Synthesis and Evaluation of Some 4,4″-Disubstituted Lateral Fluoro-1,1′:4′,1″-terphenyls

Abstract

A number of laterally fluorinated 4,4″-di-n-alkyl-, 4,4″-di-n-alkoxy- and 4-n-alkyl-4″-n-alkoxy-l,r:4′,1″-terphenyls of structure (I) have been synthesised, with the lateral fluoro-substituent in the central benzene ring. The nematic and smectic thermal stabilities for all three series of compounds, have been examined. A typical example is (I), X = n–C₅ H_U, Y = n–C₃ H₇, C–N 50°C and N–I 140.6°C. For the 4,4″-di-n-alkyl-1,1′:4′,1″-terphenyls, the position of the lateral fluoro-substituent with respect to the longest n-alkyl chain is found to be important in determining the smectic behaviour of this class of compound. By using a combination of optical microscopy, X-ray diffraction and miscibility studies, the complex smectic behaviour of the higher homologues of this series has also been investigated. A comparison of the liquid crystal behaviour of the laterally fluorinated ter-phenyls of structure (I) with their non-fluorinated analogues is also given. A selected number of these compounds, have been further examined to assess their usefulness as high T_{N −I} additives for multiplexed mixtures used in electro-optic display devices.