Synthesis of Mixed Tail Triphenylene Discotic Liquid Crystals: Molecular Symmetry and Oxygen-Atom Effect on the Stabilization of Columnar Mesophases

✍ Scribed by Ke-Qing Zhao; Ping Hu; Bi-Qin Wang; Wen-Hao Yu; Hong-Mei Chen; Xin-Ling Wang; Yo Shimizu

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 205 KB
• Volume: 25
• Category: Article
• ISSN: 0256-7660
• DOI: 10.1002/cjoc.200790072

✦ Synopsis

Small change in chemical structure of discotic liquid crystals can cause big difference in their mesomorphism. Replacing of the alkoxy peripheral chains of triphenylene by oxygen-atom containing ester chains would result in novel mesomorphism. A series of mixed tail triphenylenes containing propoxyacetyloxy and alkoxy, abbreviated as C 18 H 6 (OC n H 2n＋1 ) 3 (OCOCH 2 OC 3 H 7 ) 3 , n＝4-8, and hexa(propyloxyacetyloxy)triphenylene, C 18 H 6 (OCOCH 2 -OC 3 H 7 ) 6 were synthesized. Thermal gravimetry analysis (TGA) of three discogens showed that they had good thermal stability till 350 ℃. The mesomorphism was investigated through differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The preliminary X-ray diffraction (XRD) results of one compound showed that it exhibited ordered hexagonal columnar (Col ho ) mesophase. These mixed tail triphenylene derivatives possessed much stable Col ho mesophase and wider mesophase ranges than their hexaalkoxytriphenylene C 18 H 6 (OR) 6 and hexaalkanoyloxytriphenylene C 18 H 6 (OCOR') 6 analogues. The asymmetrical compounds 2,6,11-trialkoxy-3,7,10-tri(2-propyloxyacetyloxy)triphenylenes with n＝5-8 displayed higher clearing points and wider temperature ranges than their symmetrical isomers 2,6,10-trialkoxy-3,7,11-tri(2-propyloxyacetyloxy)triphenylenes, while C 18 H 6 (OCOCH 2 OC 3 H 7 ) 6 had the highest clearing point due to the β-oxygen-atom effect.