Nonsymmetrical dithienylethenes bearing dithieno[3,2-b:2′,3′-d] thiophene units with photochromic performance in the crystalline phase

Article abstract of DOI:10.1002/chem.201202520

Four novel nonsymmetrical photochromic diarylethene compounds containing dithieno[3,2-b:2′,3′-d]thiophene units were designed and synthesized to investigate their photochromic properties. All these molecules adopt a photoactive antiparallel conformation in single crystals, as revealed by X-ray crystallographic analysis, and exhibit excellent photochromism in solution as well as in the crystalline phase. Photochromic crystals: Four new nonsymmetrical diarylethenes containing dithieno[3,2-b:2′,3′-d]thiophene units, which exhibit excellent photochromic performance in the crystalline phase (see figure), have been designed and synthesized to investigate their photophysical, electrochemical, and photochromic reactions in solution and in the crystalline phase. They have also been studied through DFT calculations. This study provides a new strategy for the design of diarylethenes that undergo photochromic reactions in the crystalline phase. Copyright

Full text of DOI:10.1002/chem.201202520

DOI: 10.1002/chem.201202520
Nonsymmetrical Dithienylethenes Bearing Dithieno[3,2-b:2’,3’-d]thiophene
Units with Photochromic Performance in the Crystalline Phase
Hongke Wang,[a, b] Hui Lin,[a, b] Wei Xu,*[a] and Daoben Zhu*[a]
Abstract: Four novel nonsymmetrical photochromic diarylethene compounds con-
taining dithieno[3,2-b:2’,3’-d]thiophene units were designed and synthesized to in-
vestigate their photochromic properties. All these molecules adopt a photoactive
antiparallel conformation in single crystals, as revealed by X-ray crystallographic
analysis, and exhibit excellent photochromism in solution as well as in the crystal-
line phase.
Keywords: density functional calcu-
lations · photochromism · diaryl-
AHCTUNGTRENNUNG
Introduction
they have shown highly efficient photoluminescence and
nonlinear optical and field-effect properties.[8] Our recent in-
terest in the design and synthesis of diarylethene-functional-
ized molecules stemmed from the idea that the incorpora-
tion of oligothienoacene moieties into diarylethenes would
generate organic semiconductors with photoswitchable elec-
trical transport properties. In a previous attempt, we synthe-
sized a symmetrical dithienylethene derivative, BDDTP
(1,2-bis(3,5-dimethyldithieno[3,2-b:2’,3’-d]thiophen-2-yl)per-
fluorocyclopentene; Scheme 1), bearing DTT units. Howev-
er, this molecule proved not to be photoactive in the solid
state.[9] As a result of the photochromic unfavorable confor-
mation of this molecule in the single crystal, it did not re-
spond to light stimulation in the solid state. In an effort to
improve the photochromic performance of diarylethenes in
the solid state, we focused our attention on nonsymmetrical
diarylethenes. Thus, in this work we synthesized four ana-
logues (1–4) of BDDTP; in each of these molecules only
one DTT unit is linked to the perfluorocyclopentene group
directly or through a thiophene bridge. Their single-crystal
structure analyses and photochromic reactions in the solid
state showed that, in contrast to BDDTP, these four non-
symmetrical molecules adopt an antiparallel conformation
in the single crystals and undergo reversible photochromic
reactions. These results indicate that the nonsymmetrical
structure could be a practical strategy for the molecular
design of diarylethenes that undergo photochromism in the
crystalline phase. Herein, we present the synthetic strategy
of these molecules and their single-crystal structure analyses
and photochromic characterizations in the crystalline phase
as well as their photochromic properties in solution.
Photochromic materials undergo light-triggered structural
changes at the molecular level. Therefore photochromic re-
actions can be used not only to construct single-molecule
switches, but also to tune the bulk physical properties of
such materials.[1] Owing to their high thermal stability, fast
response time, and high fatigue resistance,[2] diarylethenes
are among the most promising photochromic materials for
practical applications, for example, in three-dimensional op-
tical memory and optical switches, color displays, and photo-
driven nanoscale actuators.[3–5] In such applications, photo-
chromic reactions in the solid state, for example, in the crys-
talline phase or thin films, are desired. The photochromism
of diarylethenes in solution has been well investigated and
significantly developed, but diarylethenes that exhibit pho-
tochromism in the crystalline phase are still rare.[2,6] It has
been demonstrated that an antiparallel conformation with
the distance between the active carbon atoms at less than
4.2 ꢀ is critical for diarylethenes to exhibit photochromic
performance in the crystalline phase. However, it is still a
challenge to ensure that diarylethenes pack in the crystalline
phase with an antiparallel conformation as there is no fun-
damental guide to controlling the molecular conformation
and stacking pattern in the crystalline phase.[7]
Oligothienoacene derivatives such as dithieno[3,2-b:2’,3’-
d]thiophene (DTT) have received increasing attention as
[a] H. Wang, H. Lin, Prof. W. Xu, Prof. D. Zhu
Beijing National Laboratory for Molecular Sciences
Organic Solids Laboratory, Institute of Chemistry
Chinese Academy of Sciences, Beijing 100190 (P.R. China)
E-mail: wxu@iccas.ac.cn
Results and Discussion
zhudb@iccas.ac.cn
[b] H. Wang, H. Lin
Synthesis: Although diarylethene molecules containing DTT
have been reported previously,[10] none of them underwent
photochromic reactions in the solid state. Recently, our
group reported a symmetrical diarylethene, BDDTP, with
Graduate School of the Chinese Academy of Sciences
Beijing 100049 (P.R. China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202520.
3366
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FULL PAPER
Scheme 1. Chemical structures of diarylethenes 1o–4o and BDDTP.
Scheme 2. Synthetic routes to diarylethenes 1o–4o. Reagents and conditions: a) NBS, DMF; b) 2-methyl-5-thienylboronic acid, [PdACHTUNGTRENNUNG
(2m), THF; c) nBuLi, THF, À788C; d) 2-methyl-3-bromo-5-thienylboronic acid, [Pd
ACHTUNGTRENNUNG
f)nBuLi, THF, À788C.
two b-substituted DTT units, which also did not undergo
photochromic reaction in the crystalline phase.[9] To obtain
the desired performance in the solid state, nonsymmetrical
diarylethenes 1o–4o containing DTT units were designed
(Scheme 1). They were synthesized according to the route il-
lustrated in Scheme 2. The key starting material, 3,5-dime-
thyldithieno[3,2-b:2’,3’-d]thiophene (7), was synthesized by
an efficient method developed by our group.[9] Compound 7
was converted into mono-bromine-substituted derivative 8
by treatment with N-bromosuccinimide (NBS). Suzuki
cross-coupling reaction of compound 8 with an excess of 2-
methyl- or 3-bromo-2-methylthiopheneboronic acid and [Pd-
be toggled between their open-ring isomers 1o–4o and their
closed-ring isomers 1c–4c by alternating irradiation with
UV and visible light at the appropriate wavelengths. Fig-
ure 1a shows the absorption spectral change of 1o induced
by photoirradiation in hexane. Irradiation of a hexane solu-
tion of 1o with light of 380 nm for 100 s led to a decrease in
the absorption at 396 nm and a new band appeared at
476 nm, which has been attributed to the formation of the
closed-ring isomer 1c. It can be seen that the absorption
spectrum of the mixture recorded after the ring-closing reac-
tion is a simple combination of the spectra of the two isolat-
ed isomers. In the photostationary state, the conversion
ratio from 1o to 1c was 62.6%, as estimated by HPLC anal-
ysis (see Figure S1 in the Supporting Information). The new
broad absorption band at 476 nm disappeared on irradiation
with visible light (500 nm), which indicates that 1c returned
to the original state 1o. The absorption characteristics of
2o–4o and 2c–4c are similar to those of 1o and 1c (Fig-
ure 1b–d). Upon irradiation with UV light, a new absorption
band in the visible region appeared as a result of cyclization
to produce 2c–4c. The solutions of 2c–4c can be decolor-
ized by irradiation with visible light of a wavelength longer
than 500 nm, which induced cycloreversion to reproduce
2o–4o. In the photostationary state, the conversion ratios
from the open-ring isomer to the closed-ring isomer are
53.1% for 2, 78.3% for 3, and 71.1% for 4 (see Figures S2–
S4 in the Supporting Information).
ACHTUNGTRENNUNG(PPh3)4] as catalyst in a mixture of aqueous Na2CO3 (2m)
and THF under reflux conditions gave 9 and 10 in yields of
50 and 56%, respectively. Compounds 6a and 6b were ob-
tained by controlling the ratio of starting materials and re-
agents according to the established procedures.[11,12] Com-
pounds 9 and 10, lithiated with nBuLi, were coupled with
6a to afford 1o and 2o in yields of 46 and 60%, respective-
ly. Compound 7, also lithiated, was coupled with compound
6a or 6b to afford 3o and 4o in yields of 46 and 58%, re-
spectively. The molecular structures of diarylethenes 1o–4o
1
were confirmed by H and 13C NMR spectroscopy, EI-MS,
HRMS, elemental analysis, and X-ray crystallography.
Photochromic reactions in solution: Diarylethenes 1–4
showed good photochromic properties in solution and could
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W. Xu, D. Zhu et al.
Figure 1. Absorption spectra of diarylethenes 1o–4o (solid line), 1c–4c (dashed line), and the photostationary state (dotted line) under UV irradiation in
hexane solution (c=1.5ꢂ10À5 molLÀ1). a) 1, b) 2, c) 3, and d) 4.
As these four compounds possess similar molecular struc-
tures, it was interesting to compare the absorption bands of
1–4 before and after photoirradiation. Compounds 1 and 2
are positional isomers with different modes of connection
between the perfluorocyclopentene and thienyl-dithieno-
thiophene moieties. Although 1o (396 nm) exhibits an ab-
sorption band at a longer wavelength than 2o (341 nm), the
absorption maximum of 2c (568 nm) is redshifted by 92 nm
in comparison with that of 1c (476 nm), which indicates a
significantly larger decrease in the HOMO–LUMO energy
gap when compound 2o is converted into 2c. For com-
pounds 1, 3, and 4, the longest absorption bands of 3o and
4o appear at around 362 nm, blueshifted by about 30 nm
compared with that of 1o. This is because the extra thio-
phene unit attached to the DTT unit in 1o causes its p con-
jugation to be more extended than that of 3o and 4o. With
the introduction of the phenyl group at the 5-position of the
thiophene ring in diarylethene 4, the absorption maximum
of the closed-ring isomer 4c (510 nm) exhibits a redshift of
about 34 nm in comparison with diarylethene 3c (476 nm).
This indicates that in the closed state, the phenyl group
makes a greater contribution to the frontier molecular orbi-
tals.
X-ray crystallographic analysis: Crystals suitable for single-
crystal X-ray diffraction analysis were obtained by slow
evaporation of solutions of the compounds in hexane at
room temperature. The X-ray crystallographic analysis data
are collected in Table 1. ORTEP drawings of the structures
of 1o–4o as single crystals are shown in Figure 2 and their
packing views are shown in Figure S5 in the Supporting In-
formation.
It can be observed that, in contrast to previously reported
symmetric BDDTP molecules,[9] all four nonsymmetrical
compounds 1o–4o adopt photoactive antiparallel conforma-
tions in the crystalline phase. For molecule 1o, which can
undergo photocyclization in the crystalline phase,[7] the dis-
tance between the reactive carbon atoms is 3.561 ꢀ. The dis-
tance between the photoactive carbon atoms in 2o is
3.479 ꢀ (C22···C25) and in 4o it is 3.778 ꢀ (C10···C18). As
shown in Figure 2c–h, for diarylethene 3o, there are six in-
dependent molecules in the nonsymmetrical unit and all of
them are packed in a photoactive antiparallel conformation
in the crystalline phase. The distances between the two reac-
tive carbon atoms (C20···C104, C39···C95, C34···C62,
C50···C109, C44···C92, and C76···C99) for molecules I–VI
are 3.737, 3.551, 3.656, 3.598, 3.616, and 3.573 ꢀ, respective-
ly (Table 2), which are significantly shorter than the critical
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Dithienylethenes Bearing Dithienothiophene Units
FULL PAPER
Table 1. Crystal data for diarylethenes 1o–4o.
This indicates that they could potentially be used for the
construction of certain optoelectronic devices.[6d,13]
Althougth diarylethenes containing large p-conjugated
groups have been reported previously,[10] their photochromic
reactions in the solid state have not been investigated. The
above results suggest that the nonsymmetrical structures of
our diarylethenes could result in packing modes favorable
to photochromic reactions in the crystalline phase.
In most cases, the diarylethene crystals do not show con-
version ratios as high as 100%. The photochromic conver-
sion ratios of crystals of 1–4 in the photostationary state
were evaluated by HPLC. The colored crystal of compound
1 obtained after irradiation with UV light (380 nm) for
100 min was dissolved in ethyl acetate/hexane (1:100, v/v)
and submitted to HPLC analysis. The separation of the two
isomers 1o and 1c by HPLC indicated a photochromic con-
version ratio of 84.6% (see Figure S6 in the Supporting In-
formation), which is very high for a diarylethene crystal.
The conversion ratio in the photostationary state from the
open-ring isomer to the closed-ring isomer in the crystalline
phase was 37.6% for 2, 12.5% for 3, and 12.0% for 4 (see
Figures S7–S9). It can be seen that there is no clear relation-
ship between the conversion ratio and the distance between
the reactive carbon atoms.
Compounds
1o
2o
3o
4o
empirical formu- C26H18F6S5 C26H18F6S5
la
C21H14F6S4 C26H16F6S4
formula mass
T [K]
crystal system
space group
a [ꢀ]
b [ꢀ]
c [ꢀ]
a [8]
604.70
113(2)
triclinic
604
173(2)
orthorhombic triclinic
Pbca
508.56
173(2)
570.63
173(2)
orthorhombic
Pbca
¯
¯
P1
P1
8.3470(1) 8.5401(17)
8.9697(2) 12.773(3)
18.5753(5) 47.714(10)
83.975(7) 90.00
8.1705(16) 7.0967(14)
23.049(5) 20.826(4)
36.190(7) 36.522(7)
106.98(3) 90
91.23(3)
92.22(3)
6509(2)
12
b [8]
77.106(8) 90.00
90
90
g [8]
75.289(6) 90.00
V [ꢀ3]
Z
1309.5
2
5204.8(18)
8
5397.8(18)
8
1.404
density
(calcd)
1.534
1.543
1.557
[gmÀ3
]
goodness of fit
1.062
1.142
1.043
1.063
on F2
final R indices [I/
2s(I)]
R1
wR2
0.0499
0.1238
0.0496
0.1152
0.1011
0.3962
0.0859
0. 2636
R indices (all
data)
R1
wR2
0.0743
0.1372
0.0551
0.1182
0.1188
0.4189
0.0948
0.2713
Electrochemical properties of diarylethenes 1–4: Switching
behavior triggered by electrochemical reactions has been ex-
ploited for the development of molecular-scale electronic
switches.[14] It has already been demonstrated that ring-
opening and -closing reactions of diarylethenes can also be
induced by electrochemical redox reactions.[10b,14,15] Thus, it
should be interesting to investigate the electrochemical be-
havior of the diarylethenes synthesized in this work.
Figure 4 shows the cyclic voltammograms of diarylethenes
1–4 in acetonitrile. The oxidation onsets of the open-ring
isomers 1o–4o are at 1.06, 1.09, 1.39, and 1.35 V, and those
of the closed-ring isomers 1c–4c are at 0.98, 1.02, 0.99, and
1.11 V, respectively. The differences in the oxidation onsets
between the open- and closed-ring isomers of diarylethenes
1–4 (~Vo-c) are 0.08 V for 1, 0.07 V for 2, 0.40 V for 3, and
0.24 V for 4. The results show that the oxidation of the
open-ring isomers 1o–4o occurs at higher potentials than
the oxidation of the corresponding closed-ring isomers 1c–
4c, which indicates the extension of the p-conjugation
length in the closed-ring isomers. This is in accordance with
the theory that the longer conjugation length of a closed-
ring isomer generally leads to a less positive oxidation po-
tential.[16,17] After the cyclization reaction, the p electrons
are delocalized throughout the two connected aryl moieties
and extend to the substituents so that the p-conjugation
length in the closed-ring isomers 1c–4c is much longer than
in their open-ring isomers 1o–4o, resulting in a cathodic
shift of the oxidation onsets of 1c–4c. However, no ring-
closing or -opening reactions were observed during the elec-
trochemical characterizations.
Table 2. Distance between the reaction carbon atoms of diarylethenes
1o–4o.
Compound
d [ꢀ]
Crystal
conformation
1o
2o
3o
C4···C13
C22···C25
C20···C104
C39···C95
C34···C62
C50···C109
C44···C92
C76···C99
C10···C18
3.561
3.479
3.737
3.551
3.656
3.598
3.573
3.616
3.778
antiparallel
antiparallel
antiparallel
antiparallel
antiparallel
antiparallel
antiparallel
antiparallel
antiparallel
4o
distance required for the photocyclization reaction in the
crystalline phase.[7]
Photochromism in the single-crystal phase: All of the single
crystals 1o–4o exhibited photochromism in the crystalline
phase (Figure 3). The photographs of single crystals of 1o–
4o show color changes upon photoirradiation. Upon irradia-
tion with light of 365 nm, the pale yellow crystal of 1o
turned deep yellow, the yellow crystal of 2o turned yellow-
green, the colorless crystal of 3o turned deep yellow, and
the yellow crystal of 4o turned orange-red. The absorption
spectra of these crystals dissolved in hexane exhibit absorb-
ance maxima identical to those of their corresponding
closed-ring isomers in solution. The colored crystals re-
turned to their original color upon irradiation with visible
light of the appropriate wavelength (500 nm). Furthermore,
the crystals in the photostationary state remained stable for
more than four months in the dark at room temperature.
The HOMO and LUMO energy levels derived from the
CV data and the HOMO–LUMO energy gap (HLG) of
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W. Xu, D. Zhu et al.
each compound are summar-
ized in Table 3. The data show
that
the
HOMO–LUMO
energy gaps of the closed-ring
isomers 1c–4c (1.9–2.15 eV) are
smaller than those of the corre-
sponding open-ring isomers 1o–
4o (2.4–2.79 eV). This is in
good agreement with the batho-
chromic shifts observed in the
UV/Vis spectra and can mainly
be ascribed to the extension of
the conjugation length in the
closed-ring isomers 1c–4c com-
pared with in the open-ring iso-
mers 1o–4o.
Theoretical investigations: We
carried out molecular orbital
calculations on the open- and
closed-ring isomers of the di
arylethenes to gain an insight
into the nonsymmetrical struc-
tures and electronic absorption
properties of diarylethenes 1–4.
The geometries were optimized
by performing DFT calculations
using the B3LYP functional and
6-31G* basis set. To reduce the
computational cost, only the
photoactive antiparallel confor-
mation in the open form was
considered.
Figure 5 illustrates the calcu-
lated HOMOs and LUMOs of
the optimized structures in the
ground state for diarylethenes
1–4. The electron densities in
both the HOMOs and LUMOs
of the open-ring isomers are
different to those of the closed-
ring isomers. For the open-ring
isomers 1o–4o, the electron
density in the LUMO orbital is
distributed over the whole
moiety except in the case of 4o.
For 4o, the introduction of the
phenyl group does not affect
the distribution of the electron
density in the LUMO, it is es-
sentially the same as in 3o. For
closed-ring isomers 1c–4c, the
electron densities of the
HOMOs are localized over the
whole molecule whereas in the
LUMOs they are localized on
one side, with the exception of
Figure 2. ORTEP drawings of crystals 1o–4o (displacement ellipsoids are drawn at the 30% probability level):
a) 1o, b) 2o, c) 3o-I, d) 3o-II, e) 3o-III, f) 3o-IV, g) 3o-V, h) 3o-VI, and i) 4o.
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Dithienylethenes Bearing Dithienothiophene Units
FULL PAPER
Table 3. Electrochemical properties of diarylethenes 1–4 in acetonitrile.
Compound
Oxidation
Reduction
HLG [eV]
Eonset [V] EHOMO [eV] Eonset [V] ELUMO [eV]
1o
1c
2o
2c
3o
3c
4o
4c
1.06
0.98
1.09
1.02
1.39
0.99
1.35
1.11
À5.46
À5.38
À5.49
À5.42
À5.79
À5.39
À5.75
À5.51
À1.37
À1.17
À1.40
À1.13
À1.16
À1.15
À1.34
À0.99
À3.03
À3.23
À3.03
À3.25
À3.00
À3.25
À3.06
À3.41
2.43
2.15
2.46
1.99
2.79
2.14
2.69
2.10
smaller energy gaps were calculated for the corresponding
closed-ring isomers 1c–4c (3.05–2.34 eV) as a more extend-
ed p-conjugation system leads to an increase in energy of
the p orbitals and a decrease in energy of the p* orbitals.[18]
This is in agreement with data extracted from the electro-
chemical studies.
Figure 3. Photographs demonstrating the photochromic changes observed
in diarylethenes 1–4 in the crystalline phase.
2c. The electron densities in both the HOMO and LUMO
of 2c are spread over the whole molecule.
Conclusion
The calculated HOMO–LUMO gaps (HLGs) of these iso-
mers are summarized in Table S1 in the Supporting Informa-
tion. The HLGs of the open-ring isomers 1o–4o were calcu-
lated to be in the range 3.64–3.29 eV, whereas significantly
Four new nonsymmetrical photochromic diarylethenes pos-
sessing DTT units have been synthesized to investigate their
photophysical, electrochemical, and photochromic behavior
Figure 4. Cyclic voltammagrams of 1o–4o (solid lines) and 1c–4c (dash line). a) 1, b) 2, c) 3, and d) 4. Experiments were performed in acetonitrile (c=
1.0ꢂ10À3 m) with a platinum electrode. Scan rates: 50 mVsÀ1
.
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W. Xu, D. Zhu et al.
matrix least-squares on F2. The com-
putations were performed by using the
SHELXL-97 program.[19] Hydrogen
atoms bound to carbon were placed at
calculated positions and resolved by
using a riding model.
CCDC-862537 (1o), CCDC-862538
(2o), CCDC-862539 (3o), and CCDC-
862540 (4o) contain the supplementa-
ry crystallographic data for this paper.
These data can be obtained free of
charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.ca-
m.ac.uk/data_request/cif.
2-Bromo-3,5-dimethyldithieno[3,2-
b:2’,3’-d]thiophene (8): NBS (0.089 g,
0.5 mmol) was added dropwise to a
stirred solution of 3,5-dimethyldithie-
no[3,2-b:2’3’-d]thiophene
(7)[9]
(0.112 g, 0.5 mmol) in DMF at 08C.
The mixture was stirred for another
2 h at this temperature and then al-
lowed to warm to room temperature.
After stirring for 1 h, water (10 mL)
was added. The mixture was then ex-
tracted with diethyl ether and the or-
ganic layer was washed with water,
dried over magnesium sulfate, filtered,
Figure 5. Frontier molecular orbital densities for diarylethenes 1–4 calculated at the B3LYP/6-3 1G* level of
theory.
in solution as well as in the crystalline phase. They have also
and the solvent evaporated. The crude product was purified by column
chromatography on silica (hexane) to afford compound 8 (0.109 g) as a
white powder. Yield: 71.9%; m.p. 147–1488C; 1H NMR (400 MHz,
CDCl3, 258C, TMS): d=6.95 (s, 1H), 3.31 (s, 3H), 2.37 ppm (s, 3H);
13C NMR (100 MHz, CDCl3, 258C, TMS): d=141.559, 140.827, 131.141,
130.895, 129.451, 121.410, 108.935, 14.965, 14.458 ppm; HRMS (EI): m/z
calcd for C10H7BrS3: 301.8893, 303.8873; found: 301.8898 (94.72%),
303.8875 (100%).
been studied through DFT calculations. The new nonsym-
metrical photochromic diarylethenes exhibit remarkable
photochromism in the crystalline phase, in contrast to the
symmetrical diarylethenes. This study has provided a new
strategy for the design of diarylethenes that undergo photo-
chromic reactions in the crystalline phase. Extension of this
work to the fabrication of photoswitchable field-effect tran-
sistors based on these diarylethene compounds is in prog-
ress.
2-(2-Methyl-5-thienyl)-3,5-dimethyldithieno[3,2-b:2’,3’-d]thiophene (9):
Compound 9 was prepared by treating compound 8 (3.25 g, 10.7 mmol)
with 2-methyl-5-thienylboronic acid (1.52 g, 10.7 mmol) in the presence
of [PdACTHNUGTREN(UNG PPh3)4] (0.3 g) and Na2CO3 (4.2 g, 40 mmol) in THF (50 mL con-
taining 10% water) for 6 h at 708C. The crude product was purified by
column chromatography on silica (hexane) to afford compound 9 (1.71 g)
as a white powder. Yield: 50%; m.p. 124–1258C; 1H NMR (400 MHz,
CDCl3, 258C, TMS): d=6.98 (d, J=3.6 Hz, 1H), 6.95 (s, 1H), 6.75 (d, J=
3.2 Hz, 1H), 2.53 (s, 3H), 2.47 (s, 3H), 2.38 ppm (s, 3H); 13C NMR
(100 MHz, CDCl3, 258C, TMS): d=144.3, 141.9, 140.7, 134.7, 131.9,
131.3, 131.0, 128.3, 126.1, 121.3, 15.7, 14.9, 14.6 ppm; HRMS (EI): m/z
calcd for C15H12S4: 319.9822; found: 319.9825.
Experimental Section
General: THF was distilled over sodium benzophenone ketyl before use.
All other reagents and solvents were purchased from commercial suppli-
ers and used directly as received. 1H and 13C NMR spectra were per-
formed in CDCl3 with TMS as internal standard on Bruker Advance
400 MHz spectrometers. EI-MS was performed on Shimadzu
GCMSQP2010 or UK GCT-Micromass spectrometers. MALDI-TOF
mass spectra were recorded with a Bruker Biflex III 45 MALDI-TOF
2-(3-Bromo-2-methyl-5-thienyl)-3,5-dimethyldithieno[3,2-b:2’,3’-d]thio-
phene (10): Compound 10 was prepared by a method similar to that used
for the synthesis of 9. The crude product was purified by column chroma-
tography on silica (hexane) to afford compound 10 (0.235 g) as a yellow
spectrometer. HRMS measurements were performed on
a Bruker
1
powder. Yield: 56%; m.p. 147–1488C; H NMR (400 MHz, CDCl3, 258C,
APEXIIFT-ICRMS spectrometer. Elemental analyses were performed
on a Carlo Erba 1106 elemental analyzer. UV/Vis spectra were recorded
on a JASCO V-570 spectrometer. Electrochemical experiments were per-
formed on a CHI660 voltammetric analyzer (CH instruments, USA).
They were carried out in a conventional three-electrode cell with plati-
num disk working electrodes, a platinum wire counter electrode, and an
Ag/AgCl reference electrode at room temperature. Typically, acetonitrile
containing 0.1m tetrabutylammonium hexafluorophosphate was used as
TMS): d=6.97 (s, 2H), 2.47 (s, 3H), 2.45 (s, 3H), 2.39 ppm (s, 3H);
13C NMR (100 MHz, CDCl3, 258C, TMS): d=144.2, 142.2, 134.8, 134.2,
131.3, 130.9, 130.2, 128.7, 128.3, 127.9, 121.7, 120.1, 15.1, 14.9, 14.5 ppm;
HRMS (EI): m/z calcd for C15H11BrS4: 397.8927, 399.8907; found:
397.8933 (83.07%), 399.8910 (100%).
1-(2,5-Dimethyl-3-thienyl)perfluorocyclopentene (6a): nBuLi (4.2 mL,
2.5m solution in hexanes) was added dropwise to a stirred solution of 3-
iodo-2,5-dimethylthiophene (2.38 g, 10.0 mmol) in THF at À788C under
nitrogen. After stirring at this low temperature for 2 h, perfluorocyclo-
pentene (1.43 mL, 10.5 mmol) was added to the reaction mixture at
À788C and the mixture was stirred for another 2 h at this temperature.
The mixture was then allowed to warm to the room temperature and the
reaction stopped by the addition of water. The product was extracted
with diethyl ether and the organic layer was washed with water and dried
over magnesium sulfate, filtered, and the solvent evaporated. The crude
electrolyte with 1ꢂ10À3 m dithienylethene at a scan rate of 50 mVsÀ1
Photoirradiation was performed with a PLS-SXE300UV xenon arc lamp
(Beijing Trusttech Co. Ltd). The appropriate wavelength was achieved by
passing the light through a band filter.
.
X-Ray crystallographic data were collected with a Bruker Smart CCD
diffractometer by using graphite-monochromated MoKa radiation (l=
0.71073 ꢀ). Data were collected at 113 K for 1o and at 173 K for 2o–4o
and the structures were resolved by direct methods and refined by full-
3372
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ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 3366 – 3373

Dithienylethenes Bearing Dithienothiophene Units
FULL PAPER
product was purified by column chromatography on silica (hexane) to
afford compound 6a (2.23 g) as a colorless oil. Yield: 73.4%; 1H NMR
(400 MHz, CDCl3, 258C, TMS): d=6.73 (s, 1H), 2.43 (s, 3H), 2.39 ppm
(s, 3H).
Acknowledgements
The authors acknowledge financial support from the National Natural
Science Foundation of China (20872147 and 20952001) and the State Key
Basic Research Program (2011CB808401).
1-(2-Methyl-5-phenyl-3-thienyl)perfluorocyclopentene (6b): Compound
6b was prepared by a method similar to that used for the synthesis of 6a.
The crude product was purified by column chromatography on silica
(hexane) to afford compound 6a (4.91 g) as a white powder. Yield:
71.5%; 1H NMR (400 MHz, CDCl3, 258C, TMS): d=7.51 (d, J=7.2 Hz,
2H), 7.38 (t, J=7.4 Hz, 2H), 7.27 (t, J=11.4 Hz, 1H), 7.10 (s, 1H),
2.42 ppm (s, 3H).
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1-(2,5-Dimethyl-3-thienyl)-2-[6-(2-methyl-5-thienyl)-3,5-dimethyldithie-
no[3,2b:2’,3’-d]thiophen-2-yl]perfluorocyclopentene (1o): nBuLi (2.5m
solution in hexanes, 0.136 mL) was added dropwise to a stirred solution
of compound 9 (0.1 g, 0.312 mmol) in THF at À788C under nitrogen and
stirring was continued for 2 h at this temperature. Compound 6a (0.104 g,
0.34 mmol) in THF was slowly added to the reaction mixture at À788C
and the mixture was stirred for another 2 h at this temperature. Then the
reaction was quenched with water. The product was extracted with dieth-
yl ether and the organic layer was washed with water, dried with anhy-
drous magnesium sulfate, and concentrated under reduced pressure. The
crude product was purified by column chromatography on silica (hexane)
to afford compound 1o (94.2 mg) as a pale-yellow powder. Yield: 46%;
m.p. 115.8–117.98C; 1H NMR (400 MHz, CDCl3, 258C, TMS): d=7.0 (s,
1H), 6.75 (d, J=2 Hz, 2H), 2.53 (s, 3H), 2.46 (s, 3H), 2.44 (s, 3H),
1.90 ppm (s, 6H); 13C NMR (100 MHz, CDCl3, 258C, TMS): d=145.4,
142.2, 141.2, 140.4, 138.2, 133.9, 123.9, 127.3, 126.4, 126.3, 126.0, 125.0,
124.8, 123.1, 15.5, 15.3, 14.6, 14.5, 14.4 ppm; MS (EI): m/z: 604; elemental
analysis calcd (%) for C26H18F6S5 (604.74): C 51.64, H 3.00, found: C
51.63, H 3.01.
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biol. A 2008, 196, 84–93.
1-(2,5-Dimethyl-3-thienyl)-2-[2-methyl-5-(3,5-dimethyldithieno[3,2-
b:2’,3’-d]thiophen-2-yl)-3-thienyl)]perfluorocyclopentene (2o): Com-
pound 2o was prepared by a method similar to that used for the synthesis
of 1o. The crude product was purified by column chromatography on
silica (hexane) to afford compound 2o (87 mg) as a yellow powder.
Yield: 60%; m.p. 147–1488C; 1H NMR (400 MHz, CDCl3, 258C, TMS):
d=7.08 (s, 1H), 6.98 (s, 1H), 6.74 (s, 1H), 2.44 (s, 6H), 2.39 (s, 3H), 1.98
(s, 3H), 1.90 ppm (s, 3H); 13C NMR (100 MHz, CDCl3, 258C, TMS): d=
144.0, 141.8, 139.9, 138.0, 134.7, 131.1, 128.9, 127.7, 124.6, 121.6, 15.3,
14.8, 14.4, 14.3, 13.9 ppm; HRMS (EI): m/z calcd for C26H18F6S5:
603.9916; found: 603.9923.
1-(2,5-Dimethyl-3-thienyl)-2-[3,5-dimethyldithieno[3,2-b:2’3’-d]thiophen-
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1183–1186.
2-yl]perfluorocyclopentene (3o): Compound 3o was prepared by
a
method similar to that used for the synthesis of 1o. The crude product
was purified by column chromatography on silica (hexane) to afford
compound 3o (0.115 g) as a yellow powder. Yield: 46%; m.p. 133–
1348C; 1H NMR (400 MHz, CDCl3, 258C, TMS): d=7.04 (s,1H), 6.76 (s,
1H), 2.43 (s, 3H), 2.38 (s, 6H), 1.89 ppm (s, 3H); 13C NMR (100 MHz,
CDCl3, 258C, TMS): d=143.5, 142.9, 140.3, 138.0, 133.8, 132.8, 131.0,
130.3, 124.9, 124.6, 122.8, 15.2, 14.6, 14.4 ppm; MS (EI): m/z: 508. ele-
mental analysis calcd (%) for C21H14F6S4 (508.59): C 49.59, H 2.77;
found: C, 49.73, H, 3.00.
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1-(2-Methyl-5-phenyl-3-thienyl)-2-[3,5-dimethyldithieno[3,2-b:2’3’-d]thio-
phen-2-yl]perfluorocyclopentene (4o): Compound 4o was prepared by a
method similar to that used for the synthesis of 1o. The crude product
was purified by column chromatography on silica (hexane) to afford
compound 4o (0.101 g) as a yellow powder. Yield: 58%; m.p. 140–
1418C; 1H NMR (400 MHz, CDCl3, 258C, TMS): d=7.56 (d, J=4 Hz,
2H), 7.39 (t, J=8 Hz, 2H), 7.31 (t, J=8 Hz, 2H), 7.05 (s, 1H), 2.37 (s,
3H), 1.99 (s, 3H), 1.95 ppm (s, 3H); 13C NMR (100 MHz, CDCl3, 258C,
TMS): d=143.9, 143.2, 142.7, 141.8, 133.4, 133.2, 131.2, 130.4, 129.2,
128.1, 126.0, 125.8, 123.2, 122.7, 14.7 ppm; MS (EI): m/z: 570.0; elemental
analysis calcd (%) for C26H16F6S4 (570.66): C 54.72, H 2.83; found: C,
54.89, H, 3.03.
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Tetrahedron 2005, 61, 6623–6629.
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5205.
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Received: July 15, 2012
Revised: November 5, 2012
Published online: January 17, 2013
Chem. Eur. J. 2013, 19, 3366 – 3373
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3373