Esters Of Fluorinated Biphenol Liquid Crystal Material Synthesis And Performance

Above all the literatures, we designed to synthesize two kinds of ester liquid crystal compounds which were not reported. Trans-4-alkyl cyclohexane benzoic acid-4'-fluoro diphenol ester(An), 4-alkylbenzoic acid -4'-fluoro diphenol ester(Bn).The targe compounds were synthesized as follows: (1)4-fluoro phenyl bromide reacted with Mg , then with Tributyl borate to get 4-fluoro phenylboronic acid under nitrogen at -30℃. We also optimized the conditions to get the best technics: n(Mg): n(tributyl borate): n(p-fluorobromobenzene)=1.1: 1.0: 1.5 at -30℃, reaction time was 120min. (2)Through the Suzuki cross-coupling reaction, we obtained 4-fluoro diphenol. Also the best technics was discussed. n(p-fluorophenyl boronic acid): n(p-bromophenol): n(potassium carbonate) = 1.1: 1.0: 2.0, PdCl₂(2%eq) as catalyst at room temperature for 6 h. (3)4-fluoro diphenol reacted with trans-alkyl cyclohexane benzene-1-carbonyl chloride so as to get the targe compounds. Totle yield of the objective products were higher than 30%. The mass fractions of the products by GC were over 98%.Structures of the liquid crystal compounds were confirmed by IR, ¹HNMR. We surveyed their phase-transition temperature by DSC and obtained their POM patterns. The results showed that these liquid crystal compounds exihibit high clearing points(>209℃) and broad temperature range of mesomorphic phases(>98℃). They were thermotropic tantomeric liquid crystals. The clearing points were reducing with the alkyl growth. The liquid crystals with end-cyano had higher clear points than the end-fluoro. An with one more transcyclohexane had higher clear points than Bn.AM1 calculation has been performed to obtain moleculer geometries of An,Bn by energy gradient completed optimization. The stable configuration, electronic structure and some molecular properties of these compounds are discussed. The theoretical analysis showed that liquid crystals with end group and center bridge bond that can be conjugated with benzene had higher melting points and clearing points. That was in accord with experiment.