Crystal structures, thermal properties, and emission behaviors of N, N -R-phenyl-7-amino-2,4-trifluoromethylquinoline derivatives: Supercooled liquid-to-crystal transformation induced by mechanical stimuli

Article abstract of DOI:10.1021/cg5001842

N,N-R-Phenyl-7-amino-2,4-trifluoromethylquinoline derivatives (R = Me (1), Et (2), isopropyl (3), and Ph (4)) were prepared as a new type of fluorophore responsive to external stimuli. 1, 2, 3, and 4 were obtained as single crystals including three crystal polymorphs (1, 1β, and 1γ) of 1 and two (2 and 2β) of 2. In 4, a phase transition from 4₁₇₃ and 4 ₉₀ between 173 and 90 K was observed. The solid-state emission showed a red shift by 30-58 nm compared with the emission in n-hexane, and their emission properties depended on the molecular arrangements. The modes of molecular arrangements for 1, 1β, and 1γ were a slipped parallel (SP), head-to-tail γ-type herringbone (HT-γ-HB), and head-to-head γ-type herringbone (HH-γ-HB); those for 2 and 2β were HT-γ-HB and head-to-tail dimer (HT-dimer), and that for 3 was head-to-tail columnar (HTC). 4₁₇₃ and 4₉₀ were similar HT-γ-HB. The crystal-to-crystal transformations from 1γ to 1β and from 2β to 2 were observed by heating and grinding the crystal, respectively, with emittance changes. After melting, on cooling, all crystals formed supercooled liquid (SCL) and then glass states. In the SCL state, molecules were amorphous and were quickly crystallized by a mechanical stimulus such as scratching. By taking advantage of the difference of emitting intensity between the SCL and the crystal states for 1, writing and erasing of a letter with scratching and heating, respectively, were demonstrated.

Full text of DOI:10.1021/cg5001842

Article
pubs.acs.org/crystal
Crystal Structures, Thermal Properties, and Emission Behaviors of
N,N‑R-Phenyl-7-amino-2,4-trifluoromethylquinoline Derivatives:
Supercooled Liquid-to-Crystal Transformation Induced by
Mechanical Stimuli
Satoru Karasawa, Ryusuke Hagihara, Yuichiro Abe, Naomi Harada, Jun-ichi Todo, and Noboru Koga*
Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-Ku, Fukuoka 812-8582, Japan
S
* Supporting Information
ABSTRACT: N,N-R-Phenyl-7-amino-2,4-trifluoromethylquinoline deriva-
tives (R = Me (1), Et (2), isopropyl (3), and Ph (4)) were prepared as a
new type of fluorophore responsive to external stimuli. 1, 2, 3, and 4 were
obtained as single crystals including three crystal polymorphs (1α, 1β, and
1γ) of 1 and two (2α and 2β) of 2. In 4, a phase transition from 4173 and
4
90 between 173 and 90 K was observed. The solid-state emission showed a
red shift by 30−58 nm compared with the emission in n-hexane, and their
emission properties depended on the molecular arrangements. The modes of molecular arrangements for 1α, 1β, and 1γ were a
slipped parallel (SP), head-to-tail γ-type herringbone (HT-γ-HB), and head-to-head γ-type herringbone (HH-γ-HB); those for
2α and 2β were HT-γ-HB and head-to-tail dimer (HT-dimer), and that for 3 was head-to-tail columnar (HTC). 4173 and 490
were similar HT-γ-HB. The crystal-to-crystal transformations from 1γ to 1β and from 2β to 2α were observed by heating and
grinding the crystal, respectively, with emittance changes. After melting, on cooling, all crystals formed supercooled liquid (SCL)
and then glass states. In the SCL state, molecules were amorphous and were quickly crystallized by a mechanical stimulus such as
scratching. By taking advantage of the difference of emitting intensity between the SCL and the crystal states for 1, “writing” and
“erasing” of a letter with scratching and heating, respectively, were demonstrated.
emitting diodes (OLEDs) the SCL-to-C transformation is one
of the problems for amorphous molecular materials,10 the
difference in the emission color or intensity caused by SCL-to-
C transformation by external stimuli was expected to be useful
as a switching device for solid-state emitting materials. On the
basis of the TFMAQ studies, fluorophore molecules incorpo-
rating diarylamine moieties being apt to form a SCL state11 into
a TFMAQ framework were prepared, and the alterations of
emission properties through the phase transition from SCL to
C caused by external stimuli were investigated. We report
herein the preparations of TFMAQ derivatives having phenyl
and R, Me (1), Et (2), isopropyl (3), and Ph (4), as
substituents at the amino moiety, the molecule and crystal
structures of their crystal polymorphs, and the mechanochro-
mic emission alterations through the SCL-to-C phase
transition. In addition, the thermal and mechanochromic
emission alterations through C-to-C phase transition are
reported.
INTRODUCTION
■
Organic molecules and metal complexes showing solid-state
emission have attracted much interest as new functional
materials for practical application in electronic and photo-
devices,1 photosensors,2 and solid lasers.3 The characteristic of
solid-state emission is that the emission behavior is strongly
affected by the molecular structure and arrangement in the
solid state. The wavelength and intensity of the solid-state
emission can thus be reversibly tuned and controlled by altering
the molecular structure and arrangement by external stimuli.4
In such solid-state emission alteration, strategies taking
advantage of crystal-to-crystal (C-to-C) phase transitions in
polymorphs are a promising approach, and many studies on the
emission alteration induced by thermal5 and mechanical4a,6
stimuli have been reported. We have also reported on the solid-
state emissions of 7-amino-2,4-ditrifluoromethylquinoline
(TFMAQ) derivatives7 and analogous 1,8-naphthyridine
derivatives.8 They provided many crystal polymorphs9 and
exhibit polymorph-dependent emissions through the thermal
single-crystal-to-single-crystal (SC-to-SC) phase transitions
between the polymorphs. Along the studies on thermal
interconversion between the polymorphs, furthermore, we
found that a TFMAQ derivative formed a supercooled liquid
(SCL) state after melting. Since the molecule in the SCL state
subsequently crystallized, we considered using an SCL-to-C
transformation by external stimuli as a new function of the
emitting molecule. Although in the field of organic light-
RESULTS AND DISCUSSION
■
Preparations of N-Phenyl TFMAQ Derivatives. To
investigate the substituent effect on the SCL state, different
sizes of substituents, methyl (1), ethyl (2), isopropyl (3), and
Received: February 4, 2014
Revised: March 20, 2014
Published: March 31, 2014
© 2014 American Chemical Society
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drastic change of the crystal parameters with space group and
crystal class between 173 and 90 K, suggesting thermal crystal
phase transition. The molecules crystallized in space groups
(crystal class), P1 (triclinic), C2/c (monoclinic), and Cc
̅
(monoclinic), for 1α, 1β, 1γ, respectively, Pna21 (orthorhom-
bic) and P1 (triclinic), for 2α and 2β, respectively, P2 /c for 3,
̅
1
and C2/c (monoclinic) and P1 (triclinic) at 173 and 90 K for
̅
phenyl (4) moieties, were incorporated into 2,4-di-
(trifluoromethyl)-7-phenylaminoquinoline (H). A parent mol-
ecule, H, prepared by the procedure reported previously7 was
methylated with methyl iodide in the presence of sodium
hydride to afford 1. Similarly, 2 and 3 were prepared in a
manner similar to the procedure for 1 using ethyl iodide and 2-
iodopropane in place of methyl iodide. Fluorophore 4 was
prepared by the reaction of H with bromobenzene in the
presence of tri-tert-butylphosphine/palladium acetate/potassi-
um tert-butoxide under a nitrogen atmosphere. Fluorophore 1
was crystallized to give three kinds of single crystals as yellowish
plates (crystal 1α) and needles (crystal 1β) from n-hexane−
Et2O at 4 °C and rt, respectively, and yellowish needles (crystal
1γ) from acetone−Et2O at rt. Crystals 1β and 1γ showed
similar morphologies and emitting colors and could not be
distinguished (Figure S1, Supporting Information). Recrystal-
lization of 2 afforded crystal of 2α as yellowish needles from n-
hexane−Et2O and crystal of 2β as yellowish plates from ethyl
acetate. Two crystals, 2α and 2β, emitted a yellowish green and
a green color, respectively, and could be visually told apart by
the emission colors. Single crystals of 3 and 4 were obtained
from n-hexane−Et2O as yellowish blocks. Photographs of
crystals, 1−4, irradiated by light at 365 nm under a microscope
(×40) are shown in Figure S1.
4173 and 490, respectively. In 1, the Z′ values for crystals 1α and
1γ were 2, indicating that the both crystals had two
crystallographically independent molecules. In 2, the Z′ values
for 2α and 2β were 2 and 1, respectively, and that value for 3
was 1. In 4, the Z′ value of 1 at 173 K increased to 4 by
decreasing temperature to 90 K, suggesting that the symmetry
of the crystal decreased with decreasing the temperature.
Crystallographic data and experimental details are listed in
Table S1 for 1, S2 for 2 and 3, and S3 for 4 in Supporting
Information (S2).
The three crystals, 1α, 1β, and 1γ, for 1 showed similar
molecular structures, in which the phenyl ring located in the
side of the nitrogen atom of quinoline (syn conformer) and the
disorders of phenyl rings were observed in 1β and 1γ. On the
other hand, the crystal polymorphs, 2α and 2β, for 2 had a
phenyl ring on the opposite side from each other (syn and anti
conformers for 2α and 2β, respectively), and no disorders of
the phenyl rings were observed in either molecule. 3 as well as
2β was an anti conformer. In 4, two phenyl rings and one
quinoline ring were tilted in the same direction to form a
propeller shape.12 The molecular structures are shown in Figure
1 for 1α, 2β, 3, and 490 and Figure S2, Supporting Information
for 1β, 1γ, 2α, and 4173
.
In 1, 2, 3, and 4, no noticeable differences in the lengths and
angles of molecular structures from those of the parent
molecule H and the analogues reported previously7 were
observed. The bond lengths, rC7−Na, of C7 and Na of amine
were 1.37−1.39 Å and were somewhat shorter, suggesting the
double bond character. The dihedral angles of the quinoline
Crystal Structure Analyses. The molecular and crystal
structures for 1, 2, 3, and 4 were investigated by single-crystal
X-ray diffraction (SXRD) at various temperatures (273 and 90
K for 1, 2, and 3, and 273, 223, 173, and 90 K for 4). In X-ray
crystallography at both temperatures, 1, 2, and 3, showed no
significant differences in cell parameters, while 4 showed a
Figure 1. ORTEP drawings of the molecular structures of 1α (a), 2β (b), 3 (c), and 490 (d) at 50% probability level. In (a) and (b), one of two and
four crystallographically independent molecules of 1α and 490 are shown.
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Figure 2. Molecular arrangements of crystals, 1α (a), 1β (b), 1γ (c), 2α (d), 2β (e), 3 (f), and 490 (g). Gray, black, pink, and green molecules and
blue atoms indicate crystallographically independent molecules and nitrogen atoms, respectively. Red and black dotted lines indicate short distances
due to the π−π and CH−π interaction, respectively.
(Q) and phenyl rings toward the planes defined by the carbons
of benzene and alkyl moieties and the nitrogen of amine
increased in the order of 1, 2, 3, and 4, depending on the
bulkiness of substituents (methyl, ethyl, isopropyl, and phenyl
moieties). The dihedral angles, CPh1,Na,CR−Q; CR = the carbon
of substituent R attached to the amine nitrogen, were 3.5−7.6°,
6−17°, and 24° for 1, 2, and 3, respectively, which
corresponded to the torsion angles, ∠C6,C7,Na,CPh, and
C7,Na,CR−Ph were 55−64°, 62 (64)°, and 70° for 1, 2, and
3, respectively. The small former angles suggested that the
charge transfer effectively took place in the excited state. The
latter large dihedral angles might affect the crystal packings. In
4, two phenyl rings and one quinoline plane were tilted by 28,
58, and 73°, respectively, toward the plane defined by C7, Ph1,
and Ph1′. The selected bond lengths, bond angles, and dihedral
angles for 1, 2, 3, and 490 are summarized in Tables S4-1 and
S4-2, Supporting Information.
The molecular arrangements for 1, 2, 3, and 4 were different
layered structures. In 1, the modes of molecular arrangement13
for 1α, 1β, and 1γ were a slipped parallel (SP), head-to-tail γ-
type herringbone (HT-γ-HB), and head-to-head γ-type
herringbone (HH-γ-HB), respectively. Those for 2α and 2β
were HT-γ-HB and head-to-tail dimer (HT-dimer), respec-
tively, and that for 3 was a head-to-tail columnar (HTC). 4173
and 490 were similar HT-γ-HB. The molecular arrangements for
1α, 1β, 1γ, 2α, 2β, 3, and 490 are shown in Figure 2 (Figure S3,
Supporting Information for 4173).
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a
Table 1. Modes of Molecular Arrangements and Intermolecular Distances and Angles for 1α, 1β, 1γ, 2α, 2β, 3, and 4
1α
1β
1γ
2α
2β
3
4173
490
Space Group (Z′)
P1 (2)
C2/c (1)
HT-γ-HB
4.95
Cc (2)
Pna21(2)
Mode of Molecular Arrangement
HT-γ-HB HT-dimer
P1 (1)
P21/c (1)
C2/c (1)
P1 (4)
̅
̅
̅
SP
HH-γ-HB
HT-C
HT-γ-HB
HT-γ-HB
4.90−5.16
Intercentroid Distances between the Quinoline Ring
4.79 3.60 3.59
4.73, 5.16
4.93
5.08
Nearest Distance (Å) between the Quinoline and Benzene Planes for π−π Interactions
C9−C6′ 3.61
C7−C3″ 3.65
Na−C7′ 3.53
C2−C5′ 3.53
Na−C7′ 3.62
Na″−C7‴ 3.62
Na−C8′ 3.47
C8−Na′ 3.48
C1−C6′ 3.53 C5−C1′ 3.62 Na−C6″ 3.76
C8−C5″ 3.66
Na−C6″ 3.62
Cph3‴−Cph6⁗ 3.42
Nearest Distance between the H of Phenyl Ring and Aromatic Planes for CH−π Interactions
b
Cph1−Hph2′ 3.08
Cph1−Hph2″ 3.30
Cph1−Hph2
′
′
Cph3−Hph3′ 2.64
Cph5−Hph5″ 2.80
Na−Hph5
″
Cph11−Hph9
″
Cph9−Hph9 2.66−2.74
3.01
2.71
2.67
Cph4−Hph3
Cph2′−Hph2 2.75
Cph8−Hph6′ 2.90
3.23
CH−N Hydrogen Bonds
Hph4−Nq 2.91, HEt−Nq 2.86
2.92
Hph4−Nq 2.90,
Hph4−Nq 2.85 Hph4−Nq 2.60,
Hph3−Nq
Hph4−Nq 2.70
Hph4−Nq 2.62, 2.65, 2.68,
3.01
2.64
2.82
2.71
a
b
SP; a slipped parallel, HT; head-to-tail, HH; head-to-head, HB; herringbone, C; columnar. Includes six short distances of Cph9−Hph9‴, Cph9′
−
H
ph9⁗, Cph9″−Hph9⁗′, Cph9‴−Hph9, Cph9⁗−Hph9′, and Cph9⁗′−Hph9″, respectively.
In layered structures such as columnar and herringbone, the
CH−π interaction14 in addition to the π−π interaction
effectively operates to stabilize the crystal structure. As shown
in Figure 2, syn and anti conformers formed the head-to-head
and head-to-tail layered structures of quinoline rings,
respectively. A head-to-head structure for syn conformer
could gain stability due to the CH−π interaction between the
phenyl rings in addition to the π−π interaction between the
quinoline rings. The formation of syn and anti conformers
depended on the substituents, R, and the anti conformer
became dominant with increasing bulkiness of R in the order of
methyl, ethyl, and isopropyl. Three crystals, 1α, 1β, and 1γ, of 1
took syn conformation to form the SP and HB structures
consisting of head-to-head overlaps of molecules. In 2, 2α, and
2β took syn and anti conformation to form the HB- and HT-
dimer structures consisting of head-to-head and head-to-tail
overlaps, respectively. In the HT-dimer structure, interdimer
short contacts for the CH−π interactions between the phenyl
and quinoline rings were observed. Crystal 3 was obtained only
as anti conformer and had a HT-C structure consisting of head-
to-tail overlap. In this HT-C structure, the intercolumn short
contacts between the phenyl rings, indicating the π−π
interaction, were observed. 4 had a head-to-head overlap of
quinoline rings to form the HB structure. In 4, additional
intermolecular π−π interactions between the phenyl rings were
observed.
In 1, 2, 3, and 4, the intercentroid distances between
quinoline rings estimated from the Mercury CSD 3.0 software15
were ca. 3.6−5.2 Å, suggesting that the π−π interactions were
weak. Furthermore, the short distances between the phenyl
rings and between the phenyl and the quinoline rings indicating
the CH−π interaction were 2.7−3.3 Å, which might have
stabilized the layered structures. The observed short contacts
are shown in Figure 2, and their intermolecular distances and
angles are summarized in Table 1 together with the molecular
arrangement modes.
To confirm if three, two, and two kinds of crystals for 1, 2,
and 4, respectively, were polymorphous, the Hirshfeld finger-
print (di − de) plots16 were carried out. Those plots for 1, 2,
and 4 are shown in Figure S4, Supporting Information. In visual
comparisons of the Hirshfeld fingerprint plots, the molecules,
1α-1 and 1α-2, and 1γ-1 and 1γ-2, with Z′ = 2, and 1β might
look different from each other. Therefore, it was judged that 1
had three crystal polymorphs containing five crystallographi-
cally independent molecules. In contrast, the plots for 2α (Z′ =
2) and 2β containing three crystallographically independent
molecules were visually different, indicating that they were
crystal polymorphs. The plots for 4173 and 490 (Z′ = 4)
containing five crystallographically independent molecules were
also visually different, indicating that they were crystal
polymorphs.
Absorption and Emission Spectra. The absorption and
emission properties of fluorophores 1, 2, 3, and 4 were
investigated in various solvents and in the solid state. The solid-
state absorption spectra were obtained by measurements of the
diffractive reflection spectra followed by Kubelka−Munk
conversion. For the fluorescence spectra, the absorption
maxima (370−400 nm) in the visible region were used as the
excitation wavelength.
(A). In Solutions. The absorption and emission spectra of 1,
2, 3, and 4 were measured in n-hexane, dibutyl ether,
chloroform, ethyl acetate, and dimethyl sulfoxide (Figure S5,
Supporting Information). Absorption spectra in the solution
samples were similar to those for the TFMAQ derivatives
reported previously.7 In n-hexane, the wavelengths of the
ab
charge transfer band were at λmax = 392, 398, 404, 402, and
415 nm for H, 1, 2, 3, and 4, respectively, and depended on the
ab
substituents. Solvent dependence of the λmax values was also
observed, indicating that the molecules in the ground state were
significantly polarized. The solutions of 1, 2, 3, and 4 in organic
solvents intensely emitted fluorescence, and the wavelength of
the emission maximum, λmaxf, was longer compared with the
f
parent molecule (H). In n-hexane, the emission for H was λmax
of 446 nm, while those for 1, 2, 3, and 4 were λmaxf of 471, 477,
472, and 479 nm with fluorescence quantum yields, Φf, of 0.49,
0.47, 0.31, and 0.63, respectively. The emission color and
intensity depended on the solvent polarity. With increasing
f
polarity, the λmax for 1, 2, 3, and 4 shifted to a longer
wavelength, while the Φf values decreased. The observed
emission properties in solution (solvatochromism)17 were
typical of the fluorescence for TFMAQ derivatives. From the
Lipper−Mataga model,18 the differences (Δμ) between the
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ground and excited state dipole moments for 1, 2, 3, and 4 were
estimated to be 14.9 (5.4), 14.7 (5.4), 14.7 (5.3), and 15.0 D
(5.7), respectively, in which the numbers in the parentheses
were Onsager Cavities estimated by density functional theory
calculation using the B3LYP/6-31G(d) base set.19 The
obtained values of 15 D were larger than that (12 D) for H,
indicating that the photoexcited states for 1, 2, 3, and 4 were
largely stabilized by the polar solvent. The values of Δμ, and
Thermal Properties. To investigate the thermal properties
of 1, 2, 3, and 4, differential scan calorimetry (DSC)
measurements were performed at heating and cooling rates of
10 and 5 °C/min in two temperature ranges: high ranges of
25−150, 0−100, 0−130, and 30−160 °C, and low ranges of
−30 to 150, −40 to 100, −40 to 130, and −40 to 160 °C for 1,
2, 3, and 4, respectively. The observed DSC curves were
different between the first and second scans. Furthermore, the
second scan depended on the measuring temperature range.
The DSC curves are shown in Figure 4 for 1α, 2α, 3, and 4 and
in Figure S7 for 1β, 1γ, and 2β.
In the high temperature range, crystals 1α and 1β showed a
single endothermic peak at 98 °C, Tm, due to the melting point
on heating in the first cycle, and no other peaks were observed
in the second cycles, while crystal 1γ showed a weak
endothermic peak at 89 °C, Tt (Figure S7b, Supporting
Information) in addition to the peak of Tm in the first cycle, and
no peaks were observed in the second cycles. The weak
endothermic peak, Tp, might be due to the thermal phase
transition, suggesting enantiotropic transformation8,21 to a
polymorph from 1γ. Similar thermal profiles of DSC curves for
2, 3, and 4 were observed in the high temperature ranges. In
the DSC curves of 2, 3, and 4, only the endothermic peaks of
Tm at 72 and 62 °C for 2α and 2β, respectively, and 94 and 118
°C for 3 and 4, respectively, were observed in the first cycle,
and no peaks were observed in the second cycle. Lack of any
peak after melting in the first cycle for 1, 2, 3, and 4 indicated
that the samples were in a SCL state after melting. In the Tm
values of polymorphs 2α and 2β, relatively large differences
were observed, indicating that the molecules of syn conformer
in HB structure for 2α were packed more tightly than those of
anti conformer in HT-dimer for 2β.
In the low temperature ranges, on the other hand, the DSC
curves of 1, 2, 3, and 4 showed the peaks for Tg and Ts, due to
the glass (G) transition and the solidification, respectively, in
addition to that for Tm in the cooling and heating processes
after melting. The DSC curves for 1 showed a weak and broad
exothermic peak at −10 to 10 °C, Tg−, in the cooling process
following melting at 98 °C, and then a corresponding broad
endothermic peak at −15 to −10 °C, Tg+, and an exothermic
peak at 31 °C in the heating process from −30 °C. The
observed pair of weak exo- and endothermic peaks and the
exothermic peak at 31 °C, Ts, were assigned as the glass (G)
transition and the solidification, respectively. The temperature
of Ts depended on the heating rate, and the Ts value of 31 °C
for 5 °C/min shifted to 40 °C for 10 °C/min. Furthermore, the
exothermic peak at 40 °C was accompanied by an endothermic
peak at 89 °C for Tt due to the phase transition (Figure S7a,b,
Supporting Information), suggesting that the solid formed at Ts
contained crystal 1γ. In 2α, after melting, a pair of weak exo-
(endothermic) peaks for Tg− (Tg+) at −25 (−20) °C and a
f
λmax and Φf for 1, 2, 3, and 4 in various solvents are listed in
Table S5, Supporting Information together with those for the
parent molecule H.
(B). In the Solid State. In the absorption spectra for the
ab
crushed crystalline samples, the λmax values of the long
wavelength absorption were nearly constant by ca. 418 nm for
1α, 1β, 1γ, 2α, 2β, and 3 and 425 nm for 4 and showed red
shifts, Δλmaxab; λmaxab(c) − λmaxab(n-C6), of 10−20 nm
compared with the corresponding values in n-hexane, where
the contribution of stabilization by the solvent was negligible.
f
In contrast, the λmax and Φf, values of solid-state emission
strongly depended on the molecular arrangements of crystals.20
f
The λmax (Φf) values of the crystalline samples were 509
(0.52), 517 (0.51), and 520 (0.46) nm for 1α, 1β, and 1γ were
531 (0.40) and 510 (0.11) for 2α and 2β, and were 502 (0.10)
and 537 (0.52) nm for 3 and 4, respectively. When the solid-
state emission properties were compared with those in n-
hexane, the crystals, 1β, 1γ, 2α, and 4, having HB structures
showed large shifts to longer wavelengths by 46−58 nm, while
crystals 2β and 3, having HT-dimer and HT-C structures,
respectively, showed smaller shifts by 33 and 30 nm with large
reductions of Φf values. Crystal 1α having a slipped parallel
arrangement showed an intermediate property. These observa-
tions were consistent with the results for the analogous 1-
quinoline and 1,8-naphthyridine derivatives reported previ-
ously.7,8 Absorption and emission spectra of crushed crystalline
samples are shown in Figure 3 for 1 and Figure S6, Supporting
f‑ab
Information for 2, 3, and 4. The values of λmaxab, λmaxf, Δλmax
,
and Φf, are summarized in Table 2 together with those in n-
hexane.
Figure 3. Solid-state absorption (dotted line) and emission (solid line)
spectra for 1α (red), 1β (blue), and 1γ (green). Black lines show the
spectra in n-hexane.
Table 2. Values of Absorption and Emission Maxima (λmaxab and λmaxf, respectively), Δλmaxf‑ab, and Φf, for 1α, 1β, 1γ, 2α, 2β, 3,
a
and 4 in Crystalline State
1α
1β
1γ
2α
2β
3
4
b
λmaxab/nm
417 (398)
509 (471)
92
419 (398)
517 (471)
98
418 (398)
520 (471)
102
418 (404)
531 (477)
92
418 (404)
510 (477)
113
419 (402)
502 (472)
83
425 (415)
537 (479)
112
λmaxf/nm
Δλmaxf‑ab/nm
Φf
0.52 (0.49)
0.50 (0.49)
0.46 (0.49)
0.40 (0.47)
0.11 (0.47)
0.10 (0.31)
0.52 (0.63)
a
b
The numbers in the parentheses are those in n-hexane. The value obtained by measurements of the diffractive reflection spectra followed by
Kubelka−Munk conversion.
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Figure 4. DSC curves of 1α (a), 2α (b), 3 (c), and 4 (d) for two cycles; first (red) and second (blue), in the high (upper) and low (bottom)
temperature ranges; the high ranges of 25−150, 0−100, 0−130, and 30−160 °C, and the low ranges of −30 to 150, −40 to 100, −40 to 130, and
−40 to 160 °C for (a), (b), (c), and (d), respectively. The rates of heating and cooling are 5 °C/min in (a) and 10 and 5 °C/min in the high and low
temperature ranges, respectively, in (b), (c), and (d). Insets show the expansion in the temperature range observed at the glass transition. Solid and
dotted arrows indicate the direction of heating and cooling, and the glass transition, respectively.
−
+
broad exothermic peak at 46 °C for Ts appeared, followed by
the two endothermic peaks at 62 and 70 °C, which were
consistent with the values of Tm for 2β and 2α, respectively.
This result suggested that the solid formed at 46 °C was a
mixture of 2α and 2β. The observed intensity ratio of the peaks
of Tm for 2α and 2β depended on the scan rate, and the ratio of
2α/2β decreased with decreasing scan rate. The intensity for 2β
became dominant at the scan rate of 1 °C/min (Figure S7d).
This result suggested that 2α and 2β having modes of HB- and
HT-dimer molecular arrangements might be kinetically and
thermodynamically stable, respectively. Similarly, 3 and 4
showed pairs of weak exo- (endothermic) peaks for Tg− (Tg+)
at −15 to 0 (−9) and 10−30 (23) °C, respectively, and
followed by the broad exothermic peaks for Ts at 53 and 95 °C,
respectively, just before reaching the melting point in the
second cycle. The melting points in the second cycle for 3 and
4 were consistent with those for the first scan, indicating that
the original 3 and 4 were solidified. It is noted that the Tg+
value of 4 was 25 °C and relatively high, and 4 was in the G
state near room temperature.
As shown in DSC measurements in the low temperature
range, the sample via the G state spontaneously solidified from
the SCL. The nucleus of a crystal might form in the G state and
induce the crystallization in the SCL state. The values of Tm,
Tg−, and Tg+ for 1, 2, 3, and 4 are summarized in Table 3.
Emission Alteration with a Mechanical Stimulus.
(A). SCL-to-C Transformation. As suggested by DSC, after
melting, 1, 2, 3, and 4 formed the SCL and G states at room
temperature and below Tg. The samples in the G states were
stable, while those in the SCL state were somehow labile
depending on the fluorophore. The samples in SCL state were
highly viscous oils, and the viscosity at room temperature
increased in the order of 2 < 1 < 3 < 4, which might correspond
Table 3. Values of Tm, Tt, Ts, Tg , and Tg (°C), for 1, 2, 3,
a
and 4
(°C) 1α
1β
1γ
2α
2β
3
4
Tm
Tt
98
98
n.d.
89
70
62
94
53
118
Ts
31
46
∼95
10−30 (br)
23
Tg−
Tg+
−10 to 10 (br)
−13
n.d.
−20
−15 to 0 (br)
−9
a
Tg− and Tg+ are in the cooling and heating process, respectively. n.d.;
not determined.
to the order of Tg+. The obtained SCL state for 1 was
maintained by leaving it at room temperature in a closed vessel
for 1 week, and it had solidified 3 weeks later. 2 in the SCL
state was relatively easily solidified after 24 h (Figure S8,
Supporting Information). Photographs indicating the time
dependence of transformation from SCL to solid at 20 2 °C
for 1−4 are shown in S8′. In contrast, upon scratching the
surface of the viscous oil, the scratched part solidified and a
bright emission was observed. Observation under a microscope
suggested that solidification (crystallization) rapidly took place
and then gradually and entirely expanded with time. The time
dependence of solidification of 1 after scratching is shown in
photographs in Figure 5.
The crystals were heated above Tm and the alterations of
emission before and after scratching were examined using
fluorescence spectroscopy. All samples in the SCL state showed
emissions with similar wavelengths and Φf (540 7 nm and
0.2, respectively). The emission showed red shifts of wave-
lengths by 21−32, 13−34, 34, and 10 nm for 1, 2, 3, and 4,
respectively, and reduction of intensity except for 2β and 3,
f
compared with the solid state. The observed red shifts of λmax
and the reductions of Φf in the SCL state might suggest that the
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Figure 5. Photographs of 1 after scratching 15 (a), 20 (b), and 30 min (c) later. Upper and lower panels are under room light and light at 365 nm,
respectively. In lower panels, the green and black area are solid and SCL parts, respectively.
intermolecular π−π interaction was stronger than that in the
solid state. In contrast, the increase of Φf for 2β and 3 might be
due to the molecular arrangements, columnar structures,
becoming amorphous in the SCL state. The absorption and
emission spectra of 1, 2, 3, and 4 in the SCL state are shown in
ab
Figure S9, Supporting Information and the values of λmax
,
λmaxf, and Φf, are listed in Table 4.
Figure 6. Photographs for 1 in the cycle of heating at 100 °C, cooling
at 25 °C, and scratching. The letters “P” and “L” were written by
scratching with a fine wire. The white scale bar indicates 5 mm.
ab
Table 4. Values of Absorption and Emission Maxima (λmax
and λmaxf, respectively) and Φf for 1, 2, 3, and 4 in the SCL
State
2, 3, and 4 also showed “write” and “erase” behaviors similar
to 1 (Figure S11, Supporting Information). However, the
written letters for 3 and 4 were not clear. In 3, the difference of
brightness between the letter and background was small
because the Φf value in the crystal state was smaller than that
in the SCL states. In 4, on the other hand, the emission
wavelengths in the crystal and SCL states were close to each
other.
1
2
3
4
λmaxab/nm
λmaxf/nm
Φf
412
541
0.22
417
544
0.18
416
536
0.20
430
547
0.22
The sample of 1 in the SCL state showed a broad and weak
emission at λmax of 541 nm with Φf = 0.2, while the scratched
sample emitted an intense yellowish green (λmax = 515 nm).
The fluorescence intensity increased more by annealing at 80
°C (10 min) for the complete solidification, and the obtained
spectrum was similar to those for 1β and 1γ rather than 1α.
Similarly, crystals, 2, 3, and 4 in the SCL state also showed
alteration of their emission intensity in response to the
mechanical stimuli. The observed emission intensity change
f
(B). C-to-C Transformation. Interestingly, the emitted green
color for 2β in the crystalline state could be changed to
yellowish green by grinding the crystal. In the emission spectra,
f
f
the λmax value of 510 nm shifted to ca. 530 nm after grinding,
which was close to that for 2α, suggesting the formation of 2α
through C-to-C transformation induced by mechanical stimuli.
The spectral alterations before and after grinding 2β are shown
in Figure S12, Supporting Information together with photo-
graphs under light at 365 nm. Furthermore, 2β also turned to
2α by exposure to CH2Cl2 vapor.22
PXRD Measurements. To investigate the crystal structures
of the products formed through SCL-to-C and C-to-C
transformations, powder X-ray diffraction (PXRD) measure-
ments were carried out. The obtained PXRD patterns for 1, 2,
3, and 4 were consistent with those simulated by the data
obtained from SXRD.
(A). SCL-to-C. PXRD patterns for 1α, 2α, 3, and 4 were
measured in various conditions. The alterations of PXRD
patterns are shown in Figure 7 for 1α and 2α and Figure S13,
Supporting Information for 3 and 4.
After heating over mp and then cooling to 23 °C (30 °C for
4) for 1α, 2α, 3, and 4, all sharp signals disappeared and broad
signals were observed (Figure 7(a-ii) and (b-ii)), indicating that
the samples were in the SCL state, which were amorphous.
After scratching, the sharp signals appeared, indicating that the
sample in SCL was crystallized. In 1α, the observed PXRD
could be repeated using the cycle of heating above Tm
−
scratching at room temperature, which are shown in Figure
S10, Supporting Information. The rates of solidification in the
SCL state after scratching were different and became faster in
the order of 2 > 1 > 3 > 4, which might correspond to the order
of Tg+.
By taking advantage of the differences in the emission
intensity depending on the state, that is, SCL or solid, writing
and erasing were possible, as follows. The SCL of 1 emitted
weakly. When the letter P was written by scratching several
times with a fine wire, the letter P rapidly appeared under black
light due to the crystallization at the stimulation point. With
time, the letter P became blurred. Subsequently, when the
temperature was raised to 100 °C and cooled to room
temperature, the letter P disappeared and the sample returned
to the SCL state. A different letter, L, was then written with a
fine wire. The emission behavior of 1 in the cycle of heating
and cooling is shown in Figure 6.
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Figure 7. PXRD patterns of 1α (a) and 2α (b) under various
conditions. For (a), before (a-i) and after heating at 100 °C (a-ii), after
scratching (a-iii), after annealing at 80 °C for 10 min (a-vi), and those
for crystal 1β (a-v) and 1γ (a-vi). Circles and triangles in (a-iii)
indicate the peaks due to crystals 1β and 1γ, respectively. For (b),
before (b-i) and after heating at 100 °C (b-ii), after scratching (b-iii),
after leaving SCL for 6 h. (b-iv), and simulation of 2β (b-v).
Figure 8. PXRD patterns of 1γ (a) and 2β (b). For (a), the simulation
patterns for 1γ (a-i) and 1β (a-iv), and PXRD patterns before (a-ii)
and after (a-iii) heating crystal at 80 °C, and for (b), simulation
patterns for 2β(b-i), 2α (b-iv), and PXRD patterns before (b-ii) and
after (b-iii) grinding of 2β.
a new one, which was consistent with that for 2α. This result
indicated that the phenyl moiety of 2 rotated from anti to syn
position by a mechanical stimulus, grinding. The alterations of
PXRD patterns for the samples for both of 1γ and 2β induced
by thermal and mechanical stimuli, respectively, are shown in
Figure 8. IR spectra measurements of 2β under various
conditions also supported the C-to-C transformation from 2β
to 2α (Figure S14, Supporting Information).
Thermal and Mechanical Phase Transitions. As
observed in DSC and PXRD experiments, crystals 1, 2, 3,
and 4 showed various thermal phase transitions including
transitions in response to the mechanical stimuli, which are
summarized in Scheme 1.
signal pattern after scratching suggested that a mixture of crystal
1β and 1γ formed (Figure 7(a-iii)). After annealing at 80 °C
(Figure 7(a-iv)), the signals due to crystal 1γ disappeared, and
the signals due to crystal 1β remained. In a separate PXRD
experiment, a thermal transformation from 1γ to 1β was
confirmed (Figure 8a). In 2α, the PXRD patterns after
scratching were consistent with those before heating the
samples, indicating that 2α was recovered. In contrast, when
the sample in the SCL state was left for 6 h without scratching,
a new pattern, which was consistent with that for 2β, appeared
(Figure 7(b-iv)). In the initial stage of scratching 3 in the SCL
state, a new PXRD pattern in addition to the one for 3
appeared, while in the final stage the new pattern disappeared,
and the original one for 3 remained. The observed new pattern
might be due to a polymorph of 3. At the present stage, a
polymorph of 3 has not been isolated. The PXRD patterns for
3 and 4 were obtained after scratching, which indicated that 3
and 4 were mainly recovered (Figure S13, Supporting
Information).
It was worth noting that the samples in the SCL state rapidly
crystallized by a mechanical stimulus, scratching, and the
produced crystals in 1 and 2 were mixture of polymorphs, 1β
and 1γ, and 2α having HB structure, which might be kinetically
stable.
CONCLUSION
(B). C-to-C. PXRD patterns for 1γ and 2β before and after
heating and grinding, respectively, were investigated.
When crystal 1γ was heated at 80 °C, the PXRD pattern for
1γ changed to a new one consistent with that for crystal 1β.
This result indicated that a thermal transformation from 1γ to
1β took place. By grinding, the PXRD pattern for 2β altered to
■
TFMAQ-Ph derivatives having methyl (1), ethyl (2), isopropyl
(3), and phenyl (4) substituents were prepared as a new type of
external stimuli responsive fluorophore. The TFMAQ-Ph
derivatives were obtained as single crystals, in which 1 and 2
provided three (1α, 1β, and 1γ) and two (2α and 2β)
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structures were solved by direct methods (SIR 9223 or SHELXL 9724
or SIR 200425). The refinements were converged using the full-matrix
least-squares method from the Crystal Structure software package26 to
Scheme 1. Phase Transitions of 1 (a), 2 (b), and 3 and 4 (c)
by Heating (Δ) and Cooling (−Δ) Processes
a
give P1 (No. 2), C2/c (No. 15), Cc (No. 9), Pna2 (No. 33), P1 (No.
̅
̅
1
2), P2 /c (No. 14), P1 (No. 2), and C2/c (No. 15) for crystals, 1α, 1β,
̅
1
1γ, 2α, 2β, 3, 4173, and 490, respectively. All non-hydrogen atoms were
refined anisotropically and hydrogen atoms were refined isotropically.
Crystallographic data for the structure reported in this paper have been
deposited with the Cambridge Crystallographic Data Center as
supplementary publications nos. CCDC 917133, 917134, 917135,
980547, 980548, 980549, 980550, and 980551 for crystals, 1α, 1β, 1γ,
2α, 2β, 3, 490, and 4173, respectively. Powder X-ray diffraction (PXRD)
spectra were performed with a Bruker AXS D2PHASER. PXRD
measurements for the crystal and powder samples were carried out at a
2θ angle of 5−50° at 25 °C.
Absorption and Emission Spectra and Fluorescence
Quantum Yield Measurements. In the measurement of the
solution sample, the compounds were dissolved in the solvents and
nitrogen gas was bubbled through the needle. Roughly crushed crystals
and ground crystals were used as crystal and powdered samples,
respectively. UV−vis spectra were recorded on a JASCO V570
spectrometer. The absorption spectra of the powder samples diluted
by KBr were obtained by the measurements of the diffractive reflection
spectra followed by Kubelka−Munk conversion using a JASCO ISN-
470 integrating sphere assembly. The fluorescence spectra were
recorded on a PerkinElmer LS 50B spectrometer. The fluorescence
quantum yield was determined with Hamamatsu C9920-01 instru-
ments equipped with a CCD by using a calibrated integrating sphere
system.
a
Ms, Mg, and L indicate giving mechanical stimuli, scratching and
grinding, and leaving for a long time, respectively.
polymorphs, respectively, having different molecular arrange-
ments. The obtained polymorphs showed C-to-C trans-
formation from 1γ to 1β and from 2β to 2α induced by heat
and grinding, respectively, with an alteration of emission color.
In addition, 4 showed a crystal phase transition between 173
and 90 K. These four fluorophores, 1, 2, 3, and 4, exhibited
characteristic alterations of emission intensity through SCL-to-
C transformation induced by mechanical stimuli. After melting,
the molecules formed the SCL and G states at room
temperature, and those in the SCL state rapidly crystallized
by scratching. 1, 2, 3, and 4 in the SCL state were confirmed to
mechanically provide a mixture of crystals, 1β and 1γ, only 2α,
3, and 4, respectively, by PXRD patterns. The emissions in the
SCL state were weak, while those in the solid state were
intense. By taking advantage of the alteration of emission
intensity caused by SCL-to-C transformation, we could “write”
and “erase” letters with the cycle of scratching and heating. Use
of the SCL-to-C transformation with a tuned emitting intensity
(write and erase) might be a useful approach for switchable
emitting materials.
Materials. 2,4-Di(trifluoromethyl)-7-phenylaminoquinoline
(TFMAQ-Ph) was prepared by the procedure reported previously.7
2,4-Di(trifluoromethyl)-7-methylphenylaminoquinoline, 1,. So-
dium hydride (27 mg, 1.1 mmol) was added to a solution of
TFMAQ-Ph (0.20 g, 0.56 mmol) in THF (4 mL) with stirring. The
suspension was stirred for 20 min, and then methyl iodide (0.32 g,
2.25 mmol) was added. The solution was stirred at room temperature
for 6 h. The reaction mixture was poured into water and extracted
three times with ether (60 mL). Organic layers were combined, dried
over MgSO4, and evaporated under reduced pressure. Crude residue
was chromatographed on a silica gel using n-hexane/ether = 50:1 as
eluents to separately afford a pale yellow solid (0.18 g, 0.49 mmol) in
1
87% yield. Mp 93 °C, H NMR (500 MHz, CD2Cl2) δ 7.89 (dd, J =
9.4 and 2.1 Hz, 1H), 7.70 (s, 1H), 7.48 (d, J = 2.1 Hz, 1H), 7.45 (d, J =
8.6 Hz, 2H), 7.32 (dd, J = 9.4 and 2.6 Hz, 1H), 7.30 (m, 3H), and 3.49
(s, 3H) ppm. 13C NMR (127 Hz, CD2Cl2) δ 151.56, 151.00, 147.73,
147.11, 136.00, 130.47, 126.92, 126.69, 126.59, 124.46, 122.71, 120.68,
117.67, 110.32, 109.61, and 40.93 ppm. FAB MS (in m-NBA matrix),
370 [1]+. Anal. Calcd for C18H12N2F6: C 58.38, H 3.27, N 7.57%;
Found: C58.20, H 3.32, N 7.59%.
2,4-Di(trifluoromethyl)-7-ethylphenylaminoquinoline, 2,. Fluoro-
phore 2 was prepared in a manner similar to the procedure for 1 by
using ethyl iodide in place of methyl iodide. Crude residue was
chromatographed on a silica gel using n-hexane/EtOAc = 100:1 as
eluents to separately afford a pale yellow solid in a quantitative yield.
Mp 69 °C (from DSC), 1H NMR (500 MHz, CD2Cl2) δ 7.87 (dd, J =
9.5, 1.9 Hz, 1H), 7.67 (s, 1H), 7.47 (t, J = 7.8 Hz, 1H), 7.41 (d, J = 2.6
Hz, 1H), 7.32 (t, J = 7.5 Hz, 1H), 7.27 (d, J = 7.4 Hz, 2H), 7.24 (d, J =
7.4 Hz, 2H), 3.95 (q, J = 7.1 Hz, 2H), and 1.32 (t, J = 7.1 Hz, 3H)
ppm. 13C NMR (126 MHz, CD2Cl2) δ 151.23, 150.87, 147.80, 145.96,
136.03, 130.73, 127.92, 127.03, 124.91, 124.53, 123.13, 120.86, 117.55,
110.21, 109.29, 47.69, and 12.43 ppm. ESI-MS, 407.1 [2 + Na]+. Anal.
Calcd for C19H14N2F6: C 59.38, H 3.67, N 7.29%; Found: C 59.66, H
3.97, N 7.07%.
EXPERIMENTAL SECTION
■
General Methods. Infrared spectra were recorded on a JASCO
420 FT-IR spectrometer. 1H and 13C NMR spectra were measured on
a Bruker Biospin AVANCE III 500 and Varian 500 Fourier transform
spectrometer using CDCl3 and CD2Cl2 as solvent and referenced to
TMS (Figure S15, Supporting Information). Differential scanning
calorimetry (DSC) curves were recorded by a SII SSC 5200 and 7000,
and NETZSCH DSC200 F3. Fast atom bombardment mass spectra
(FAB MS) were recorded on a JEOL JMS-SX102 spectrometer.
Electron spray mass spectra (ESI MS) were recorded on a Bruker
Daltonics microTOF spectrometer. Melting points were obtained with
a MEL-TEMP heating block and are uncorrected. Elemental analyses
were performed at the Analytical Center of the Faculty of Science in
Kyushu University.
2,4-Di(trifluoromethyl)-7-isopropylphenylaminoquinoline, 3,.
Fluorophore 3 was prepared in a manner similar to the procedure
for 1 by using 2-iodopropane in place of methyl iodide. Crude residue
was chromatographed on a silica gel using n-hexane/EtOAc = 100:1 as
eluents to separately afford a pale yellow solid in a quantitative yield.
Mp 94 °C (from DSC), 1H NMR (500 MHz, CDCl3) δ 7.82 (dd, J =
9.6 and 2.0 Hz, 1H), 7.64 (s, 1H), 7.49 (m, 2H), 7.42 (m, 2H), 7.17 (d,
X-ray Crystallography. Single-crystal X-ray diffraction (SXRD)
data and experimental details are summarized in Table S1, Supporting
Information for crystal 1α, 1β, and 1γ, Table S2 for 2α, 2β, and 3, and
Table S3 for 4 at various temperatures. Suitable single crystals were
glued onto a glass fiber using epoxy resin. All SXRD data were
collected on a Bruker AXS APEX-II diffractometer with graphite
monochromated MoKα radiation (λ = 0.71069 Å). The molecular
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Article
J = 8.5 Hz, 2H), 4.52 (quin, J = 6.6 Hz, 1H), and 1.24 (d, J = 6.5 Hz,
3H) ppm. 13C NMR (126 MHz, CDCl3) δ 151.59, 151.11, 148.15,
141.37, 136.24, 135.99, 131.80, 128.35, 124.71, 124.51, 122.79, 120.66,
117.11, 109.89, 108.14, 49.28, and 21.31 ppm. ESI-MS, 421.3 [3 + Na]
+. Anal. Calcd for C20H16N2F6: C 60.30, H 4.05, N 7.03%; Found: C
60.37, H 4.07, N 7.00%.
F.; Ghosh, S.; Muchharla, B.; Talapatra, S.; Terrones, H.; Terrones, M.
Adv. Funct. Mater. 2013, 23, 5511−5517.
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2007, 2, 180−184.
(4) (a) Seki, T.; Kurenuma, S.; Ito, H. Chem.Eur. J. 2013, 19,
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Chem. Soc. 2007, 129, 1520−1521.
2,4-Di(trifluoromethyl)-7-diphenylaminoquinoline, 4,. TFMAQ-
Ph (200 mg, 0.56 mmol), tri-tert-butylphosphine (11 mg, 10 mol %),
palladium acetate (6.3 mg, 5 mol %), potassium tert-butoxide (94 mg,
0.84 mmol) were placed on the Schlenk flask and degassed toluene (2
mL) was added. Bromobenzene (188 mg, 1.2 mmol) was added under
nitrogen atmosphere, and the reaction mixture was heated at 110 °C
for 6 h. Crude residue was chromatographed on a silica gel using n-
hexane/EtOAc = 300:1−200:1 as eluents to afford a pale yellow solid
(230 mg, 0.53 mmol) in 95% yield. Mp 118 °C (from DSC), 1H NMR
(500 MHz, CDCl3) δ 7.96 (d, J = 9.3 Hz, 1H), 7.74 (s, 1H), 7.64 (d, J
= 1.8 Hz, 1H), 7.55 (dd, J = 9.4 and 1.9 Hz, 1H), 7.36 (d, J = 7.6 Hz,
2H), 7.35 (d, J = 7.6 Hz, 2H), 7.21 (d, J = 8.2 Hz, 4H), and 7.18 (m,
1H). 13C NMR (126 MHz, CDCl3) δ 151.26, 150.59, 148.35, 146.53,
136.40, 130.44, 126.69, 126.31, 125.87, 124.79, 122.38, 120.47, 119.40,
117.22, and 111.55 ppm. ESI-MS, 455.1 [4 + Na]+. Anal. Calcd for
C23H14N2F6: C 63.89, H 3.26, N 6.48%; Found: C 64.07, H 3.25, N
6.54%.
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12828−12832. (b) Kwon, M. S.; Gierschner, J.; Yoon, S.-J.; Park, S. Y.
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Fraser, C. L. J. Am. Chem. Soc. 2010, 132, 2160−2162. (d) Sagara, Y.;
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S.; Koga, N. Org. Lett. 2012, 14, 6282−6285.
(9) (a) Zeidan, T. A.; Trotta, J. T.; Chiarella, R. A.; Oliveira, M. A.;
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ASSOCIATED CONTENT
* Supporting Information
■
́
S
Am. Chem. Soc. 2012, 134, 9872−9875. (c) Reany, O.; Kapon, M.;
Botoshansky, M.; Keinan, E. Cryst. Growth Des. 2009, 9, 3661−3670.
(d) Braum, D. E.; Gelbrich, T.; Kahlenberg, V.; Tessadri, R.; Wieser, J.;
Griesser, U. J. J. Pharm. Sci. 2009, 98, 2010−2026.
Photographs of crystals for 1−4, crystallographic data for 1−4
including ORTEP drawings, molecular arrangements, selected
bond lengths and angles, Harshfeld fingerprint plots, photo-
physical data in solution and solid state for 1−4, DSC curves
for 1β, 1γ, and 2β, alteration of fluorescence spectra and
photographs (irradiating at 365 nm) in the SCL state after
scratching for 2−4, PXRD patterns for 3 and 4, IR spectra
before and after grinding for 2β, and 1H and 13C NMR spectra
for 1−4. These materials are available free of charge via the
Internet at http://pubs.acs.org. Full crystallographic data
(CCDC-917133, 917134, 917135, 980547, 980548, 980549,
980550, and 980551 for crystals, 1α, 1β, 1γ, 2α, 2β, 3, 490, and
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AUTHOR INFORMATION
Corresponding Author
*Tel: 81-92-642-6590. Fax: 81-92-642-6590. E-mail: koga@fc.
phar.kyushu-u.ac.jp.
Notes
■
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
This work was supported by a Grant-in-Aid for Scientific
Research (B)(2)(No. 25288038) from the Ministry of
Education, Science, Sports and Culture, Japan, and partially
supported by Platform for Drug Discovery, Informatics, and
Structural Life Science from the Ministry of Education, Culture,
Sports, Science and Technology, Japan.
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