J O U R N A L O F C H E M I S T R Y Materials Communication New 1,3-oxathiane type ionic liquid crystal compounds Yuichiro Haramoto,*a Yoshiharu Akiyama,a Ryouichi Segawa,a Seiji Ujiieb and Masato Nanasawaa aDepartment of Applied Chemistry and Biotechnology, Yamanashi University, T akeda 4, Kofu 400, Japan bDepartment of Chemistry, Shimane University, Nishikawatu,Matsue 690, Japan New pyridinium type thermotropic ionic liquid crystal materials having a 1,3-oxathiane ring in the central core, Nethyl- 4-(5-alkyl-1,3-oxathian-2-yl)pyridinium bromides 8, were synthesized.These compounds exhibited a smectic A phase over a very wide range including room temperature (for example 8c: G-30 SA 21 I). There are not many reports concerning ionic thermotropic liquid crystal compounds having two rings in the central core.Some liquid crystal polymers with pyridinium side chains1 and N-alkylpyridinium halides have been reported,2–4 as have stilbazole (styrylpyridine) type metal-containing liquid crystals. 5 On the other hand, we have studied 1,3-dioxane, 1,3- oxathiane and 1,3-dithiane type new liquid crystal materials. 6–15 Ionic liquid crystal materials having these structures in the central core have not been encountered to date and their possibilities as liquid crystal materials are interesting.In the last year the first of these compounds with a 1,3-dioxane R OH OH R Br OH R Br Br R SH OH R SH SH H2N S NH2 N S O R N+ S O R N H O R¢ PBr3 + Alkali R¢Br CH3CN R = C10H21, C11H23, R¢ = C2H5, CH2CH Br– 1 2 3 5 4 4 + 6 7 H+ 7 8 CH2 structure was reported.16 We wish to report a new system of Scheme 1 pyridinium type ionic liquid crystal compounds having a 1,3- oxathiane ring in the principal structure. of a micro-melting point apparatus equipped with polarizers, a diVerential scanning calorimeter (DSC), and X-ray diVraction.Phase transition temperatures for compounds 8 are given in Table 1. S O N R R¢ + Br– 8 N-Alkyl-4(5-alkyl-1,3-oxathian-2-yl)pyridinium bromides 8 were synthesized by the route shown in Scheme 1.In the bromination of compounds 1, both mono- and di-bromides were produced. This mixture was used for the syntheses of compounds 4 and 5. The monothiol 4 and dithiol 5 were N+ S O R R¢ Br– 8 N+ O O R R¢ Br– 9 Table 1 Phase transition temperatures for compounds 8 and the separated by column chromatography, in which 4 and 5 were corresponding 1,3-dioxanes 9 eluted with diethyl ether and hexane, respectively.In the syntheses of compounds 7, both trans and cis isomers were phase transition produced which diVered at the C-5 position of the 1,3-oxathiane R R¾ temperatures/°Ca ring. Repeated recrystallizations were required to obtain only the trans isomers.In the 1H NMR spectra for compounds 7, 8a C10H21 C2H5 K 45 SA 166 I 8b C11H23 C2H5 K 50 SA 192 I the C-2 proton signals for the trans and cis isomer are at 5.75 8c C10H21 CH2CHNCH2 G -30 SA 21 I and 5.80 ppm, respectively. Therefore, removal of the cis isomer 9a C10H21 C2H5 G -24 SA 152 I can be checked by the disappearance of its peak in the 9b C11H23 C2H5 G -9 SA 181 I 1H NMR spectrum.On N-alkylation, 1H NMR signals for the 9c C10H21 CH2CHNCH2 pyridinium proton and the C-2 proton of the 1,3-oxathiane ring were shifted downfield about 0.8 and 0.45 ppm, respectively. The purity of compounds 8 was checked by 1H NMR G I SA –19 62 78 spectroscopy and elemental analyses. Good data were obtained for these compounds. To determine the existence of liquid aK: Crystal, G: Glass, SA: Smectic A, I: Isotropic.crystal phases, observation was performed using a micromelting point apparatus equipped with polarizers. Compounds 8 exhibited a liquid crystal phase, so further detailed measure- Observation of the textures indicates that these compounds exhibited a smectic A phase. To confirm this result, conoscopic ments were made. Measurement of transition temperatures and assignment of the mesophases were carried out by means figures and X-ray diVraction were measured for the phase of J.Mater. Chem., 1998, 8(2), 275–276 275compound 8a (Fig. 1). These results also support the assignment of the liquid crystal phase as smectic A. That is, a uniaxial conoscopic figure was observed, and the diVraction pattern of the typical smectic A phase was also obtained.The sharp peak in the small-angle region indicates that the layer spacing of this phase is 38.9 A ° . This value is somewhat larger than that of the corresponding 1,3-dioxane type ionic liquid crystal compound (34.3 A ° ). From the value of the layer spacing and the peculiar properties of ionic liquid crystal compounds, the molecular arrangement in the smectic A phase may be as shown in Fig. 2. In this model, cationic pyridinium ions and Fig. 1 X-Ray diVraction pattern of the smectic phase of compound 8a anionic bromide ions stabilize each other, and the long alkyl chains orient to form the smectic phase. The temperature of the isotropic to mesophase transition of compound 8c having a terminal double bond is lower than those of compounds 8a or 8b.This is the same tendency as that observed for 1,3-dioxane type compounds (Table 1). The compound having a (CH2)8CHNCH2 group instead of the C10H21 group of compound 9a also exhibited a lower isotropic to mesophase transition temperature.16 Generally, the transition temperatures of the isotropic to mesophase transition tend to be decreased by the existence of a terminal double bond in the molecule.17,18 Therefore, this eVect seems to originate in the presence of the terminal double bond.The most remarkable feature of these new ionic liquid crystal materials is that they exhibit a liquid crystal phase over a very wide range including ordinary room temperature (e.g. 8c: G -30 SA 21 I). We would like to express our gratitude to the director Dr A.B. Holmes, Dr S. C. Moratti and all the members of the Melville Laboratory, University of Cambridge, for extensive support. References 1 V. Hessel and H. Ringdorf, Makromol. Chem. Rapid Commun., 1993, 14, 707. 2 C. G. Bazuin, D. Guillon, A. Skoulion and J. F. Nicoud, L iq. Cryst., 1986, 1, 181. 3 D. N. Rodriguez, Y. Frere, P. 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