Syntheses and photochromic properties of diaryl acenaphthylene derivatives

Article abstract of DOI:10.1016/j.dyepig.2010.04.004

A series of diaryl acenaphthylenes has been synthesized, and their photochromic properties are studied both in solution and in the crystalline state. 2,4-Dimethyl-5-phenylthiophene derivative 1a showed no photochromic reaction, while 2-methyl-5-phenylthio

Full text of DOI:10.1016/j.dyepig.2010.04.004

Dyes and Pigments 89 (2011) 297e304
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Syntheses and photochromic properties of diaryl acenaphthylene derivatives
*
Sayo Fukumoto, Tetsuya Nakagawa, Shigekazu Kawai, Takuya Nakashima, Tsuyoshi Kawai
Graduate School of Materials Science, Nara Institute of Science and Technology, NAIST, 8916-5, Takayama-cho, Ikoma, Nara 630-0192, Nara, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of diaryl acenaphthylenes has been synthesized, and their photochromic properties are studied
both in solution and in the crystalline state. 2,4-Dimethyl-5-phenylthiophene derivative 1a showed no
photochromic reaction, while 2-methyl-5-phenylthiophene derivative 2a and 5-methyl-2-phenylthiazol
derivative 3a showed reversible photochromism in solution. Fluorescence spectrum of compound 3a
changed upon photoirradiation. In the single-crystal state, compound 3a showed no photochromic
Received 25 February 2010
Received in revised form
31 March 2010
Accepted 13 April 2010
Available online 24 April 2010
reaction possibly because of
pep and CH/S inter-molecular interactions. The photocyclization quantum
yield of 3a was determined to be as low as 0.7%. The closed-isomer 3b showed relatively high thermal
stability by the rigidity of acenaphtylene.
Keywords:
Photochromism
Photochemistry
Dyes
Ó 2010 Elsevier Ltd. All rights reserved.
Heterocycles
Acenaphthylene
Fluorescence
1. Introduction
cyclopentene and ethylene [23]. The double bond character in the
ethylene bridge is, thus, considered to be lowered by its strained
Considerable recent attention in the field of organic materials
chemistry has been focused on photochromic molecules, which
exhibit reversible color change upon light irradiation [1e5]. Among
wide variety of synthetic photochromic molecules, those having
hexatrieneecyclohexadiene type structure such as diarylethenes
and terarylenes have been extensively studied due to their thermal
stability in both colored and bleached states and relatively high
photochromic reactivity in solutions and even in solid states
[6e10]. Various types of photochromic hexatriene molecules with
different kinds of central and side ethene units have been recently
reported [11e15]. For example, usual diarylethenes and terarylenes
contain cyclopentene and various aromatic units, respectively,
which are served as the central ethene unit of the hexatriene
structure, which may also affect on the photochromic reactivity if it
is used as the central ethene unit of the hexatriene motif. In the
present work, we synthesized three diaryl acenaphthylene deriv-
atives having 5-methyl-2-phenylthiazole, 2-methyl-5-phenyl-
thiophene and 2,4-dimethyl-5-phenylthiophene moieties as the
side aromatic units and their photochromic properties are studied.
2. Results and discussion
2.1. Photochromism
Scheme 1 shows molecular structures of diaryl acenaphthylene
derivatives synthesized in the present study. Compound 1a having 2,4-
dimethyl-5-phenylthiophenes as the side units showed no photo-
chromic color change even after UV light irradiation for 3 h and its
absorption spectrum also showed no marked photoresponsive change.
As shown in Fig. 1(a), 2a having 2-methyl-5-phenylthiophenes as the
side units exhibited a weak absorption band between 400 and 500 nm
before irradiation [24], while a new absorption band appeared at
structure. In the sense of the number of
unit, diarylethenes and terarylenes have 2
systems, respectively. The photoisomerization from hexatriene to
cyclohexadiene which proceeds under UV light irradiation induces
p
p
electrons in the central
-electron
- and (4nþ2)
p
considerable alteration in the
p-electron systems. We here report
on the photochromic properties of terarylene analogs having a 12
p
system, acenaphthylene unit as the central ring. Acenaphthylene is
a simple and stable nonalternant aromatic hydrocarbon consisting
of naphthalene with an ethylene bridge [16e22]. The bond length
of double bond of its ethylene bridge is longer than those in
580 nm after irradiation with UV light (
l
¼ 313 nm).
Similarly, the 5-methyl-2-phenylthiazol derivative 3a also
showed specific absorption band at 560 nm after irradiation with UV
light as shown in Fig. 1(b). These colorations also occurred under
irradiation between 400 and 500 nm. The colored solutions were
bleached after visible light irradiation with longer than 500 nm and
original absorption spectra of 2a and 3a were recovered. Since
* Corresponding author. Tel.: þ81 743 72 6170; fax: þ81 743 72 6179.
E-mail address: tkawai@ms.naist.jp (T. Kawai).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.04.004

298
S. Fukumoto et al. / Dyes and Pigments 89 (2011) 297e304
Fig. 1. Absorption spectral changes of 2(a) and 3(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 2 and 3 were 7.6 ꢀ 10ꢁ6 and
1.8 ꢀ 10ꢁ5 M, respectively.
Scheme 1. Photochromic reactions of acenaphthylene derivatives 1e4.
isosbestic points were clearly observed, these reversible spectral
changes are attributed to the two-component photochromic reaction
as observed for diarylethene and terarylene derivatives.
which were determined to be the most stable geometries by the
vibrational frequency calculations. The evaluated distance between
the reacting carbon atoms are also given in Fig. 2. 1a is expected to
have twisted structure due to the steric hindrance between the
methyl groups at 4- and 40-positions of the thiophene rings and
acenaphthylene unit, which should make the distance between the
reacting carbon atoms longer and suppress the photochromic
reactivity. Moreover, LUMO is rather localized on the acenaph-
thylene moiety as shown in Fig. 2 (a), which may also suppress the
peri-cyclization reactivity of 1a regarding its reaction machanism.
3a has lowest steric hindrance between the side aryl groups and the
central acenaphthylene unit among these derivatives.
The colored compound formed after UV light irradiation was
isolated from the reddish hexane solution by a normal-phase HPLC.
The isolated compound was characterized as the ring-closed
isomer 3b by the 1H NMR spectroscopy in a CDCl3 solution. No
considerable by-product was detected by the HPLC. 3b showed
same mass-number as that of 3a, also supporting its chemical
structure. Although isolation of 2b from the colored solution was
tried, its amount was too low to characterize the colored compound
2b by NMR measurements. Judging from the similar photochromic
behavior of 2 as those of 3, however, the colored compound having
the absorption band at 560 nm might be attributed to the ring-
closed isomer 2b. The colored compound isolated by HPLC also
showed same mass-number of 2a.
2.3. Photomodulation of emission spectra of 3 in solution
The values of lmax and
3 in 1e3 are summarized in Table 1. The
conversion ratios from 2a to 2b and from 3a to 3b at their photo-
stationary states achieved under irradiation with UV light
In the following discussions, we focus on the photochromic
performance of the compounds 3a and 3b. Compound 3a showed
(
l
¼ 313 nm) of long period (for 5e10 h) were estimated to be 14
and 75%, respectively. These results suggested that 3a has higher
photochromic reactivity than that of 2a.
Table 1
Absorption maxima and coefficients of acenaphtylene derivatives 1e3, together
with the conversion ratios at photostationary states in hexane.
[104 Mꢁ1 cmꢁ1])
Conversion[%]
2.2. DFT calculations
Compounds
lmax[nm] (
3
a
b
Since photochromic cyclization reactivity of similar hexatriene-
type diarylethene and terarylene derivatives have been reported to
markedly depend on the conformation of the ring-open-form
isomer, we evaluated stable conformation of the compounds by
using density functional theory (DFT) [25] calculations at the B3LYP/
6-31Gþþ [26] level. Fig. 2 shows the optimized structures of 1ae3a,
1
2
3
323(1.5)
429(0.18)
313(2.5)
433(0.19)
338(2.8)
442(0.28)
e
e
399(0.82)
566(0.27)
353(2.8)
553(1.4)
14
75

S. Fukumoto et al. / Dyes and Pigments 89 (2011) 297e304
299
Fig. 2. Spatial plots of selected TDDFT frontier molecular orbitals of (a) 1a, (b) 2a and (c) 3a.
characteristic fluorescence emission at 580 nm as shown in Fig. 3,
which is attributed to the LUMO-HOMO transition with certain
Stokes’ shift. The fluorescence peak wavelength of 3 was found to
reversibly change along with the photochromic reactions in the
hexane solution. Fig. 3 shows emission spectrum of pure 3b in the
hexane solution, where a clear emission band was observed at
680 nm and no emission of 3a at 580 nm. The excitation spectrum
of the colored state at the detection wavelength of 650 nm revealed
an excitation band at 550 nm which is specific for 3b. Similar
modulation of emission wavelength has also been reported in
bisbenzothiophenylethene derivatives [27,28].
2.4. Crystal structures of 3a and 3b
Crystals of 3a and 3b were obtained by recrystallization from
their hexane solutions and were characterized by X-ray analyses.
The ORTEP drawings of 3a and 3b are presented in Fig. 4 [29,30]. The
structure of 3a in crystal phase was found to be similar to the
optimized structures estimated by the DFT calculation (Fig. 2(c)). 3a
exhibits the conformation of quasi-C2 symmetry around the central
hexatriene moiety, which is favorable for the photochromic cycli-
zation reaction with a contra-rotational cyclization reaction [31].
The 3a crystal is the racemic crystal having a couple of enantiomeric
comformers in the unit cells. The distance between the reacting
carbon atoms in 3a was evaluated to be 0.358 nm, which roughly
coincides with the evaluated value by the DFT calculation. It seems
to be short enough for the photochromic ring-cyclization reaction.
Fig. 3. Emission spectral change of 3 in hexane (1.8 ꢀ 10ꢁ5 M, lex ¼ 420 nm): open-
form 3a (dotted line), closed-form 3b (solid line) and emission at photo-stationary
state under irradiation with 313 nm light (dashed line).

300
S. Fukumoto et al. / Dyes and Pigments 89 (2011) 297e304
Fig. 4. ORTEP drawings of open-ring isomer in crystal 3a (a) and closed-ring isomer in crystal 3b (b), showing 50% probability displacement ellipsoids.
The distances between N1eC6 and N2eC12 were estimated to be
0.318 and 0.321 nm, respectively, which suggests the distance
between CH and N of about 0.265e0.267 nm and less than sum of
the van der Waals radii of (Ce)H (0.155 nm) and N (0.12 nm) [32].
Weak intramolecular CH/N hydrogen bonding interactions between
N1eH1 and N2eH6 seem to contribute to the stable conformation
of 3a in the crystalline phase as well as in solution phase. Similar
intramolecular hydrogen bonding has been also observed in 4,5-bis
(2,4-dimethyl-5-phenylthiophen-3-yl)-2-phenylthiazole and 4,5-
bis(5-methyl-2-phenylthiazol-4-yl)-2-phenylthiazole (4a), which
modulates their photocyclization reactivity in the crystal and
solution phases [33]. Despite its conformation suitable for the
photocyclization, compound 3a showed no photochromic colora-
tion in the crystalline phase.
units, which should be responsible for the orange emission. The
distance between the proton in CH3e and S atom of adjacent
molecules were evaluated to be 0.28 nm, suggesting the inter-
molecular CH/S interaction. That is, 3a molecules forms rather rigid
3D network with pep and CH/S interactions in the crystalline state,
and photochromic cyclization which requires the collapse of the
network structure is much suppressed in the crystalline lattice.
2.5. Quantum yield and temperature dependent 1H NMR
The cyclization quantum yield of 3a in hexane was determined
to be as low as
F
¼ 0.007 by using 4,5-bis(5-methyl-2-phenyl-
thiazol-4-yl)-2-phenylthiazole (4a) as a reference compound [33].
This value is surprisingly lower than those of usual hexatriene-type
molecules such as terarylene and diarylethene derivatives and
seems to be the lowest one among them so far reported. In the
hexane solution, 3a seems to be stabilized into the photoreactive
conformation by the intramolecular hydrogen bondings, as
observed in the single crystals. In order to evaluate conformation of
3a in the solution phase, the temperature dependence of the
Upon irradiation with 365 nm light, the crystal of 3a exhibited
fluorescence at 630 nm instead of photochromic coloration. The
fluorescence peak of crystal showed considerable bathochromic-
shift from that at 580 nm in the hexane solution. In the crystal
structure of 3a, specific
pep stacking interaction was suggested
from the distance of about 0.35 nm between the acenaphthylene

S. Fukumoto et al. / Dyes and Pigments 89 (2011) 297e304
301
chemical shifts of C6eH, C12eH (3,8-protons, i.e.
a-position, of
acenaphthylene) and methyl protons was studied by temperature
dependent 1H NMR. 1H NMR signal of equivalent C6eH and C12eH
protons was observed at 8.17 ppm at 293 K as a doublet signal,
which was the most low-field signal in 3a because of the ring-
current effects of the two aromatic groups. This peak showed
systematic high-field shift to 8.08 ppm upon heating to 353 K in D8-
toluene. No other peak of the acenaphtylene unit exhibited such
the significant temperature dependent chemical shift. These results
suggest the decrease of the CH$$$N interaction and change in the
conformation with rising temperature. At the higher temperature,
that is, the distance of CHeN and the twisting angle between
acenaphthylene and thiazole rings should become larger. NMR
signal of the methyl protons also showed characteristic low-field
shift at higher temperature as shown in Fig. 5. This characteristic
shift suggests decrease in deshielding effect on the methyl groups
from the adjacent thiazole groups. These observations suggest that
the reactive conformation of quasi-C2 symmetry with relatively
short CeC distance indicated by the DFT calculation and by the
X-ray study would be dominant in the solution phase at 293 K
and its population would decrease at higher temperature. Some
diarylethene and terarylene derivatives with relatively high ring-
cyclization quantum yield have been reported to have stable reac-
tive conformation of quasi-C2 symmetry [34]. Although 3a seems
to also have conformation of quasi-C2 symmetry, it exhibits
Scheme 2. Schematic illustration of specific structural parameters around the reaction
center and a part of central unit.
markedly small photochromic quantum yield of
F
¼ 0.007. Since
the fluorescence emission quantum yield of 3a is about 2% in the
solution phase, the emission process should not be the dominant
origin of the suppressed photochromic reactivity. It has been
reported that acenaphthylene has the lifetime of singlet excited
state as short as 300 ps [16] because of efficient vibrational relax-
ations, which would be one of possible origins of the low photo-
chromic quantum yield of 3a to 3b. The decreased double bond
character in the ethene moiety in the acenaphthylene unit may
also contribute to the suppressed reactivity.
2.6. Comparison of 3 and 4 in crystal structures
Effects of steric rigidity of acenaphthylene unit of 3a and struc-
tural distortion in the ring-closed form isomer are then discussed by
comparing structural change in 3a to 3b with that of a usual triangle
tertarylene 4a, whose quantumyield of photocyclization is 38% in the
hexane solution. The changes in the crystal structure and the most
stable structure evaluated by DFT calculations of 3a and 3b were
compared with those of terthiazole 4a and 4b, respectively. Upon
cyclization of 1,2-diaryl-fivemembered cycloethene structure, the
C]C double bond in the central unit becomes single bond and thus
both distances between 1,2-atoms and between 3,5-atoms should
become longer as schematically illustrated in Scheme 2. In the
following discussion, differences in distances between S and N
atoms, DSN, and SeCeN angles, qSCN, in the central thiazole of
compounds 4a and 4b are compared with those of distances
between C9 and C11, DCC and C9eC12eC11 angles, qCCC of acenaph-
thylene units in the 3a and 3b, respectively. Table 2 summarizes the
measured and calculated values of these structural parameters. The
characteristic angles qSCN of 4b and qCCC of 3b were considerably lager
than those of 4a and 3a, respectively, and DSN and DCC also expand in
the ring-closed forms from those of the ring-open forms. Degree of
change in DCC, (
D
DCC ¼ DCC(3b) ꢁ DCC(3a),) and that of DSN
,
(DDSN ¼ DSN(4b) ꢁ DSN(4a)) were 0.003 nm and 0.011 nm, receptivity.
Table 2
Structural parameters of 3a,b and 4a,b in crystal structure and their differences.
(a)
q CeCeC/degree
DCeC/nm
3a
3b
Difference
110.75 (110.32*)
113.10 (112.39*)
2.35 (2.07*)
0.232 (0.232*)
0.235 (0.231*)
0.003 (0.001*)
(b)
qNeCeS/degree
DSꢁN/nm
4a
4b
Difference
114.27 (113.50*)
118.87 (115.86*)
4.60 (2.36*)
0.257 (0.257*)
0.268 (0.264*)
0.011 (0.007*)
Fig. 5. Temperature dependence of 1H NMR spectra of 3a in toluene-d8 in (a) low-field
and (b) hight-field ranges.
*Based on optimized structures with DFT calculation.

302
S. Fukumoto et al. / Dyes and Pigments 89 (2011) 297e304
Table 3
Also, DqSCN of 4 and DqCCC of 3 were 4.6 deg and 2.35 deg, respectively.
These changes in the structural parameters are considerably larger
for thiazole derivative 4a, 4b than those for 3a, 3b. The rigid ace-
naphtylene unit seems to suppress structural change upon isomer-
ization of 3a to 3b, contributing to the significantly low
photocyclization quantum yield.
Arrhenius parameters of thermal cycloreversion reactions of the closed-ring isomers
and their half-lifetime in toluene solution.
Ea [kJ molꢁ1
]
A [sꢁ1
]
t1/2 (20 ꢂC)
3b
4b
74
112
3.1 ꢀ 104
11 years
3.3 years
7.1 ꢀ 1011
2.7. Thermal stability of 3b
suggest specific nature of the 4n
p electron system as the central
The thermal stability of the closed-ring isomer 3b was then
examined. 3b did not show the thermal cycloreversion reaction in
the dark place at room temperature as well as 4b. Fig. 6(a) shows
the decay profile of the peak optical absorbance of ring-closed
isomer 3b at several temperatures. The decay profiles were well
characterized with the simple exponential function indicating
unimolecular first order bleaching kinetics. The bleaching rate
constant exhibited Arrhenius-type temperature dependence as also
shown in Fig. 6(b). The activation energy was evaluated from the
slope of the Arrhenius plot to be 7.4 ꢀ 10 kJmolꢁ1 (Table 3). This
activation energy is obviously smaller than that of terthiazole 4b
(134 kJmolꢁ1). The activation energy of the thermal cycloreversible
reactions of diarylethenes and terarylenes have been reported to
decrease with increasing aromatic stabilization energy of the ring-
unit in the hexatriene systems. It is also worth to note that the
frequency factor of the thermal kinetics is considerably small in the
present molecule, which make the lifetime of 3b as long as 11 years
at the room temperature. The molecular rigidity of acenaphtylene
as previously discussed might be responsible for both the small
activation energy and frequency factor.
3. Conclusions
In summary, 4np electron system was firstly introduced as the
central unit of the hexatrieneecyclohexadiene type photochromic
molecules. 3a exhibited well defined reversible photochromic
cyclization reaction with significantly low quantum yield. 3 shows
reversible fluorescence switching behavior in the solution phase.
Specific intra- and/or inter-molecular CH/N and CH/S interactions
are suggested in the crystal structure of 3a and also in the solution
phase.
open form isomers. Since acenaphtylene has 4n
p electron system
and the aromatic naphthalene unit is preserved in the ring-closed
form isomer 3b, one may expect larger activation energy from 3b to
3a than that from 4b to 4a. Although the origin of this remarkable
contradiction is not clear at the moment, present results may
4. Experimental section
4.1. General
1H NMR spectra were recorded on a JEOL AL-300 spectrometer
(300 MHz). Separative HPLC was performed on a HITACHI LaChrom
ELITE HPLC system and a JASCO LC-2000 Plus Series. Mass spectra
were measured with a mass spectrometer JEOL JMS-T100LC Accu-
TOF. Absorption spectra in solution were studied with JASCO V-550
and V-670 spectrophotometers with a temperature control unit.
Photoirradiation was carried out using an USHIO 500 W ultra-high-
pressure mercury lamp or a Panasonic Aicure UV curing system
(LED,
l
¼ 365 nm) as the exciting light source. Monochromic light
was obtained by passing the light through a monochromator
(Shimazu SPG-120S, 120 mm, f ¼ 3.5). X-ray crystallographic
analyses were carried out with a Rigaku R-AXIS RAPID/s Imaging
Plate diffractometer with Mo Ka radiation at 296 K.
4.2. Syntheses
Diaryl acenaphthylene derivatives 1ae3a were synthesized
according to Scheme 3.
5. 1,2-bis(2,4-dimethyl-5-phenylthiophen-3-yl)
acenaphthylene(1a)
A 100 ml four-necked flask was charged with 1,2-dibromoace-
naphthylene [35] (5, 0.15 g, 0.5 mmol), 4(0.31 g, 1.0 mmol), triphe-
nylphosphane (0.08 g, 0.29 mmol), Pd(PPh3)4 (0.07 g, 0.06 mmol),
and K3PO4 (2 M) in water/1,4-dioxane (10 mL/10 mL) solution. The
mixture was then stirred at 110 ꢂC under N2. After having been
stirred for a day the reaction mixture was extracted with ethyl
acetate and the organic layer was dried with anhydrous magnesium
sulfate, filtered, and concentrated. Silica gel column chromatography
(hexane/ethyl acetate 10:1) and normal-phase HPLC (hexane/ethyl
acetate 19:1) afforded 1a (0.14 g, 0.26 mmol, 56%) as a yellow solid.
Fig. 6. Decay lines of peak absorbance by thermal cycloreversion reactions of 3b at
various temperatures (a), and temperature dependence of the thermal fading rates of
3b and 4b (b) in toluene.

S. Fukumoto et al. / Dyes and Pigments 89 (2011) 297e304
303
Scheme 3. Synthetic route for compounds 1ae3a.
1H NMR(300 MHz, CD2Cl2):
d
7.90e7.87(dd, 2 H), 7.64e7.58(m,
1H NMR(300 MHz, ACETN-D6):
d
7.99e7.96(d, 2 H), 7.82e7.80(d,
4 H), 7.50e7.40(m, 8 H), 7.34e7.32(m, 2 H), 2.28(s, 3 H), 2.18(s, 3 H),
2 H), 7.70e7.66(m, 6 H), 7.54(s, 2 H), 7.44e7.39(t, 4 H), 7.32e7.30(t,
2.13(s, 3 H), 2.04(s, 3 H).
2 H), 2.14(s, 6 H).
13C NMR(75 MHz, CDCl3/TMS):
d
140.19, 136.52, 136.42, 135.58,
13C NMR(75 MHz, CDCl3/TMS):
d 140.48, 140.30, 136.59, 134.40,
135.52, 135.23, 134.90,134.54, 134.36, 132.91, 132.72,128.98,128.45,
128.30, 128.23, 127.71, 127.11, 126.82, 124.13, 15.65, 15.40, 14.93,
134.26, 133.47, 128.90, 128.27, 128.15, 127.91, 127.25, 127.19, 125.43,
125.12, 123.70, 14.65.
14.65.
EI HRMS (m/z) [M]þ calcd. for C34H24Sþ2 : 496.1314; Found:
496.1320.
EI HRMS (m/z) [M]þ calcd. for C34H24Sþ2 : 524.1627; Found:
524.1633.
Anal. Calcd. For C34H24S2þ1/2H2O: C, 80.75; H, 4.98; N, 0. Found:
Anal. Calcd. For C36H28S2: C, 82.40; H, 5.38; N, 0. Found: C, 81.92;
H, 5.28; N, 0.17.
C, 80.85; H, 4.63; N, 0.18.
8. 1,2-bis(5-methyl-2-phenylthiazol-4-yl)acenaphthylene(3a)
6. 4,4,5,5-Tetramethyl-2-(2-methyl-5-phenylthio-
phen-3-yl)-1,3,2-dioxaborolane(7)
3a was prepared by same procedure as had been used as for 1a,
except that 4 was replaced by 8. From 8 (0.63 g, 2.0 mmol), 5 (0.31 g,
1.0 mmol), triphenylphosphane (0.13 g, 0.50 mmol), Pd(PPh3)4
(0.07 g, 0.06 mmol), and K3PO4 (2 M) in water/1,4-dioxane (20 mL/
20 mL) solution, 3a (0.40 g, 0.80 mmol, 81%) was obtained as
a yellow solid.
nBuLi (1.6 M in hexane, 5.7 mL, 9.1 mmol) was added slowly
under Ar at ꢁ78 ꢂC to a solution of 3-bromo-2-methyl-5-phe-
nylthiophene (6, 2.23 g, 8.8 mmol) in dry THF (60 mL), and the
mixture was stirred for 1 h at that temperature. 2-Isopropoxy-
4,4,5,5,-tetramethyl-1,3,2,dioxaboro lane (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 allowed to warm to room
temperature. Methanol was added to the reaction mixture, which
was extracted with ethyl acetate. The combined organic fraction
was washed with water, dried with anhydrous magnesium
sulfate, and concentrated to give 2.0 g (6.7 mmol, 76%) of 7 as
colorless solid.
1H NMR(300 MHz, CDCl3):
2H), 7.64e7.62(t, 2H), 7.48e7.46(m, 6H), 2.03(s, 6H).
13C NMR(75 MHz, CDCl3):
164.56, 148.10, 139.88, 133.85,
d 8.06e8.01(m, 6H), 7.90e7.87(d,
d
133.13, 131.68, 129.74, 128.92, 128.54, 128.25, 127.88, 127.60, 126.33,
125.48, 12.56.
FAB HRMS (m/z) [M þ H]þ calcd. for C32H23N2Sþ2 : 499.1297;
Found: 499.1297.
Anal. Calcd. For C32H22N2S2: C, 77.07; H, 4.45; N, 5.62. Found: C,
76.88; H, 4.15; N, 5.67.
1H NMR(300 MHz ACETN-D6):
d 7.61e7.58(d, 2 H), 7.40e7.35(t,
3b: 1H NMR(300 MHz, CDCl3):
d 8.19e8.17(d, 2H), 8.19e8.07
3 H), 7.28e7.16(t, 1 H), 2.66(s, 3 H), 1.33(s, 12 H).
(dd, 4H), 7.76e7.73(d, 2H), 7.66e7.60(t, 2H), 7.54e7.52(m, 6H), 2.03
(s, 6H).
7. 1,2-bis(2-methyl-5-phenylthiophen-
3-yl)acenaphthylene(2a)
Acknowledgments
This compound was prepared by same procedure as had been
used for 1a, except that 4 was replaced by 7. From 7 (0.16 g,
0.5 mmol), 5 (0.08 g, 0.25 mmol), triphenylphosphane (0.03 g,
0.12 mmol), Pd(PPh3)4 (0.05 g, 0.04 mmol), and K3PO4 (2 M) in
water/1,4-dioxane (8 mL/8 mL) solution, 2a (0.07 g, 0.14 mmol, 58%)
was obtained as a yellow solid.
The authors thank Mr. S. Katao and Mrs. Y. Nishikawa, technical
staffs of NAIST for X-ray crystallographic analyses and mass spec-
troscopic measurements. This work was partly supported by Grant-
in-Aids for Scientific Research on Priority Areas, “Photochromism”
from the Ministry of Education, Culture, Sports, Science and Tech-
nology (MEXT) of Japan.

304
S. Fukumoto et al. / Dyes and Pigments 89 (2011) 297e304
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