
guests are omitted for clarity. Schematic representation of the interpenetration manners of the diamond networks in d-POS 1b (e) and 1c (f).
2-AS, with the longest distance between any two carbon atoms
being 4.9 and 2.8 Å, respectively (Figure 1b,ii). Thus, 1-PyS and
TPMA form a more sterically bulky cluster than 2-AS and
TPMA to cause more effective prevention of the inter-
penetration (Figure 2d). These results demonstrate that the
relative ratio of the diameter of the cluster’s cores to the length
of the polyaromatic groups should have a great influence on the
avoidance of highly interpenetrated structures. The shorter
length and wider width of polyaromatic groups provide a larger
relative ratio of the cores of the clusters. Consequently, the
resultant tetrahedral clusters cause larger steric hindrance to
avoid interpenetrated structures of the yielded diamond
networks. On the other hand, the organic salt composed of
2-NS and TPMA did not form any diamond networks and
porous structures (Figure S4). This is because the naphthyl
group of 2-NS (the longest distance between the sulfur atom
and any carbon atoms is 6.7 Å) is too short to jut out in the
tetrahedral direction from the cluster and to affect π−π
interactions between each other. Therefore, the clusters form a
close-packed structure without the formation of any diamond
networks. These results indicate that the diamond networks
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and the degree of their interpenetration can be readily tuned by
selection of suitable sulfonic acid derivatives.
Structural Diversification of d-POS Depending on
Guest Molecules. Interestingly, the diamond network also
shows structural flexibility depending on species and amount of
the guest molecule. Here, we show a representative example of
the previously mentioned organic salt composed of 2-AS and
TPMA. The organic salt also gave two other pseudopolymor-
phic crystals, d-POS 1b and 1c, by recrystallization from a
mixture of ethanol and TMB. Slow recrystallization gave d-POS
1b, whereas quick recrystallization gave mainly 1c. Crystallo-
graphic studies revealed that these crystals are also d-POSs
containing TMB molecules used for recrystallization solvent in
1D void space as guest molecules (Figure 3a,b). d-POS 1b has
indented 1D void space with the maximum size of a cross-
section in the void space being 10.6 × 9.6 Å and the minimum
size being 4.5 × 3 Å (Figure 3c). The void space is calculated to
be 29% per unit cell (PLATON/VOID). In contrast, d-POS 1c
possesses comparatively straight 1D void space (Figure 3d).
The largest size in the void space is found to be 11.2× 9.9 Å,
whereas the smallest is 6.5 × 6.0 Å. As compared to d-POS 1b,
the void space in d-POS 1c is slightly larger and without any
pocket (36% calculated by PLATON/VOID). These d-POSs
are constructed via the same hierarchical process described
above. That is to say, three independent diamond networks,
topologically the same, are interpenetrated within the
structures. These results indicate that stable diamond networks
can form regardless of the guests. Interestingly, however, the
shape and size of the diamond networks are significantly
different. The diamond network in d-POS 1b has 31 × 36 Å
hexagonal windows, while that in 1c has 35 × 37 Å hexagonal
windows (Figure 3e,f, inset). Such expansion and contraction of
the diamond networks are related to the host−guest ratio. In d-
POS 1b, three guest molecules are included per cluster. In
contrast, four guest molecules are included per cluster in d-POS
1c. Furthermore, the guest species also affected the structure of
the diamond networks. d-POS 1c has slightly larger hexagonal
windows than those in the former d-POS including TCB
molecules (Figure 2a,c) despite the same host−guest ratio. This
may be because TMB is slightly larger than TCB. These results
indicate that the diamond networks are both stable and flexible
in response to the guest molecules, which is distinctly different
from conventional diamond networks constructed by strong
interactions such as covalent bonding. The flexibility of the
diamond networks is derived from not only the conformational
flexibility of the clusters themselves but also the orientational
flexibility of π−π stacking between the clusters. The manner of
the interpenetration of the networks is also shown to be
variable (Figure S5). These phenomena are attributed to
surprising stability and reproducibility of the cubic-like
hydrogen bonding network. As demonstrated in a previous
paper, the cubic-like networks are formed universally regardless
of sulfonic acid derivatives.12 Therefore, π−π stacking should
be preferentially affected from the guest molecules to provide a
variety of forms and void space. The structural flexibility leads
to high inclusion ability and external stimuli-responsiveness of
the porous structures.
Figure 4. TGA data of the d-POSs composed of 2-AS and TPMA: (a)
1a, (b) 1b, and (c) 1c.
The second steps over 200 °C following to large weight loss
indicate decomposition of the components for the host
frameworks. As shown in Figure 4a, d-POS 1a completely
releases the guest molecules of TCB before 100 °C. After that,
no weight loss is observed up to 200 °C. On the other hand,
TGA data of d-POS 1b display gradual weight loss up to
decomposition of the components over 200 °C, although those
of 1c show a guest release profile of TMB similar to that of 1a.
These differences are probably due to the shape differences of
the void space. The void space of d-POS 1b has protruded
pockets incorporating the guest molecule, whereas those of 1a
and 1c do not have any pockets. The pockets of the void space
enable the structure to keep the guest molecules more tightly,
resulting in gradual guest release up to high temperature. As
shown in Figure 5, powder X-ray diffraction (PXRD)
Figure 5. PXRD patterns of the d-POSs composed of 2-AS and
TPMA: (a) 1a, (b) 1b, (c) 1c, and (d) 1b after guest release.
measurements revealed good crystallinity of these crystals
even after guest release. The PXRD measurements also indicate
that all d-POSs transform to the same structure upon guest
release. Before guest release, the PXRD patterns of d-POS 1b
and 1c display one sharp peak at 2θ = 5.46° (d = 16.2 Å) and
5.52° (d = 16.0 Å) corresponding to distances between the
channels, respectively. These peaks disappear and new two
peaks appear at 6.02° (d = 14.7 Å) and 6.62° (d = 13.3 Å) after
Structure Transformability of d-POS on Guest
Release. To clarify the porous property of the d-POSs, we
investigated structure stability upon guest release. Thermal
gravimetric analysis (TGA) data of single crystals of d-POS
1a−c show different guest release profiles (Figure 4). The first
steps in all TGA data indicate guest release from the d-POSs.
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The single crystals were picked from the solution by filtration and used
for the measurements.
guest release, indicating anisotropic shrinkage of the structures.
By considering the contraction degree of the distance
(approximately 1.5−3.0 Å) between the channels, the trans-
formed structure could have void space, although molecular
arrangement and unit cell of the transformed structure were not
determined from the PXRD pattern. These results indicate that
the d-POSs have a potential utility for both molecular and gas
storage.
Crystallographic Analysis of Single Crystals. X-ray diffraction
data of the crystals of d-POS 1a and 1c were collected by using
synchrotron radiation (λ = 0.7000 Å) via the BL38B1 in the SPring-8
with the approval of JASRI (Proposal No. 2007B1988, 2005, 2039, and
2008A1422). The cell refinements were performed by HKL2000
software.19 X-ray diffraction data of other crystals were measured on a
Rigaku R-AXIS RAPID diffractometer with a 2-D area detector using
graphite-monochromatized Cu Kα radiation (λ = 1.54187 Å). Direct
methods (SIR-2004 and SHELXS-97) were used for the structure
solution.20,21 All calculations were performed with the observed
reflections [I > 2σ(I)] by the program CrystalStructure crystallo-
graphic software packages22 except for refinement, which was
performed using SHELXL-97. All non-hydrogen atoms were refined
with anisotropic displacement parameters, and hydrogen atoms were
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 PLATON15,23 to solve the
structures without the influence of the disordered guest molecules.
The CIF files of the crystal structures of d-POS-1a and 1b including
disordered guest molecules can be also obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif.
CONCLUSIONS
■
In summary, we have achieved the construction of a new class
of porous structure with diamond networks, diamondoid
porous organic salts (d-POSs), by a supramolecular-based
strategy. The sterically hindered tetrahedral clusters suppress
the excessive interpenetration of the diamond networks and
yielded porous structures. Furthermore, these diamond net-
works are easily tuned by alteration of the sulfonic acid,
resulting in a change in interpenetration degree and void space.
In addition, flexible accumulation of the clusters gives not only
stability but flexibility to the diamond networks. Our proposed
strategy opens up the possibility to construct organic porous
structures with a variety of functionalities. The tetrahedral
cluster is a good platform for arranging ubiquitous organic
molecules into tetrahedral geometries, even if the organic
molecules themselves do not have tetrahedral configurations.
This applicability contributes to the easy modification and
functionalization of the structures. For example, introduction of
polyaromatic groups in porous structures is expected to result
in the achievement of fluorescent properties in response to
guest molecules. Furthermore, the porous properties (e.g., pore
size) can also be controlled by selecting molecular combination.
We are currently investigating actively the extension of this
strategy to other sulfonic acid derivatives for the construction of
unique functional organic porous structures.
Thermoanalysis Measurements. Thermal gravimetric analyses
(TGA) were performed on a Rigaku Thermoplus TG8120, ca. 1−2 mg
from 30 to 300 °C at a heating rate of 5 °C min−1.
Powder X-ray Diffraction Analysis. Powder X-ray diffraction
(PXRD) patterns were measured via a Rigaku Ultima IV using graphite
monochromatized Cu Kα radiation (λ = 1.54187 Å) at room
temperature.
ASSOCIATED CONTENT
* Supporting Information
■
S
Additional figures for the crystals and X-ray crystallographic
files in cif format for the d-POSs. This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: tohnai@mls.eng.osaka-u.ac.jp.
Notes
■
EXPERIMENTAL SECTION
■
Preparation of the Organic Salt of 2-NS and TPMA.
Commercially available naphthalene-2-sulfonic acid, 2-NS, and
triphenylmethylamine (TPMA) were mixed in methanol in a 1:1
molar ratio to yield an organic salt. The solution was evaporated under
reduced pressure, and the white precipitate of the salt was obtained.
Preparation of the Organic Salt of 2-AS and TPMA. The
potassium salt of anthracene-2-sulfonic acid was prepared according to
the published procedure.17 The potassium salt was converted to the
acid form, 2-AS, by passing its aqueous solution through an ion-
exchange column filled with an Amberlite IR 120B NA resin (Organo).
The aqueous solution of 2-AS was mixed immediately with the
methanol solution of TPMA in a 1:1 molar ratio to yield an organic
salt. The solution was evaporated under reduced pressure, and the
white precipitate of the salt was obtained.
Preparation of the Organic Salt of 1-PyS and TPMA. The
pyrene-1-sulfonic acid, 1-PyS, was prepared according to the published
procedure.18 1-PyS and TPMA were mixed in methanol in a 1:1 molar
ratio to yield an organic salt. The solution was evaporated under
reduced pressure, and the white precipitate of the salt was obtained.
Preparation of Single Crystals. The organic salt comprising 2-AS
and TPMA was dissolved in ethanol, and then 1,2,4-trichlorobenzene
(TCB) was added to the solution. Slow evaporation of the solvent at
room temperature gave the single crystals of d-POS 1a. Slow cooling
of the solution mixed with ethanol and 1,3,5-trimethylbenzene (TMB)
almost gave the block crystals of d-POS 1b, whereas fast cooling
yielded columnar crystals of d-POS 1c. The organic salt comprising 1-
PyS and TPMA was dissolved in ethanol, and then 1,3,5-
trimethylbenzene (TMB) was added to the solution. Slow evaporation
of the solvent at room temperature gave the single crystals of d-POS 2.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the Research fellow-
ships of the Japan Society for the Promotion of Science (JSPS)
for Young Scientists and Grant-in-Aids for Scientific Research
on Innovative Areas “Coordination Programming” (area 2107,
no. 24108723) from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), Japan. The synchrotron
radiation experiments were performed at BL38B1 in the Spring-
8 with the approval of the Japan Synchrotron Radiation
Research Institute (JASRI) (Proposal nos. 2007B1988, 2005,
2039, and 2008A1422).
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