supplementary materials


HTML versionpdf versioncif file3d viewstructure factorssupplementary materialsCIF check reportsimilar papers Open access

dn2342 scheme

Acta Cryst. (2008). E64, o1028    [ doi:10.1107/S1600536808013330 ]

1-(2-Chlorophenyl)-2-(2-methyl-5-phenyl-3-thienyl)-3,3,4,4,5,5-hexafluorocyclopent-1-ene: a new photochromic diarylethene

S. Gong, C. Fan, W. Liu and G. Liu

Abstract top

The title compound, C22H13ClF6S, is a hybrid diarylethene derivative with one 3-thienyl substituent, and a Cl-substituted six-membered aryl unit bonded to the double bond of a hexafluorocyclopentene ring. In the crystal structure, the molecule adopts a photo-active antiparallel conformation that can undergo effective photocyclization reactions. The distance between the two reactive C atoms is 3.848 (3) Å. The dihedral angles between the least-squares cyclopentene plane and those of the adjacent thiophene and chlorophenyl rings are 49.39 (8) and 59.88 (8)°, respectively. The F atoms are disordered over two positions, with site occupancy factors of 0.6 and 0.4.

Comment top

Organic photochromic materials have attracted much attention, because of their potential application to optical memory media and optical switches. (Dürr & Bouas-Laurent, 1990; Tian & Yang, 2004). Among all organic photochromic compounds, diarylethenes with heterocyclic aryl groups are the most promising candidates for those application, mainly due to the excellent thermal stability of the respective isomers, notable fatigue resistance, and high reactivity in the solid state (Irie, 2000). The backbone of all photochromic perfluorocyclopentene systems are composed of five-membered heterocyclic rings (Zheng et al., 2007) or the combination of a five-membered aryl ring and a vinyl group. we decided to investigate if replacing the five-membered heterocyclic ring in the diarylethene with a six-membered aryl ring would induce novel characteristics. This paper presents the synthesis and crystal structure of the title compound a six-membered aryl ring group bearing a Cl atom.

The thienyl and the 2-chlorophenyl rings are in cis-position with respect to the C7=C11 double bond (Fig. 1). They are located on each side of the fluorocyclopentene ring, as reflected by the torsion angles C1—C6—C7—C11 [-60.52 ( 0.31)°] and C7—C11—C12—C13 [45.95 (23)°]. The dihedral angles between the least-square cyclopentene plane and those of the adjacent thiophene and chloro-phenyl rings are 49.39 (8)° and 59.88 (8)° respectively.

Such conformation is crucial for the compound to exhibit photochromic and photoinduced properties (Woodward & Hoffmann, 1970). The intramolecular distance between the two reactive C atoms (C1—C13) is 3.848 (3) Å. This distance indicates that the crystal can be expected to undergo photochromism to form compound (Ib)( Fig. 2), because photochromic reactivity usually appears when distance between the reactive C atoms is less than 4.2 Å (Ramamurthy & Venkatesan, 1987; Kobatake et al., 2004). Crystal of (Ib) shows photochromism in accordance with the expected ring closure to form (Ib). Upon irradiation with 313 nm light, the colorless single-crystal of (Ia) turned red quickly. When the red crystal was dissolved in hexane, the solution also showed a red color, with an absorption maximum at 523 nm, consistent with the presence of the closed-ring isomer (Ib). Upon irradiation with visible light with wavelength greater than 510 nm, the red crystal can return to its initial colorless state, and the absorption spectrum of the hexane solution containing the colorless crystal is the same as that of solution of the open-ring form, (Ia), with the absorption maximum at 273 nm.

Related literature top

For related literature, see: Dürr & Bouas-Laurent (1990); Irie (2000); Kobatake & Irie (2004); Ramamurthy & Venkatesan (1987); Tian & Yang (2004); Woodward & Hoffmann (1970); Zheng et al. (2007); Peters et al. (2003).

Experimental top

Compound (Ia) was prepared from (2-methyl-5-phenyl-3-thienyl)- 3,3,4,4,5,5-hexafluorocyclopent-1-ene (1.83 g, 5.00 mmol) (Peters et al., 2003) and 2-bromo-chlorobenzene (0.96 g, 5.00 mmol). To a stirred solution of compound 2-bromo-chlorobenzene (0.96 g, 5.00 mmol) in THF (80 ml) was added dropwise a 2.5 mol/L n-BuLi in hexane (2.0 ml) at 195 K under a nitrogen atmosphere (Fig. 3). Stirring was continued for 30 min, (2-methyl-5-phenyl-3-thienyl)- 3,3,4,4,5,5-hexafluorocyclopent-1-ene (1.83 g, 5.00 mmol) was slowly added to the reaction mixture, and the mixture was stirred for 2.0 h at 195 K. The reaction was stopped by the addition of water. Through a series of operations, [1-(2-methyl-5-phenyl-3-thienyl), 2-(2-chlorophenyl)]- 3,3,4,4,5,5-hexafluorocyclopent-1-ene (1.32 g, 2.88 mmol) was obtained in 57.5% yield by column chromatography on SiO2 using hexane as the eluent. Finally the colorless crystals were obtained by slow vapour diffusion of chloroform and hexane(1:2). The title compound was characterized by melting point, elemental analysis and NMR(m.p.361.1–361.7 K). 1HNMR (400 MHz, CDCl3, TMS): δ 2.08 (s, 3H, –CH3), 7.14 (s, 1H, thiophene-H), 7.27, 7.29 (d, 2H, J = 8.0 Hz, benzene-H), 7.33–7.38 (m, 4H, benzene-H), 7.40 (m, 1H, benzene-H), 7.46, 7.48 (d, 2H, J = 8.0 Hz, benzene-H); 13C NMR (100 MHz, CDCl3): δ 14.55, 123.10, 125.11, 125.59, 126.98, 127.75, 128.91, 130.43, 130.55, 131.25, 133.45, 133.70, 140.70, 141.73; IR (KBr, cm-1): 754, 853, 987, 1053, 1132, 1192, 1272, 1330, 1441, 1473, 1502, 1598, 1674, 2925, 3064; Anal. Calcd. for C24H19ClF6S(%): C, 57.59, H, 2.86, Found: C, 57.28, H, 2.59.

Refinement top

All H atoms attached to C were fixed geometrically and treated as riding with C—H = 0.96 Å (methyl) or 0.93 Å (aromatic) with Uiso(H) = 1.2Ueq(aromatic) or Uiso(H) = 1.5Ueq(methyl).

The F atoms attached to the cyclopentene ring are disordered over two positions. The occupancy factors of the two positions were refined using an overall isotropic thermal parameter and by restraining the sum of the occupancy to remain equal to 1.0. The ratio between the two occupancies was found to be 0.6/0.4. The C-F distances were restrained using SADI (SHELXL-97) instructions and similar Uij restraints as well as rigid bond restraints were used in the final refinement cycles.

Computing details top

Data collection: SMART (Bruker,1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPIII (Burnett & Johnson, 1996) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Molecular view of title compound with the atom-labelling scheme. Ellipsoids are drawn at the 30% probability level. H atoms are represented as small spheres of arbitrary radii. Only the major component of the disordered F atoms are shown for clarity.
[Figure 2] Fig. 2. Photochromic interconvertion of the title compound.
[Figure 3] Fig. 3. Synthesis of the title compound.
1-(2-Chlorophenyl)-2-(2-methyl-5-phenyl-3-thienyl)-3,3,4,4,5,5- hexafluorocyclopent-1-ene top
Crystal data top
C22H13ClF6SZ = 2
Mr = 458.83F000 = 464
Triclinic, P1Dx = 1.506 Mg m−3
Hall symbol: -P 1Melting point: 361 K
a = 8.8064 (10) ÅMo Kα radiation
λ = 0.71073 Å
b = 10.4185 (12) ÅCell parameters from 3385 reflections
c = 11.6563 (13) Åθ = 2.4–26.1º
α = 85.265 (1)ºµ = 0.35 mm−1
β = 76.935 (1)ºT = 291 (2) K
γ = 76.324 (1)ºBlock, colorless
V = 1011.8 (2) Å30.46 × 0.37 × 0.27 mm
Data collection top
Bruker SMART CCD area-detector
diffractometer		3741 independent reflections
Radiation source: fine-focus sealed tube3039 reflections with I > 2σ(I)
Monochromator: graphiteRint = 0.013
T = 291(2) Kθmax = 25.5º
φ and ω scansθmin = 2.4º
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		h = −10→10
Tmin = 0.835, Tmax = 0.910k = −12→12
7557 measured reflectionsl = −14→14
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.036H-atom parameters constrained
wR(F2) = 0.100  w = 1/[σ2(Fo2) + (0.0465P)2 + 0.2265P]
where P = (Fo2 + 2Fc2)/3
S = 1.03(Δ/σ)max = 0.011
3741 reflectionsΔρmax = 0.15 e Å−3
326 parametersΔρmin = −0.17 e Å−3
66 restraintsExtinction correction: none
Primary atom site location: structure-invariant direct methods
Crystal data top
C22H13ClF6Sγ = 76.324 (1)º
Mr = 458.83V = 1011.8 (2) Å3
Triclinic, P1Z = 2
a = 8.8064 (10) ÅMo Kα
b = 10.4185 (12) ŵ = 0.35 mm−1
c = 11.6563 (13) ÅT = 291 (2) K
α = 85.265 (1)º0.46 × 0.37 × 0.27 mm
β = 76.935 (1)º
Data collection top
Bruker SMART CCD area-detector
diffractometer		3741 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)		3039 reflections with I > 2σ(I)
Tmin = 0.835, Tmax = 0.910Rint = 0.013
7557 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.03666 restraints
wR(F2) = 0.100H-atom parameters constrained
S = 1.03Δρmax = 0.15 e Å−3
3741 reflectionsΔρmin = −0.17 e Å−3
326 parameters
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2sigma(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Cl11.14956 (8)0.27691 (8)0.88868 (6)0.0850 (2)
S11.13849 (8)0.12027 (6)0.49405 (5)0.06425 (19)
C11.0219 (3)0.4151 (2)0.84413 (19)0.0613 (6)
C21.0746 (4)0.5329 (3)0.8166 (2)0.0871 (9)
H21.17900.53500.81850.105*
C30.9723 (5)0.6447 (3)0.7868 (3)0.0994 (11)
H31.00860.72220.76730.119*
C40.8182 (5)0.6444 (3)0.7854 (3)0.0918 (9)
H40.74920.72170.76670.110*
C50.7651 (3)0.5291 (2)0.8119 (2)0.0710 (6)
H50.65960.52950.81130.085*
C60.8666 (3)0.4114 (2)0.83974 (17)0.0538 (5)
C70.8062 (2)0.28882 (19)0.86731 (17)0.0508 (5)
C110.8598 (2)0.17209 (19)0.81392 (17)0.0491 (5)
C120.9819 (3)0.13402 (19)0.70679 (17)0.0497 (5)
C130.9865 (3)0.2030 (2)0.60054 (17)0.0543 (5)
C141.1993 (3)−0.0064 (2)0.59067 (18)0.0556 (5)
C151.1036 (3)0.0151 (2)0.69936 (18)0.0535 (5)
H151.1161−0.04260.76350.064*
C160.8792 (3)0.3280 (2)0.5679 (2)0.0715 (7)
H16A0.77350.33480.61550.107*
H16B0.87560.32720.48630.107*
H16C0.91960.40220.58100.107*
C171.3338 (3)−0.1188 (2)0.5501 (2)0.0620 (6)
C181.4225 (4)−0.1226 (3)0.4357 (3)0.0872 (8)
H181.4001−0.05180.38350.105*
C191.5454 (4)−0.2320 (4)0.3981 (3)0.1079 (11)
H191.6042−0.23320.32090.130*
C201.5801 (4)−0.3361 (4)0.4721 (4)0.1062 (11)
H201.6610−0.40930.44570.127*
C211.4962 (4)−0.3333 (3)0.5850 (3)0.1009 (10)
H211.5212−0.40420.63660.121*
C221.3741 (3)−0.2260 (3)0.6245 (3)0.0823 (8)
H221.3180−0.22580.70230.099*
C80.6691 (4)0.2848 (3)0.9689 (2)0.0766 (7)
F810.5227 (6)0.3659 (5)0.9349 (4)0.0822 (12)0.60
F820.6655 (6)0.3429 (5)1.0655 (3)0.0934 (13)0.60
F81A0.5616 (11)0.3714 (7)0.9937 (8)0.129 (4)0.40
F82A0.7574 (8)0.2683 (6)1.0735 (4)0.104 (2)0.40
C90.6459 (3)0.1441 (2)0.9782 (2)0.0668 (6)
F910.6251 (6)0.0807 (5)1.0781 (4)0.1038 (17)0.60
F920.5129 (5)0.1513 (4)0.9324 (4)0.1069 (12)0.60
F91A0.7063 (9)0.1016 (7)1.0795 (5)0.101 (2)0.40
F92A0.4934 (7)0.1351 (6)1.0116 (6)0.098 (2)0.40
C100.7729 (3)0.0714 (2)0.8807 (2)0.0700 (7)
F1010.7425 (5)−0.0114 (4)0.8142 (4)0.0895 (11)0.60
F1020.8871 (6)−0.0155 (4)0.9402 (5)0.0906 (13)0.60
F11A0.6530 (8)0.0595 (7)0.8101 (5)0.1013 (18)0.40
F12A0.8365 (11)−0.0405 (6)0.9036 (7)0.105 (3)0.40
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cl10.0693 (4)0.1060 (5)0.0829 (5)−0.0199 (4)−0.0218 (3)−0.0053 (4)
S10.0813 (4)0.0650 (4)0.0454 (3)−0.0197 (3)−0.0090 (3)0.0011 (2)
C10.0701 (14)0.0671 (14)0.0502 (12)−0.0294 (11)−0.0016 (10)−0.0122 (10)
C20.100 (2)0.095 (2)0.0793 (18)−0.0620 (18)0.0027 (15)−0.0207 (15)
C30.147 (3)0.0639 (18)0.091 (2)−0.058 (2)0.009 (2)−0.0118 (15)
C40.129 (3)0.0499 (14)0.088 (2)−0.0247 (16)−0.0012 (18)−0.0013 (13)
C50.0841 (17)0.0511 (13)0.0742 (15)−0.0175 (12)−0.0073 (13)−0.0013 (11)
C60.0685 (13)0.0472 (11)0.0465 (11)−0.0224 (10)−0.0023 (9)−0.0061 (8)
C70.0599 (12)0.0462 (11)0.0484 (11)−0.0188 (9)−0.0088 (9)−0.0016 (8)
C110.0628 (12)0.0438 (10)0.0450 (10)−0.0169 (9)−0.0160 (9)0.0020 (8)
C120.0646 (12)0.0444 (10)0.0448 (10)−0.0184 (9)−0.0148 (9)−0.0015 (8)
C130.0725 (14)0.0486 (11)0.0466 (11)−0.0207 (10)−0.0160 (10)0.0007 (9)
C140.0656 (13)0.0533 (12)0.0525 (12)−0.0199 (10)−0.0143 (10)−0.0051 (9)
C150.0675 (13)0.0471 (11)0.0485 (11)−0.0152 (9)−0.0161 (10)0.0002 (8)
C160.0987 (19)0.0595 (13)0.0574 (13)−0.0132 (13)−0.0271 (13)0.0076 (10)
C170.0607 (13)0.0640 (14)0.0649 (14)−0.0175 (11)−0.0122 (11)−0.0163 (11)
C180.0876 (19)0.0861 (19)0.0776 (18)−0.0161 (15)0.0043 (15)−0.0154 (14)
C190.086 (2)0.120 (3)0.103 (2)−0.013 (2)0.0134 (18)−0.040 (2)
C200.081 (2)0.097 (2)0.135 (3)0.0066 (18)−0.025 (2)−0.041 (2)
C210.099 (2)0.088 (2)0.108 (3)0.0151 (17)−0.038 (2)−0.0191 (18)
C220.0875 (18)0.0765 (17)0.0766 (17)0.0023 (14)−0.0240 (14)−0.0102 (14)
C80.0927 (19)0.0690 (16)0.0682 (16)−0.0414 (15)0.0130 (14)−0.0194 (13)
F810.0592 (15)0.061 (2)0.114 (4)−0.0057 (13)−0.002 (2)−0.001 (2)
F820.111 (3)0.117 (3)0.0605 (18)−0.061 (3)0.013 (2)−0.035 (2)
F81A0.133 (9)0.061 (3)0.146 (9)−0.027 (5)0.081 (6)−0.034 (6)
F82A0.156 (6)0.113 (4)0.055 (2)−0.086 (4)0.019 (3)−0.024 (3)
C90.0682 (15)0.0615 (14)0.0710 (15)−0.0266 (12)−0.0060 (12)0.0075 (11)
F910.141 (4)0.087 (2)0.074 (2)−0.055 (3)0.025 (3)0.0028 (16)
F920.070 (2)0.098 (2)0.159 (4)−0.0215 (17)−0.029 (3)−0.014 (3)
F91A0.165 (7)0.084 (4)0.045 (2)−0.011 (4)−0.028 (4)0.014 (2)
F92A0.076 (3)0.071 (3)0.140 (5)−0.039 (2)0.017 (4)−0.007 (4)
C100.106 (2)0.0546 (14)0.0540 (13)−0.0381 (13)−0.0062 (12)−0.0007 (10)
F1010.131 (3)0.069 (2)0.081 (2)−0.0582 (19)−0.003 (2)−0.0177 (19)
F1020.102 (3)0.063 (3)0.089 (3)−0.009 (2)−0.0082 (19)0.033 (2)
F11A0.138 (5)0.130 (5)0.067 (3)−0.094 (4)−0.015 (3)−0.013 (3)
F12A0.141 (7)0.033 (2)0.109 (7)−0.022 (3)0.041 (5)−0.003 (3)
Geometric parameters (Å, °) top
Cl1—C11.727 (3)C16—H16C0.9600
S1—C131.719 (2)C17—C181.383 (4)
S1—C141.729 (2)C17—C221.384 (4)
C1—C61.390 (3)C18—C191.396 (4)
C1—C21.400 (3)C18—H180.9300
C2—C31.366 (5)C19—C201.350 (5)
C2—H20.9300C19—H190.9300
C3—C41.361 (5)C20—C211.356 (5)
C3—H30.9300C20—H200.9300
C4—C51.378 (4)C21—C221.382 (4)
C4—H40.9300C21—H210.9300
C5—C61.398 (3)C22—H220.9300
C5—H50.9300C8—F81A1.144 (8)
C6—C71.481 (3)C8—F821.313 (4)
C7—C111.345 (3)C8—F811.481 (6)
C7—C81.493 (3)C8—C91.520 (3)
C11—C121.465 (3)C8—F82A1.566 (7)
C11—C101.506 (3)C9—F911.288 (5)
C12—C131.377 (3)C9—F92A1.334 (6)
C12—C151.427 (3)C9—F921.378 (4)
C13—C161.494 (3)C9—F91A1.400 (6)
C14—C151.357 (3)C9—C101.511 (3)
C14—C171.477 (3)C10—F12A1.205 (7)
C15—H150.9300C10—F1011.315 (4)
C16—H16A0.9600C10—F1021.446 (6)
C16—H16B0.9600C10—F11A1.510 (6)
C13—S1—C1493.38 (10)C19—C20—H20120.3
C6—C1—C2120.2 (3)C21—C20—H20120.3
C6—C1—Cl1120.61 (17)C20—C21—C22120.7 (3)
C2—C1—Cl1119.2 (2)C20—C21—H21119.7
C3—C2—C1119.8 (3)C22—C21—H21119.7
C3—C2—H2120.1C21—C22—C17121.2 (3)
C1—C2—H2120.1C21—C22—H22119.4
C4—C3—C2121.1 (3)C17—C22—H22119.4
C4—C3—H3119.5F81A—C8—F8265.8 (5)
C2—C3—H3119.5F81A—C8—F8134.6 (5)
C3—C4—C5119.6 (3)F82—C8—F81100.4 (4)
C3—C4—H4120.2F81A—C8—C7124.0 (5)
C5—C4—H4120.2F82—C8—C7117.8 (3)
C4—C5—C6121.4 (3)F81—C8—C7107.7 (3)
C4—C5—H5119.3F81A—C8—C9120.2 (5)
C6—C5—H5119.3F82—C8—C9118.8 (3)
C1—C6—C5117.9 (2)F81—C8—C9104.6 (3)
C1—C6—C7122.0 (2)C7—C8—C9106.1 (2)
C5—C6—C7120.1 (2)F81A—C8—F82A104.8 (6)
C11—C7—C6129.06 (19)F82—C8—F82A39.3 (2)
C11—C7—C8111.42 (18)F81—C8—F82A139.3 (4)
C6—C7—C8119.51 (18)C7—C8—F82A100.1 (3)
C7—C11—C12130.30 (18)C9—C8—F82A95.4 (3)
C7—C11—C10110.21 (19)F91—C9—F92A70.4 (4)
C12—C11—C10119.49 (17)F91—C9—F92107.3 (3)
C13—C12—C15112.38 (19)F92A—C9—F9239.2 (3)
C13—C12—C11124.34 (19)F91—C9—F91A34.3 (3)
C15—C12—C11123.14 (17)F92A—C9—F91A103.0 (5)
C12—C13—C16130.1 (2)F92—C9—F91A141.3 (4)
C12—C13—S1110.26 (16)F91—C9—C10115.5 (3)
C16—C13—S1119.55 (16)F92A—C9—C10127.6 (4)
C15—C14—C17129.2 (2)F92—C9—C1099.4 (3)
C15—C14—S1109.74 (17)F91A—C9—C10103.5 (4)
C17—C14—S1121.03 (17)F91—C9—C8121.5 (3)
C14—C15—C12114.24 (19)F92A—C9—C8114.0 (3)
C14—C15—H15122.9F92—C9—C8104.8 (3)
C12—C15—H15122.9F91A—C9—C898.6 (3)
C13—C16—H16A109.5C10—C9—C8105.60 (19)
C13—C16—H16B109.5F12A—C10—F10169.7 (4)
H16A—C16—H16B109.5F12A—C10—F10232.6 (4)
C13—C16—H16C109.5F101—C10—F102101.7 (3)
H16A—C16—H16C109.5F12A—C10—C11124.5 (5)
H16B—C16—H16C109.5F101—C10—C11114.7 (2)
C18—C17—C22117.3 (2)F102—C10—C11105.3 (3)
C18—C17—C14121.4 (2)F12A—C10—F11A105.4 (5)
C22—C17—C14121.3 (2)F101—C10—F11A38.6 (2)
C17—C18—C19120.5 (3)F102—C10—F11A138.0 (3)
C17—C18—H18119.8C11—C10—F11A105.3 (3)
C19—C18—H18119.8F12A—C10—C9116.6 (4)
C20—C19—C18120.9 (3)F101—C10—C9122.1 (3)
C20—C19—H19119.6F102—C10—C9104.9 (3)
C18—C19—H19119.6C11—C10—C9106.42 (18)
C19—C20—C21119.5 (3)F11A—C10—C993.3 (3)
Acknowledgements top

This work was supported by the Natural Science Foundation of Jiangxi, China (0620012) and the Science Fund of the Education Office of Jiangxi, China ([2007]279).

references
References top

Bruker (1997). SMART, SAINT and SHELXTL. Bruker AXS Inc., Madison, Wisconsin, USA.

Burnett, M. N. & Johnson, C. K. (1996). ORTEPIII. Report ORNL-6895. Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA.

Dürr, H. & Bouas-Laurent, H. (1990). Photochromism, Molecules and Systems in Organic Chemistry. Amsterdam: Elsevier.

Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.

Irie, M. (2000). Chem. Rev. 100, 1685–1716.

Kobatake, S. & Irie, M. (2004). Bull. Chem. Soc. Jpn, 77, 195–210.

Peters, A., Vitols, C., McDonald, R. & Branda, N. R. (2003). Org. Lett. 5, 1183–1186.

Ramamurthy, V. & Venkatesan, K. (1987). Chem. Rev. 87, 433–481.

Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.

Tian, H. & Yang, S.-J. (2004). Chem. Soc. Rev. 33, 85–97.

Woodward, R. B. & Hoffmann, R. (1970). The Conservation of Orbital Symmetry. Weinheim: Verlag Chemie GmbH.

Zheng, C.-H., Pu, S.-Z., Xu, J.-K., Luo, M.-B., Huang, D.-C. & Shen, L. (2007). Tetrahedron, 63, 5437–5449.