Photochromic properties of terarylene derivatives having a π-conjugation unit on central aromatic ring

Article abstract of DOI:10.1039/b823413b

A series of terarylenes based on 4,5-bisbenzothienylthiazole have been synthesized, and their photochromic properties are studied both in solution and in the crystalline state. The substitution effect of the central aromatic ring on the photochromic reactivity were also studied. The introduction and expansion of the π-conjugated system at the 2-position of the thiazole ring led to a red-shift of the absorption peaks for both open- and closed-ring isomers of terarylenes. 2-Hydro and 2-phenyl derivatives of 4,5-bisbenzothienylthiazoles displayed a photochromic reaction, even in the single-crystal state. X-Ray crystal analysis showed their molecular structure to have quasi-C₂ symmetry, suggesting significant CH...N and CH...S interactions. Although the 2-hydro and 2-phenyl derivatives exhibited high photocyclization reaction quantum yields over 0.5, the 2-phenylthienyl derivative showed a considerably smaller reactivity, even though it is supposed to have a similar conformation to those of the other two derivatives. Meanwhile, these molecules showed similar photocycloreversion quantum yields as high as 0.3. The relationship between their electronic structures and photochromic reactivity is also discussed by means of quantum chemical calculations. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009.

Full text of DOI:10.1039/b823413b

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/njc | New Journal of Chemistry
Photochromic properties of terarylene derivatives having a p-conjugation
unit on central aromatic ringw
Yuichiro Kutsunugi, Shigekazu Kawai, Takuya Nakashima and Tsuyoshi Kawai*
Received (in Montpellier, France) 5th January 2009, Accepted 11th February 2009
First published as an Advance Article on the web 13th March 2009
DOI: 10.1039/b823413b
A series of terarylenes based on 4,5-bisbenzothienylthiazole have been synthesized, and their
photochromic properties are studied both in solution and in the crystalline state. The substitution
effect of the central aromatic ring on the photochromic reactivity were also studied. The
introduction and expansion of the p-conjugated system at the 2-position of the thiazole ring led
to a red-shift of the absorption peaks for both open- and closed-ring isomers of terarylenes.
2-Hydro and 2-phenyl derivatives of 4,5-bisbenzothienylthiazoles displayed a photochromic
reaction, even in the single-crystal state. X-Ray crystal analysis showed their molecular structure
to have quasi-C2 symmetry, suggesting significant CHꢀ ꢀ ꢀN and CHꢀ ꢀ ꢀS interactions. Although the
2-hydro and 2-phenyl derivatives exhibited high photocyclization reaction quantum yields over
0.5, the 2-phenylthienyl derivative showed a considerably smaller reactivity, even though it is
supposed to have a similar conformation to those of the other two derivatives. Meanwhile, these
molecules showed similar photocycloreversion quantum yields as high as 0.3. The relationship
between their electronic structures and photochromic reactivity is also discussed by means of
quantum chemical calculations.
photoinduced cyclization and cycloreversion reactions in a
similar manner to diarylethenes and fulgide.23–25 While most
Introduction
There has been much interest in molecular switching materials
diarylethenes show on–off switching of the p-conjugation,
terarylenes can extend their p-conjugation in multiple ways
that modulate physical and chemical properties by some
external stimulus from the viewpoint of developing molecular
devices.1–3 Among these materials, considerable attention
and behave as photoswitching re-routers of p-conjugation
pathways.26 The photochromic reactivity of terarylenes,
has been focused on photochromic molecules, especially on
both in solution and in the crystalline state, and the thermal
photochromic diarylethenes,4–8 which undergo reversible
stability of their closed-ring isomers can be systematically
photoisomerization between pairs of bistable isomers with
modulated by means of varying the aromatic units making
different absorption spectra upon irradiation at appropriate
up the terarylenes and also the substituents on the side
aromatic rings connected to the central aryl unit.23a,b
wavelengths. Photoswitching effects in diarylethenes have been
extensively studied for controlling various chemical and
However, the effect of substituents at the central aryl unit
physical properties, such as fluorescence intensity and
on its photochromic properties has never been studied,
wavelength,9–13 refractive index,14,15 dielectric properties,16
even though the most fascinating advantage that differentiates
electronic conduction,17,18 electrochemical response,19,20 and
terarylenes from conventional diarylethenes relies on its
magnetic interactions.21 Most of these photoswitching effects
functionalization.23c,d The introduction and expansion of
are based, at least partly, on changes in the extent of
the p-conjugation system in the side aryl units for
diarylethenes have been extensively studied, leading to a
p-conjugation in diarylethenes during the course of photo-
chromic reactions. Various types of molecular electronic
considerable decrease in their photocycloreversion quantum
yields.27,28
devices based on p-conjugation connection pathways have
been designed,22 and photon mode modulations of conjugation
systems are still worthy of extensive study. In this context, we
have recently proposed a new class of the hexatriene-type
photochromic molecules composed of three aromatic rings in
a triangular shape, so-called ‘‘terarylenes’’, that undergo
In this study, the effect of the introduction and expansion
of the p-conjugation system at the central aryl unit of
terarylenes on their photochemical properties has been
systematically investigated for a series of 2-substituted-4,5-
bisbenzothienylthiazoles. The introduction of the benzothio-
phene unit into the molecular structure of diarylethenes is
known to enhance their fatigue resistivity29,30 because of
their high oxidation potentials, giving relatively high photo-
cycloreversion quantum yields.31 The central thiazole unit
is also expected to improve the chemical stability against
oxidation, as well as photocyclization reactivity, due to the
reduced steric hindrance.23a
Graduate School of Materials Science, Nara Institute of Science and
Technology, NAIST, 8916-5 Takayama, Ikoma, Nara 630-0192,
Japan. E-mail: tkawai@ms.naist.jp
w Electronic supplementary information (ESI) available: Absorp-
tion spectra change of 2 in hexane. CCDC 720060. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/b823413b
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
1368 | New J. Chem., 2009, 33, 1368–1373

View Article Online
Results and discussion
A series of 2-substituted-4,5-bisbenzothienylthiazoles, 1a, 2a
and 3a, whose molecular structures are shown in Scheme 1,
were synthesized according to Scheme 2. The thiazole ring was
formed by the cyclization reactions of the corresponding
a-hydroxyketones with thioamides, as reported by Krayushkin
and co-workers.25 Their chemical structures were confirmed by
1H NMR, mass spectrometry and/or X-ray crystallography.
Each colorless solution in hexane of 1a, 2a and 3a turned red
upon UV light irradiation, and the colored solutions were
bleached by visible light irradiation. As typical examples,
Fig. 1 shows the absorption spectral changes in the photo-
chromic reactions of 1a and 3a. The reversible absorption
spectral change was observed at room temperature for all
compounds, and the presence of isosbestic points supports the
reversible two-component photochromic reaction shown in
Scheme 1. The coloration and bleaching cycles could be
repeated at least 20 times without marked photodegradation.
Closed-ring isomers 1b, 2b and 3b were prepared by
irradiation of hexane solutions of the corresponding open-ring
isomers 1a, 2a and 3a with UV light, and were isolated
from the colored solutions by normal-phase HPLC with
hexane/ethyl acetate as the eluent or reversed-phase HPLC
with acetonitrile as the eluent. The conversion ratios between
1a and 1b, and between 3a and 3b, at their photostationary
states, achieved by irradiation with UV light (l = 313 nm),
were estimated to be 54 and 32%, respectively. The values
of lmax and molecular extinction coefficient e of each
compound are summarized in Table 1 with the photochromic
Scheme 2 The syntheses of photochromic terarylenes 1a, 2a and 3a.
Conditions a: (i) nBuLi, (ii) iodomethane; b: AcCl, AlCl3; c: SeO2/
H2O, 1,4-dioxane; d: SnCl4/toluene; e: TFA.
reaction quantum yields, which were evaluated by
standard procedure using 1,2-bis(2-methylbenzo[b]thiophen-3-yl)-
3,3,4,4,5,5-hexafluoro-1-cyclopentene in hexane29,31 as
a
a
standard. The absorption peak positions for both bleached
and colored states showed a clear relationship with the
substituent at 2-position of the central thiazole ring. The
expansion of the p-conjugation system of the central unit
led to a red-shift of the absorbance peak. Relatively high
photochemical cyclization quantum yields, as high as 50%,
were found for 1a and 2a. On the other hand, 3a, having a
2-phenylthienyl thiazole unit, showed a considerably lower
cyclization quantum yield than those of the 1a and 2-phenyl-
substituted 2a. Similar to diarylethenes, the photocyclization
quantum yield of terarylenes is expected to show a considerable
dependence on the conformation of their open-ring isomer
in the ground state.23a Compounds 1, 2 and 3 are expected
to have a similar conformation around the reaction center
because the photoreactive hexatriene structure for each
molecule is composed of same aromatic unit. Consequently,
the low quantum yield of 3a might be attributable to its
Fig. 1 Absorption spectral changes of (a) 1 and (b) 3 in hexane:
open-form a (ꢀ ꢀ ꢀ), closed-form b (TT) and photostationary state under
irradiation with 313 nm light (--). The concentrations of 1 and 3 were
2.9 ꢂ 10ꢃ6 and 4.9 ꢂ 10ꢃ6 M, respectively.
Table 1 Absorption maxima and molecular extinction coefficients of
the open- and closed-ring isomers of 1, 2 and 3, together with their
quantum yields in hexane
l
max/nm (e/104 Mꢃ1 cmꢃ1
)
lmax/nm (calc.)
fa-b
fb-a
1a
1b
2a
2b
3a
3b
295 (1.1)
534 (1.4)
329 (1.3)
539 (1.2), 556 (1.2)
370 (2.6)
550 (1.0), 590 (0.82)
325.6
564.4
369.5
601.8
404.2
654.5
0.56
—
0.58
—
0.078
—
—
0.30
—
0.45
—
0.29
electronic structure, derived from its expanded p-electron
system. The fact that compound 3 shows fluorescence emission
with a quantum yield of 7.8% may also decrease the
Scheme 1 The photochromic reactions of terarylenes 1–3.
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 1368–1373 | 1369

View Article Online
photochemical reaction quantum yield. On the other hand, the
cycloreversion quantum yield showed no systematic decrease
upon expanding the p-conjugation system, which is specifically
different from the case of the cycloreversion reactivity of
diarylethenes.27
Interestingly, compounds 1a and 2a showed photochromic
coloration and bleaching reactions, even in their crystalline
states, whereas the corresponding diarylethene, 1,2-bis(2-methyl-
benzo[b]thiophen-3-yl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene,
doesn’t exhibit photochromism in its crystalline state. Fig. 2
shows the photoinduced coloration and bleaching behavior of
a single-crystal of 1a under a polarizing microscope. Under
this polarizing microscope, the source and detection polarizers
were set in parallel, and the crystal was colored in red at a
certain polarization angle (01) and was colorless with the
rotation angle of the polarizer set at 901. The peak absorption
wavelength of the colored state was observed at 550 nm, as
shown in Fig. 3. This wavelength was slightly longer than that
in hexane solution (534 nm). When the polarizer was rotated
by 901 under the microscope, the red color weaken and the
optical density decreased, as also shown in Fig. 3. The changes
in optical density seen upon rotating the polarizer indicate that
the closed-ring isomers are partially oriented in one direction
in the crystal and that the photochromic reaction takes place
in the crystal lattice. As shown in Fig. 4, the ORTEP drawing
of 1a indicates two different conformations that are packed
alternately in the crystal.32 These two structures are quite
similar, and the distances between the reacting carbon atoms,
C5ꢀ ꢀ ꢀC14 and C26ꢀ ꢀ ꢀC35 in Fig. 4, for example, were evaluated
to be 0.358 and 0.369 nm, respectively. Both distances are
short enough for the photochromic ring cyclization reaction to
take place in a topochemical manner.33,34 Each conformation
has a central hexatriene moiety with a quasi-C2 symmetric
structure, which is favorable for the photochromic cyclization
reaction with a contra-rotatory mechanism.35 We thus expect
that both conformers will have similar photochromic reactivities.
Kobatake et al. have reported that diarylethene derivatives
possessing a distance between the reacting carbon atoms
shorter than 0.4 nm should show a similar photochromic
reactivity in the single-crystal state.34 The distances between
the sulfur atoms in the thiazole rings and the 4-H positions in
the benzothienyl units of the two conformers, S1ꢀ ꢀ ꢀH5
and S4ꢀ ꢀ ꢀH20, were estimated to be 0.277 and 0.295 nm,
respectively, which are appreciably shorter than the sum of
the van der Waals radii of S (0.185 nm) and H (0.120 nm).
Similarly, the distances between the nitrogen atoms in the
Fig. 3 Polarized absorption spectra of the photogenerated colored
crystal of 1a.
Fig. 4 An ORTEP drawing, showing 50% probability displacement
ellipsoids, of open-ring isomer 1a in the crystal. Two different
alternately-packed conformations exist for 1a in the single-crystalline
phase.
thiazole rings and the 4-H0 positions in the benzothienyl
units of the two conformers, N1ꢀ ꢀ ꢀH12 and N2ꢀ ꢀ ꢀH27, are
estimated to be 0.264 and 0.254 nm, respectively. These
distances are again shorter than the sum of the van der
Waals radii of N (0.150 nm) and H (0.120 nm). The specific
photoactive antiparallel-type conformation of compound 1a
would be stabilized by these weak hydrogen bonding inter-
actions, resulting in the reversible photochromic reactivity
of 1a in the crystalline state, unlike the corresponding
diarylethene. Similar structural features were also observed
in the results of the X-ray crystallographic analysis of
compound 2a, which will be reported elsewhere.36
We further investigated the electronic structures of 1a and
3a, and 1b and 3b using time dependent density functional
theory (TDDFT)37 calculations at the B3LYP/6-311G++
38
*
level. These calculated absorption peaks are summarized in
Table 1. Characteristic red-shifts in the absorption band of
both open- and closed-ring isomers were reproduced with the
expansion of the p-conjugated system. Fig. 5 shows the
spatial profile of the most stable structure, and selected
frontier molecular orbitals of 1 and 3 in their open- and the
closed-ring forms. The most stable structure of 1a was calculated
to be in good agreement with the result of our X-ray crystallo-
graphic analysis. Both the HOMO and LUMO of 1a expand
Fig. 2 Photographs of single-crystal 1a with light irradiation and
rotation.
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
1370 | New J. Chem., 2009, 33, 1368–1373

View Article Online
Fig. 5 Spatial plots of selected TDDFT frontier molecular orbitals of (a) 1a, (b) 1b, (c) 3a and (d) 3b.
over the whole molecule, and both carbon atoms of the
Experimental section
photochemical reaction centers contribute considerably to
these frontier orbitals. On the other hand, the frontier
LUMO of 3a is rather localized on the phenylthienyl moiety,
and the contribution of these two reactive carbon atoms
seems to be considerably small. This excited state nature of
3a might be responsible for the decreased photochemical
quantum yields of the cyclization reaction of 3a to 3b,
regardless of its photochromic reactive quasi-C2 symmetry
conformation. Meanwhile, the HOMO and LUMO around
the 1,2-cyclohexadiene moieties of both 1b and 3b are almost
identical and moderately distributed across the reactive center,
which may result in their similarly high photocycloreversion
quantum yields. The spatial overlap of the HOMO and
LUMO of 1b is considerably larger than that of 3b, and
this confined nature of 1b may be responsible for its larger
extinction coefficient than that of 3b.
General
Organic chemicals were purchased from Nacalai, Wako and
TCI, and were used as received. 1H (300 MHz) and 13C
(75 MHz) NMR spectra were recorded on a JEOL AL-300
spectrometer. Mass spectra were measured using a JEOL
JMS-T100LC AccuTOF mass spectrometer. Purification by
high-performance liquid chromatography (HPLC) and gel
permeation chromatography (GPC) was performed using
HPLC (JASCO PU-2080, UV-2075) and GPC (JASCO
PU-2080, UV-2086) systems with appropriate columns.
UV-vis absorption spectra were recorded on a JASCO V-550
spectrophotometer. An ultra-high pressure Hg lamp (500 W)
and a Hg–Xe lamp (150 W) were used as light sources for
steady-state measurements. Monochromic light was obtained
by passing the light through a monochromator (Shimadzu
SPG-120S, 120 mm, f = 3.5). Absorption spectra in the
single-crystalline phase were measured using an Olympus
BX-51 polarizing microscope connected to a Hamamatsu
PMA-11 photodetector with an optical fiber. The polarizer
and analyzer were set in parallel to each other. X-Ray
crystallographic analyses were carried out using a Rigaku
R-AXIS RAPID/s imaging plate diffractometer with Mo-Ka
radiation at 296 K.
Conclusions
We have designed and synthesized new terarylene derivatives
based on 4,5-bisbenzothienylthiazole and studied the effect
of expanding their p-conjugation system at the 2-position
of the thiazole ring. The wavelength of their optical absorption
peaks shift to longer wavelengths by introducing the
p-conjugation unit. Compound 3a, having phenylthienyl units,
showed a significantly lower photocyclization quantum yield
than those of 1a and 2a, whereas the photocycloreversion
quantum yield was comparable. Terarylene derivatives
1 and 2 exhibited reversible photochromism in the crystalline
phase, whereas the corresponding diarylethene does not. The
difference in the photochromic reactivity in the crystalline
state was attributed to the specific interactions between the
heteroatoms of the central thiazole unit and the 4-H hydrogen
atoms of both sides of the benzothiophene units, stabilizing
the photoreactive antiparallel conformation in the crystalline
state. Quantum chemical calculations explained the decrease
of the photocyclization quantum yield and unchanged
Syntheses
2-Methylbenzo[b]thiophene (4). A hexane solution of butyl
lithium (120 ml, 1.6 M in hexane, 0.19 mol) was added to a
stirred solution of benzo[b]thiophene (25 g, 0.19 mol) in dry
THF (150 ml) at ꢃ78 1C under a nitrogen atmosphere. After
30 min, MeI (12 ml, 0.19 mol) was added and the mixture
allowed to warm up to room temperature. After 4 h, the
reaction mixture was quenched by adding water, followed by
extraction with diethyl ether. The organic layer was washed
with a saturated NaCl solution, dried with anhydrous
MgSO4 and the drying agent filtered off. After removing
the solvent in vacuo, the residue was purified by column
chromatography on silica gel using hexane as the eluent to
photocycloreversion reactivity of
3 with its expanded
p-system. The authors believe the present study provides a
guiding principle for designing future photoswitching
molecules, accompanied by expanded p-electron systems for
controlling their nature.
1
give 4 (27 g, 97%). H NMR (300 MHz, acetone-d6): d 2.56
(3H, s), 7.06 (1H, s), 7.21–7.32 (2H, m), 7.67–7.69 (1H, d) and
7.78–7.81 (1H, d).
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 1368–1373 | 1371

View Article Online
1-(2-Methylbenzo[b]thiophen-3-yl)ethanone (5). A mixture of
2-methylbenzo[b]thiophene (4) (11 g, 73 mmol), acetyl chloride
(5.5 ml, 73 mmol) and anhydrous aluminum chloride (12 g,
73 mmol) in dry DCM (200 ml) was stirred overnight. After
removing the DCM, an equal amount of water and ethyl
acetate was added. The organic layer was separated and
washed with a saturated NaCl solution, dried with anhydrous
MgSO4 and the drying agent filtered off. After removing
the solvent in vacuo, the residue was purified by column
chromatography on silica gel using chloroform/hexane
(30–40%) as the eluent to give 5 as a colorless solid
(11 g, 80%). 1H NMR (300 MHz, CDCl3): d 2.66 (3H, s),
2.79 (3H, s), 7.37 (2H, m), 7.75 (1H, d) and 8.19 (1H, d).
to a slurry of 70% sodium hydrosulfide hydrate (1.8 g,
20 mmol) and magnesium chloride hexahydrate (2.0 g,
10 mmol) in 20 ml of DMF, was added 5-phenylthiophene-
2-carbonitrile (1.6 g, 8.0 mmol) in one portion, and the
mixture stirred at room temperature for 2 h. The resulting
green slurry was poured into 20 ml of water, resuspended in
1N HCl, stirred for 20 min, and then filtered and washed with
water to give pure 8c (0.72 g, 41%). 1H NMR (300 MHz,
acetone-d6): d 7.35–7.50 (4H, m), 7.66–7.74 (3H, m) and
8.87–8.80 (2H, d)
4,5-Bis(2-methylbenzo[b]thiophen-3-yl)thiazole (1a). Crude 7
was added to a solution of 8a (0.80 g, 13 mmol) in 3.0 ml of
TFA, and the mixture kept for 24 h at room temperature,
diluted with diethyl ether and neutralized with an aqueous
solution of sodium hydroxide. The aqueous phase was
extracted with diethyl ether, the extracts washed in succession
with water, a 20% solution of sodium hydroxide and water
again, dried over MgSO4 and evaporated (yield 1.3 g, 68%).
1H NMR (300 MHz, DMSO-d6): d 1.97 (s, 3H), 2.00 (s, 3H),
2,2-Dihydroxy-1-(2-methylbenzo[b]thiophen-3-yl)ethanone (6).
To a solution of selenium dioxide (3.4 g, 30 mmol) in
dioxane (25 ml) and water (1.0 ml) at 60 1C was added 5
(5.7 g, 30 mmol). The mixture was refluxed for 8 h, filtered
(removal of Se) and the filtrate evaporated under reduced
pressure. The oily residue thus obtained was crystallized from
water. The precipitate was removed by filtration and washed
with a small amount of water, affording colorless crystals
of 6 (5.8 g, 87%). 1H NMR (300 MHz, DMSO-d6): d 2.77
(3H, s), 5.59 (1H, t), 6.67 (2H, d), 7.38 (2H, d), 7.93 (1H, d)
and 8.15 (1H, d).
7.30–7.23 (m, 4H), 7.49 (br, 2H), 7.89–7.82 (m, 2H) and 9.51
(M+):
+
(s, 1H). EI-HRMS (m/z) calc. for C27H19NS3
378.0445; found: 378.0450. Anal. calc. for C27H19NS3: C,
66.81; H, 4.00; N, 3.71; found: C, 66.57; H, 3.69; N, 3.76%.
4,5-Bis(2-methylbenzo[b]thiophen-3-yl)-2-phenylthiazole (2a).
This compound was prepared by the same procedure as that
1
used to prepare 1a (yield 0.15 g, 6.7%). H NMR (300 MHz,
2-Hydroxy-1,2-bis(2-methylbenzo[b]thiophen-3-yl)ethanone (7).
A solution of tin tetrachloride (0.58 ml, 5.0 mmol) in
toluene (10 ml) was added drop-wise to a stirred solution of
6 (1.1 g, 5.0 mmol) and 4 (0.82 g, 5.5 mmol) in toluene (25 ml).
The reaction mixture was stirred for 9 h at room temperature.
The solution was then carefully poured into water (20 ml) and
extracted with diethyl ether. The organic layer was separated,
washed with a saturated NaCl solution, dried over MgSO4 and
evaporated. The crude product was used without further
purification.
CD3CN): d 2.14 (s, 6H), 7.28–7.20 (m, 4H), 7.56–7.50 (m, 3H),
7.64–7.57 (m, 2H), 7.79–7.74 (m, 2H) and 8.09–8.05 (m, 2H).
13C NMR (75 MHz, acetone-d6): d 14.9, 15.0, 122.6, 122.8,
122.9, 123.7, 123.8, 124.8, 125.0, 125.2, 125.6, 127.2, 128.3,
128.7, 130.1, 131.3, 134.5, 138.6, 138.7, 140.2, 140.3, 140.5,
+
141.3, 149.5 and 168.0. EI-HRMS (m/z) calc. for C27H19NS3
(M+): 453.0680; found: 453.0685. Anal. calc. for C27H19NS3:
C, 71.49; H, 4.22; N, 3.09; found: C, 71.36; H, 4.13; N, 3.05%.
4,5-Bis(2-methylbenzo[b]thiophen-3-yl)-2-(5-phenylthiophen-
2-yl)thiazole (3a). This compound was prepared by the same
Thioformamide (8a). To a cooled (0–5 1C) solution of
formamide (3.1 ml, 76 mmol) in 100 ml diethyl ether was
added phosphorus pentasulfide (8.9 g, 19 mmol) in small
portions. The reaction mixture was allowed warm to ambient
temperature, stirred for 2 h, filtered and concentrated under
vacuum to afford 8a as a pungent yellow oil that was used
without purification (0.8 g, 17%). 1H NMR (300 MHz,
CDCl3): d 7.28 (1H, t), 7.98 (1H, t) and 9.46 (1H, dd).
1
procedure as that used to prepare 1a (yield 0.15 g, 5.6%). H
NMR (300 MHz, DMSO-d6): d 2.04 (s, 3H), 2.06 (s, 3H),
7.39–7.27 (m, 5H), 7.48–7.43 (m, 2H), 7.68–7.61 (m, 3H),
7.78–7.76 (m, 2H) and 7.91–7.84 (m, 3H). 13C NMR
(75 MHz, CDCl3): d 14.9, 15.0, 121.6, 121.9, 122.0, 122.6,
122.9, 123.7, 123.8, 124.2, 124.3, 124.6, 125.9, 126.6, 127.0,
127.6, 128.2, 129.0, 133.7, 136.3, 137.9, 138.0, 139.5, 139.6,
139.9, 140.7, 146.8, 148.3 and 161.1. EI-HRMS (m/z) calc. for
C31H21NS4+ (M+): 535.0557; found: 535.0560. Anal. calc. for
C31H21NS4: C, 69.50; H, 3.95; N, 2.61; found: C, 69.30; H,
4.00; N, 2.62%.
5-Phenylthiophene-2-carbothioamide (8c).
A suspension
of potassium carbonate (5.5 g, 40 mmol), tetra-n-butyl-
ammonium bromide (5.2 g, 16 mmol) and palladium acetate
(0.18 g, 0.80 mmol) in an acetonitrile/water mixture
(3.7/0.4 ml) was stirred under nitrogen for
5 min.
2-Cyanothiophene (3.0 g, 32 mmol) and iodobenzene (1.8 g,
16 mmol) were then successively added, and the mixture
heated at 80 1C for 5 h. After cooling to room temperature,
water and diethyl ether were added, the organic phase washed
with water and dried over MgSO4. After removal of the
solvent under vacuum, the residue was crystallized from
hexane. The precipitate was removed by filtration and washed
with a small amount of hexane, affording yellow crystals of
5-phenylthiophene-2-carbonitrile (1.555 g, 50%). Subsequently,
Acknowledgements
The authors thank Mr S. Katao and Mrs Y. Nishikawa,
technical staff members of NAIST, for X-ray crystallographic
analyses and mass spectroscopy measurements. This work was
supported by the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), Japan: Grants-in-Aid
for Scientific Research on Priority Area ‘‘New Frontiers in
Photochromism’’.
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009
1372 | New J. Chem., 2009, 33, 1368–1373

View Article Online
36, 372; (d) T. Nakashima, M. Goto, S. Kawai and T. Kawai,
J. Am. Chem. Soc., 2008, 130, 14570.
References
1 Molecular Switches, ed. B. L. Feringa, Wiley-VCH, Weinheim,
2001.
2 V. Balzani, M. Venturi and A. Credi, Molecular Devices and
Machines: A Journey into the Nanoworld, Wiley-VCH, Weinheim,
2003.
3 S. Shinkai, Pure Appl. Chem., 1987, 59, 425.
4 Photochromism, ed. G. H. Brown, Wiley-Interscience, New York,
1971.
24 X. Li and H. Tian, Tetrahedron Lett., 2005, 46, 5409.
25 (a) M. M. Krayushkin, S. N. Ivanov, A. Yu. Martynkin,
B. V. Lichitsky, A. A. Dudinov and B. M. Uzhinov, Russ. Chem.
Bull., 2001, 50, 116; (b) M. M. Krayushkin, S. N. Ivanov, A.
Yu. Martynkin, B. V. Lichitsky, A. A. Dudinov and
B. M. Uzhinov, Russ. Chem. Bull., 2001, 50, 2424;
(c) M. M. Krayushkin, B. V. Lichitskii, A. P. Mikhalev,
B. V. Nabatov, A. A. Dudinov and S. N. Ivanov, Russ. J. Org.
Chem. (Transl. of Zh. Org. Khim.), 2006, 42, 860.
26 T. Kawai, T. Iseda and M. Irie, Chem. Commun., 2004, 72.
27 M. Irie, T. Eriguchi and K. Uchida, Tetrahedron, 1997, 53,
12263.
28 (a) A. T. Bens, D. Frewert, K. Kodatis, C. Kryschi, H.-D. Martin
and H. P. Trommsdorf, Eur. J. Org. Chem., 1998, 2333;
(b) T. Yamaguchi, Y. Fujita, H. Nakazumi, S. Kobatake and
M. Irie, Tetrahedron, 2004, 60, 9863.
5 M. Irie, Chem. Rev., 2000, 100, 1683.
6 Photochromism: Molecules and Systems, ed. H. Durr and
¨
H. Bouas-Laurent, Elsevier, Amsterdam, 1990.
7 P. Belser, L. De Cola, H. Frantisek, V. Adamo, B. Bozic,
Y. Chriqui, V. M. Iyer, R. T. F. Jukes, J. Kuhni, M. Querol,
¨
S. Roma and N. Salluce, Adv. Funct. Mater., 2006, 16, 195.
8 H. Tian and S. Yang, Chem. Soc. Rev., 2004, 33, 85.
9 G. M. Tsuvgoulis and J.-M. Lehn, Angew. Chem., Int. Ed. Engl.,
1995, 34, 1119.
10 (a) T. Norsten and N. R. Branda, J. Am. Chem. Soc., 2001, 123,
1784; (b) A. J. Myles and N. R. Branda, Macromolecules, 2003, 36,
298; (c) A. J. Myles, B. Gorodetsky and N. R. Branda, Adv.
Mater., 2004, 16, 922; (d) E. Murguly, T. B. Norstern and
N. R. Branda, Adv. Mater., 2001, 13, 347.
11 (a) T. Kawai, T. Sasaki and M. Irie, Chem. Commun., 2001, 711;
(b) M. Irie, T. Fukaminato, T. Sasaki, N. Tamai and T. Kawai,
Nature, 2002, 420, 759; (c) T. Fukaminato, T. Sasaki, T. Kawai,
N. Tamai and M. Irie, J. Am. Chem. Soc., 2004, 126, 14843.
12 (a) A. Osuka, D. Fujikane, H. Shinmori, S. Kobatake and M. Irie,
J. Org. Chem., 2001, 66, 3913; (b) K. Yagi, C. F. Soong and
M. Irie, J. Org. Chem., 2001, 66, 5419.
13 R. T. F. Jukes, V. Adamo, F. Hartl, P. Belser and L. De Cola,
Inorg. Chem., 2004, 43, 2799.
14 N. Tanio and M. Irie, Jpn. J. Appl. Phys., 1994, 33, 1550.
15 M.-S. Kim, H. Maruyama, T. Kawai and M. Irie, Chem. Mater.,
2003, 15, 4539 and references therein.
16 T. Kawai, T. Koshido and K. Yoshino, Appl. Phys. Lett., 1995, 67,
795.
17 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 and B. J. van
Wees, Phys. Rev. Lett., 2003, 91, 207402–1.
18 T. Kawai, Y. Nakashima and M. Irie, Adv. Mater., 2005, 17, 309.
19 (a) S. L. Gilat, S. H. Kawai and J.-M. Lehn, J. Chem. Soc., Chem.
Commun., 1993, 1439; (b) S. L. Gilat, S. H. Kawai and J.-M. Lehn,
Chem.–Eur. J., 1995, 1, 275; (c) S. H. Kawai, S. L. Gilat, R. Ponsinet
and J.-M. Lehn, Chem.–Eur. J., 1995, 1, 285; (d) S. H. Kawai,
S. L. Gilat and J.-M. Lehn, Eur. J. Org. Chem., 1999, 2359.
20 R. Baron, A. Onopriyenko, E. Katz, O. Lioubashevski, I. Willner,
S. Wang and H. Tian, Chem. Commun., 2006, 2147.
21 (a) K. Matsuda and M. Irie, J. Am. Chem. Soc., 2000, 122, 7195;
(b) K. Matsuda and M. Irie, J. Am. Chem. Soc., 2000, 122, 8309;
(c) K. Matsuda, M. Matsuo, S. Mizoguti, K. Higashiguchi and
M. Irie, J. Phys. Chem. B, 2002, 106, 11218; (d) N. Tanifuji, M. Irie
and K. Matsuda, J. Am. Chem. Soc., 2005, 127, 13344.
22 (a) R. M. Metzger, B. Chen, U. Hoepfine, M. V. Lakshmikantham,
D. Vuillaume, T. Kawai, X. Wu, H. Tachibana, T. V. Hughes and
H. Sakurai, J. Am. Chem. Soc., 1997, 119, 10455; (b) A. Dhirani,
P. H. Lin, P. Guyot-Sionnest, R. W. Zehner and L. R. Sita,
J. Chem. Phys., 1997, 106, 5249; (c) C. Joachim,
J. K. Gimzewski and A. Aviram, Nature, 2000, 408, 541.
23 (a) T. Nakashima, K. Atsumi, S. Kawai, T. Nakagawa,
Y. Hasegawa and T. Kawai, Eur. J. Org. Chem., 2007, 3212;
(b) S. Kawai, T. Nakashima, K. Atsumi, T. Sakai, M. Harigai,
Y. Imamoto, H. Kamikubo, M. Kataoka and T. Kawai, Chem.
Mater., 2007, 219, 3479; (c) T. Nakagawa, K. Atsumi,
T. Nakashima, Y. Hasegawa and T. Kawai, Chem. Lett., 2007,
29 K. Uchida, M. Fujita, Y. Aoi, M. Saito and M. Irie, Chem. Lett.,
2001, 30, 366.
30 M. Irie and K. Uchida, Bull. Chem. Soc. Jpn., 1998, 71, 985.
31 K. Uchida, E. Tsuchida, Y. Aoi, S. Nakamura and M. Irie, Chem.
Lett., 1999, 63.
32 Crystallographic data for 1a: C21H15NS3, a = 24.7188(14), b =
12.7989(9), c = 13.7089(8) A, b = 122.7144(14)1, monoclinic,
space group P21/c, Z = 8, V = 3649.1(4) A3, rcalc = 1.374 g cmꢃ3
.
Of 28998 reflections up to 2y = 50.61, 6600 were independent
(Rint = 0.091) and 6600 were with I 4 2s(I). The structure was
solved by direct methods and refined with a full matrix against
all F2 data. Hydrogen atoms were calculated in riding positions.
R = 0.0447, wR = 0.0401w.
33 V. Ramamurthy and K. Venkatesan, Chem. Rev., 1987, 87, 433.
34 (a) S. Kobatake, T. Yamada, K. Uchida, N. Kato and M. Irie,
J. Am. Chem. Soc., 1999, 121, 2380; (b) S. Kobatake, M. Yamada,
T. Yamada and M. Irie, J. Am. Chem. Soc., 1999, 121, 8450;
(c) S. Kobatake, K. Shibata, K. Uchida and M. Irie, J. Am. Chem.
Soc., 2000, 122, 12135.
35 M. Irie, O. Miyatake, K. Uchida and T. Eriguchi, J. Am. Chem.
Soc., 1994, 116, 9894.
36 S. Kawai, T. Nakashima, Y. Kutsunugi, H. Nakagawa,
H. Nakano and T. Kawai, J. Mater. Chem., 2009, DOI: 10.1039/
b823354c.
37 (a) R. E. Stratmann, G. E. Scuseria and M. J. Frisch, J. Chem.
Phys., 1998, 109, 8218; (b) R. Bauernschmitt and R. Ahlrichs,
Chem. Phys. Lett., 1996, 256, 454; (c) M. E. Casida, C. Jamorski,
K. C. Casida and D. R. Salahub, J. Chem. Phys., 1998, 108, 4439.
38 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr.,
T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam,
S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi,
G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida,
T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li,
J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
A. J. Austin, R. Cammi, C. Pomelli, J. Ochterski, P. Y. Ayala,
K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg,
V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain,
O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford,
J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham,
C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill,
B. G. Johnson, W. Chen, M. W. Wong, C. Gonzalez and
J. A. Pople, GAUSSIAN 03 (Revision D.01), Gaussian, Inc.,
Wallingford, CT, 2004.
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2009 New J. Chem., 2009, 33, 1368–1373 | 1373