DE10229169B4 - New discotic compounds and methods of making optically anisotropic elements - Google Patents

Abstract

Nematic discotic compound with a star-shaped structure of the general formula I, where DS represent independent structural units selected from structural units of the general formula V

Description

The present invention relates to novel discotic compounds which form a stable nematic phase and a process for producing optically anisotropic elements containing such compounds and which are known in the art. a. can be used as optical compensation layers.

Optical compensation layers are used to reduce the viewing angle dependence of LCD display elements. For this purpose, it is advantageous if the compensation layers have a negative birefringence and the optical axis is inclined.

Previous solutions, such. B. specially stretched and cut polycarbonate films ( EP 576,304 ) or with polymeric liquid crystals ( EP 628,847 ) are difficult to produce on an industrial scale with stable quality parameters and their effect is not optimal.

Various discotic liquid crystals ( EP 646 826 . WO 96/37804 ) which form a stable discotic nematic phase and are arranged on alignment layers in a preferred direction. Discotic liquid crystals have long been known (C. Destrade, et al., Physics Lett, A, Vol. 78, p. 82, 1980) and consist of a rigid disc-shaped central part, preferably triphenylene, truxene or phthalocyanine and symmetrically arranged longer-chain substituents.

In order to use such discotic liquid crystal materials for improving the viewing angle dependence of LCD displays, they must be applied to a base (glass, polymer material preferably cellulose triacetate) by conventional methods such as vapor deposition, dip casting or spin coating. An optically anisotropic layer only forms when the molecules in the discotic nematic phase are uniformly aligned on the support. This can be done by electrical or magnetic methods or preferably by applying an orientation layer.

The orientation layer is placed directly onto the substrate or, if appropriate, onto a previously applied adhesion-promoting layer by conventional casting processes. As orientation layers predominantly polyimide layers are used. On the orientation layer is then by mechanical action (rubbing, brushing) creates a preferred direction along which arrange the discotic liquid crystalline compounds during application. In this case, the discotic compounds are inclined with respect to the pad, wherein the angle of inclination changes continuously as a function of the layer thickness.

The discotic nematic phase generated upon heating the layer can be frozen by polymerization. The discotic materials can be directly crosslinked by active side chains or a mixed monomer is polymerized.

The likewise possible fixation by transition into a glassy state by slow cooling entails the risk of crystallization at room temperature in the discotic monomers used hitherto.

Materials found to be suitable from the group of star-shaped discotic materials. They consist of a central linker unit and additionally have discotic units in the side chains.

So far, only star-shaped discotic materials are known which form a stable columnar discotic phase and have good properties as organic photoconductors ( DE 41 26 496 ).

The WO 96/00208 describes oligomeric liquid-crystalline triphenylene derivatives and their use as charge transport substances in electrophotography.

In the DE 43 32 733 A1 are liquid crystalline compounds, in particular for use in displays or for the production of light-reflecting layers disclosed.

The EP 1 153 019 B1 deals with photoactive propane derivatives and orientation layers.

In the DE 41 09 262 A1 Dialkinmalonatderivate and their use are described.

The DE 196 29 841 A1 describes a rectangular optical compensatory sheet, a method for its manufacture and liquid crystal displays.

Proceeding from this, it was an object of the present invention to provide star-shaped discotic compounds having a discotic nematic phase, which retain this property permanently by cooling in the glass state at room temperature.

This object is achieved by the nematic discotic compounds having the features of claim 1 and the method for producing optically anisotropic elements having the features of claim 2. The other dependent claims show advantageous developments. In claim 9 a possible use is shown.

bereitgestellt. Hierbei stellen die Gruppen DS voneinander unabhängige Struktureinheiten dar, die eine stabile diskotisch nematische Phase aufweisen. Die Gruppe L stellt einen Linker dar, der die einzelnen Struktureinheiten DS miteinander verbindet.According to the invention nematic discotic compounds with star-shaped structure of the general formula I.

provided. Here, the groups DS represent independent structural units which have a stable discotic nematic phase. The group L represents a linker which connects the individual structural units DS with one another.

The star-shaped discotic compounds each form a nematic discotic (N _D ) liquid-crystalline phase. Upon cooling to room temperature, no recrystallization occurs. As a result of the heating process, a glass stage is reproducibly found before the transition to the isotropic phase takes place. The compounds show long-term stable optical transparency and birefringent properties.

Preferably, the groups DS represent aromatic moieties having a nematic discotic phase. At the same time, the groups DS are connected to the linker via an ester bridge. The groups DS preferably have oxycarbonyl and / or carbonyloxy functionalities for forming the ester bridges.

mit R = unabhängig voneinander H, Alkyl (C₁-C₁₂), Alkoxy (C₁-C₁₂), Y = O und n = 7 bis 17As the structural unit DS according to the invention the following radical is suitable:

with R = independently of one another H, alkyl (C ₁ -C ₁₂ ), alkoxy (C ₁ -C ₁₂ ), Y = O and n = 7 to 17

mit Z = CO oder
der allgemeinen Formel VIII

mit p = 1 und Z = CO.As linker L according to the invention the following groups are suitable:

with Z = CO or
the general formula VIII

with p = 1 and Z = CO.

The groups Y and the groups Z are in each case coordinated so that ester bridges are formed between DS and the linker.

The invention also provides a process for producing optically anisotropic elements in which a transparent substrate, optionally provided with an orientation layer, is coated with a nematic discotic layer. It is essential to the invention here that the nematic discotic layer is composed of the nematic discotic compounds according to claim 1.

To produce a birefringent film, the materials were spin-coated in a suitable solvent onto a transparent support which optionally has an orientation layer. Suitable solvents are benzene, toluene, alkyl halides, such as. B. chloroform. The solvents may be used singly or in combination.

It is likewise possible to apply the materials by means of other, in particular continuous, coating methods (such as, for example, spray, dip or roll coating methods).

Subsequently, the layer is heated to the temperature required for forming the discotic nematic phase and then cooled to room temperature. As a support, any transparent material such. As glass or triacetyl cellulose are used, as long as it has a low self-birefringence. Also, materials with greater self-birefringence such as polycarbonate or polysulfone are einsetztbar if the substrate is made optically isotropic in the preparation by suitable treatment.

To ensure a preferred orientation of the star-shaped discotic compounds on the substrate, it is advantageous to accommodate an orientation layer between the substrate and the film. Examples of the orientation layer are polymers, such as. As polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, polyvinyl alcohol, polyester, polyimide or polycarbonate. Preferably, polyimide is used. The orientation layer is pretreated by rubbing according to the invention.

Likewise suitable are obliquely deposited inorganic alignment layers containing SiO ₂ , TiO ₂ , MgF ₂ or ZnO.

The preferential orientation can also be achieved by the action of obliquely directed electric or magnetic fields at temperatures which enable the formation of the discotic nematic phase.

In the films produced in this way, the star-shaped discotic compounds are arranged in the direction predetermined by the orientation layer and inclined with respect to the substrate plane at an angle of 0 ° <γ <90 °, preferably 10 ° <γ <25 °.

Likewise, mixtures of the star-shaped discotic compounds according to the invention or mixtures of the star-shaped discotic compounds according to the invention with non-discotic nematic compounds for varying the use temperature can be present in the films.

The films with birefringent properties produced on the basis of the star-shaped discotic compounds provided according to the invention can be used in optoelectronic components such as, for B. optical compensators for LCD displays are used.

The invention will be illustrated by the following examples, without limiting them to these embodiments.

example 1

Preparation of star-shaped discotic compounds:

Benzene-1,3,5-tricarboxylic acid tri- (11- (pentakis ((4-propylphenyl) ethynyl) phenoxy) undecyl) ester

1.17 g (1.2 mmol) of 11- {pentakis [(4-propylphenyl) ethynyl] phenoxy} undecan-1-ol are dissolved in 10 ml of abs. CH ₂ Cl ₂ dissolved (N ₂ , exclusion of moisture). To the solution 5 ml abs. Pyridine and 10 mg (0.1 mmol) of 4-dimethylaminopyridine were added. Then, with stirring at room temperature, a solution of 100 mg (3.77 mmol) of benzene-1,3,5-tricarboxylic acid trichloride (trimesic acid chloride) in 10 ml of abs. Dichloromethane added dropwise. After stirring for 24 hours at room temperature under N ₂ atmosphere, the mixture is washed once with water, three times with 1N HCl and a further two times with water (until the neutral reaction) and concentrated by evaporation with Na ₂ SO ₂ . The crude product is purified by flash chromatography (eluent: petroleum ether / ethyl acetate 10: 2).
Yield: 0.79 g (68%)
Thermal conversion data (DSC, 2nd heating at 10 K / min, data in ° C):
T _g 24 N _D 142 I
(T _g : glass transition temperature, N _g : nematic-discotic, I: isotropic)
IR (KBr): v = 2200 (C≡C), 1750 (C = 0) cm ^-1 ,
¹ H-NMR (CDCl ₃ ): δ = 0.92-0.97 (m, 45H, CH ₃ ), 1.25-1.91 (m, 84H, CH ₂ ), 2.60 (t, 30H, CH ₂ , J = 7.5 Hz), 4.34 (t, 6H, CH ₂ , J = 6.5 Hz), 4.35 (t, 6H, CH ₂ , J = 6.2 Hz), 7.15-7.17 (m, 30H, phenyl), 7.49-7.54 (m, 30H, phenyl ), 8.83 (s, 3H, phenyl) ppm.

Example 2

filming

From the compound according to Example 1, a solution with a concentration of 7.5% in a mixture consisting of chloroform and toluene (9: 1 parts by volume) was prepared. The solution is cleaned by a 0.2 μm filter. From this solution, a spin-coating film is produced on a glass substrate coated with rubbed polyimide SE-3140 (Merck) at a rotation speed of 1000 rpm and a rotation time of 30 seconds. The mixture is then spun for 60 seconds at a speed of 2000 revolutions per minute. The film is then post-dried in vacuo at 45 ° C for 24 hours. The layer thickness of the thus prepared film is 1 μm. However, the layer thickness can be varied between 500 nm and 1.5 μm by means of the spin-coating parameters (concentration of the solution, rotational speed, duration of the rotation).

Example 3

Optically anisotropic element

A spin-coating film according to Example 2 is heated at a heating rate of 10 K / min to 120 ° C and held at this temperature for 5 min. It is then cooled to 100 ° C. at 1 K / min and annealed at 100 ° C. for 30 min. Subsequently, the film is cooled to room temperature. Cooling to room temperature can be carried out at a controlled cooling rate, but also without temperature control. The Schlieren textures typical of a nematic-discotic liquid-crystal phase, which are attributable to the formation of domains with different orientation of the molecule director, are not detectable by polarization microscopy after the thermal treatment of the film. Thus, the molecules are uniformly arranged on the orientation layer. The film has macroscopic out-of-plane anisotropy between crossed polarizers. The determination of the angle of inclination of the discotic molecular groups was carried out by measuring the optical phase difference as a function of the angle of incidence of the incident light.

The curve in Figure 1 shows the change in the optical phase difference as a function of the angle of incidence of the incident light (oriented film of the benzene-1,3,5-tricarboxylic acid tri- (11-pentakis ((4-propylphenyl) ethynyl) phenoxy) undecyl). ester on polyimide; Layer thickness 1.0 μm).

The asymmetric course of the curve indicates a tilted molecular orientation. The angle of inclination between the planes of discotic molecular disks and the substrate is on average 14 °.

Claims (9)

Nematic discotic compound with star-shaped structure of general formula I.

wherein DS represent independent structural units selected from structural units of general formula V

with R = independently of one another H, alkyl (C ₁ -C ₁₂ ), alkoxy (C ₁ -C ₁₂ ), Y = O and n = 7 to 17, which have a stable discotic nematic phase and via a linker L of the general Formula VI

with Z = CO, the general formula VII,

with Z = CO or the general formula VIII

with p = 1 and Z = CO, are interconnected. Process for the production of optically anisotropic elements, in which a transparent substrate optionally provided with an orientation layer is coated with a nematic discotic layer, characterized; in that the nematic discotic layer is composed of nematic discotic compounds according to claim 1. A method according to claim 2, characterized in that the discotic compound in an organic solvent, for. As benzene, toluene or alkyl halides, dissolved and then deposited by spin-coating. A method according to claim 2, characterized in that the deposition of the discotic compound by means of spraying, dipping or roll coating process takes place. Method according to at least one of claims 2 to 4, characterized in that as a substrate materials with low self-birefringence, z. As glass or triacetyl cellulose can be used. Method according to at least one of claims 2 to 4, characterized in that as substrate materials with high self-birefringence, z. As polycarbonate or polysulfone can be used, wherein the materials are made optically isotropic by pretreatment. Method according to at least one of claims 2 to 6, characterized in that an orientation layer of polymer materials, for. As polymethyl methacrylate, acrylic acid / methacrylic acid copolymer, polyvinyl alcohol, polyester, polyimide or polycarbonate is used. Method according to at least one of claims 2 to 6, characterized in that an orientation layer of inorganic materials, such as SiO ₂ , TiO ₂ , MgF ₂ or ZnO is used. Use of the optically anisotropic elements produced by the process according to at least one of claims 2 to 8 as optoelectronic components.

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