organic compounds
1,2-Bis[5-(4-cyanophenyl)-2-methyl-3-thienyl]-3,3,4,4,5,5-hexafluorocyclopent-1-ene: a photochromic diarylethene compound
aJiangxi Key Laboratory of Organic Chemistry, Jiangxi Science & Technology Normal University, Nanchang 330013, People's Republic of China
*Correspondence e-mail: liugang0926@yahoo.com.cn
The molecules of the title compound, C29H16F6N2S2, a photochromic dithienylethene with 4-cyanophenyl substituents, adopt an antiparallel arrangement that is reponsible for photoactivity. The molecule lies on a twofold rotation axis. The dihedral angle between the nearly planar cyclopentenyl and heteroaryl rings is 142.5 (3)°, and that between the heteroaryl and benzene rings is 22.4 (3)°. The distance between the heteroaryl rings of adjacent molecules is 3.601 (2) Å, indicating a π–π interaction.
Related literature
For a review of dithienylethylenes as photochromic compounds, see: Irie (2000). For phenyl-substituted derivatives, see: Pu, Liu et al. (2005); Pu, Yang et al. (2005). For another similar structure, see: Kobatake et al. (2004). For the manifestation of possible photochromic activity in relation to the conformation, see: Woodward & Hoffmann (1970).
Experimental
Crystal data
|
Data collection: CrystalClear (Rigaku/MSC, 2001); cell CrystalClear; data reduction: CrystalStructure (Rigaku/MSC, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: CrystalStructure.
Supporting information
10.1107/S1600536808011653/ng2448sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536808011653/ng2448Isup2.hkl
The title compound was originally derived from 2-methylthiophene(1). 3-Bromo-2-methyl-5-(4-cyanophenyl)thiophene, (4) (4.60 g, 16.5 mmol), in 78.8% yield was synthesized by reacting(3) (4.62 g, 20.9 mmol) (Pu, Liu et al., 2005) with 4-cyano-brombenzene (3.82 g, 21.0 mmol) in the presence of Pd(PPh3)4 (0.5 g) and Na2CO3 (2 mol/L, 30 ml) in tetrahydrofuran (THF, 80 ml) for 16 h at 343 K. To a stirred THF solution (60 ml) of (4) (2.21 g, 7.96 mmol) 3.3 ml of n-BuLi/hexane solution (2.5 M, 8.2 mmol) was slowly added at 195 K under a nitrogen atmosphere. 30 min later, octa-fluorocyclopentene (0.54 ml, 4.0 mmol) was added and the mixture was stirred for 2 h. The reaction mixture was extracted with diethyl ether and evaporated in vacuo, then purified by δ 2.03 (s, 6H),δ 7.41 (s, 2H), δ 7.64, 7.70 (d, 8H, J = 8.0 Hz); 13C NMR (400 MHz, CDCl3) δ 14.67, 111.33, 118.47, 124.41, 125.87, 126.28, 132.86, 137.34, 140.20, 143.42; IR (n, KBr, cm-1): 743, 831, 846, 887, 987, 1054, 1108, 1184, 1267, 1309, 1338, 1385, 1413, 1438, 1438, 1508, 1551, 1603, 1633, 2223.
(petroleum ether) to give the title compound (1.21 g, 2.12 mmol) in 53.3% yield. The compound crystallized from hexane at room temperature and produced single crystals suitable for X-ray analysis. The structure of (Ia) was confirmed by melting point, IR and NMR. Analysis calculated for C29H16F6N2S2, m.p.: 485.7 k 1H NMR (400 MHz, CDCl3)H atoms were positioned theoretically and allowed to ride on their parent atoms in the final refinement[C—H = 0.93–0.96Å and Uiso(H) = 1.2Ueq(C) or 1.5Ueq(methyl C)].The methyl groups were treated as rigid groups and allowed to rotate about the C—C bond.
Data collection: CrystalClear (Rigaku/MSC, 2001); cell
CrystalClear (Rigaku/MSC, 2001); data reduction: CrystalStructure (Rigaku/MSC, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: CrystalStructure (Rigaku/MSC, 2004).C29H16F6N2S2 | F(000) = 1160 |
Mr = 570.56 | Dx = 1.526 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71070 Å |
Hall symbol: -C2yc | Cell parameters from 3563 reflections |
a = 24.987 (10) Å | θ = 1.6–27.9° |
b = 9.276 (4) Å | µ = 0.28 mm−1 |
c = 10.774 (4) Å | T = 113 K |
β = 95.911 (7)° | Block, colorless |
V = 2483.8 (17) Å3 | 0.36 × 0.20 × 0.10 mm |
Z = 4 |
Rigaku Saturn diffractometer | 2437 independent reflections |
Radiation source: rotating anode | 2130 reflections with I > 2σ(I) |
Confocal monochromator | Rint = 0.032 |
Detector resolution: 7.31 pixels mm-1 | θmax = 26.0°, θmin = 1.6° |
ω scans | h = −30→30 |
Absorption correction: multi-scan (Jacobson, 1998) | k = −11→11 |
Tmin = 0.905, Tmax = 0.972 | l = −12→13 |
9917 measured reflections |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.057 | H-atom parameters constrained |
wR(F2) = 0.145 | w = 1/[σ2(Fo2) + (0.0692P)2 + 6.3864P] where P = (Fo2 + 2Fc2)/3 |
S = 1.07 | (Δ/σ)max = 0.001 |
2437 reflections | Δρmax = 0.90 e Å−3 |
180 parameters | Δρmin = −0.65 e Å−3 |
0 restraints | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0031 (9) |
C29H16F6N2S2 | V = 2483.8 (17) Å3 |
Mr = 570.56 | Z = 4 |
Monoclinic, C2/c | Mo Kα radiation |
a = 24.987 (10) Å | µ = 0.28 mm−1 |
b = 9.276 (4) Å | T = 113 K |
c = 10.774 (4) Å | 0.36 × 0.20 × 0.10 mm |
β = 95.911 (7)° |
Rigaku Saturn diffractometer | 2437 independent reflections |
Absorption correction: multi-scan (Jacobson, 1998) | 2130 reflections with I > 2σ(I) |
Tmin = 0.905, Tmax = 0.972 | Rint = 0.032 |
9917 measured reflections |
R[F2 > 2σ(F2)] = 0.057 | 0 restraints |
wR(F2) = 0.145 | H-atom parameters constrained |
S = 1.07 | Δρmax = 0.90 e Å−3 |
2437 reflections | Δρmin = −0.65 e Å−3 |
180 parameters |
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 > σ(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. |
x | y | z | Uiso*/Ueq | ||
S1 | 0.12440 (3) | 0.06080 (7) | 0.81522 (6) | 0.0293 (2) | |
F1 | 0.04313 (8) | 0.57014 (18) | 0.94258 (16) | 0.0469 (5) | |
F2 | 0.09200 (7) | 0.57943 (19) | 0.7907 (2) | 0.0607 (7) | |
F3 | −0.02249 (10) | 0.7331 (3) | 0.8302 (2) | 0.0846 (10) | |
N1 | 0.34207 (11) | 0.1164 (3) | 1.4057 (3) | 0.0492 (7) | |
C1 | 0.13504 (10) | 0.1761 (3) | 0.9418 (2) | 0.0252 (6) | |
C2 | 0.09893 (10) | 0.2871 (3) | 0.9294 (2) | 0.0248 (6) | |
H2 | 0.0981 | 0.3621 | 0.9893 | 0.030* | |
C3 | 0.06264 (10) | 0.2802 (3) | 0.8183 (2) | 0.0244 (6) | |
C4 | 0.07183 (10) | 0.1622 (3) | 0.7454 (2) | 0.0270 (6) | |
C5 | 0.17915 (10) | 0.1560 (3) | 1.0408 (2) | 0.0248 (6) | |
C6 | 0.17718 (11) | 0.2247 (3) | 1.1548 (2) | 0.0281 (6) | |
H6 | 0.1462 | 0.2791 | 1.1693 | 0.034* | |
C7 | 0.21958 (11) | 0.2150 (3) | 1.2473 (3) | 0.0308 (6) | |
H7 | 0.2177 | 0.2624 | 1.3248 | 0.037* | |
C8 | 0.26506 (10) | 0.1355 (3) | 1.2265 (3) | 0.0287 (6) | |
C9 | 0.26789 (11) | 0.0656 (3) | 1.1132 (3) | 0.0292 (6) | |
H9 | 0.2990 | 0.0118 | 1.0988 | 0.035* | |
C10 | 0.22495 (11) | 0.0750 (3) | 1.0215 (3) | 0.0286 (6) | |
H10 | 0.2265 | 0.0260 | 0.9445 | 0.034* | |
C11 | 0.30895 (11) | 0.1252 (3) | 1.3245 (3) | 0.0350 (7) | |
C12 | 0.02472 (10) | 0.3973 (3) | 0.7823 (2) | 0.0228 (5) | |
C13 | 0.04203 (10) | 0.5483 (3) | 0.8172 (3) | 0.0274 (6) | |
C14 | 0.0000 | 0.6490 (4) | 0.7500 | 0.0306 (8) | |
C15 | 0.04599 (12) | 0.1178 (3) | 0.6201 (3) | 0.0331 (6) | |
H15A | 0.0714 | 0.0602 | 0.5775 | 0.040* | |
H15B | 0.0358 | 0.2039 | 0.5704 | 0.040* | |
H15C | 0.0138 | 0.0603 | 0.6302 | 0.040* |
U11 | U22 | U33 | U12 | U13 | U23 | |
S1 | 0.0312 (4) | 0.0264 (4) | 0.0297 (4) | 0.0058 (3) | −0.0006 (3) | −0.0016 (3) |
F1 | 0.0697 (13) | 0.0316 (9) | 0.0346 (10) | 0.0099 (8) | −0.0174 (9) | −0.0094 (7) |
F2 | 0.0327 (10) | 0.0317 (10) | 0.122 (2) | −0.0050 (8) | 0.0302 (11) | 0.0038 (11) |
F3 | 0.0843 (17) | 0.0847 (17) | 0.0741 (15) | 0.0586 (14) | −0.0430 (13) | −0.0557 (13) |
N1 | 0.0378 (15) | 0.0602 (18) | 0.0466 (16) | −0.0076 (13) | −0.0110 (12) | 0.0141 (14) |
C1 | 0.0246 (12) | 0.0227 (12) | 0.0283 (13) | 0.0003 (10) | 0.0023 (10) | 0.0013 (10) |
C2 | 0.0240 (12) | 0.0234 (12) | 0.0269 (13) | 0.0005 (10) | 0.0017 (10) | 0.0004 (10) |
C3 | 0.0232 (12) | 0.0235 (13) | 0.0263 (13) | −0.0004 (10) | 0.0012 (10) | 0.0023 (10) |
C4 | 0.0277 (13) | 0.0263 (13) | 0.0268 (13) | 0.0018 (10) | 0.0012 (10) | 0.0016 (11) |
C5 | 0.0233 (12) | 0.0221 (12) | 0.0289 (13) | −0.0006 (10) | 0.0016 (10) | 0.0044 (10) |
C6 | 0.0272 (13) | 0.0262 (13) | 0.0306 (14) | 0.0038 (10) | 0.0011 (10) | 0.0026 (11) |
C7 | 0.0357 (15) | 0.0266 (14) | 0.0292 (14) | −0.0003 (11) | −0.0012 (11) | 0.0032 (11) |
C8 | 0.0260 (13) | 0.0267 (13) | 0.0324 (14) | −0.0014 (10) | −0.0023 (11) | 0.0096 (11) |
C9 | 0.0229 (13) | 0.0280 (14) | 0.0366 (15) | 0.0022 (10) | 0.0022 (11) | 0.0064 (11) |
C10 | 0.0282 (13) | 0.0275 (13) | 0.0301 (14) | 0.0022 (10) | 0.0033 (11) | 0.0025 (11) |
C11 | 0.0304 (14) | 0.0348 (15) | 0.0393 (16) | −0.0022 (12) | 0.0007 (13) | 0.0072 (13) |
C12 | 0.0249 (12) | 0.0219 (12) | 0.0216 (12) | −0.0018 (10) | 0.0032 (10) | 0.0007 (10) |
C13 | 0.0218 (13) | 0.0261 (13) | 0.0342 (14) | −0.0021 (10) | 0.0027 (11) | −0.0006 (11) |
C14 | 0.038 (2) | 0.0211 (18) | 0.032 (2) | 0.000 | −0.0003 (16) | 0.000 |
C15 | 0.0375 (15) | 0.0310 (15) | 0.0292 (14) | 0.0076 (12) | −0.0038 (12) | −0.0051 (12) |
S1—C4 | 1.724 (3) | C6—H6 | 0.9500 |
S1—C1 | 1.732 (3) | C7—C8 | 1.392 (4) |
F1—C13 | 1.363 (3) | C7—H7 | 0.9500 |
F2—C13 | 1.341 (3) | C8—C9 | 1.390 (4) |
F3—C14 | 1.331 (3) | C8—C11 | 1.446 (4) |
N1—C11 | 1.144 (4) | C9—C10 | 1.384 (4) |
C1—C2 | 1.367 (4) | C9—H9 | 0.9500 |
C1—C5 | 1.465 (3) | C10—H10 | 0.9500 |
C2—C3 | 1.427 (4) | C12—C12i | 1.354 (5) |
C2—H2 | 0.9500 | C12—C13 | 1.502 (3) |
C3—C4 | 1.380 (4) | C13—C14 | 1.531 (3) |
C3—C12 | 1.467 (3) | C14—F3i | 1.331 (3) |
C4—C15 | 1.493 (4) | C14—C13i | 1.531 (3) |
C5—C6 | 1.389 (4) | C15—H15A | 0.9800 |
C5—C10 | 1.402 (4) | C15—H15B | 0.9800 |
C6—C7 | 1.380 (4) | C15—H15C | 0.9800 |
C4—S1—C1 | 93.15 (13) | C8—C9—H9 | 120.3 |
C2—C1—C5 | 127.3 (2) | C9—C10—C5 | 120.8 (3) |
C2—C1—S1 | 110.0 (2) | C9—C10—H10 | 119.6 |
C5—C1—S1 | 122.54 (19) | C5—C10—H10 | 119.6 |
C1—C2—C3 | 113.8 (2) | N1—C11—C8 | 177.0 (3) |
C1—C2—H2 | 123.1 | C12i—C12—C3 | 131.76 (14) |
C3—C2—H2 | 123.1 | C12i—C12—C13 | 110.66 (14) |
C4—C3—C2 | 112.6 (2) | C3—C12—C13 | 117.6 (2) |
C4—C3—C12 | 125.3 (2) | F2—C13—F1 | 104.8 (2) |
C2—C3—C12 | 121.7 (2) | F2—C13—C12 | 113.5 (2) |
C3—C4—C15 | 130.6 (2) | F1—C13—C12 | 111.3 (2) |
C3—C4—S1 | 110.39 (19) | F2—C13—C14 | 112.1 (2) |
C15—C4—S1 | 118.9 (2) | F1—C13—C14 | 108.70 (19) |
C6—C5—C10 | 118.7 (2) | C12—C13—C14 | 106.5 (2) |
C6—C5—C1 | 119.6 (2) | F3i—C14—F3 | 108.2 (4) |
C10—C5—C1 | 121.6 (2) | F3i—C14—C13i | 111.45 (14) |
C7—C6—C5 | 120.9 (2) | F3—C14—C13i | 110.49 (15) |
C7—C6—H6 | 119.5 | F3i—C14—C13 | 110.49 (15) |
C5—C6—H6 | 119.5 | F3—C14—C13 | 111.45 (14) |
C6—C7—C8 | 119.8 (3) | C13i—C14—C13 | 104.8 (3) |
C6—C7—H7 | 120.1 | C4—C15—H15A | 109.5 |
C8—C7—H7 | 120.1 | C4—C15—H15B | 109.5 |
C9—C8—C7 | 120.3 (2) | H15A—C15—H15B | 109.5 |
C9—C8—C11 | 120.5 (2) | C4—C15—H15C | 109.5 |
C7—C8—C11 | 119.2 (3) | H15A—C15—H15C | 109.5 |
C10—C9—C8 | 119.4 (2) | H15B—C15—H15C | 109.5 |
C10—C9—H9 | 120.3 | ||
C4—S1—C1—C2 | 0.4 (2) | C8—C9—C10—C5 | 1.1 (4) |
C4—S1—C1—C5 | −176.3 (2) | C6—C5—C10—C9 | −1.2 (4) |
C5—C1—C2—C3 | 176.4 (2) | C1—C5—C10—C9 | 175.4 (2) |
S1—C1—C2—C3 | −0.1 (3) | C4—C3—C12—C12i | 37.9 (5) |
C1—C2—C3—C4 | −0.3 (3) | C2—C3—C12—C12i | −149.8 (3) |
C1—C2—C3—C12 | −173.6 (2) | C4—C3—C12—C13 | −140.0 (3) |
C2—C3—C4—C15 | −176.1 (3) | C2—C3—C12—C13 | 32.3 (3) |
C12—C3—C4—C15 | −3.2 (5) | C12i—C12—C13—F2 | −131.7 (3) |
C2—C3—C4—S1 | 0.6 (3) | C3—C12—C13—F2 | 46.7 (3) |
C12—C3—C4—S1 | 173.5 (2) | C12i—C12—C13—F1 | 110.5 (3) |
C1—S1—C4—C3 | −0.6 (2) | C3—C12—C13—F1 | −71.2 (3) |
C1—S1—C4—C15 | 176.6 (2) | C12i—C12—C13—C14 | −7.9 (3) |
C2—C1—C5—C6 | 21.9 (4) | C3—C12—C13—C14 | 170.46 (19) |
S1—C1—C5—C6 | −162.0 (2) | F2—C13—C14—F3i | 7.2 (3) |
C2—C1—C5—C10 | −154.7 (3) | F1—C13—C14—F3i | 122.5 (2) |
S1—C1—C5—C10 | 21.4 (3) | C12—C13—C14—F3i | −117.5 (3) |
C10—C5—C6—C7 | 0.6 (4) | F2—C13—C14—F3 | −113.2 (3) |
C1—C5—C6—C7 | −176.0 (2) | F1—C13—C14—F3 | 2.2 (3) |
C5—C6—C7—C8 | 0.0 (4) | C12—C13—C14—F3 | 122.2 (3) |
C6—C7—C8—C9 | −0.1 (4) | F2—C13—C14—C13i | 127.3 (3) |
C6—C7—C8—C11 | −179.4 (3) | F1—C13—C14—C13i | −117.3 (2) |
C7—C8—C9—C10 | −0.4 (4) | C12—C13—C14—C13i | 2.69 (11) |
C11—C8—C9—C10 | 178.9 (2) |
Symmetry code: (i) −x, y, −z+3/2. |
Experimental details
Crystal data | |
Chemical formula | C29H16F6N2S2 |
Mr | 570.56 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 113 |
a, b, c (Å) | 24.987 (10), 9.276 (4), 10.774 (4) |
β (°) | 95.911 (7) |
V (Å3) | 2483.8 (17) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.28 |
Crystal size (mm) | 0.36 × 0.20 × 0.10 |
Data collection | |
Diffractometer | Rigaku Saturn diffractometer |
Absorption correction | Multi-scan (Jacobson, 1998) |
Tmin, Tmax | 0.905, 0.972 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 9917, 2437, 2130 |
Rint | 0.032 |
(sin θ/λ)max (Å−1) | 0.617 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.057, 0.145, 1.07 |
No. of reflections | 2437 |
No. of parameters | 180 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.90, −0.65 |
Computer programs: CrystalClear (Rigaku/MSC, 2001), CrystalStructure (Rigaku/MSC, 2004), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).
S1—C4 | 1.724 (3) | C5—C10 | 1.402 (4) |
S1—C1 | 1.732 (3) | C7—C8 | 1.392 (4) |
N1—C11 | 1.144 (4) | C8—C11 | 1.446 (4) |
C1—C2 | 1.367 (4) | C9—C10 | 1.384 (4) |
C1—C5 | 1.465 (3) | C12—C12i | 1.354 (5) |
C4—C15 | 1.493 (4) | C12—C13 | 1.502 (3) |
C5—C6 | 1.389 (4) | C13—C14 | 1.531 (3) |
C4—S1—C1—C5 | −176.3 (2) | C2—C1—C5—C10 | −154.7 (3) |
C5—C1—C2—C3 | 176.4 (2) | C4—C3—C12—C12i | 37.9 (5) |
C1—C2—C3—C12 | −173.6 (2) | C2—C3—C12—C12i | −149.8 (3) |
C2—C3—C4—C15 | −176.1 (3) | C2—C3—C12—C13 | 32.3 (3) |
S1—C1—C5—C6 | −162.0 (2) |
Symmetry code: (i) −x, y, −z+3/2. |
Acknowledgements
This work was partially supported by the Natural Science Foundation of Jiangxi, China (grant No. 0620012), the Science Funds of the Education Office of Jiangxi, China (grant No. [2007] 279) and the Research Fund of Jiangxi Science and Technology Normal University.
References
Irie, M. (2000). Chem. Rev. 100, 1685–1716. Web of Science CrossRef PubMed CAS Google Scholar
Jacobson, R. (1998). Private communication to the Rigaku Corporation, Tokyo, Japan. Google Scholar
Kobatake, S., Kuma, S. & Irie, M. (2004). Bull. Chem. Soc. Jpn, 77, 945–951. Web of Science CSD CrossRef CAS Google Scholar
Pu, S.-Z., Liu, G., Chen, B. & Wang, R.-J. (2005). Acta Cryst. C61, o599–o601. Web of Science CSD CrossRef CAS IUCr Journals Google Scholar
Pu, S.-Z., Yang, T.-S., Xu, J.-K., Li, G.-Z., Shen, L., Xiao, Q. & Chen, B. (2005). Tetrahedron, 61, 6623–6629. Web of Science CrossRef CAS Google Scholar
Rigaku/MSC (2001). CrystalClear. Rigaku/MSC, The Woodlands, Texas, USA. Google Scholar
Rigaku/MSC (2004). CrystalStructure. Rigaku/MSC, The Woodlands, Texas, USA. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Woodward, R. B. & Hoffmann, R. (1970). The Conservation of Orbital Symmetry, pp. 98–100. Weinheim: Verlag Chemie GmbH. Google Scholar
This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
Dithienylethenes are the most promising organic photochromic compounds for photoelectronic devices(Irie, 2000).Dithienylethenes bearing terminal phenyl groups are of special interest, because phenyl group can be substituted by many electron-donating or electron-withdrawing groups that influence the properties(Pu, Yang,Xu et al.,2005). In order to investigate the substituent effect at the para-position on the photochemical properties, we have now synthesized the title compound, (Ia), and its structure is presented in this paper.
To the best of our knowledge,this is the first symmetrical dithienylethene compound with phenyl groups bearing para substituent. The molecular structure of (Ia) is shown in Fig. 1 and selected geometric parameters are given in Table 1.
The molecule contains two thiophene rings substituted by two para-cyanophenyl rings in a photoactive antiparallel conformation. In the cyclopent-1-ene ring, the C12=C12A bond is clearly a double bond, and the other bonds in the ring are clearly single bonds(see Table 1). The two thiophene rings are linked by the C12=C12A double bond.The two methyl groups are located on different sides of the double bond and are thus trans with respect to the double bond. Such a configuration is crucial for the compound to exhibit photochromic and photoinduced properties (Woodward & Hoffmann, 1970). The dihedral angles between the least-squares plane of the atoms of the central cyclopent-1-ene ring and the adjacent thiophene rings are 142.5 (3)°, and those between thiophene rings and the adjacent benzene rings are both 22.4 (3)°.The distance between the two reactive C atoms (C4_C4A) is 3.601 (2) Å. This distance indicates that the crystal can undergo photochromism in the crystalline phase because the photochromic reactivity of crystals depends on the distance between the reactive C atoms being less than 4.2 Å(Kobatake et al., 2004).
Upon irradiation with 313 nm light, colorless single crystals of (Ia) turned to blue rapidly, and the blue color remained stable in the dark. When the blue crystals were dissolved in hexane, the solution also remained blue.The absorption maximum of this solution is observed at a wavelength of 596 nm, consistent with the presence of the closed-ring isomer, (Ib).This result suggests that the title compound undergoes a photochromic reaction to produce the closed-ring molecule of (Ib) in the single-crystal phase. We have not, so far, been able to determine the crystal structure of (Ib). Furthermore, upon irradiation with wavelengths longer than 450 nm, the blue crystal changes back to colorless, and the absorption spectrum of a hexane solution of the colorless crystals is the same as that of a solution of the open-ring form, (Ia), with the absorption maximum at 314 nm.