1-(2-Methyl-5-phenyl-3-thienyl)-2-(3-methyl-5-phenyl-2-thienyl)-3,3,4,4,5, 5-hexafluorocyclopent-1-ene: A novel photochromic hybrid diarylethene

Article abstract of DOI:10.1107/S0108270105028143

The title compound, C₂₇H₁₈F₆S₂, a novel photochromic hybrid diarylethene derivative containing 2- and 3-thienyl substituents, is one of the most promising photochromic candidates with shorter wavelength for optical storage and other optoelectronic devices. In the crystal structure, the molecule adopts a photoactive antiparallel conformation. The distance between the two reactive C atoms, i.e. the ring C atoms to which the methyl groups are attached, is 3.430 (4) A. The dihedral angles between the thienyl and adjacent phenyl rings are 26.8 (2) and 33.98 (9)°.

Full text of DOI:10.1107/S0108270105028143

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
thienylethane is localized in a cyclohexadiene structure, so
that it has a shorter absorption wavelength (Sun et al., 2003).
Although many photochromic diarylethenes have been
reported, they are mainly symmetric diarylethene derivatives
with both aryl substituents attached through either their 2- or
3-positions (Irie, 2000; Tian & Yang, 2004; Pu et al., 2004; Pu,
Yang, Wang & Xu, 2005; Pu, Yang & Yan, 2005; Pu, Liu & Yan,
2005); diarylethenes with aryl substituents attached through a
mixture of their 2- or 3-positions and which absorb at a short
wavelength (400±500 nm) (Sun et al., 2003; Takami & Irie,
2004) are very rare. Therefore, it is desirable to prepare
diarylethene derivatives of this type for short wavelength
memories. In the present paper, the structure of the title
compound, i.e. 1-(2-methyl-5-phenyl-3-thienyl)-2-(3-methyl-5-
phenyl-2-thienyl)-3,3,4,4,5,5-hexa¯uorocyclopent-1-ene, (Ia),
is presented.
ISSN 0108-2701
1-(2-Methyl-5-phenyl-3-thienyl)-
2-(3-methyl-5-phenyl-2-thienyl)-
3,3,4,4,5,5-hexafluorocyclopent-1-ene:
a novel photochromic hybrid
diarylethene
Shou-Zhi Pu,a* Gang Liu,a Bing Chena and Ru-Ji Wangb
aJiangxi Key Laboratory of Organic Chemistry, Jiangxi Science & Technology Normal
University, Nanchang 330013, People's Republic of China, and bDepartment of
Chemistry, Tsinghua University, Beijing 100084, People's Republic of China
Correspondence e-mail: pushouzhi@tsinghua.org.cn
Received 22 August 2005
Accepted 7 September 2005
Online 17 September 2005
The molecule of (Ia) shows a photoactive antiparallel
conformation (Fig. 1). The two thiophene moieties are linked
by the C1 C2 double bond, with the S1-containing thiophene
ring attached to the ethylene moiety via the 2-position and the
S2-containing thiophene ring attached via the 3-position. The
two methyl groups are located on different sides of the double
The title compound, C27H18F6S2, a novel photochromic hybrid
diarylethene derivative containing 2- and 3-thienyl substitu-
ents, is one of the most promising photochromic candidates
with shorter wavelength for optical storage and other
optoelectronic devices. In the crystal structure, the molecule
adopts a photoactive antiparallel conformation. The distance
between the two reactive C atoms, i.e. the ring C atoms to
Ê
which the methyl groups are attached, is 3.430 (4) A. The
dihedral angles between the thienyl and adjacent phenyl rings
are 26.8 (2) and 33.98 (9)ꢀ.
Comment
Photochromism is described as a photoinduced reversible
transformation of a chemical species between two isomeric
È
forms having different absorption spectra (Brown, 1971; Durr
& Bouas-Laurent, 1990). Photochromic compounds have
attracted much attention because of their potential uses for
optical memory, and for photo-optical switching and display
devices (Takami & Irie, 2004). Of all the photochromic
compounds, diarylethene derivatives are the most promising
candidates because of their good thermal stability, high
sensitivity, fast response and high fatigue resistance (Irie, 2000;
Tian & Yang, 2004). For application to a full color display and
for increasing the optical storage density, it is indispensable to
prepare diarylethene derivatives whose ring-closure isomers
show red and yellow colours (Takami & Irie, 2004). One
approach to shorten the absorption wavelength of diaryl-
ethene is to attach 2-thienyl rings to the ethylene moiety
(Uchida et al., 1998). For diarylethene, the absorption spec-
trum depends on the substituent and the ꢀ conjugation length.
Compared with the closed-ring isomer of di-3-thienylethane,
where the ꢀ conjugation extends throughout the whole mol-
ecule, the ꢀ conjugation in the closed-ring isomer of di-2-
Figure 1
The structure of (Ia), drawn with 35% probability displacement ellipsoids,
showing the atomic numbering scheme.
Acta Cryst. (2005). C61, o599±o601
DOI: 10.1107/S0108270105028143
# 2005 International Union of Crystallography o599

organic compounds
(5) (2.4 g, 6.5 mmol), was synthesized in 53% yield according to the
procedure of Peters et al. (2003) from (4) (3.1 g, 12.3 mmol), n-BuLi/
hexane solution (2.5 mol l 1, 12.3 mmol) and per¯uorocyclopentene
(1.7 ml, 12.5 mmol); (v) 4-methyl-2-phenylthiophene, (7) (4.6 g,
26.4 mmol), was prepared in 67% yield by reacting (6) (3.9 g,
39.7 mmol) with 1-bromobenzene (6.2 g, 39.7 mmol) according to the
procedure of Pu, Liu & Yan (2005); (vi) 2.8 ml of n-BuLi/hexane
solution (2.5 mol l 1, 7.0 mmol) was added slowly at 273 K under a
nitrogen atmosphere to a stirred THF solution (50 ml) containing
compound (7) (1.2 g, 6.9 mmol). After 30 min, compound (5) (2.4 g,
6.5 mmol) was added and the mixture was stirred for 3 h at this
temperature. The reaction mixture was extracted with ether, evapo-
rated in vacuo and purifed by column chromatography (hexane) to
give the title compound (Ia) (1.9 g, 3.6 mmol) in 56% yield. Crystals
of (Ia) were grown from a chloroform solution by slow evaporation
(m.p. 403.2±403.5 K). Analysis calculated for C27H18F6S2 (%): C 62.30,
bond and are thus trans with respect to the double bond. Such
a conformation is crucial for the compound to exhibit
photochromic and photoinduced properties (Woodward &
Hoffmann, 1970). The dihedral angle between the thiophene
and adjacent benzene ring is 33.98 (9)ꢀ for the C10±C15
benzene ring and 26.8 (2)ꢀ for the C21±C26 benzene ring. The
distance between the two reactive C atoms (C7Á Á ÁC17) is
Ê
3.430 (4) A, which is short enough, theoretically, for the ring-
closure reaction to take place in the crystalline phase
(Ramamurthy & Venkatesan, 1987).
In fact, the crystal of (Ia) undergoes a photochromic reac-
tion in accordance with the expected ring closure, forming (Ib)
(see scheme). Upon irradiation with light of wavelength
254 nm, the colourless crystal of (Ia) rapidly turned red. When
observed under polarized light, the intensity of the red colour
changed on rotation of the crystalline sample. This phenom-
enon suggested that the closed-ring isomers were regularly
oriented in the crystal and that the photochromic reaction
took place in the crystal lattice (Yamamoto et al., 2003). When
the red crystal was dissolved in hexane, the solution turned red
and the absorption maximum was observed at 501 nm, as for
the closed-ring isomer (Ib). The red colour of the crystal
disappeared upon irradiation with either light of wavelength
500 nm or daylight, and the absorption spectrum of the solu-
tion containing the colourless crystal was the same as that of
the open-ring isomer (Ia), with the maximum absorption at
292 nm.
1
H 3.49; found: C 62.44, H 3.57. H NMR (400 MHz, CDCl3): ꢁ 1.794
(s, 3H), 2.014 (s, 3H), 7.073 (s, 1H, thiophene H), 7.284 (s, 1H,
thiophene H), 7.301±7.341 (t, 2H, J = 8.0 Hz, phenyl H), 7.369±7.407
(t, 4H, J = 7.6 Hz, phenyl H), 7.543±7.587 (m, 4H, J = 8.8 Hz, phenyl
H). 19F NMR (400 MHz, CDCl3): ꢁ 109.33 (2F), 109.50 (2F), 131.42
(2F).
Crystal data
3
C27H18F6S2
Mr = 520.53
Monoclinic, P21=c
Ê
a = 11.5406 (12) A
Dx = 1.449 Mg m
Mo Kꢃ radiation
Cell parameters from 36
re¯ections
Ê
b = 9.2179 (7) A
ꢄ = 5.1±12.6ꢀ
ꢅ = 0.28 mm
T = 295 (2) K
1
Ê
c = 22.432 (2) A
ꢂ = 90.263 (8)ꢀ
V = 2386.3 (4) A
Z = 4
3
Ê
Prism, colourless
0.6 Â 0.5 Â 0.4 mm
Experimental
Data collection
The novel title photochromic diarylethene (Ia) was derived originally
from 2-methylthiophene, (1), and 3-methylthiophene, (6) (see reac-
tion scheme below). The reaction was carried out in six steps: (i) 3,5-
dibromo-2-methylthiophene, (2) (50.7 g, 198.1 mmol), was obtained
in 81.2% yield by brominating (1) (24.0 g, 244.8 mmol) in acetic acid
at 273 K; (ii) 3-bromo-2-methyl-5-thienylboronic acid, (3) (12.0 g,
54.3 mmol), was prepared in 85.5% yield in the presence of
compound (2) (16.3 g, 63.7 mmol), n-BuLi/hexane solution
(2.5 mol l 1, 65 mmol) and tri-n-butylborate (18.8 ml, 68.9 mmol) at
195 K under a nitrogen atmosphere; (iii) 3-bromo-2-methyl-5-
phenylthiophene, (4) (6.3 g, 24.9 mmol), was prepared in 70% yield
Bruker P4 diffractometer
! scans
h = 13 ! 1
k = 10 ! 1
5525 measured re¯ections
4201 independent re¯ections
3121 re¯ections with I > 2ꢆ(I)
Rint = 0.028
l = 26 ! 26
3 standard re¯ections
every 97 re¯ections
intensity decay: none
ꢄ
max = 25.0ꢀ
Re®nement
Re®nement on F2
R[F2 > 2ꢆ(F2)] = 0.054
wR(F2) = 0.112
w = 1/[ꢆ2(Fo2) + (0.001P)2
+ 2.7P]
2
where P = (Fo + 2Fc2)/3
S = 1.02
4201 re¯ections
318 parameters
H-atom parameters constrained
(Á/ꢆ)max < 0.001
3
Ê
Áꢇmax = 0.48 e A
3
Ê
0.34 e A
Áꢇmin
=
Table 1
Selected geometric parameters (A, ).
ꢀ
Ê
S1ÐC9
S1ÐC6
S2ÐC17
S2ÐC20
C1ÐC2
C1ÐC6
C1ÐC5
C2ÐC18
C2ÐC3
C3ÐC4
1.724 (3)
1.726 (3)
1.715 (3)
1.727 (3)
1.346 (4)
1.460 (4)
1.501 (4)
1.464 (4)
1.500 (4)
1.534 (5)
C4ÐC5
C6ÐC7
C7ÐC8
C7ÐC16
C8ÐC9
C17ÐC18
C17ÐC27
C18ÐC19
C19ÐC20
1.508 (5)
1.367 (4)
1.429 (4)
1.501 (5)
1.387 (4)
1.371 (4)
1.496 (4)
1.456 (4)
1.385 (4)
by reacting (3) (7.8 g, 35.3 mmol) with 1-bromobenzene (5.6 g,
35.7 mmol) in the presence of Pd(PPh3)4 (0.9 g) and Na2CO3
(2 mol l 1, 130 mmol) in tetrahydrofuran (THF, 120 ml) for 15 h at
343 K; (iv) 1-(2-methyl-5-phenyl-3-thienyl)per¯uorocyclopent-1-ene,
C6ÐC1ÐC2ÐC18
C2ÐC1ÐC6ÐC7
S1ÐC9ÐC10ÐC11
10.5 (5)
43.7 (5)
35.1 (4)
C1ÐC2ÐC18ÐC17
S2ÐC20ÐC21ÐC22
38.9 (5)
27.7 (5)
ꢁ
o600 Pu et al. C27H18F6S2
Acta Cryst. (2005). C61, o599±o601

organic compounds
Ê
Methyl H atoms were positioned geometrically (CÐH = 0.96 A)
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Ê
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ꢁ
Acta Cryst. (2005). C61, o599±o601
Pu et al. C27H18F6S2 o601