Photochromism of thiazole-containing triangle terarylenes

Article abstract of DOI:10.1002/ejoc.200700074

Triangle terarylene derivatives based on the 4,5-diarylthiazole structure have been synthesized and their photochromic properties have been studied both in solution and in the crystalline state. The thiazolyl-substituted terarylenes displayed reversible p

Full text of DOI:10.1002/ejoc.200700074

FULL PAPER
DOI: 10.1002/ejoc.200700074
Photochromism of Thiazole-Containing Triangle Terarylenes
Takuya Nakashima,[a] Kazuhiko Atsumi,[a] Shigekazu Kawai,[a] Tetsuya Nakagawa,[a]
Yasuchika Hasegawa,[a] and Tsuyoshi Kawai*[a]
Keywords: Photochromism / Photochemistry / Dyes / Heterocycles
Triangle terarylene derivatives based on the 4,5-diarylthi-
azole structure have been synthesized and their photochro-
mic properties have been studied both in solution and in the
crystalline state. The thiazolyl-substituted terarylenes dis-
played reversible photochromism in solution, with photo-
cyclization quantum yields as high as 60%, while a 4,5-dithi-
enylthiazole derivative underwent photochromic reaction
even in the single-crystal state, although a 4,5-dithiazolylthi-
azole (terthiazole) showed no photochromic reaction in the
crystalline phase. The difference in photochromic reactivity
between the 4,5-dithienylthiazole and the 4,5-dithiazolylthi-
azole was found by X-ray crystallographic analyses to origi-
nate from conformational differences in the crystalline state.
The thermal cycloreversion activation energies in the solu-
tion phase were measured for thiazolyl-substituted teraryl-
enes and for a corresponding terthiophene derivative. The
activation energy for the transition from photogenerated
closed-ring isomer to open-ring isomer increased with the
number of substitutions of thiazole unit for thiophene. The
lower aromatic stabilization energy of thiazole in relation to
that of thiophene was considered to be responsible for the
thermal stability of the closed-ring isomers of thiazolyl-sub-
stituted terarylenes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
study. In this context we have recently reported on photo-
chromic triangle terthiophene derivatives, which behave as
photoswitching two-way rerouters of π-conjugation expan-
sion.[26] These molecules include hexatriene components in
their molecular structures and undergo photoinduced cycli-
zation and cycloreversion reactions in a similar manner to
diarylethenes. Tian et al. also proposed a similar very easily
prepared photochromic triangle terthiophene while this
work was in progress.[27] These terthiophene derivatives
have thus been put forward as a novel category of photo-
chromic molecules, the so-called “triangle terarylenes”. In
terms of aromatic stabilization energies, however, the
closed-ring form of triangle terthiophene seems to be less
stable than that of dithienylethene because three aromatic
units collapse simultaneously with the photocyclization. As
in diarylethenes, the aryl group aromaticity might suppress
the thermal stability of the closed-ring isomers of teraryl-
enes.[28]
Here we describe the photochromic triangle terarylenes
1 and 2, containing one and three thiazole substituent(s),
respectively. The aromatic stabilization energy of thiazole
was calculated to be 21.3 kcalmol–1 whereas that of thio-
phene was 22.4 kcalmol–1,[29] and the lower aromaticity of
thiazole was expected to reduce the energy difference be-
tween the open- and closed-ring isomers of terarylenes, giv-
ing thermally bistable isomers. In addition to the energetic
aspect mentioned above, the introduction of the thiazole
group may be advantageous for the cyclization reaction be-
cause of its low steric hindrance. The diarylthiazole struc-
Introduction
There is much interest in molecular switching materials
that modulate a given physical property through the action
of some external trigger, with the goal of the development
of molecular devices.[1–3] Among these materials, consider-
able attention has focused on photochromic molecules,[4–7]
especially on photochromic diarylethenes,[8,9] which un-
dergo reversible photoisomerizations between pairs of bi-
stable isomers with different absorption spectra upon irra-
diation at appropriate wavelengths. Photoswitching effects
in diarylethenes have been extensively studied for con-
trolling various chemical and physical properties such as
fluorescence intensity and wavelength,[10–14] refractive in-
dex,[15,16] dielectric properties,[17] electronic conduc-
tion,[18,19] electrochemical response,[20,21] magnetic interac-
tions,[22] and self-assembling behavior.[23,24] Most of these
photoswitching effects are based, at least partly, on changes
in the extent of π-conjugation in the diarylethenes in the
course of photochromic reactions. While various types of
molecular electronic devices based on π-conjugation con-
nection pathways have been designed,[25] photon mode
modulations of conjugation systems are worthy of extensive
[a] Graduate School of Materials Science, Nara Institute of Science
and Technology, NAIST,
8916-5 Takayama, Ikoma, Nara 630-0192, Japan
Fax: +81-743-72-6179
E-mail: tkawai@ms.naist.jp
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
3212
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3212–3218

Photochromism of Triangle Terarylenes
FULL PAPER
ture might offer considerable advantages, as the steric hin- throline,[31] and tetraazaporphyrin[32] on the central ethene
drance between the 3(N)- and the 4Ј-methyl positions in 1 group have been proposed. Functions such as fluorescence
and between the 3(N)- and the 3Ј(N)- positions in 2 and electrochemical activity dependent on the central π-
(Scheme 1) should be suppressed in relation to that in the conjugated group were modulated through photochromic
terthiophene derivatives 3[26] and 4 [between 4-H and 4Ј-H reactions. These molecules also represent a stimulating pos-
(or methyl) positions]. From the perspective of the develop- sibility for the development of novel photofunctional mo-
ment of photofunctional molecular materials, these mole- lecular materials, but no-one has yet made detailed studies
cules should act as switching modules connecting the π-con- of the photochromic reactivities and thermal stabilities of
jugation pathways in multiple ways. In their open-ring the closed-ring forms of this new class of photochromic
forms, compounds 1 and 2 each consist of three aromatic compounds. A guiding principal for designing future pho-
π-conjugation units. Upon photochromic reaction the three tofunctional molecular materials relating to the photochro-
aromatic rings collapse simultaneously and the two ex- mic triangle terarylenes is proposed for the first time.
panded π-conjugation systems are formed: one is extended
throughout the molecule and the other is extended between
the central and “right-hand side” phenyl groups. Since the
expansion of π-conjugating connection markedly affects the
Results and Discussion
optical and electrical properties of organic molecules and
Compounds 1a and 2a were synthesized by conventional
polymers, these photochromic molecules might be expected cross-coupling reactions of arylene derivatives and their
to function as active materials for future molecular devices chemical structures were confirmed by 1H NMR, mass
based on nonlinear optical materials and conducting poly- spectrometry, and X-ray crystallography. The ring-closed
mers.
isomers 1b and 2b were prepared by irradiation of hexane
solutions of the corresponding open-ring isomers 1a and 2a
with UV light and were isolated from the colored solutions
by reversed-phase HPLC with methanol as the eluent. The
formation of the ring-closed isomers 1b and 2b was con-
1
firmed by H NMR spectroscopy in CDCl3 solution.[33]
Colorless solutions of the open-ring isomers 1a and 2a
were observed to turn blue upon irradiation with UV light
(λ = 313 nm), while the colored solutions were bleached by
visible light irradiation (λ Ͼ 400 nm). As shown in Figure 1
(a), 1a had no absorption band in the visible range, but a
new absorption band at 610 nm appeared upon irradiation
with UV light. An isosbestic point appeared at 340 nm, sup-
porting the two-component photochromic reaction as
shown in Scheme 1. The colored solution could be com-
pletely bleached upon irradiation with visible light, produc-
ing an absorption spectrum identical with that of the initial
solution of 1a, and the coloration and bleaching cycles
could be repeated at least twenty times without any photo-
degradation. Similar photochromic behavior was also ob-
served for 2 (Figure 1, b). The conversion ratios between 1a
and 1b and between 2a and 2b at their photostationary
states, achieved by irradiation with UV light (λ = 313 nm)
were estimated to be 90 and 93%, respectively. The values
of λmax and ε in 1 and 2 are summarized in Table 1 with
photochromic reaction quantum yields evaluated by the
standard procedure with 1,2-bis[5-(2,4-diphenylphenyl)-2,4-
dimethyl-3-thienyl]perfluorocyclopentene in hexane[16] as a
standard. Relatively high quantum yields were found for
compounds 1 and 2 in their cyclization reactions, the values
being not less than those observed for well established diar-
ylethenes.[8b] On the other hand, the previously reported tri-
angle terthiophene derivative 3a showed a low cyclization
quantum yield (φa–b = 0.04).[26] Part of the enhancement in
the photocyclization quantum yields may therefore presum-
Scheme 1. Photochemical and thermal interconversion of teraryl-
enes 1–4.
In the development of photochromic hexatriene com- ably be attributed to the reduced steric hindrance due to
pounds, some diarylethene derivatives incorporating ex- the substitution of thiazole for thiophene. The trisubsti-
panded π-conjugation systems such as quinone,[30] phenan- tuted terthiazole 2 showed a lower cyclization quantum
Eur. J. Org. Chem. 2007, 3212–3218
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3213

T. Kawai et al.
FULL PAPER
yield than the monothiazolyl-substituted 1, and the differ- Table 1. Absorption maxima and coefficients of the open- and
closed-ring isomers of 1 and 2, together with the quantum yields
in hexane.
ence in the population ratios of the conformations in solu-
tion is presumed to be responsible for the difference in the
λmax [nm]
φa–b
φb–a
cyclization quantum yields of 1a and of 2a. Briefly, as in
the case of diarylethene, terarylenes may have two confor-
mations – photochemically inactive parallel and active anti- 1a
ε [104 –1 cm–1]
269 (3.5)
610 (0.94)
315 (3.0)
587 (1.6)
0.6
–
0.4
–
–
0.07
–
parallel[34] – and they interconvert in solution at room tem-
1b
2a
perature. The photocyclization quantum yields should, in
2b
0.03
general, depend on the population ratios of the two confor-
mations,[8b] so the lower cyclization quantum yield of dithi-
azolylthiazole 2 in relation to dithienylthiazole 1 might be
attributable to the lower population ratio of the photo-
chemically active conformation in solution. The crystal
structure study discussed in the following paragraphs does
not contradict this explanation. Meanwhile, the low photo-
cycloreversion reaction quantum yields observed in 1b and
2b are characteristic of closed-ring diarylethenes with ex-
tended π-conjugation systems.[8b]
tene[36] – of a compound that will undergo thermally
irreversible and photochemically reversible photochromic
reactions in the crystalline phase. Under a polarized micro-
scope, with the source and the detection polarizers set in
parallel, the crystal was colored blue at a certain angle (0°).
As shown in Figure 2(c), the peak absorption wavelength
of the colored state was 640 nm, slightly longer than that
observed in hexane solution. When the crystal was rotated
by 90° under the microscope, the blue color was bleached
and the optical density decreased. The changes in optical
density seen on rotating the crystal sample indicate that the
closed-ring isomers are macroscopically oriented in the
crystal and that the photochromic reaction takes place in
the crystal lattice. No spectral shift was observed in the ab-
sorption band of the colored state even when the coloration
and bleaching cycles in the single crystal were repeated
many times.
Figure 1. Absorption spectral changes of 1(a) and 2(b) in hexane:
open-form a (dotted lines), closed-form b (solid lines) and photo-
stationary state under irradiation with 313 nm light (dashed lines).
The concentrations of 1 and 2 were 2.5ϫ10–5 and 2.9ϫ10–5 ,
respectively.
Figure 2. Photographs of crystal 1 before (a) and after (b) irradia-
tion with UV light. c) Polarized absorption spectra of the photo-
generated blue crystal of 1.
Unlike 1a, compound 2a showed no photochromic per-
Compounds 1a and 2a both formed plate-shaped color- formance in the crystalline phase. To investigate the differ-
less crystals on recrystallization from their hexane solutions. ence in photochromic reactivity between 4,5-dithienylthi-
The single crystal of 1a turned blue upon irradiation with azole 1a and ter-thiazole 2a, we then performed X-ray crys-
UV light (330 Ͻ λ Ͻ 385 nm) and the blue color disap- tallographic analyses.[37] The ORTEP drawing of 1a indi-
peared upon irradiation with visible light (λ Ͼ 500 nm) cates two different conformations packed alternately in the
(Figure 2). In the absence of light, the coloration of the sin- crystal, as shown in Figure 3(a). The two structures are
gle crystal was maintained for days at room temperature. quite similar: the distances between the reacting carbon
Terarylene 1 is thus one of the few examples[35] – with the atoms – C11–C23 and C44–C56 in Figure 3 (a), for exam-
exception of diarylethenes based on hexafluorocyclopen- ple – were evaluated to be 0.364 nm and 0.366 nm, respec-
3214
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3212–3218

Photochromism of Triangle Terarylenes
FULL PAPER
tively. Both of them are very close and short enough for the
In order to investigate the effect of thiazolyl substitution
photochromic ring-cyclization reaction.[38,39] The two con- on the thermal stability of the closed-ring isomers 1b and
formations each have a central hexatriene moiety with a 2b, the thermal cycloreversion kinetics of 1b and 2b were
quasi-C2 symmetric structure, which is favorable for the examined at various temperatures. Toluene was used as sol-
photochromic reaction with a contrarotational cyclization vent in these measurements in order to avoid changes in
mechanism.[34] Although we do not have further evidence, concentration caused by the evaporation of solvent upon
it is speculated that the two conformations should have sim- heating. The corresponding terthiophene derivative 4 was
ilar photochromic reactivity. Kobatake et al. have reported also used as a reference. The absorption spectrum of the
that the diarylethene derivatives possessing C–C distances colored state was measured at elevated temperature and the
shorter than 0.4 nm between the reacting carbon atoms bleaching of the visible absorption band was monitored
show similar photochromic reactivity in the single-crystal over several hours. All spectra were recorded at the elevated
state.[39]
temperature and absorbance change (A/A0) is plotted loga-
rithmically as a function of time. Figure 4 shows the decay
lines of the absorbance of the ring-closed isomers at several
temperatures. The decay lines followed first-order kinetics.
In these experiments, the thermal fading due to the decom-
position of the colored isomer was negligible, because the
absorption spectra of the thermally bleached solutions after
photocoloration/thermal bleaching cycles remained the
same in shape and intensity as the initial spectra of the ring-
open isomers. The thermal bleaching of the visible absorp-
tion band is thus attributed only to the thermal cyclorever-
sion to the open-ring isomer.
Figure 3. ORTEP drawings of open-ring isomer in crystal 1a (a)
and in crystal 2a (b), showing 50% probability displacement ellip-
soids. Two different alternately packed conformations existed for
1a in the single-crystalline phase.
On the other hand, as shown in Figure 3 (b), the packed
structure of 2a is very different from that of 1a. The dis-
tance between the two carbon atoms C12 and C22 is evalu-
ated as 0.492 nm, which might be too long for the photo-
cyclization reaction.[39] This specific conformation may be
stabilized by the weak CH/N hydrogen bonding interaction
between N1 and C29-H.[40] The distance between N1 and
C29-H was estimated to be 0.257 nm, which is appreciably
shorter than the sum of the van der Waals radii of (C–)H
(0.155 nm) and N (0.12 nm). A similar interaction may sta-
bilize and enrich the photoinactive conformation even in
solution, resulting in a lower photocyclization quantum
yield in solution for 2a (0.4) than for 1a (0.6).
Figure 4. Decay lines of peak absorbance by thermal cycloreversion
reactions of 1b (a), 2b (b), and 4b (c) at various temperatures in
toluene.
Eur. J. Org. Chem. 2007, 3212–3218
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3215

T. Kawai et al.
FULL PAPER
The first-order thermal cycloreversion reaction rate con- enhanced by the introduction of the thiazole group, which
stants (k) at various temperatures were evaluated from Fig- possesses a smaller aromatic stabilization energy than that
ure 4 and their temperature dependences are illustrated in of thiophene. Monothiazolyl-substituted 1 and trisubsti-
Figure 5. The activation energy (Ea) and frequency factor tuted 2 had half-lifetimes 30 times and 2600 times longer,
(A) of the thermal cycloreversion reaction of each com- respectively, than that of trithiophene-substituted 4. We ex-
pound are estimated from the linear regression lines and pect these thermal stable terarylene derivatives to play a
are summarized in Table 2. The values of Ea increased in a considerable roll in photoswitched molecular devices.
manner depending on the number of substituted thiazole
rings, giving the order of thermal bleaching rate of 2b Ͻ 1b
Experimental Section
Ͻ 4b. Extrapolation of the temperature dependence indi-
cates that the half-lifetimes of the closed-ring isomer at
20 °C are 11 h, 14 d, and 3.3 years for 4b, 1b, and 2b, respec-
tively. This result strongly suggests that the thermal stabilit-
ies of the ring-closed isomers could be controlled, like those
of dithiazolylethenes,[41,42] through the aromatic stabiliza-
tion energies of the aryl groups that make up photochromic
terarylenes.
General: 1H NMR spectra were recorded on a JEOL AL-300 spec-
trometer (300 MHz). Separative HPLC was performed on a HITA-
CHI LaChrom ELITE HPLC system and a JASCO LC-2000 Plus
Series. Mass spectra were measured with a JEOL JMS-T100LC
AccuTOF mass spectrometer. Absorption spectra in solution were
studied with JASCO V-550 and V-670 spectrophotometers with a
temperature control unit. Photoirradiation was carried out with an
USHIO 500-W ultra-high-pressure mercury lamp or a Panasonic
Aicure UV curing system (LED, λ = 365 nm) as the exciting light
source. Monochromic light was obtained by passing the light
through a monochromator (Shimadzu SPG-120S, 120 mm, f = 3.5).
Absorption spectra in the single-crystal phase were measured with
an Olympus BX-51 polarizing microscope connected to a Hamam-
atsu PMA-11 photodetector through an optical fiber. Polarizer and
analyzer were set in parallel to each other. X-ray crystallographic
analyses were carried out with a Rigaku R-AXIS RAPID/s Im-
aging Plate diffractometer with Mo-Kα radiation at 296 K.
2-(2,4-Dimethyl-5-phenylthiophen-3-yl)-4,4,5,5-tetramethyl-1,3,2-di-
oxaborolane (6): nBuLi (1.6  in hexane, 5.6 mL, 9.0 mmol) was
added slowly under Ar at –78 °C to a solution of 3-bromo-2,4-
dimethyl-5-phenylthiophene (5, 2.1 g, 8.2 mmol) in dry THF
(60 mL), and the mixture was stirred for 1 h at that temperature
(Scheme 2). 2-Isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
(2.0 mL, 9.9 mmol) was then added in a dropwise fashion and the
system was stirred for another 1 h. The reaction mixture was al-
lowed to warm to room temperature. Methanol was added to the
reaction mixture, which was extracted with ethyl acetate. The com-
bined organic fraction was washed with water, dried with anhy-
drous magnesium sulfate, and concentrated to give 2.7 g (99%) of 6
as colorless powder. The obtained powder was used without further
purification.
Figure 5. Temperature dependence of the thermal fading rates of
1b, 2b, and 4b in toluene.
Table 2. Arrhenius parameters of thermal cycloreversion and half-
lifetimes from the closed- to the open- ring isomers in toluene.
Ea [kJmol–1]
A [s–1]
t1/2 (20 °C)
4,5-Bis(2,4-dimethyl-5-phenylthiophen-3-yl)-2-phenylthiazole (1a): A
100 mL four-necked flask was charged with 6 (1.9 g, 5.9 mmol),
4,5-dibromo-2-phenylthiazole (7,[43] 0.9 g, 2.8 mmol), tri-
phenylphosphane (0.10 g, 0.38 mmol), Pd(PPh3)4 (0.15 g,
0.13 mmol), and K3PO4 (2 ) in water/1,4-dioxane (10 mL/70 mL)
solution. The mixture was then stirred at 110 °C under N2. After
having been stirred for three days the reaction mixture was ex-
tracted with ethyl acetate and the organic layer was dried with an-
hydrous magnesium sulfate, filtered, and concentrated. Silica gel
column chromatography (hexane/ethyl acetate 19:1) and reversed
phase HPLC (methanol) afforded 1a (0.18 g, 12%) as a colorless
solid. 1H NMR (300 MHz, CDCl3/TMS): δ = 2.08 (s, 3 H), 2.13
(s, 3 H), 2.15 (s, 3 H), 2.20 (s, 3 H), 7.28–7.49 (m, 15 H) ppm. ESI
HRMS (m/z) [M + H]+ calcd. for C33H28NS3+: 534.1378; found:
534.1304.
1b
2b
4b
92
112
84
1.6ϫ1010
7.1ϫ1011
2.0ϫ1010
14 d
3.3 years
11 h
Conclusions
We have designed and synthesized triangle terarylenes
with the substitution of one or three thiazole groups as aryl
units. The thiazole-containing compounds 1 and 2 show rel-
atively high photocyclization quantum yields, comparable
with those seen in the well established diarylethenes. Inter-
estingly, the monothiazolyl-substituted terarylene 1 exhib-
ited reversible photochromism even in the crystalline phase,
whereas terthiazole 2 did not. This difference was explained
in terms of conformational differences in the crystalline
phase as revealed by X-ray crystallographic analyses. The
5-Methyl-2-phenyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
thiazole (9): This compound was prepared by the same procedure
as had been used as for 6, except that 5 was replaced by 8. From 8
(1.1 g, 4.3 mmol) in dry ether (40 mL), nBuLi (1.6  in hexane,
thermal stabilities of the ring-closed isomers were greatly 3.0 mL, 4.9 mmol) and 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-di-
3216
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3212–3218

Photochromism of Triangle Terarylenes
FULL PAPER
Scheme 2. Synthesis of photochromic terarylenes 1a, 2a, and 4a. Conditions: a; 1) nBuLi, 2) 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-diox-
aborolane. b; K3PO4, Pd(PPh3)4/H2O, 1,4-dioxane.
oxaborolane (1.5 mL, 9.9 mmol), 9 (1.3 g, 97%) was obtained as a
colorless powder.
boronic acid (0.18 g, 1.5 mmol), triphenylphosphane (0.10 g,
0.38 mmol), Pd(PPh3)4 (0.15 g, 0.13 mmol), and K3PO4 (2 ) in
water/1,4-dioxane (10 mL/40 mL) solution, 4a (41 mg, 5%) was ob-
tained as a colorless solid. 1H NMR (300 MHz, CDCl3/TMS): δ =
1.99 (s, 3 H), 2.11 (s, 3 H), 2.15 (s, 3 H), 2.33 (s, 3 H), 7.31 (m, 3
H), 7.40 (m, 11 H), 7.66 (m, 2 H) ppm. The comformational iso-
4,5-Bis(5-methyl-2-phenylthiazol-4-yl)-2-phenylthiazole (2a): This
compound was prepared by the same procedure as had been used
as for 1a, except that 6 was replaced by 9. From 9 (1.3 g, 4.1 mmol),
7 (0.53 g, 1.7 mmol), triphenylphosphane (0.075 g, 0.30 mmol),
Pd(PPh3)4 (0.075 g, 0.13 mmol), and K3PO4 (2 ) in water/1,4-di-
oxane (15 mL/15 mL) solution, 2a (50 mg, 6%) was obtained as a
1
mer[40] of 4a was also found by H NMR; conformer A: δ = 2.03
(s, 3 H), 2.11 (s, 3 H), 2.15 (s, 3 H), 2.20 (s, 3 H), 7.31 (m, 3 H),
7.40 (m, 11 H), 7.66 (m, 2 H), conformer B: δ = 1.99 (s, 3 H), 2.11
(s, 3 H), 2.15 (s, 3 H), 2.33 (s, 3 H), 7.31 (m, 3 H), 7.40 (m, 11 H),
1
colorless solid. H NMR (300 MHz, CDCl3/TMS): δ = 2.11 (s, 3
H), 2.52 (s, 3 H), 7.33 (m, 3 H), 7.43 (m, 6 H), 7.80 (m, 2 H), 7.93
(m, 2 H), 8.07 (m, 2 H) ppm. ESI HRMS (m/z) [M + H]+ calcd.
for C29H22N3S3+, 508.0970; found: 508.0974.
1
7.66 (m, 2 H) ppm, the ratio of conformer estimated from the H
NMR spectrum was 7:8. ESI HRMS (m/z) [M + H]+ calcd. for
C34H29S3+: 533.1431; found: 533.1437.
2,3-Bis(2,4-dimethyl-5-phenylthiophen-3-yl)thiophene (11): This
compound was prepared by the same procedure as had been used
as for 1a, except that 7 was replaced by 10. From 4 (2.0 g,
6.3 mmol), 10 (0.65 g, 2.7 mmol), triphenylphosphane (0.10 g,
0.38 mmol), Pd(PPh3)4 (0.15 g, 0.13 mmol), and K3PO4 (2 ) in
water/1,4-dioxane (10 mL/40 mL) solution, 11 (0.42 g, 34%) was
Supporting Information (see also the footnote on the first page of
this article): 1H NMR spectra and ESI HRMS charts of 1a, 2a and
3a.
Acknowledgments
1
obtained as a colorless solid. H NMR (300 MHz, CDCl3/TMS):
δ = 1.93 (s, 3 H), 1.98 (s, 3 H), 2.06 (s, 3 H), 2.10 (s, 3 H), 2.15 (s,
3 H), 2.28 (s, 3 H), 7.31 (m, 4 H), 7.43 (m, 8 H) ppm.
The authors thank Mr. S. Katao and Mrs. Y. Nishikawa, technical
staff members of NAIST, for X-ray crystallographic analyses and
mass spectroscopic measurements. This work was supported by the
Ministry of Education, Culture, Sports, Science and Technology
(MEXT), Japan: Grants-in-Aid for Scientific Research (B)
(No. 17350069) and Scientific Research on Priority Areas, “Super-
Hierarchy Structures” (No. 17067011) from.
2-Bromo-4,5-bis(2,4-dimethyl-5-phenylthiophen-3-yl)thiophene (12):
N-Bromosuccinimide (0.21 g, 1.2 mmol) and a trace amount of
ZnCl2 were added to a solution of 11 (0.42 g, 0.92 mmol) in THF
(10 mL). The mixture was stirred at room temperature for 2 d and
then extracted with ethyl acetate. The organic layer was dried with
anhydrous MgSO4 and concentrated under reduced pressure. The
residue (0.47 g, 95%) was used without further purification.
[1] Molecular Switches (Ed.: B. L. Feringa), Wiley-VCH,
Weinheim, 2001.
2,3-Bis(2,4-dimethyl-5-phenylthiophen-3-yl)-5-phenylthiophene (4a):
This compound was prepared by the same procedure as had been
used as for 1a, except that 6 and 7 were replaced by phenylboronic
acid and 12, respectively. From 12 (0.77 g, 1.4 mmol), phenyl-
[2] V. Balzani, M. Venturi, A. Credi, Molecular Devices and Ma-
chines–A Journey into the Nanoworld, Wiley-VCH, Weinheim,
2003.
[3] S. Shinkai, Pure Appl. Chem. 1987, 59, 425.
Eur. J. Org. Chem. 2007, 3212–3218
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3217

T. Kawai et al.
FULL PAPER
[4]
[5]
[6]
[7]
A. Dhirani, P. H. Lin, P. Guyot-Sionnest, R. W. Zehner, L. R.
Sita, J. Chem. Phys. 1997, 106, 5249; c) C. Joachim, J. K.
Gimzewski, A. Aviram, Nature 2000, 408, 541.
Photochromism: Memories and Switches: M. Irie, Chem. Rev.
2000, 100, 1683.
Photochromism (Ed.: G. H. Brown), Wiley-Interscience, New
York, 1971.
Photochromism: Molecules and Systems (Eds.: H. Dürr, H.
Bouas-Laurent), Elsevier, Amsterdam, 1990.
[26] T. Kawai, T. Iseda, M. Irie, Chem. Commun. 2004, 72.
[27] X. Li, H. Tian, Tetrahedron Lett. 2005, 46, 5409.
[28] S. Nakamura, M. Irie, J. Org. Chem. 1988, 53, 6136.
[29] A. R. Katritzky, M. Karelson, S. Sild, T. M. Krygowski, K.
Jug, J. Org. Chem. 1998, 63, 5228.
[30] X. Deng, L. S. Lieveskind, J. Am. Chem. Soc. 2001, 123, 7703.
[31] a) V. W. W. Yam, C. C. Ko, N. Y. Zhu, J. Am. Chem. Soc. 2004,
126, 12734; b) C. C. Ko, W. M. Kwok, V. W. W. Yam, D. L.
Phillips, Chem. Eur. J. 2006, 12, 5840.
P. Belser, L. De Cola, H. Frantisˇek, V. Adamo, B. Bozic, Y.
Chriqui, V. M. Iyer, R. T. F. Jukes, J. Kühni, M. Querol, S.
Roma, N. Salluce, Adv. Funct. Mater. 2006, 16, 195.
a) M. Irie, M. Mohri, J. Org. Chem. 1988, 53, 803; b) M. Irie,
Chem. Rev. 2000, 100, 1685, and references therein.
H. Tian, S. Yang, Chem. Soc. Rev. 2004, 33, 85.
G. M. Tsuvgoulis, J.-M. Lehn, Angew. Chem. Int. Ed. Engl.
1995, 34, 1119.
a) T. Norsten, N. R. Branda, J. Am. Chem. Soc. 2001, 123,
1784; b) A. J. Myles, N. R. Branda, Macromolecules 2003, 36,
298; c) A. J. Myles, B. Gorodetsky, N. R. Branda, Adv. Mater.
2004, 16, 922; d) E. Murguly, T. B. Norstern, N. R. Branda,
Adv. Mater. 2001, 13, 347.
a) T. Kawai, T. Sasaki, M. Irie, Chem. Commun. 2001, 711; b)
M. Irie, T. Gukaminato, T. Sasaki, N. Tamai, T. Kawai, Nature
2002, 420, 759; c) T. Fukaminato, T. Sasaki, T. Kawai, N. Ta-
mai, M. Irie, J. Am. Chem. Soc. 2004, 126, 14843.
a) A. Osuka, D. Fujikane, H. Shinmori, S. Kobatake, M. Irie,
J. Org. Chem. 2001, 66, 3913; b) K. Yagi, C. F. Soong, M. Irie,
J. Org. Chem. 2001, 66, 5419.
[8]
[9]
[10]
[32] a) H. Tian, B. Chen, H. Tu, K. Müllen, Adv. Mater. 2002, 14,
918; b) Q. F. Luo, B. Z. Chen, M. Z. Wang, H. Tian, Adv.
Funct. Mater. 2003, 13, 233.
[11]
[33] 1H NMR spectroscopic data for 1b: (300 MHz, CDCl3/TMS):
δ = 2.12 (s, 3 H), 2.29 (s, 3 H), 2.31 (s, 3 H), 2.41 (s, 3 H),
7.32–7.48 (m, 15 H) ppm; for 2b: (300 MHz, CDCl3/TMS): δ
= 2.10 (s, 3 H), 2.12 (s, 3 H), 7.50 (m, 9 H), 7.92 (m, 2 H), 8.05
(m, 4 H) ppm.
[12]
[34] M. Irie, O. Miyatake, K. Uchida, T. Eriguchi, J. Am. Chem.
Soc. 1994, 116, 9894.
[35] D. G. Patel, J. B. Benedict, R. A. Kopelman, N. L. Frank,
Chem. Commun. 2005, 2208.
[13]
[14]
[36] M. Morimoto, M. Irie, Chem. Commun. 2005, 3895, and refer-
ences therein.
[37] Crystallographic data for 1a: C33H27NS3, a = 11.156(4), b =
12.220(5), c = 20.683(9) Å, α = 84.218(15), β = 85.607(13), γ =
9.841(13)°, triclinic, space group P-1, Z = 4, V = 2756.5(19) Å3,
ρcalcd. = 1.286 g cm–3. Of 27074 reflections up to 2θ = 55.0°, 12
410 were independent (Rint = 0.064) and 5208 with I Ͼ 2σ(I).
The structure was solved by direct methods and refined with
full-matrix against all F2 data. Hydrogen atoms were calculated
R. T. F. Jukes, V. Adamo, F. Hartl, P. Belser, L. De Cola, Inorg.
Chem. 2004, 43, 2799.
[15] N. Tanio, M. Irie, Jpn. J. Appl. Phys. 1994, 33, 1550.
[16] M.-S. Kim, H. Maruyama, T. Kawai, M. Irie, Chem. Mater.
2003, 15, 4539, and references therein.
[17] T. Kawai, T. Koshido, K. Yoshino, Appl. Phys. Lett. 1995, 67,
795.
in riding positions. wR
= 0.1016, R = 0.064; for 2a:
[18] D. Dulic´, S. J. van der Molen, T. Kudernac, H. T. Jonkman,
J. J. D. de Jong, T. N. Bowden, J. van Esch, B. L. Feringa, B. J.
van Wees, Phys. Rev. Lett. 2003, 91, 207402-1.
C29H21N3S3, a = 9.486(4), b = 11.994(5), c = 12.546(6) Å, α =
113.333(17), β = 102.908(15), γ = 95.732(15)°, triclinic, space
group P-1, Z = 2, V = 1249.0(9) Å3, ρcalcd. = 1.350 g cm–3. Of
12405 reflections up to 2θ = 55.0°, 5674 were independent (Rint
= 0.023) and 3604 with I Ͼ 2σ(I). The structure was solved
and refined in an analogous manner to 1a. wR = 0.1943, R =
0.057. CCDC-621390 (for 1a) and -621391 (for 2a) contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[38] V. Ramamurthy, K. Venkatesan, Chem. Rev. 1987, 87, 433.
[39] a) S. Kobatake, T. Yamada, K. Uchida, N. Kato, M. Irie, J.
Am. Chem. Soc. 1999, 121, 2380; b) S. Kobatake, M. Yamada,
T. Yamada, M. Irie, J. Am. Chem. Soc. 1999, 121, 8450; c) S.
Kobatake, K. Shibata, K. Uchida, M. Irie, J. Am. Chem. Soc.
2000, 122, 12135.
[19] T. Kawai, Y. Nakashima, M. Irie, Adv. Mater. 2005, 17, 309.
[20] a) S. L. Gilat, S. H. Kawai, J.-M. Lehn, J. Chem. Soc., Chem.
Commun. 1993, 1439; b) S. L. Gilat, S. H. Kawai, J.-M. Lehn,
Chem. Eur. J. 1995, 1, 275; c) S. H. Kawai, S. L. Gilat, R. Ponsi-
net, J.-M. Lehn, Chem. Eur. J. 1995, 1, 285; d) S. H. Kawai,
S. L. Gilat, J.-M. Lehn, Eur. J. Org. Chem. 1999, 2359.
[21] R. Baron, A. Onopriyenko, E. Katz, O. Lioubashevski, I.
Willner, S. Wang, H. Tian, Chem. Commun. 2006, 2147.
[22] a) K. Mastuda, M. Irie, J. Am. Chem. Soc. 2000, 122, 7195; b)
K. Matsuda, M. Irie, J. Am. Chem. Soc. 2000, 122, 8309; c) K.
Matsuda, M. Matsuo, S. Mizoguti, K. Higashiguchi, M. Irie,
J. Phys. Chem. B 2002, 106, 11218; d) N. Tanifuji, M. Irie, K.
Matsuda, J. Am. Chem. Soc. 2005, 127, 13344.
[23] a) J. J. D. de Jong, L. N. Lucas, R. M. Kellogg, J. H. van Esch,
B. L. Feringa, Science 2004, 304, 278; b) J. J. D. de Jong, P. R.
Hania, A. Pagzlys, L. N. Lucas, M. de Loos, R. M. Kellogg,
B. L. Feringa, K. Duppen, J. H. van Esch, Angew. Chem. Int.
Ed. 2005, 44, 2373.
[24] T. Hirose, K. Matsuda, M. Irie, J. Org. Chem. 2006, 71, 7499.
[25] a) R. M. Metzger, B. Chen, U. Hoepfine, M. V. Lakshmikan-
tham, D. Vuillaume, T. Kawai, X. Wu, H. Tachibana, T. V.
Hughes, H. Sakurai, J. Am. Chem. Soc. 1997, 119, 10455; b)
[40] R. Taylor, O. Kennard, J. Am. Chem. Soc. 1982, 104, 5063.
[41] S. Iwata, Y. Ishihara, C.-P. Qian, K. Tanaka, J. Org. Chem.
1992, 57, 3726.
[42] S. Takami, S. Kobatake, T. Kawai, M. Irie, Chem. Lett. 2003,
32, 892.
[43] M. Bergtrup, L. B. L. Hansen, Acta Chem. Scand. 1992, 46,
372.
Received: January 29, 2007
Published Online: May 4, 2007
3218
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3212–3218