Phenyl-Pyrimidine Liquid Crystal Compounds and Liquid Crystal Compositions Containing the Same

1. Field of the Invention

The present invention relates to liquid crystal compounds and liquid crystal compositions containing the same.

2. Description of the Background

Display modes of liquid crystal display elements now widely in use are those of the twist nematic type (TN type) and dynamic scattering type (DS type). These modes are display modes with nematic liquid crystal cells containing nematic liquid crystals as a main component. The conventional nematic liquid crystal cells are disadvantageous in that the response speed is so slow that a response speed only of the order of several m sec is obtained at most. This drawback greatly narrows the applicable range of nematic crystal cells. However, it has recently been recognized that by using smectic liquid cells, higher response speeds are possible.

Some optically active smectic liquid crystals are known to exhibit a strong dielectric property. Examples of liquid crystals exhibiting a strong dielectric property, are representative compounds such as 4-(4-n-decyloxybenzylideneamino) cinnamic acid-2-methyl butyl ester (hereinafter abridged as DOBAMBC) as synthesized by R. B. Meyer et al. in 1975. These compounds are characterized by exhibiting a strong dielectric property in the chiral smectic C phase (J. Physique, 36, L-69 (1975).

Recently, a high speed response of .mu. sec order has been found in a thin film cell of DOBAMBC by N. A. Clark et al. (Appl. Phys. Lett. 36, 89 (1980)). Thereafter, strongly dielectric liquid crystals have been studied due to their high speed response as a material usable not only for displays such as liquid crystal televisions but also as a raw material for optoelectronics and related devices such as light printer heads, optical Fourier transform devices and light values.

Display devices using strongly dielectric liquid crystals can produce printing with short pulses, thus making memorization thereof possible, and thus also making it possible to easily produce large areas of display.

Unfortunately, display devices using a strongly dielectric crystal composition are not yet practicable due to the fact that the response speed of the composition is inadequate and the usable temperature range is prohibitively narrow. Thus, a need continues to exist for a strongly dielectric liquid crystal composition which has a high response speed over a wide range of temperature.

It is an object of the present invention to provide liquid crystal compounds and compositions containing the same which exhibit a high response speed.

It is also an object of this invention to provide such compounds and compositions exhibiting a high response speed over a wide range of temperatures.

Further, it is an object of the present invention to provide a display cell containing the above liquid crystal compounds and compositions.

FIG. 1 shows the infrared absorption spectrum by the Nujol method of 2-(4-decyloxyphenyl)-5-octyloxycarbonyloxypyrimidine as obtained in Example 1.

The present invention provides phenyl-pyrimidine liquid crystal compounds of the formula: ##STR2## wherein R.sub.1 and R.sub.2 each represent an alkyl group having 1 to about 18 carbon atoms, and X and Y each represent one of a single bond, --O--, --OCO--, --COO-- and --OCOO--, provided that one of X and Y is always --OCOO--, and liquid crystal compositions containing the same.

The present invention also provides a strongly dielectric liquid crystal composition having a high response speed over a wide range of temperature, containing one or more compounds of the present invention and one or more chiral smectic C liquid crystal compounds, or mixtures of the compounds of the present invention and a chiral smectic C liquid crystal composition.

The compounds of the formula (I) may be synthesized as follows.

A 5-hydroxypyrimidine derivative represented by the formula (a): ##STR3## where R.sub.2 represents an alkyl group having 1 to about 18 carbon atoms, and Y.sub.1 represents one of a single bond, --O--, --OCO-- and --COO--; or a 5-hydroxypyrimidine derivative represented by the formula (b): ##STR4## wherein R.sub.1 represents an alkyl group having 1 to about 18 carbon atoms, X.sub.1 represents a single bond, --O--, --OCO-- and --COO--; is reacted with a chlorocarboxylic acid alkyl ester represented by the formula (c):

wherein R.sub.3 represents an alkyl group having 1 to about 18 carbon atoms in the presence of a base such as pyridine or triethylamine in an inert solvent such as carbon tetrachloride or chloroform followed by purification to obtain a desired product.

A strongly dielectric liquid crystal composition having a high response speed over a wide range of temperature may be obtained by mixing one or more of the compounds of the present invention with one or more chiral smectic C liquid crystal compounds or with a chiral smectic C liquid crystal composition.

For example, a strongly dielectric liquid crystal composition such as the mixture comprising

exhibits a chiral smectic C phase only in a narrow temperature range of 38.degree. to 60.degree. C. However, a strongly dielectric liquid crystal composition which is the mixture of this composition with a compound of the present invention, 2-(4-nonyloxycarbonyloxyphenyl)-5-dodecylpyrimidine in the ratio of 5:35 exhibits a chiral smectic C phase over a wide temperature range of room temperature to 63.0.degree. C., and also has a very high response speed of 34 .mu.S.

The present invention will now be further illustrated by the following Examples which are provided for purposes of illustration only and are not intended to limit the present invention.

Synthesis and evaluation of 2-(4-decyloxyphenyl)-5-octyloxycarbonyloxypyrimidine (A): ##STR5##

Ethyl benzyloxyacetate (B) was obtained by esterifying benzyloxyacetic acid as obtained from benzyl alcohol and chloroacetic acid by a conventional Williamson synthesis. (B) (9.7 g) and 3.7 g of ethyl formate were dissolved in 25 ml of ether, and stirred in the presence of sodium for 2 hours, and ether was distilled away to obtain sodium 2-benzyloxy-2-ethoxycarbonylethylenolate (C). To this compound was added a solution as prepared by dissolving 14.2 g of 4-decyloxybenzamidine hydrochloride (synthesized from 4-decyloxycyanobenzene by a conventional method) in 80 ml of ethanol and adding 1.2 g of sodium, and the mixture was refluxed for 2 hours. The solvent was distilled away to obtained 2-(4-octyloxyphenyl)-4-hydroxy-5-benzyloxypyrimidine (D). (D) (2 g) together with phosphorus oxychloride was refluxed for 3 hours to obtain 2-(4-octyloxyphenyl)-4-chloro-5-benzyloxypyrimidine (E).

(E) (1.7 g) was hydrogenated in the presence of Pd-C and potassium carbonate in 1,4-dioxane at normal pressure to yield 2-(4-octyloxyphenyl)-5-hydroxypyrimidine (F). (F) (1.0 g) was dissolved in 50 ml of carbon tetrachloride. 0.8 ml of octyl chlorocarboxylate and 5 ml of pyridine were added, and the mixture was stirred for a while and then allowed to stand overnight. 1N hydrochloric acid was added thereto, and the carbon tetrachloride layer was taken and concentrated. The resulting residue was purified by repeated recrystallization from methanol to obtain 2-(4-decyloxyphenyl)-5-octyloxycarbonyloxypyrimidine (A).

The IR-spectrum of this compound is shown in FIG. 1.

The phase transition point of this compound is shown in Table 1.

Various 2-(4-alkyloxyphenyl)-5-alkyloxycarbonyloxypyrimidines were synthesized from various 2-(4-alkyloxyphenyl)-5-hydroxypyrimidines according to the method described in Example 1 and various chlorocarboxylic acid alkyl esters according to the method described in Example 1.

The phase transition point of the resulting compounds is shown in Table 1.

Synthesis and evaluation of 2-(4-nonyloxycarbonyloxyphenyl)-5-dodecylpyrmidine (H) ##STR6##

2-(4-Hydroxyphenyl)-5-dodecylpyrimidine (G) (1.0 g) was dissolved in 50 ml of carbon tetrachloride, 0.8 ml of nonyl chlorocarboxylate and 5 ml of pyridine were added, and the mixture was stirred for a while and allowed to stand overnight. 1N Hydrochloric acid was added, and the carbon tetrachloride layer was taken and concentrated. The residue was purified by repeated recrystallization from methanol to obtain (H).

Various 2-(4-alkyloxycarbonyloxyphenyl)-5-alkylpyrimidine compounds were synthesized from various 2-(4-hydroxyphenyl)-5-alkylpyrimidine compounds and various chlorocarboxylic acid alkyl esters according to the same method as described in Example 3.

The phase transition point of the resulting compounds is shown in Table 1.

A chiral smectic C liquid crystal composition having the following composition was prepared:

This composition exhibited a chiral smectic C phase over a temperature range of from room temperature to 63.degree. C., a smectic A phase over a temperature range of from 63.degree. C. to 66.degree. C. and an isotropic phase at a temperature of 66.degree. C. or more.

The response speed of the composition as determined by encapsulating it into a cell of 2.7 .mu.m which had been subjected to an orientation treatment with a polyimide and exposing it to a rectangular wave of .+-.40 V was 34 .mu.S at 25.degree. C.

A chiral smectic C liquid crystal composition having the following composition was prepared:

This composition exhibited a chiral smectic C phase over a temperature range of from room temperature to 58.degree. C., a smectic A phase over a temperature range of from 58.degree. C. to 60.degree. C., and an isotropic phase at a temperature of 60.degree. C. or more.

The response speed of the composition as determined by encapsulating it into a cell of 3.3 .mu.m which had been subjected to an orientation treatment with a polyimide and exposing it to a rectangular wave of .+-.40 V was 20 .mu.S at 25.degree. C.

A chiral smectic C liquid crystal composition having the following composition was prepared:

This composition exhibited a chiral smectic C phase over a temperature rang of from below freezing to 41.degree. C., a smectic A phase over a temperature range of from 41.degree. C. to 61.degree. C., and an isotropic phase at a temperature of 61.degree. C. or more.

The response speed of the composition as determined by encapsulating it into a cell of 3.3 .mu.m which had been subjected to an orientation treatment with a polyimide and exposing it to a rectangular wave of .+-.10 V was 24 .mu.S at 23.degree. C.

A chiral smectic C liquid crystal composition having the following composition was prepared:

This composition exhibited a chiral smectic C phase over a temperature range of from below freezing point to 35.degree. C., a smectic A phase over a temperature range of from 35.degree. C. to 59.degree. C., and an isotropic phase at a temperature of 59.degree. C. or more.

The response speed of the composition as determined by encapsulating it into a cell of 3.3 .mu.m which had been subjected to an orientation treatment with a polyimide and exposing it to a rectangular wave of .+-.10 V was 18 .mu.S at 23.degree. C.

Having now fully described the present invention, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the invention as set forth herein.