organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
and an anisyl group on opposing ends of the C C double
bond (Fig. 1). Steric hindrance is avoided by the planes of the
phenylene and thienyl rings being inclined to that of the
cyclopentene ring by 51.2 (1) and 51.3 (1)ꢀ, respectively, but
the avoidance of crowding places the aliphatic ring substi-
tuents on opposite sides of the mean cyclopentene plane. This
configuration is crucial for the manifestation of photo-
chromism and other photo-induced properties (Woodward &
Hoffmann, 1970). More importantly, the C C double bond of
the cyclopentene ring can, theoretically, change to a C—C
single bond. Such a reduction in bond order would accompany
the formation of a new C—C bond between the C atom of the
phenylene group bearing the methoxy unit and the C atom of
the thienyl group bearing the methyl substituent (Fig. 2). As
the distance between these two C atoms (C1Á Á ÁC13) is
ISSN 0108-2701
3,3,4,4,5,5-Hexafluoro-1-(2-methoxy-
phenyl)-2-[5-(4-methoxyphenyl)-2-
methyl-3-thienyl]cyclopent-1-ene: a
photochromic compound
Congbin Fan,a* Gang Liu,a Weijun Liu,a Tianshe Yanga and
Seik Weng Ngb
˚
aJiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology
Normal University, Nanchang 330013, People’s Republic of China, and bDepart-
ment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
Correspondence e-mail: congbinfan@yahoo.com.cn
3.717 (2) A, the compound can be expected to exhibit
photochromism (Fig. 2). It is known that photochromic
activity in similar compounds is usually present when this
˚
distance is less than 4.2 A (Kobatake & Irie, 2004; Rama-
murthy & Venkatesan, 1987). We have been able to verify this
experimentally. Upon irradiation with 365 nm radiation, the
colorless crystals turned blue rapidly, but if the UV light was
removed, the crystals became colorless immediately. In
hexane, the irradiated compound showed an absorption
maximum at 592 nm. Upon irradiation using a wavelength of
more than 510 nm, the blue hexane solution was rendered
colorless and showed an absorption maximum at 287 nm. In a
poly(methyl methacylate) amorphous film, the title diaryl-
Received 5 March 2009
Accepted 9 April 2009
Online 25 April 2009
The photochromic title compound, C24H18F6O2S, has thienyl
and aryl substituents on the C C double bond of the shallow
half-chair-shaped cyclopentene ring. The planes of the two
substituent rings are inclined to that of the cyclopentene ring,
with dihedral angles between the mean plane of the
cyclopentene ring and those of the phenylene and thienyl
rings of 51.2 (1) and 51.3 (1)ꢀ, respectively. The molecule
adopts an antiparallel conformation, with a distance between
˚
the two photoreactive C atoms of 3.717 (2) A.
Comment
Photochromic diarylethenes find possible applications in
optical memory-storage devices and as optical switches (Irie,
2000; Tian & Yang, 2004). In our own studies, we have found
that central to photochromic activity of the class of
perfluorocyclopentenes is a pendant five-membered hetero-
cyclic ring (Fan et al., 2008), a feature that is displayed by the
title compound, (I).
Figure 1
A displacement ellipsoid plot (Barbour, 2001) of (I). Ellipsoids are drawn
at the 50% probability level.
The cyclopentene ring has a shallow half-chair conforma-
tion twisted on C10—C11 (the r.m.s. deviation of the consti-
˚
tuent C atoms is 0.08 A) and has a substituent thienyl group
Figure 2
Photochromic interconversion of (I).
Acta Cryst. (2009). C65, o243–o244
doi:10.1107/S0108270109013468
# 2009 International Union of Crystallography o243
Fan, Congbin
