Novel substituted naphthalene compounds and liquid crystal compositions containing same

Abstract: In accordance with the present invention, there are provided substituted naphthalene compounds of formula [I]. wherein R¹ represents alkyl of 1-18 carbon atoms, R² represents alkyl of 1-18 carbon atoms, X is -OCH₂- or -CH₂CH₂-, and n is 0 or 1. The invention also provides liquid crystal compositions containing a substituted naphthalene compound such as a compound of formula [I].

Description: This invention relates to novel substituted naphthalene compounds which are highly useful as ferroelectric liquid crystal substances. CRT devices have heretofore been used most widely as display devices for office appliances. In the field of appliances such as office appliances having display devices, there has been an increasing demand in recent years for miniature and weight saving appliances or large-frame and light gage display devices. In this regard, in place of conventional CRT devices, various new types of display device have been developed with a view to the uses thereof or demands therefor. Such types of display device include liquid crystal display, plasma display, LED display, EL display and ECD display devices. Of these display devices, liquid crystal display devices basically function as follows. Electrical signals are given to switching elements having therein a liquid crystal compound, wherein the liquid crystal compound changes in state thereby controlling the shielding and transmission of light and "developing" the electrical signals in the display device. Such liquid crystal display devices have already been put to practical use, not only as display devices in office appliances but also as display devices for digital watches and portable games. Recently, liquid crystal display devices have been used in moving picture appliances such as small televisions. In display devices using liquid crystal compounds, various driving methods are known. For example, as the driving method of presently used liquid crystal displays, there is the TN (twisted nematic) mode. The TN mode effects display by using the dielectric anisotropy of the liquid crystal compound in the nematic phase, wherein the display device is driven by energy proportional to the square of the electrical field applied from outside (f α E²). Switching elements of liquid crystal displays adopting this TN mode, however, have problems such that in order to change the image being displayed the drive time is long because the positions of the molecules of the liquid crystal compound must be changed, and also the voltage necessary for changing the positions of the molecules (i.e. the electric power consumption) is large. In such switching elements, there is a problem that because the switching threshold value characteristics of the element are not good, when the positions of the molecules of the liquid crystal compound are changed at high speed and a change in operation is intended to be carried out, a lack of voltage may exert even on those portions of the image which are not displayed and the contrast of the display device may markedly decrease. Because of the above-mentioned problems associated with the conventional display method relying on the TN mode, display devices utilizing the TN mode are not particularly suitable for large frame display devices or moving picture display devices such as small digital televisions. Furthermore, display devices utilizing the STN (super twisted nematic) mode are being used, in which the switching threshold value characteristics and the like are improved over the TN mode. By virtue of utilization of the STN mode, the contrast of display devices improves because of the improved threshold value characteristics. However, the display method is identical with the method utilizing the TN mode in that both methods utilize dielectric anisotropy, and accordingly because of their long switching time, display devices utilizing the STN mode do not have the characteristics required for large frame display devices or moving picture devices such as small digital televisions. In contrast thereto, R.B. Meyer et al. suggested in 1975 that organic compounds synthesized by them exhibit ferroelectric properties, and further suggested in 1980 the possibility that by filling cells having a small gap with these ferroelectric liquid crystal compounds, said compounds may be used in optical switching elements, i.e. display devices. In distinction to switching elements utilizing the TN mode or STN mode, switching elements using such ferroelectric liquid crystal compounds are able to function as switching elements only by changing the direction of molecular orientation, and hence the switching time required for operating these switching elements is markedly shortened. Further, because the value of Ps x E obtained from the spontaneous polarization (Ps) of the ferroelectric liquid crystal compound and from the strength of the electric field (E) applied is an effective energy output for changing the direction of molecular orientation of said liquid crystal compound, the electric power consumption required therefor can be markedly minimized. Such ferroelectric liquid crystal compounds are particularly suitable for large frame or moving picture display devices, because they have two steady states depending upon the direction of electric field applied (i.e. bistability) and also very favourable switching threshold value characteristics. When these ferroelectric liquid crystal compounds are intended for use in optical switching elements, they must have characteristics such as an operating temperature range in the vicinity of ordinary temperature (room temperature), a wide operating temperature zone, a high switching speed and an appropriate switching threshold value voltage. Of these characteristics, the operating temperature range is especially important when the ferroelectric liquid crystal compounds are used in optical switching elements, and there are many ferroelectric liquid crystal compounds which are unusable because their operating temperature range does not agree with their service temperature range, in spite of the fact that other characteristics of said compounds are excellent (refer, for example, to R.B. Meyer et al., J. de Phys., Vol. 36 L, p.69 (1975)). Further, ferroelectric liquid crystal compounds having a naphthalene ring and similar compounds are disclosed, for example, in M. Taguchi and T. Harada, "Proceedings of Eleventh conference on Liquid Crystal," p.168 (1985) and JP-A-62-10045. The liquid crystal compounds disclosed therein are of relatively high practical use when viewed from the standpoint of their operating temperature range and the like; the compounds are stable because a substituent is attached directly to the naphthalene ring via an ester bond. However, these liquid crystal compounds hardly satisfy the required characteristics other than operating temperature range. Thus, there was much room for improvement. An object of the present invention is to provide novel substituted naphthalene compounds which are highly useful, in particular, as ferroelectric liquid crystal compounds. A further object of the invention is to provide liquid crystal compositions which contain substituted naphthalene compounds and have excellent characteristics, such as an operating temperature range in the vicinity of ordinary temperature (room temperature), a wide operating temperature range, a high switching speed and an appropriate switching threshold voltage. The substituted naphthalene compounds of the present invention are represented by the following formula [I] wherein R¹ represents alkyl of 1-18 carbon atoms and R² represents alkyl of 1-18 carbon atoms, X is -OCH₂- or -CH₂CH₂-, and n is 0 or 1. The compounds of the invention may be used in a liquid crystal display device. The invention includes a liquid crystal composition containing a compound of the invention. Of the substituted naphthalene compounds of the formula mentioned above, those having alkyl of 2 or more carbon atoms as R² are particularly effective as liquid crystal compounds. In these compounds, the carbon atom to which R² is attached is optically active. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a chart showing the ¹H-NMR spectrum of 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-decyloxynaphthalene. Fig. 2 is a chart showing the ¹H-NMR spectrum of 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-decyloxynaphthalene. The substituted naphthalene compounds of the present invention are illustrated below in detail. In the above formula [I], R¹ represents alkyl of 1-18 carbon atoms, preferably 6-16 carbon atoms. R² represents alkyl of 1-18 carbon atoms, preferably 1-7 carbon atoms. Furthermore, substituted naphthalenes of the above formula [I] in which R² is alkyl of two or more carbon atoms are compounds having optically an active carbon represented by the following formula [II]. Such compounds are highly effective, particularly as liquid crystal compounds. In formula [II], R¹ represents alkyl of 1-18 carbon atoms, preferably 6-16 carbon atoms. Further, R¹ is preferably straight chain alkyl of 8-12 carbon atoms when the compounds of formula [II] are used as liquid crystal substances. R³ in formula [II] represents alkyl of 2-18 carbon atoms, preferably 2-8 carbon atoms. Further, R³ is preferably ethyl or hexyl when the compounds of the formula [II] are used as liquid crystal substances. Furthermore, when R³ is ethyl, n in formula [II] is preferably 1, and when said R³ is hexyl, n is preferably 0. Further, in formula [II], X is -OCH₂- or -CH₂CH₂-. The substituted naphthalene compounds of the invention may roughly be divided according to the kind of the substituent X into compounds represented by the following formula [I-a], [II-a], and [III-a], and those represented by the following formulas [I-b], [II-b] and [III-b]. In the above formulae [I-a], [II-a] and [III-a] and also [I-b], [II-b] and [III-b], R¹ and R³ are as defined in the aforementioned formula [I]. Of the compounds represented by the above-mentioned formulae [I-a], [II-a], [III-a], [I-b], [II-b] and [III-b], examples of those which are particularly effective are listed below. 2-[4'-(2''-methylpropyloxycarbonyl)phenylmethyloxy]-6-decyloxynaphthalene, 2-[2'-{4''-(2'''-methylpropyloxycarbonyl)phenyl} ethyl]-6-decyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-decyloxynaphthalene, 2-[4'-(R-2''-methylpentyloxycarbonyl)phenylmethyloxy]-6-decyloxynaphthalene, 2-[4'-(R-2''-methylheptyloxycarbonyl)phenylmethyloxy]-6-decyloxynaphthalene, 2-[4'-(R-2''-methyloctyloxycarbonyl)phenylmethyloxy]-6-decyloxynaphthalene, 2-[4'-(R-2''-methylnonyloxycarbonyl)phenylmethyloxy]-6-decyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-pentyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-hexyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-heptyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-octyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-nonyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-undecyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-dodecyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-tridecyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6 tetradecyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-pentadecyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-hexadecyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-heptadecyloxynaphthalene, 2-[4'-(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-octadecyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-pentyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-hexyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-heptyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-octyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-nonyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-undecyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-dodecyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-tridecyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-tetradecyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-pentadecyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-hexadecyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-heptadecyloxynaphthalene, 2-[4'-(R-1''-methylheptyloxycarbonyl)phenylmethyloxy]-6-octadecyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-decyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylpentyloxycarbonyl)phenyl}ethyl]-6-decyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylhexyloxycarbonyl)phenyl}ethyl]-6-decyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-decyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylocytloxycarbonyl)phenyl}ethyl]-6-decyloxynaphlalene, 2-[2'-{4''-(R-2'''-methylnonyloxycarbonyl)phenyl}ethyl]-6-decyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl]ethyl]-6-pentyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-hexyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-heptyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-octyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-nonyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-undecyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-dodecyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-tridecyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-tetradecyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-pentadecyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-hexadecyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-heptadecyloxynaphthalene, 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-octadecyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-hexyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-heptyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-octyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-nonyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-decyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-undecyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-dodecyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-tridecyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-tetradecyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-pentadecyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-hexadecyloxynaphthalene, 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-heptadecyloxynaphthalene, and 2-[2'-{4''-(R-1'''-methylheptyloxycarbonyl)phenyl}ethyl]-6-octadecyloxynaphthalene. Processes for the synthesis of the substituted naphthalene compounds of the present invention are illustrated in detail hereinafter. Of the present substituted naphthalene compounds, those represented by the formula [II-a] or [III-a] may be prepared by the following procedure. First, an ester compound having an alkyl group corresponding to R² is prepared in the usual way by reaction of 4-halomethyl benzoic acid with an alcohol capable of forming optically active carbons such as R-2-methylbutanol or R-1-methylheptanol. Separately, 2-alkyloxy-6-hydroxynaphthalene having an alkyl group corresponding to R¹ is prepared by alkylation of one of the hydroxyl groups of 2,6-dihydroxynaphthalene. Subsequently, by reacting the above-mentioned ester compound with the above-mentioned 2-alkyloxy-6-hydroxynaphthalene, a compound represented by the formula [II-a] or [III-a] can be obtained. Furthermore, the compounds represented by the formula [I-a] may be prepared by the same procedure as above but using, for example, 2-methylpropanol in place of the R-2-methylbutanol. The compounds represented by the formula [II-b] or [III-b] may be prepared in the following manner. 6-Alkyloxy-2-carboxynaphthalene having an alkyl group corresponding to R¹ prepared in accordance with the above-mentioned procedure is reduced with a reducing agent such as lithium aluminum hydride to obtain 6-alkyloxy-2-hydroxymethylnaphthalene, and this 6-alkyloxy-2-hydroxymethylnaphthalene is oxidized with an oxidizing agent such as activated manganese dioxide to obtain 6-alkyloxy-2-formylnaphthalene. Separately, methyl 4-bromomethyl benzoate formed by reaction of p-bromomethyl benzoic acid with methanol is reacted with triphenyl phosphine to obtain (4-methyloxycarbonyl)phenylmethylphosphonium bromide. This (4-methyloxycarbonyl)phenylmethylphosphonium bromide is reacted with the above-mentioned 6-alkyloxy-2-formylnaphthalene to obtain 2-[2'-(4''-methyloxycarbonylphenyl)ethenyl]-6-alkyloxynaphthalene. This compound obtained is reduced with hydrogen gas in the presence of reduction catalyst such as palladium catalyst to obtain 2-[2'-4''-(methyloxycarbonylphenyl)ethyl]-6-alkyloxynaphthalene. This naphthalene compound obtained is reacted branched alcohol such as R-2-methylbutanol or R-1-methylheptanol having an alkyl group corresponding to R² to obtain a compound represented by the formula [II-b] or [III-b]. Furthermore, the compounds represented by the formula [I-b] may be prepared by the same procedure as above but using, for example, 2-methylpropanol in place of the R-2-methylbutanol. Because the substituted naphthalene compounds of the invention have in the molecule a naphthalene ring and a phenylene ring, the rings being bonded to each other by a specific group, the core portion of the molecule is stiff and, at the same time, the cohesive energy of the molecule is small. Accordingly, of the substituted naphthalene compounds, particularly those having an optically active carbon assume a smectic phase, especially a smectic C phase at a temperature in the vicinity of room temperature, and these compounds often have a value (Ps) and a viscosity coefficient in the smectic C phase appropriate for ferroelectric liquid crystal compounds. Therefore, the substituted naphthalene compounds are effectively usable, in particular, as ferroelectric liquid crystal compound. The substituted naphthalene compounds of the invention are usable as ferroelectric liquid crystal compounds as mentioned above, and they are also usable as intermediates for other purposes such as medicines or agricultural chemicals. The substituted naphthalene compounds may be used, for example, as liquid crystal compounds. The substituted naphthalene compounds of the invention include those having an optically active carbon, and such compounds often have a smectic layer at a temperature in the vicinity of room temperature. Accordingly, such substituted naphthalene compounds are of high usefulness, in particular, as ferroelectric liquid crystal substances. Further, the present substituted naphthalene compounds are high in chemical stability such as resistance to hydrolysis and the like, because the substituent is not bonded directly to the naphthalene ring via an ester bond. Among the substituted naphthalene compounds illustrated above, there are many compounds which are usable as ferroelectric liquid crystal compounds in switching elements to control transmission of light, for example, by placing the ferroelectric liquid crystal compound in an electric field or a magnetic field and thereby changing the tilt angle of said ferroelectric liquid crystal compounds. Ferroelectric liquid crystal compositions used in switching elements are required to contain ferroelectric liquid crystal compounds having a smectic C phase in the vicinity of room temperature, and a largeness (Ps) of spontaneous polarization and a viscosity coefficient in the chiral smectic C phase, both falling within appropriate ranges. Of the substituted naphthalene compounds mentioned above, the compounds assuming a chiral smectic C phase may be used as the principal ingredient of chiral smectic liquid crystal compositions used as ferroelectric liquid crystal compositions or as an adjuvant for liquid crystal compositions containing other compounds assuming a chiral smectic C phase as the principal ingredient. The most typical example of the compounds mentioned above is the compound of the following formula [V]. This compound has phase transition points as shown in the following Table 1. In the Tables or the like shown hereinafter, C (or Cry) represents a crystal phase, SmA represents a smectic A phase, SmC represents a chiral smectic C phase and Iso represents an isotropic liquid phase. In each phase, the numeral marked with an asterisk represents the transition temperature at which the phase is transformed to the phase shown on the right side. Compound C SmC SmA Iso [V] Temperature * 38°C* 47°C* 89°C* Of the substituted naphthalene compounds mentioned above, the compound of the following formula [VI] does not assume a chiral smectic C phase. The compound of formula [VI] has phase transition points as shown in Table 2. Compound C SmC SmA Iso [VI] Temperature * - <0°C* 48°C* The compound of formula [VI] cannot be used as a chiral smectic liquid crystal compound when used alone. However, this compound may be used in a chiral smectic liquid crystal composition, for example, in admixture with the compound of formula [V] showing a chiral smectic phase C. Furthermore, the compound of formula [VI] may also be used in a nematic liquid crystal composition or cholesteric liquid crystal composition in admixture with a cholesteric liquid crystal compound or nematic liquid crystal compound. A suitable content in the present liquid crystal composition of the compound of formula [VI] may be decided by taking into consideration the characteristics of the substituted naphthalene compound used, the viscosity coefficient of the composition and the purpose for which the compositions is to be used. In the present liquid crystal compositions, examples of the compounds assuming a chiral smectic C phase which can be used together with the liquid crystal compound of the formula [VI] in said compositions include (+)-4'-(2''-methylbutyloxy)phenyl-6-octylnapthalene-2-carboxylic acid ester, 4'-decyloxyphenyl-6-((+)-2''-methylbutyloxy)naphthalene-2-carboxylic acid ester, Besides the above-mentioned compounds assuming a chiral smectic C phase, examples of liquid crystal compounds which may be used in the present liquid crystal compositions together with the compounds of the formula [VI] include nematic liquid crystal compounds typified by Shiff's salt type liquid crystal compounds such as azoxy type liquid crystal compounds such as benzoic acid ester type liquid crystal compounds such as cyclohexylcarboxylic acid ester type liquid crystal compounds such as biphenyl type liquid crystal compounds such as terphenyl type liquid crystal compounds such as cyclohexyl type liquid crystal compounds such as and pyridine type liquid crystal compounds such as cholesteric type liquid crystal compounds such as hydrocholesteric nonanoic acid cholesterin and oleic acid cholesterin, and known smectic liquid crystal compounds. The present liquid crystal compositions may contain, for example, additives which can be incorporated into ordinary liquid crystal compositions, such as conductivity imparting agents and lifetime improving agents. The following methods may be given as examples of the display method in which the present liquid crystal compositions are used. The first display method is to effect the display by injecting the present liquid crystal composition into a thin film cell having a space, for example, of 2-5 µm, orientating the ferroelectric liquid crystal compound parallel to a substrate by utilization of controlling power of the substrate, placing the thin film cell containing the liquid crystal compound between two polarized plates, and applying an external electric field to the thin film cell to change a orientation vector of the ferroelectric liquid crystal compound, thereby effecting display by utilizing a birefringenee of the two polarized plates and of the ferroelectric liquid crystal compound. In this case, the electrodes used is preferably those having obliqueincident deposited silica and the like on the surface thereof. The second display method comprises using a mixture of the present liquid crystal composition and dichroic dyes, and utilizing dichroic properties of the dyes. This method is to effect display by changing light absorption by means of the dye while changing the orientation direction of the ferroelectric liquid crystal composition. In this case, the dyes used are usually dichroic dyes, and examples of the dichroic dyes include azo dyes, naphthoquinone type dyes, cyanine type dyes and anthraquinone type dyes. The present liquid crystal compositions may be applicable to commonly used display methods, in addition to the above-mentioned display methods. The display devices prepared by using the present liquid crystal compositions may be driven by various driving methods, for example, electric address display such as static drive, simple matrix drive and composite matrix drive, photo-address display, heat address display and electron beam display. According to the display method using the present liquid crystal composition containing a substituted naphthalene compound assuming a chiral smectic phase at ordinary temperature (room temperature) out of the present liquid crystal compositions as illustrated above, a high speed response of less than scores of µseconds can be attained, because this quiral smectic liquid crystal composition has a value of spontaneous polarization at this quiral smectic phase and a viscosity coefficient falling within very favorable ranges. Accordingly, by using this chiral smectic liquid crystal composition as switching elements of a large frame display device having a number of scanning lines, a large frame display having a clear contrast can be obtained, because the time required for each scanning line is short. Furthermore, when a thin film cell is prepared, into which the chiral smectic liquid crystal composition is injected, and a chiral smectic phase is formed within said cell, whereupon the cell come to have a memory effect, because the liquid crystal compound has a spontaneous polarization in the cell. By utilizing this memory effect, the electric power consumption of the display device can be reduced, because no continuous application of voltage is required. In this case, moreover, a very clear contrast may be obtained. The switching elements using this chiral smectic liquid crystal composition can be driven at low voltage, because switching can be performed only by changing the direction of molecular orientation of the chiral smectic liquid crystal compound and also because the primary strength of electric field applied is applied to the driving. In this way, by using the chiral smectic liquid crystal composition out of the present liquid crystal compositions as illustrated hereinbefore, a display device having a small electric power consumption and a clear contrast, though the device is of a large frame, can be prepared. Furthermore, this quiral smectic liquid crystal composition of the present invention is highly useful as switching elements for display devices for moving picture, because the composition requires a short driving time and a low driving voltage. On the one hand, the present liquid crystal compositions containing substituted naphthalene compounds which does not assume a chiral smectic C phase may be used as nematic liquid crystal, cholesteric liquid crystal and smectic liquid crystal. Even the liquid crystal compositions of the invention mentioned above which contain substituted naphthalene compounds which do not assume a chiral smectic C phase can be used to obtain liquid crystal elements exhibiting excellent characteristics such as drive time, drive voltage and sharpness, as compared with conventional liquid crystal compositions. The present invention is illustrated below in more detail with reference to examples, but it should be construed that the invention is in no way limited to those examples. Example 1 [Synthesis of liquid crystal compound] Preparation of 2-[4'(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-decyloxynaphthalene First step A mixture comprising 13.6 g(100 mmol) of 4-methylbenzoic acid, 17.8 g (100 mmol) of N-bromosuccinimide and 1 g of benzoyl peroxide was refluxed for 2 hours in 125 ml of carbon tetrachloride, followed by cooling. The reaction product was then collected by filtration. Recrystallization of then reaction product from methanol gave 14.6 g of 4-bromomethylbenzoic acid. Second step Into 40 ml of benzene were placed 1.08 g (5 mmol) of the 4-bromomethylbenzoic acid obtained in the first step, 0.61 ml (5.5 mmol) of R-2-methylbutanol and 0.1 ml of concentrated sulfuric acid, and the mixture was refluxed for 25 hours. After cooling, the reaction product was extracted with ether, and the extract was washed with aqueous sodium hydrogencarbonate solution followed by water-washing. After water-washing, the extract was concentrated and subjected to colum chromatography to obtain 0.8 g of R-2'-methylbutyl-(4-bromomethyl)benzoate. Third step To a mixture comprising 0.66 g of 85% KOH, 40 ml of ethanol and 0.2 ml of water were added 3.2 g (20 mmol) of 2,6-dihydroxynaphthalene and 3.12 g (10 mmol) of decyl tosylate, followed by stirring at 90°C for 15 hours. Subsequently, the reaction liquid is poured into water and neutralized with hydrochloric acid. After neutralization, the reaction product was extracted with ether, and the extract liquid is washed with water, followed by concentration. Using column chromatography, 1.6 g of 2-decyloxy-6-hydroxynaphthalene was separated from the concentrated mixture. Fourth step To 10 ml of dimethylformamide (DMF) were added 0.6 g (2 mmol) of the 2-decyloxy-6-hydroxynaphthalene obtained in the third step, 0.63 g (2.2 mmol) of the R-2'-methylbutyl-(4-bromomethyl) benzoate obtained in the second step and 0.28 g (2 mmol) of calcium carbonate, and the mixture was stirred at 100°C for 12 hours and the reaction mixture was chilled into water. Subsequently, the reaction product was extracted with ether, washed with water and then concentrated. From this concentrated liquid, the reaction product was separated by means of column chromatograpy. Recrystallization from hexane gave 0.27 g of white needles. The white needles was assayed and identified to be 2-[4'(R-2''-methylbutyloxycarbonyl)phenylmethyloxy]-6-decyloxynaphthalene. Melting point: 89°C. Fig.1 shows a chart of ¹H-NMR spectrum (270 MHz, CDCl₃) of the compound obtained. As is clear from Fig. 1, this compound showed a specific pack as mentioned below. δ (PPM) 0.9 - 1.0 (m, 9H, -CH₃) 1.3 - 1.8 (m, 21H) 4.0 - 4.2 (m, 4H) 7.1 - 8.1 (m, 10H,aromatic) Further, this compound had a value of mass spectrum of MS;M/e=504(P) . It was confirmed that this compound has a smectic C phase in the range of 38-47°C. The phase transition temperatures of this compound are shown below. In the above, Cry represents a crystal phase, SmA represents a smectic A phase, SmC represents a chiral smectic C phase, Iso represents an isotropic liquid, and each temperature indicated represents the phase transition temperature in the direction of the arrow. Example 2 [Synthesis of liquid crystal compound] Preparation of 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-decyloxynaphthalene First step To a mixture comprising 0.66 g of 85% KOH, 40 ml of ethanol and 0.2 ml of water were added 3.76 g (20 mmol) of 2-carboxy-6-hydroxynaphthalene and 3.12 g (10 mmol) of decyl tosylate, and the mixture was stirred at 90°C for 15 hours. Subsequently, this reaction liquid is poured into water and neutralization with hydrochloric acid. After neutralization, the reaction product was extracted with ether, the extract liquid was washed with water and concentrated. Using column chromatography, from this concentrated liquid, 1.6 g of 6-decyloxy-2-carboxynapthalene was separated. Second step In an anhydrous tetrahydrofuran (THF), 1.0 g (26.4 mmol) lithiumaluminum hydride was reacted with 1.348 g (4.1 mmol) of the 6-decyloxy-2-carboxynaphthalene obtained in the first step in an argon atmosphere at room temperature for 2 hours, and further reacted under reflux with heating for 1 hour. After cooling, the reaction was diluted with 150 ml of ether, and then excess lithiumaluminum hydride was decomposed by the addition with saturated Na₂SO₄ water to stop the reaction. The decomposed lithiumaluminum hydride was removed by filtration, and the filtrate was dried over anhydrous Na₂SO₄, followed by removal of the ether. The residue obtained by removal of the ether was recrystallized from a mixed solvent of hexane and ethyl acetate (mixing volume ratio= 10 : 1) to obtain 1.078 g of 6-decyloxy-2-hydroxynaphthalene. Yield: 85.8 %. Third step In chloroform, 84 mg (0.43 mmol) of the 6-decyloxy-2-hydroxymethylnaphthalene and 235 mg (2.57 mmol) of activated manganese dioxide were stirred at room temperature for 12 hours. The rection solution was filtered, and the filtrate was concentrated. The crude product obtained was purified by means of silica gel thin layer chromatography to obtain 72.2 mg of 2-formyl-6-decyloxynaphthalene as white needles. Fourth step In the usual way, methyl 4-bromomethylbenzoate was obtained by reaction of p-bromomethylbenzoic acid with methanol in the presence of an acid catalyst. In benzene, 2.61 g (11.4 mmol) of methyl 4-bromomethylbenzoate obtained above and 3.0g (11.4 mmol) of triphenyl phospine were heated under reflux to undergo reaction. After cooling. the crystals formed were collected by filtration, Recrystallization of the crystals from benzene gave 3.43 g of (4-methyloxycarbonyl)phenylmethylphosphonyl bromide as white needles. Fifth step In methylene chloride were dissolved 475 mg (2.47 mmol) of 2-formyl-6-decyloxynaphthalene and 1215 mg (25 mmol) of the (4-methyloxycarbonyl)phenylmethylphosphonyl bromide obtained the fourth step. To this solution was added dropwise an aqueous potassium hydroxide solution, and after the completion of the reaction, the reaction liquid was concentrated. This concentrate was purified by means of silica gel thin layer chromatography to obtain 519 mg (1.7 mmol) of 2-[2'-(4''-methyloxycarbonylphenyl)ethenyl]-6-decyloxynaphthalene as a mixture of cis form and trans form. Sixth step To ethanol were added 519 mg(1.7 mmol) of the 2-[2'-4''-(methyloxycarbonylphenyl)ethenyl]-6-decyloxynaphthalene obtained in the fifth step and 52 mg of palladium carbon catalyst (palladium content: 5 % by weight), followed by bubbling with hydrogen gas at room temperature for 5 hours. Subsequently, the reaction liquid was filtered, and the filtrate was concentrated. Separation of the concentrated reaction liquid by means of column chromatography gave 492 mg (1.1 mmol) of 2-[2'-(4''-methyloxycarbonylphenyl)ethyl]-6-decyloxynaphthalene. Seventh step To 40 ml of benzene were added 492 mg (1.1 mmol) of the 2-[2'-(4''-methyloxycabonylphenyl)ethyl]-6-decyloxynaphthalene obtained in the sixth step, 0.61 ml (8.5 mmol) of R-2-methylbutanol and 0.1 ml of t-butoxycalcium, and this reaction liquid was refluxed for 25 hours to undergo reaction. After cooling, the reaction product was extracted with ether. The extract was washed with an aqueous sodium hydrogencarbonate solution and further with water, and then concentrated. The concentrate obtained was subjected to separation by means of column chromatography obtain 485 mg of white solid powder. This crystals were assayed and confirmed to be 2-[2'-{4''-(R-2'''-methylbutyloxycarbonyl)phenyl}ethyl]-6-decyloxynaphthalene. Melting point : 48°C. Fig.2 shows a chart of ¹H-NMR spectrum (270 MHz, CDCl₃) of the compound obtained. As is clear from Fig.2, this compound showed a specific pack as mentioned below. δ (PPM) 0.7 - 1.0 (m, 9H, -CH₃) 1.1 - 1.8 (m, 21H) 3.3 (d, 2H) 3.7 - 4.1 (m, 4H) 6.9 - 7.9 (m, 10H,aromatic) Furthermore, a value of mass spectrum of this compound was MS;M/e=502(P) . It was confirmed that this compound has a smectic A phase in the range of 0-48°C. A phase transition temperature of this compound is shown below. Example 3 A liquid crystal cell was prepared in the following manner. Polyimide coating was conducted on a glass substrate provided with ITO transparent electrode film. That is, the polyimide (PIQ-5400™, a product of Hitachi Kasei Kogyo kk) was coated on the ITO transparent electrode by spin coating method. The polyimide was diluted with N-methylpyrrolidone to a 1.2% solution which was then spin-coated at 2000 rpm. The polyimide solution thus coated was cured by heating at 325 °C for 30 minutes, whereupon a polyimide film of 150 to 200 Å in thickness was formed. The polyimide film was then rubbed with a nylon cloth in one direction, thereby imparting an ability of orientating the liquid crystal thereto. Two sheets of the thus-prepared polyimide film-coated glass substrates were put upon each other to prepare a cell for evaluation. An epoxy adhesive was applied to one of the polyimide film-coated glass substrates by means of silk screen printing so that two sheets of the substrates bond to each other and a gap of the cell is controlled. The epoxy adhesive used was prepared by mixing an adhesive base (LCB™, a product of EHC) with a curing agent (LCB-304B™, a product of EHC) and beads for controlling cell gap (GP-20™, a product of EHC) in the proportion of 138:30:3. One of the two sheets of the glass substrates mentioned above was coated with the epoxy adhesive and laminated to the other glass substrate in such a manner that the polyimide films face each other. The adhesive thus coated was cured under such curing conditions that heating was conducted at 50 °C for 15 minutes, at 60 °C for 15 minutes, at 70 °C for 15 minutes, at 80 °C for 15 minutes, at 125 °C for 30 minutes and at 170 °C for 60 minutes. The thus prepared cell having a gap of about 2 µm was interposed between two sheets of polarizing plates so arranged that polarizing directions were at right angles to each other. After charging the cell thus prepared with a liquid crystal compound, the liquid crystal cell was heated to 50 °C to bring the liquid crystal compound to a liquid state. The liquid crystal cell was gradually cooled at a cooling rate of about 1 °C/min by temperature gradient method, whereby good initial orientation was obtained. When an electric field was applied to the cell in smectic A phase, there could be observed induced tilt (change in the orientation direction of the major axis of the molecule). At 0 °C, there were obtained a light (ON) state at +30V and a dark (OFF) state at -30V. The contrast of brightness between the light state and the dark state was 4. Optical response time measured at 0 °C was 52 µseconds. Thus, there could be formed the display device having excellent characteristics by virtue of using the substituted naphthalene compound as mentioned above. Example 4 A liquid crystal cell having a gap of about 2 µm, prepared in the same way as in Example 3 was interposed between two sheets of polarizing plates arranged so that polarizing directions were at right angles to each other. The liquid crystal cell was charged with a liquid crystal composition comprising a mixture of 43 parts by weight of a liquid crystal A and 57 parts by weight of a liquid crystal B liquid crystal A being a compound of the invention. The mixture exhibited the following liquid crystal phase. The liquid crystal cell was heated to 70 °C to bring the compounds into a liquid state. The cell was then gradually cooled at a cooling rate of 1 °C/min by temperature gradient method, whereby good initial orientation could be obtained. When an electric field was applied to the liquid crystal cell in a state of smectic A phase, there could be observed induced tilt (change in the orientation direction of the major axis of the molecule). At 0 °C, there were obtained a light (ON) state at +30V and a dark (OFF) state at -30V. The contrast of the brightness of the light state and the dark state was 5. Optical response time at 0 °C was 520 µseconds. Thus, there could be formed a display device having excellent characteristics by virtue of using the substituted naphthalene compound as mentioned above. The temperature range of the liquid crystal B was as follows. Example 5 One sheet of a polarizing plate was placed on the outer side of a liquid crystal cell having a gap of about 2 µm, prepared in the same way as in Example 3. The liquid crystal cell was charged with a liquid crystal compound comprising a mixture of of 99 parts by weight of the liquid crystal A of the present invention and one part by weight of a dichroic dye of the following structure formula. The liquid crystal cell was heated to 50 °C to bring the compounds to a liquid state. The cell was then gradually cooled at a cooling rate of about 1 °C/min, whereby good initial orientation could be obtained. When an electric field was applied to the liquid crystal cell in a state of smectic A phase, there could be observed induced tilt (change in the orientation direction of the major axis of the molecule). The dichroic dye caused also change in direction of the major axis of the molecule with the induced tilt of the liquid crystal. At 0 °C, there were obtained a light (ON) state at +30V and a dark (OFF) state at -30V. The contrast of the brightness of the light state and the dark state was 4. Optical response time measured at 0 °C was 780 µseconds. Thus, there could be formed a display device having excellent characteristics by virtue of using the liquid crystal composition containing the substituted naphthalene compound as mentioned above.

Claims: A substituted naphthalene compound of formula [I]. wherein R¹ represents alkyl of 1-18 carbon atoms, R² represents alkyl of 1-18 carbon atoms, X is -OCH₂- or -CH₂CH₂-, and n is 0 or 1. A substituted naphthalene compound according to claim 1 in which R² is alkyl of 2 or more carbon atoms, the carbon atom to which R² is attached being optically active. A substituted naphthalene compound according to claim 2 wherein n is 1, R² is ethyl, R¹ is decyl, and X is -OCH₂-. A substituted naphthalene compound according to claim 2, wherein n is 1, R² is ethyl, R¹ is decyl, and X is -CH₂CH₂-. A liquid crystal composition containing a substituted naphthalene compound as defined in any one of the preceding claims. Use of a liquid crystal composition as claimed in claim 5 in a liquid crystal display device.

Inventors: NISHIYAMA SHINICHI, YAMADA TOHRU, YAMANAKA TOORU, YAMAOKA HIDEO, NISHIYAMA, SHINICHI, YAMADA, TOHRU, YAMANAKA, TOORU, YAMAOKA, HIDEO
Applicants: MITSUI PETROCHEMICAL IND, MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1989
Main classification: C07C69
IPC codes: C09K19