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Synthesis of Mixed Tail Triphenylene Discotic Liquid Crystals: Molecular Symmetry and Oxygen‐Atom Effect on the Stabilization of Columnar Mesophases
Author(s) -
Zhao KeQing,
Hu Ping,
Wang BiQin,
Yu WenHao,
Chen HongMei,
Wang XinLing,
Shimizu Yo
Publication year - 2007
Publication title -
chinese journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 1001-604X
DOI - 10.1002/cjoc.200790072
Subject(s) - triphenylene , mesophase , discotic liquid crystal , chemistry , crystallography , alkoxy group , columnar phase , differential scanning calorimetry , liquid crystal , stereochemistry , molecule , organic chemistry , phase (matter) , materials science , alkyl , physics , optoelectronics , thermodynamics
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 2 n +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 °C. 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.