C 19H14F6O2, orthorhombic, Fdd2 (no. 43 Source of materialUnder an argon gas atmosphere, 1-methoxyl-2-bromobenzene (1.88 g, 10.0 mmol) was dissolved in THF (30 ml) and 4.0 ml nbutyl lithium hexane solution ( 2.5 mol / l) was added at 195 K. Stirring was continued for 30 min at this low temperature, octafluorocyclopentene (0.68 ml, 5.0 mmol) was added and stirred for further 2 hours at this temperature. After extracting with diethyl ether and evaporation in vacuo, the residue was purified by column chromatography on silica gel (petroleum ether : acetic ether = 6 : 1) to give 1.03 g of the title compound in 53 % yield (m.p. 389 K). The crystals suitable for X-ray analysis were grown from a diethyl ether solution by slow evaporation at room temperature. IR and 1 H NMR data are available in the CIF. Experimental detailsIt was obvious from electron-density maps that the CF 2 group at C9 was disordered corresponding with two orientations of the cyclopent-1-ene ring in a C9-envelope conformation. This disorder was readily modelled with C9 disordered over two sites (C9 and C9A) with four F atoms. DFIX restraints were used to keep the C9-F, C9A-F and F···F separations to be in agreement with the observed C−F geometry at the C7 and C7A sites. Initially the two disordered orientations were refined with tied occupancy parameters, but as these refined occupancy values were not significantly different from 0.5, the occupancies were then fixed at 0.5 for the final refinement cycles. All H atoms were clearly defined in difference maps and were allowed for as riding atoms with d(C-H) 0.93 to 0.96 Å with U iso(H) = 1.2 and 1.5 Ueq(C). . The two independent planar benzene ring systems are essentially indentical, and the dihedral angles between the least-squares plane of the central hexafluorocyclopentene and the adjacent benzene rings, C1-C6 and C1A-C6A, are 44.2(7)°and 53.3(7)°, respectively. The intramolecular distance between the equivalent C atoms (C1···C1A) is 3.480(8) Å. Discussion
Source of materialThe title compound was synthesized in 35 %total yield by aliterature method [1,2] using 5-n-hexyl-thiophene-2-carbaldehyde as the starting material. Crystals suitable for X-ray analysis were grown from solution (diethyl ether/hexane 1:2) by slow evaporation at room temperature (m.p. 390.9 -391.2 K). Elemental analysis -found: C, 60.19 %; H, 4.44 %; N, 8.12 %; calculated for C 33H30F6N4S2:C,59.99 %; H, 4.58 %; N, 8.48 %. 1 HNMR, 13 C NMR and IR data are available in the CIF. Experimental detailsAll Hatoms attached to Cwere fixed geometrically and treated as riding with d(C-H) =0.96 Å (methyl) or 0.93 Å (aromatic) with U iso (H) =1.2 U eq (aromatic) or U iso (H) =1.5 U eq (methyl). Bonds between the atoms C1 to C5, C1' to C5', C17 and F3 were subject to a'rigid bond' restraint, i.e. the components of the anisotropic displacement parameters in the direction of the bond were restrained to be equal within an effective standard deviation set to 0.01. The same atoms were also restrained with an effective standard deviation of 0.01 to have the same U ij components. The distance cutoff for this restraint was set to 1.70 Å.Using different "effective standard deviation" for the terminational atoms C1 and C1', the default setting (0.08) of command was used for the terminational atoms. DiscussionOrganic photochromic diarylethenes have attracted much attention for their potential application in optical memory media and optical switches [3,4]. In our previous crystallographic studies of photochromic diarylethenes, we reported. 1,2-bis[2-n-pentyl-5-(2,2-dicyanovinyl)-3-thienyl)]-3,3,4,4,5,5-hexafluorocyclopent-1-ene [1,3] and 1,2-bis[2-n-butyl-5-(2,2-dicyanovinyl)-3-thienyl)]-3,3,4,4,5,5-hexafluorocyclopent-1-ene [4,6]. These studies are extended to the n-hexyl analog, in order to investigate the substituent effect at the 2-postion of the thiophene on the photochemical properties. The title compound is an ew twofold symmetrical hybrid photochromic diarylethene derivative. In the crystal structure, the Fa toms of the central hexafluorocyclopentene ring are disordered, with site occupancies of 0.683(6) and 0.317; and the ratio of the disorder of the alky chain is 0.591(6) to 0.409. The molecule adopts ap hoto-active antiparallel conformation. The distance between the two photo-reactive Catoms is 3.941(3) Å.The dihedral angle between the central cyclopentene ring and the adjacent thiophene ring is 63.4(5)°. The two thiophene rings are condensed via the C15=C15A double bond (symmetry operator A: -x+2,y,-z+1/2) (figure, top) while the other bonds in the ring are clearly single bonds. The two n-hexyl groups are located on different sides of the double bond. This configuration is crucial to allow the compound to exhibit photochromic and photoinduced properties [7]. It may allows breaking of the central hexafluoro-cyclopentene C=C double bond to form anew C-Csingle bond to be symmetry allowed and the molecule thus may undergo aphototransition and exhibit photochromic and photoinduced properties. The dihedral angles be...
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