Synthesis and properties of some fluorinated biphenyl mesogens

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Matharu, A.S., 1992. Synthesis and properties of some fluorinated biphenyl mesogens. PhD, Nottingham Trent University.

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Abstract

The initial aim of this work was to extend and complete an investigation into the liquid crystal properties of esters derived from compounds (1) and (2) containing a polyfluorinated biphenyl nucleus.

(1) 4-n-butyl-4'-hydroxy-2,2',3,3',5,5',6,6'-oclafluorobiphenyl
(2) 4-n-alkoxy-4'-hydroxy-2,2',3,3',5,5',6,6'-octafluorobiphenyl

A range of esters derived from (1) and (2) was investigated. These compounds are generally quite low melting nematogens with an extremely wide nematic to isotropic range, but, unfortunately, because of the extensive lateral substitution, they have a rather high viscosity.

Due to the interest in the potential commercial applications of fluorinated liquid crystals generated by the synthesis of the I-compounds, members of the homologous series (3) and (4)(analogous to the I-compounds) were synthesised.

(3) l-(4'-n-alkoxy-2,2',3,3',5,5',6,6'-octafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)ethenes
(4) l-(4'-n-alkoxy-2,2',3,3',5,5',6,6'-octafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)ethanes

Replacement of the ester linkage by the ethane linkage (series (4)) resulted in lower melting nematogens possessing low birefringence and moderate viscosity.

The effect of systematically reducing the number of fluoro-substituents present on the biphenyl nucleus was also investigated. A number of polyfluorinated alkylaryl-ethenes and -ethanes were synthesised (series (5)-(12)), differing only in the number and position of the fluoro-substituents.

(5) l-(4'-n-alkoxy-3,3',5,5'-tetrafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)ethenes
(6) l-(4'-n-alkoxy-3,3',5,5'-tetrafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)ethanes
(7) l-(4'-n-alkoxy-2,3',5',6-tetrafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)ethenes
(8) l-(4'-n-alkoxy-2,3',5',6-tetrafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)ethanes
(9) l-(4'-n-alkoxy-2',3,3',5,5',6'-hexafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)ethenes
10) l-(4'-n-alkoxy-2',3,3',5,5',6'-hexafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)ethanes
(11) l-(4'-n-alkoxy-2,3,3',5,5',6-hexafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)ethenes
(12) l-(4'-n-alkoxy-2,3,3',5,5',6-hexafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)ethanes

All the compounds are low melting and mesogenic, and the type of mesophase formed is dependent upon the number and position of the fluoro-substituents. This work has resulted in a patent application.