N-substituted amino acid derivatives for use in liquid crystal m

Details N-substituted amino acid derivatives for use in liquid crystal m N-substituted amino acid derivatives for use in liquid crystal m

1987-07-17

1990-07-17

Terapane, John F.

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

3503505, 560 39, 560 41, C09K 1912

Patent

active

049419927

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to liquid crystal compounds derived from amino acids and to materials and devices using them. In particular the invention relates to the liquid crystal phases of such compounds exhibiting ferroelectric behaviour and to the use of the compounds as dopants to produce mixtures capable of forming phases with ferroelectric properties.
Liquid crystal materials exhibiting a tilted chiral smectic phase have been proposed for use in rapidly switched electro-optical devices, processing and storage devices, based upon the ferroelectric properties of tilted chiral smectic phases, as described for example by N. A. Clark and S. T. Lagerwall in App Phys Lett 36, 899, (1980). (Reference 1).
The liquid crystal materials described in Reference 1, DOBAMC (p-decyloxybenzlidene p-amino 2 methylbutylcinnamate) and HOBACPC (L-4-hexyloxybenyzlidene-4'-amino-2-chloropropylcinnamate) are for most applications far from ideal because they are relatively unstable chemically and sensitive to light, their spontaneous polarisation coefficients (Ps) are relatively small and their tilted smectic phases occur at inconveniently high temperatures and exist over inconveniently small temperature ranges.
It is becoming increasingly common to prepare ferroelectric smectic liquid crystal mixtures by mixing a liquid crystal material that shows a smectic phase, preferably the smectic C (designated Sc) phase as this is the most fluid, with a chiral (optionally active) compound or compounds to induce the smectic phase of the material to become chiral, e.g. S.sub.c * (the asterisk indicating chirality). The smectic liquid crystal material in this case is termed a `host` and the chiral compound(s) is termed a `dopant`. A good dopant should desirably induce a high Ps in the mixture. It is preferred that the dopant also shows a smectic liquid crystal phase as an indication of compatibility with a smectic lattice, but this is not essential.
As the use of ferroelectric smectic liquid crystal materials increases, e.g. in large screen displays of A4 size or larger, it is desirable to decrease the cost of the materials as far as possible. In the case of the chiral dopants the special problems of synthesis of optically pure enantiomers increases their cost.
Biochemical processes are often extremely sterospecific and result in the production of optically pure compounds, with the added advantage that some biochemical products are very cheap. If such biochemical products could be used to make liquid crystal materials it would be very useful. One attempt to achieve this is described in published copending PCT application GB 85/00512 which compounds of lactic acid are discussed, and in UK patent application 8620111 in which derivatives of .alpha.-amino acids are discussed. The amino acid derivatives described in that latter patent application contain the grouping --CO.NH.CH(A).COO-- where A represents the residue of the amino acid. The presence of the NH group in these compounds is a probable cause of their relatively high melting point.
It is an object of the present invention to identify further useful liquid crystal materials derived from optically active natural products.
According to a first aspect of the invention there is provided a derivative of an .alpha.-aminocarboxylic acid, this derivative being optically active and having a general formula I ##STR2## wherein R is C.sub.1-20 n-alkyl or n-acyl, wherein A is selected from the following groups: CH.sub.3, CH.sub.3 (CH.sub.2).sub.3, CH.sub.2 OB, CH.sub.3 CH(CH.sub.3), CH.sub.3 CH(OB), BSCH.sub.2, CH.sub.3 CH(CH.sub.3)CH.sub.2, CH.sub.3 CH.sub.2 CH(CH.sub.3), CH.sub.3 SCH.sub.2 CH.sub.2, ##STR3## BO ##STR4## BOOCCH.sub.2, BOOCCH.sub.2 CH.sub.2, B.sub.2 NCOCH.sub.2, B.sub.2 NCOCH.sub.2 CH.sub.2, B.sub.2 NCH.sub.2 CH.sub.2 CH.sub.2, B.sub.2 NCH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2, ##STR5## or ##STR6## in which B represents a group containing no hydrogens which might give strong hydrogen bonding ##STR7## wherein R.sub.1 is selected from hydrogen, halogen or C1-20 alkyl, alkoxy, fluoroal

REFERENCES:
patent: 4764619 (1988-08-01), Gunjima et al.
patent: 4784793 (1988-11-01), Coates et al.
patent: 4824217 (1989-04-01), Chan et al.

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