Solid-state optical properties of a chiral supramolecular organic fluorophore consisting of fluorescent 1-pyrenesulfonic acid and amine molecules

Article abstract of DOI:10.1002/ejoc.200900235

By using (R)-l-phenylethylamine as a chiral molecule and 1pyrenesulfonic acid as a fluorescent molecule, a chiral supramolecular organic fluorophore composed of a 2D layered structure was successfully developed. This chiral supramolecular fluorophore poss

Full text of DOI:10.1002/ejoc.200900235

FULL PAPER
DOI: 10.1002/ejoc.200900235
Solid-State Optical Properties of a Chiral Supramolecular Organic
Fluorophore Consisting of Fluorescent 1-Pyrenesulfonic Acid and Amine
Molecules
Yoshitane Imai,*[a] Katuzo Murata,[a] Yoko Nakano,[b] Takunori Harada,[c]
Tomohiro Sato,[c] Nobuo Tajima,[d] Michiya Fujiki,[b] Reiko Kuroda,[c,e] and
Yoshio Matsubara*[a]
Keywords: Chirality / Circularly polarized luminescence / Crystal engineering / Fluorescence / Supramolecular chemistry
By using (R)-1-phenylethylamine as a chiral molecule and 1-
molecular fluorophore possesses circularly polarized lumi-
pyrenesulfonic acid as a fluorescent molecule, a chiral supra- nescence (CPL) properties in the solid state.
molecular organic fluorophore composed of a 2D layered
structure was successfully developed. This chiral supra-
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
and achiral or chiral amine molecules).[4] These complexes
have a characteristic 1D columnar hydrogen- and ionic-
bonded network structure formed by the carboxylate oxy-
gen atom of a carboxylic acid anion and the ammonium
hydrogen atom of a protonated amine.
Introduction
Solid-state optical properties of organic compounds are
very important physical properties that must be considered
in the development of new functional materials. The poten-
tial application of solid-state fluorescence techniques in or-
ganic electroluminescence (EL) devices, optoelectronic de-
vices, and so on has recently attracted much attention.[1]
To date, several organic fluorophores possessing solid-state
organic fluorescence properties have been developed; how-
ever, these fluorophores are composed only of a single
molecule.[2] Recently, two-component supramolecular or-
ganic fluorophores have attracted considerable attention, as
the physical and chemical properties of these fluorophores
can be easily controlled by changing the component mole-
cules.[3] However, the study of circularly polarized lumines-
cence (CPL) properties in these fluorophores has not been
reported. We have developed a two-component, chiral sup-
ramolecular organic fluorophore exhibiting CPL in the so-
lid state; these fluorophores were developed by combining
two types of organic molecules (fluorescent carboxylic acid
In this paper, we report the complexation behaviors and
solid-state optical properties of novel achiral and chiral
supramolecular organic fluorophores composed of fluores-
cent sulfonic acid molecules instead of fluorescent carbox-
ylic acid molecules. Two types of basic amine molecules
were used in this study, that is, achiral benzylamine (1) and
chiral (R)-1-phenylethylamine [(R)-2]. 1-Pyrenesulfonic acid
(3) was used as the fluorescent sulfonic acid. To the best
of our knowledge, a supramolecular organic fluorophore
composed of sulfonic acid and amine molecules exhibiting
CPL properties has not been reported to date. It is believed
that the resultant supramolecular organic fluorophore will
play an important role in the development of chiral supra-
molecular organic fluorophores exhibiting CPL in the solid
state.
[a] Department of Applied Chemistry, Faculty of Science and
Engineering, Kinki University
3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502, Japan
Fax: +81-6-6727-2024
E-mail: y-imai@apch.kindai.ac.jp
y-matsu@apch.kindai.ac.jp
[b] Graduate School of Materials Science,
Nara Institute of School and Technology
Takayama, Ikoma, Nara 630-0192, Japan
[c] JST ERATO-SORST Kuroda Chiromorphology Team
4-7-6 Komaba, Meguro-ku, Tokyo 153-0041, Japan
[d] First-Principles Simulation Group, Computational Materials
Science Center, NIMS
Results and Discussion
The formation of a 1/3 supramolecular organic fluoro-
phore was first attempted by crystallization from ethanol
(EtOH) solution. A mixture of 1 and 3 was dissolved in the
EtOH solution and left to stand at room temperature. After
Sengen, Tsukuba, Ibaraki 305-0047, Japan
[e] Department of Life Sciences, Graduate School of Arts and Sci-
ences, The University of Tokyo
3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
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Solid-State Optical Properties of a Chiral Supramolecular Organic Fluorophore
a week, a large number of supramolecular crystals (I) were network structure is formed by the association of the am-
obtained. Although the formation of a supramolecular or- monium hydrogen atom of one protonated amine in 1 and
ganic fluorophore composed of 1 and 1-pyrenecarboxylic the sulfonate oxygen atom of a sulfonic acid anion in 3.
acid (4) was attempted in the same way, good-quality crys- Moreover, this 2D layered network structure is maintained
tals were not obtained. Furthermore, the formation of a by two types of pyrene–pyrene edge-to-face interactions
chiral supramolecular organic fluorophore composed of (Figure 1, a and b; arrows A and B, 2.59 and 2.63 Å, respec-
(R)-2 and 3 was attempted in the same way. This resulted tively).[6] The self-assembly of the 2D layered network struc-
in a large number of chiral supramolecular crystals (II) ture (Figure 2, a and b; represented by a dotted border)
composed of (R)-2 and 3. However, powder-like solids in- without interlayer interactions along the a axis results in
stead of good-quality crystals composed of (R)-2 and 4 the formation of complex I.
were obtained.
The most serious problem in solid-state organic fluoro-
phores is fluorescence quenching in the crystalline state. To
study the solid-state optical properties of the obtained sup-
ramolecular complexes I and II, the solid-state fluorescence
spectra of these complexes were measured. Complexes I and
II exhibited fluorescence in the solid state. The solid-state
fluorescence maximum (λem) of complex I was observed at
466 nm, and the absolute value of the photoluminescence
quantum yield (ΦF) in complex I was 0.15 in the solid state.
The values of solid-state fluorescence maximum (λem) and
photoluminescence quantum yield (ΦF) in complex II were
similar to those of complex I (λem = 467 nm and ΦF = 0.11).
These fluorescence emissions may originate from the exci-
mer state of pyrene units of complexes in the solid state by
comparing with that of pyrene in the crystal.[5]
X-ray crystallographic analyses of complexes I and II
were attempted to study their crystal structures. The crystal
structure of complex I is shown in Figures 1 and 2.
Figure 2. Packing structure of complex I. The dotted borders indi-
cate the 2D layered network structure. Arrow C shows the distance
between the centers of two neighboring parallel pyrene rings. (a)
Packing structure comprising 2D layered network structure ob-
served along the b axis; (b) packing structure observed along the c
axis.
The crystal structure of chiral complex II is shown in
Figures 3 and 4. The stoichiometry of complex II is (R)-2/
3/H2O = 1:1:1 and its space group is P21. The crystal struc-
ture of complex II has a supramolecular 2D layered hydro-
gen-bonded network along the a and b axes (Figure 3, a
and b). This 2D layered network structure is formed by the
association of the ammonium hydrogen atom of one pro-
tonated amine in 2 and the sulfonate oxygen atom of a sul-
Figure 1. Crystal structure of the extracted 2D layered network
fonic acid anion in 3. Moreover, the included water mole-
structure in complex I. Arrows A and B show pyrene–pyrene edge-
cules (Figures 3 and 4, represented by black balls) link one
to-face interactions. Arrow C shows the distance between the cen-
protonated amine group of (R)-2 with two sulfonic acid
anion groups of 3 through hydrogen bonds and contribute
to the maintenance of the layered structure. In contrast to
ters of two neighboring parallel pyrene rings. (a) View along the b
axis; (b) view along the a axis.
The stoichiometry of complex I is 1/3 = 1:1 and its space complex I, although aromatic–aromatic edge-to-face inter-
group is P21/c. This crystal structure of complex I has a actions are not observed in complex II, CH–π interactions
supramolecular 2D layered hydrogen-bonded network between the methyl group of (R)-2 and the pyrene ring of
along the b and c axes (Figure 1, a and b). The 2D layered 3 are observed (Figures 3a and 4b; arrow A, 2.95 Å) in the
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Y. Imai, Y. Matsubara et al.
FULL PAPER
2D layered network structure.[6] The self-assembly of this
2D layered structure (Figure 4, represented by dotted bor-
ders) without interlayer interactions along the c axis results
in the formation of a chiral complex II (Figure 4).[6]
Figure 4. Packing structure of chiral complex II. Water molecules
are represented by black balls. The dotted borders indicate the 2D
layered network structure. Arrow A indicates CH–π interactions.
Arrows B and C show the distance between the centers of two
neighboring parallel pyrene rings. (a) Packing structure comprising
2D layered network structure observed along the a axis; (b) packing
structure observed along the b axis.
Figure 3. Crystal structure of the extracted 2D layered network
structure in chiral complex II. Water molecules are represented by
black balls. Arrow A indicates CH–π interactions. Arrows B and C
show the distance between the centers of two neighboring parallel
pyrene rings. (a) View along the a axis; (b) view along the c axis.
in the CD spectrum. The circular anisotropy (gCD = ∆OD/
OD) factor of the last Cotton effect (λCD = 365 nm) is ap-
proximately –0.1ϫ10–3. To check if the crystal has caused
any artifact in the spectrum, complex IIЈ was prepared by
using (S)-1-phenylethylamine [(S)-2], and the CD and ab-
sorption spectra of complex IIЈ were measured (Figure 5,
gray line). The CD spectrum of complex IIЈ was found to
be a mirror image of the CD spectrum of complex II. These
results show that an effective chirality transfer from chiral
When compared with chiral complex II, the pyrene rings
in the 2D layered structure of complex I exhibit a zigzag
arrangement along the c axis. However, two pyrene rings of
neighboring 2D layered structure units are parallel to each
other (Figure 1b). The distance between the centers of two
neighboring parallel pyrene rings (Figures 1b and 2b, arrow
C) is 3.59 Å. In contrast, the pyrene rings in the 2D layered
structure of complex II exhibit a planar arrangement along
the c axis without stacking (Figure 3, a and b). However,
pyrene rings of neighboring 2D layered structure units are
opposite to each other but not perfectly parallel. The dis-
tances between the centers of two neighboring pyrene rings
are 4.85 and 4.15 Å, respectively (Figures 3b and 4b, arrows
B and C). The solid-state fluorescence maximum (λem) and
photoluminescence quantum yield (ΦF) of complexes I and
II are similar. It is believed that this similarity is due to the
stacked arrangement of the pyrene rings of neighboring 2D
layered structure units.
Fluorescent complex II is a chiral fluorophore; therefore,
this fluorescence may be CPL in the solid state. To study the
CPL properties of chiral complex II, the solid-state circular
dichroism (CD) spectra of complex II were measured by
using a KBr pellet. The solid-state samples were prepared
according to the standard procedure for obtaining glassy
KBr matrices.[7] The solid-state CD and absorption spectra
of complex II (indicated by the black line) are shown in
Figure 5. CD and absorption spectra of chiral complexes II (black
Figure 5. Pyrene ring peaks are observed at 353 and 365 nm line) and IIЈ (gray line) in the solid state (KBr pellets).
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Eur. J. Org. Chem. 2009, 3244–3248

Solid-State Optical Properties of a Chiral Supramolecular Organic Fluorophore
unit 2 to fluorescent unit 3 takes place through complex-
Experimental Section
ation. Consequently, the measurement of the solid-state
CPL spectrum of chiral complex II was attempted by using
a KBr pellet.[7] The CPL spectrum was successfully ob-
served in the solid state. The solid-state CPL and fluores-
cence spectra of complex II are shown in Figure 6.
General Methods: All reagents were used directly as obtained com-
mercially. Compound 1 and crystallization solvent EtOH were pur-
chased from Wako Pure Chemical Industry. Compounds (R)- and
(S)-2 were purchased from Tokyo Kasei Kogyo Co., Ltd. Com-
pounds 3 and 4 were purchased from Sigma–Aldrich Co., Ltd.
Formation of the Complex by Crystallization from EtOH Solution:
Compounds 1 [or (R)-2] (0.05 mmol) and 3 (or 4) (0.05 mmol) were
dissolved in EtOH solution (2 mL). After a week, a large number
of crystals [crystals of complex I (10 mg) for 1/3 system, and crys-
tals of complexes II (10 mg) and IIЈ (9 mg) for (R)-2/3 and (S)-2/3
system, respectively] were obtained. The weight of the crystal is the
total weight of the obtained crystals in one batch.
X-ray Crystallographic Study: X-ray diffraction data for single crys-
tals were collected by using Bruker Apex. The crystal structures
were solved by direct methods[8] and refined by full-matrix least-
squares by using SHELX97.[9] The diagrams were prepared by
using PLATON.[10] Absorption corrections were performed by
using SADABS.[11] Non-hydrogen atoms were refined with aniso-
tropic displacement parameters, and hydrogen atoms were included
in the models in their calculated positions in the riding model
approximation. Crystallographic data for I: C7H9N·C16H10O3S, M
= 389.45, Monoclinic, space group P21/c, a = 16.7416(16) Å, b =
Figure 6. CPL and fluorescence spectra of chiral complex II in the
10.9788(10) Å,
c
Z
=
=
10.9788(10) Å,
β
=
101.781(2)°,
V
=
=
solid state (KBr pellet).
1869.8(3) Å3,
4, Dcalcd.
=
1.383 gcm–3, µ(Mo-Kα)
0.198 mm–1, 11315 reflections measured, 4279 unique, final R(F2)
= 0.0607 using 3384 reflections with IϾ2.0σ(I), R(all data) =
The fluorescence spectrum obtained by using a KBr pel-
let is similar to the fluorescence spectrum of complex II in
the solid state without KBr matrices. This result confirmed
0.07767,
T
=
115(2) K. Crystallographic data for II:
C8H11N·C16H10O3S·H2O, M = 421.49, Monoclinic, space group
the lack of influence of the KBr matrix on this measure- P21, a = 8.3164(12) Å, b = 8.6126(12) Å, c = 14.890(2) Å, β =
105.964(2)°, V = 1025.4(3) Å3, Z = 2, Dcalcd. = 1.365 gcm–3, µ(Mo-
ment. A negative CPL spectrum was obtained for complex
Kα) = 0.190 mm–1, 3908 reflections measured, 3908 unique, final
II. The circular anisotropy [gem = 2(IL – IR)/(IL + IR)] factor
R(F2) = 0.0712 using 3833 reflections with IϾ2.0σ(I), R(all data)
of complex II is approximately –1.0ϫ10–3. This shows that
= 0.0720, T = 115(2) K.
chiral complex II exhibits CPL in the solid state. To the
best of our knowledge, this is the first example of solid-
state CPL observed in a chiral supramolecular organic flu-
CCDC-720383 (for I) and -720384 (for II) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
orophore composed of sulfonic acid and amine molecules.
Centre via www.ccdc.cam.ac.uk/data_request/cif.
In other words, it is possible to measure the solid-state CPL
spectrum of a sulfonic acid/amine supramolecular complex.
Measurement of Solid-State Fluorescence Spectra: Solid-state fluo-
rescence spectra and absolute photoluminescence quantum yields
were measured with an absolute PL quantum yield measurement
system (C9920-02, Hamamatsu Photonics K.K.) under air atmo-
sphere at room temperature. The excited wavelengths were 377 and
375 nm for complexes I and II, respectively.
Conclusions
Measurement of Solid-State CD and Absorption Spectra: The CD
and absorption spectra were measured with a Jasco J-800KCM
Supramolecular organic fluorophores were successfully
formed by using fluorescent 1-pyrenesulfonic acid and achi-
ral benzylamine and chiral (R)-1-phenylethylamine. Supra-
molecular complexes composed of a 2D layered network
structure were obtained. Most organic fluorophores lose
fluorescence in the solid state; however, these supramolec-
spectrophotometer. The solid-state samples were prepared accord-
ing to the standard procedure for obtaining glassy KBr matrices.[7]
Measurement of Solid-State CPL Spectrum: The CPL spectrum was
measured by using a Jasco CPL-200 spectrophotometer. The ex-
cited wavelength was 350 nm. The solid-state samples were pre-
ular organic fluorophores exhibit fluorescence in the solid
pared according to the standard procedure for obtaining glassy
state. Especially, 1-pyrenesulfonic acid/(R)-1-phenylethyl-
amine–supramolecular organic fluorophore exhibits solid-
state CPL and its spectrum was recorded successfully. To
the best of our knowledge, this is the first example of solid-
state CPL observed in a chiral supramolecular organic flu-
orophore composed of sulfonic acid and amine molecules.
It is believed that such a chiral supramolecular complex and
its optical properties will be useful in the development of
novel solid-state chiral fluorophores.
KBr matrices.[7] The power of an incident beam of the CPL spec-
trometer was 8.0 µW/0.04 cm2 at the installation position of the
sample. The CPL spectrum was approached by simple moving
average (SMA).
Acknowledgments
This work was supported by a Grant-in-Aid for Scientific Research
from the Ministry of Education, Culture, Sports, Science and Tech-
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FULL PAPER
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Published Online: May 13, 2009
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