Laterally fluorinated 4-cyanophenyl and 4'-cyanobiphenyl benzoat

Details Laterally fluorinated 4-cyanophenyl and 4'-cyanobiphenyl benzoat Laterally fluorinated 4-cyanophenyl and 4'-cyanobiphenyl benzoat

1990-08-30

1992-10-20

Stoll, Robert L.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

560 65, 560102, C09K 1920, C07C 6976

Patent

active

051567636

DESCRIPTION:

BRIEF SUMMARY
This invention relates to laterally fluorinated 4-cyanophenyl and 4'-cyanobiphenyl benzoates, and to liquid crystal mixtures and devices using them.
Liquid crystal materials are well known for use in electrooptical display devices such as calculators, watches and the like. A commonly used type of liquid crystal material is that which shows a nematic liquid crystalline phase. Desirable characteristics in a nematic liquid crystal material include a high nematic to isotropic (N-I) transition temperature, a low solid crystal to nematic (K-I) transition temperature, and the absence of smectic (S) phases. Other desirable characteristics include low viscosity, ease of manufacture, chemical and thermal stability.
Nematic liquid crystal materials generally consist of a mixture of chemical compounds. One class of such compounds are 4-cyanophenyl and 4'cyanobiphenyl esters of structure: ##STR2## where R may be alkyl, alkoxy, acyloxy or alkylcarbonato disclosed respectively in U.S. Pat. Nos. 4,138,359 and 3,951,846. Some halogenated analogues of these compounds have been investigated, for example fluorinated compounds such as: ##STR3## are described in Mol Cryst Liq Cryst 109(2-4), (1984) (
169-78 and in Japanese Patent Applications 58/210982, 60/69190, 63/122669, 61/30565 and 61/50953, and German Offenlegungschrift 3339216.
JPA 61/106550 describes compounds of structure: ##STR4##
JPA 61/63645 describes the compound: ##STR5##
U.S. Pat. No. 4,689,176 discloses optically active compounds of formula: ##STR6## where R is alkyl, 1 is 1 or 2 and m is 0 or 1.
To date, the extent to which fluorinated compounds for use as liquid crystal compounds could be investigated has been hampered by the unavailability of suitable starting materials, and the difficulties of organofluorine chemistry.
The present inventors have investigated the field of fluorinated 4-cyanophenyl and 4'-cyanobiphenyl esters and have identified a range of novel compounds which are useful components of liquid crystal materials. In the course of this a number of novel and potentially useful fluorinated intermediates have also been prepared.
According to the present invention, novel compounds are provided, having a formula I: ##STR7## in which R is R.sup.1 or R.sup.1 O, wherein R.sup.1 is C.sub.1 -C.sub.12 alkyl, n and m are 0 or 1 provided that (n+m) is 0 or 1, each of a, b, c and d are independently 0 or 1, provided (a+b+c+d) is not zero, but excluding the case where a and b are 0 and one of c or d is one.
Compounds of formula I are useful as constituents of liquid crystal compositions, particularly nematic liquid crystal materials. The structural preferences expressed below are based inter alia on relative usefulness in nematic liquid crystal materials.
Preferably R.sup.1 contains 3 to 8 carbon atoms, especially 3, 4 or 5, and R.sup.1 is n-alkyl or an asymmetrically substituted alkyl group such as 2-methylbutyl which may be in an optically active or racemic form. It is particularly preferred that R is n-alkyl or n-alkoxy.
Some preferred overall structures for compounds of Formula I are listed in table 1 below.


TABLE 1 ______________________________________ ##STR8## 1.1 ##STR9## 1.2 ##STR10## 1.3 ##STR11## 1.4 ##STR12## 1.5 ##STR13## 1.6 ##STR14## 1.7 ##STR15## 1.8 ##STR16## 1.9 ##STR17## 1.10 ##STR18## 1.11 ##STR19## 1.12 ##STR20## 1.13 ##STR21## 1.14 ______________________________________
Of the structural types listed in table 1, those where R is n-alkyl or n-alkoxy and which contain three phenyl rings generally have higher K-N and N-I transistions than their two-ringed counterparts, whereas the latter often show nematic phases which supercool to well below room temperature. Both of these characteristics are of value in liquid crystal compositions.
Compounds of formula I, including those listed in table 1 may be prepared by a number of routes. Being phenylzoate esters they may for example be prepared from a phenol and benzoic acid carrying fluorine and other substituents R and CN in appropriate positions. Esterification may

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