HK1007195B - Optical element for generating short wave laser light - Google Patents

Description

The invention relates to an optical element for the efficient generation of shortwave laser light by frequency conversion with a conductive layer of a liquid crystal material, which has a periodic structure allowing a quasi-phase adjustment of a guided laser beam, the periodicity of the spatial structure being defined by the coherence length lc = π/Δβ of the material, where Δβ = β0 (2ω) - β0 (ω), with ω = fundamental wave frequency, 0 = mode of zero order and β = mode constant. The invention also relates to compounds suitable for the production of this layer.

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Err1:Expecting ',' delimiter: line 1 column 170 (char 169)

Since the conversion efficiency is quadratically dependent on the power density of the base wave, the relatively low light intensities of the available laser diodes require unpractical large and expensive nlo crystals. Much more favorable conditions are when waveguide configurations can be used instead of such crystals for conversion. The first is to exploit the dispersion properties of different modes in the waveguide.This method is suitable for the situation in double-breaking crystals and is only applicable to materials with suitable double-breaking. In this case, conversion between modes of the same order (e.g. TE → TM) and thus large values of the overlap integral are possible.3. Use of periodic structures. This method, known as quasi-phasing, modulates the nonlinearity of the periodic structure of the wave conductor.The conversion between modes of the same order (e.g. TEo(ω) → TEo(2ω)) also takes place.

The following classes of substances are, in essence, the most suitable χ (x) active materials for the above-mentioned waveguides according to the current state of the art: 1. monocrystalline inorganic layers. A typical example is LiNbO3, which has been studied particularly intensively, for example, because of its large nonlinear coefficients d31 = - 5.95 pm/V and d33 - 37 pm/V and is often used as a reference material for the assessment of nlo substances. 2. χ(2) -active long-wall blocket multi-layers. These have the disadvantage of being unstable, especially not temperature stable.

US-A-4,865,406 describes such frequency doubling optical waveguides consisting of thin layers of polished liquid crystal polymer. The waveguide layers of nlo material have a periodic structure that allows a quasi-phase adjustment of a guided laser beam. Such polished layers have a strong tendency to relaxation.

EP-A-338 845 is a known nlo material suitable for frequency doubling, a FLC polymer with very low χ(2) activity, endowed with known nlo chromophores, which does not achieve the nlo efficiency necessary for a technically useful application in such a guest-host system.

The purpose of the invention is to provide a frequency converting optical element whose conductive layer does not have the above disadvantages.

According to the invention, this was achieved by an optical element of the type described at the outset, in which the periodicity of the spatial structure is twice the coherence length lc and the liquid crystalline material is either a ferroelectric, χ(2) active mixture of chiral molecules with an nlo-molecular group, whose χ(2) active axis is oriented essentially along the longitudinal axis of the chiral molecule, and liquid crystal molecules forming Sc phases, or a χ(2) active, Sc*-phase forming side-chain copolymer, which contains χ (a) chiral side-chains with an nlo-molecular group, whose active axis is oriented essentially along the longitudinal axis of the sides.

In an alternative embodiment of the invention, the material allows phase adjustment of the d21 component of the nlo tensor due to its double refractive property.

In another embodiment, the ferroelectric liquid crystal material forms an SC* phase or a higher order ferroelectric phase which can be dipolarly oriented in the electric field.

In another embodiment, the ferroelectric liquid crystal material forms an SC* phase oriented by bistable homogeneous edge forces, in the SSF configuration with materials having a large helical height or with SBF materials.

Preferably, the ferroelectric liquid crystal material consists of a mixture of chiral nlo-active molecules forming SC* phases.

Preferably, the dipole orientation is fixed by cooling below the glass temperature.

In another embodiment, the optical element operates as an electro-optical switch or light modulator in the spectral range 1300 to 430 nm by exploiting the pockle effect.

The mixture preferably has the phase sequence I-Chol-SmA-SC* glass. The element can be operated in the SC* phase in such a way that when an electric field is applied the χ(2) property is activated and disappears when the electric field is switched off.

The optical element may be used specifically for the frequency doubling of laser light of wavelength 850-1300 nm, preferably 900-1300 nm, and may be optically coupled to form a frequency doubling module with a laser diode emitting in the range 850-1300 nm.

In another embodiment, the dipolar axis is perpendicular to the plane of the waveguide

Ferroelectric liquid crystals have the following very attractive properties for the use of nonlinear effects 2. order. They combine the property of relatively easy preparation and suitability for building the structures required for components, which characterizes the polished nlo polymers, with the characteristic property of noncentrosymmetric structure for χ(2) active single crystals.

In principle, both low molecular and polymer ferroelectric liquid crystals are candidates for χ(2) active materials, since they assume a non-centrosymmetric structure in the ferroelectric phase, e.g. the chiral smectic C phase (SC*). Under suitable conditions, these substances form a helix structure in the SC* phase, which can be transferred to a flat dipolar oriented structure, e.g. by applying a small electric field.

These properties of ferroelectric liquid crystals have been well studied and form the basis for their use in liquid crystal displays (LCDs), for example, liquid crystal displays based on the so-called surface stabilized ferroelectric effect (SSF) (see Clark N.A. et al., Appl.Phys.Lett. 36 (1980), 899), and the so-called short-pitch bistable ferroelectric effect (SBF) (see J. et al., Jpn.J.Appl.Phys. 30 (1991) 741).

The low molecular weight of χ(2) active films from low-molecular ferroelectric liquid crystal mixtures has been neglected because all previously published SHG studies on ferroelectric liquid crystal mixtures with such low non-linear coefficients (e.g. d22 = 0.027 pm/V; d23 = 0.07 pm/V; d16 = 0.0026 pm/V Ref. 4) show that their technical use as SHG material did not seem to make sense.

Ferroelectric liquid crystal mixtures consist either of chiral mesogenic molecules that induce SC* phases or of a combination of mesogenic molecules that form Sc phases with chiral donor substances that are capable of inducing the SC* phase.

Efficient χ(2)-active ferroelectric liquid crystal materials can now be produced by incorporating nlo-active structural elements with high second order hyperpolarizability into the above-mentioned chiral substances, so that the axis relevant for nonlinearity is dipolarised in the ferroelectric liquid crystal configuration.

It is known that groups of molecules of the form A Π D, where A means an electron acceptor, Π means a bridge with delocalised electron system and D means an electron donor, are hyperpolarizable along the donor-acceptor axis.

Since mesogenic molecules that form ferroelectric liquid crystal phases are rod-shaped (length extension >> width), the nlo-molecule group built across the director must be compact, as it would otherwise destroy the liquid crystal phase.

In addition, there is a direct correlation between the magnitude of the nonlinearity and the shortwave limit of the transparent spectral range of the nlo molecule.

For example, 5-amino-2-nitro-1,4-phenylenes have been found to be excellent as an nlo-active structural element, and surprisingly, the incorporation of this nlo-structural element into a suitable smectogenic molecule has been found to lead to the formation of the SC* phase.

It was also shown that the axis relevant for the non-linearity of the nlo group is highly dipolar in the SC* phase if the nlo unit is installed as close as possible to the chiral group of the liquid crystal molecule or chiral dopant molecule.

SHG measurements (1064 nm-532 nm conversion) yield values of the order of 10 pm/V and 5 pm/V for the nonlinear coefficients d22 and d21. These values are 103 times greater than the highest data published to date and are quite comparable to those of LiNbO3. These large nonlinear coefficients correspond to the observed high values of spontaneous polarization (up to 700 nC/cm2).

These are p-nitro-aniline derivatives of the general formula For the purposes of this Regulation: X1, X2 :one -NO2 and the other -NR5R6, where R5 and R6 are independently H or Ni-alkyl;R3, R4 :independently H, F, Cl, Br, NH2, NO2, CN, Ni-alkyl or Ni-alkyl-coxy, provided that X1 is different from R4 and X2 is different from R3;R1:Chiral alkyl or cycloalkyl, wherein, independently of each other, one or two non-adjacent -CH2 groups can be replaced by O, S, -COO-, -OOC-, -HC=CH-, and in the aliphatic residue by -CC-, and which can be simply or repeatedly substituted with Cl, Federal, CN, Ni-alkyl and Ni-alkyl, giving the mass,The centre of chirality is located in an alkyl chain at the first or second C-atom and a cycloalkyl residue is located at a ring C-atom;A1:1 to 4 hexagonal rings directly linked to each other or to the p-nitroaniline ring and/or at one or more places, if any, via -CH2-CH2, -CH2O, -CH2O, -OCH2-, -COO-, -OOC-, -COS-, -SOC-, -CH=CH-, -CC-, -N=N-, -N=NO-, -ON=N-, -N=N=CH=CH, or polyols, in which a -CH2CH2 group is replaced by a -COO-, -CH-CH-CH1, -CH-CH-CH-CH and -C/CH group, or by a mono- or non-substituted oxide, or, if applicable, by a mono- or non-substituted polyols, or, if necessary, by a substituent, a substituent or a substituent.4-phenyls in which one or two -CH groups may be replaced by nitrogen, or 1,4-cyclohexyls in which one or two -CH2 groups (preferably not adjacent) may be replaced by O or S, or a -CH2CH2 group by -CH=CH- or naphthalene-2,5-diyl, decalin-2,6-diyl, tetralin-2,6-diyl, thiadiazolyl or oxodiazolyl;Z1:a simple covalent bond, -CH2-CH2, -CH2O, -CH2O, -COO2, -OOC2, -COSSO, -C, -CH=CH2, -CC, -N=N, -N=NO, -N=N, -N=NCH=NCH, -CH=CH or -CH-CH, but may be a -C, -C, -O2, -C, -O2, -C, -O2, -C, -O2, -C, -O2, -C, -O2, -C, -O2, -C, -O2, -C, -O2, -C, -O2, -C, -O2, -C, -O2, -C, -O2, -O2, -C, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, -O2, - where X1, X2, R3 and R4 have the values described above;n:the number 0 or 1;R2:chiral or achiral alkyl or cycloalkyl wherein,independently of each other, one or more -CH2 groups may be replaced by O, S, -COO, -HC=CH-, and in the aliphatic residue by -CC or 1,4-phenyls, and which may be simply or repeatedly replaced by F, Cl, CN, niederalkyl and niederalcoxy, provided that any chiral centre present in an alkyl chain is at the first or second C atom and in the case of a cycloalkyl residue at a ring C atom, or, where n is 0, the group is also replaced by where X1, X2, R1, R3, R4 and A1 have the above meanings and m is an integer from 6 to 16, where one or two non-adjacent -CH2 groups are separated independently by O,S, -COO, -CH=CH or -CC- can be replaced.

Compounds of formula I, in which R2 chirales or achiralic alkyl or cycloalkyl worin, independently of one another, can have one or two non-adjacent -CH2 groups replaced by -O-, -S-, -COO-, -HC=CH-, and in the aliphatic residue also -CC-, and which can be simply or repeatedly replaced by F, Cl, CN, niederalkyl and niederalkoxy, are preferred, i.e. the measure of the presence of any chiral centre in an alkyl chain at the first or second C-atom and in a cycloalkyl residue at a ring C-A, or, if n is 0, the measure of the presence of any chiral centre in an alkyl chain at the first or second C-atom, or where X1, X2, R1, R3, R4 and A1 have the above meanings and m is an integer from 6 to 16 in which one or two non-adjacent -CH2 groups are independently replaced by -O, -S, -COO, -HC=CH- or -CC-.

In the compounds of formula I above, if desired, the residues R1 and R4 and/or, if n=1, R2 and R3 or R2 and R4 may also be interchanged.

Err1:Expecting ',' delimiter: line 1 column 56 (char 55)

Err1:Expecting ',' delimiter: line 1 column 57 (char 56)

Err1:Expecting ',' delimiter: line 1 column 56 (char 55)

Err1:Expecting ',' delimiter: line 1 column 56 (char 55)

Err1:Expecting ',' delimiter: line 1 column 56 (char 55)

The nonlinear optical compounds of the invention all contain a multiple substituted p-nitroaniline group which, when combined with known liquid crystal building blocks, gives the outstanding properties of these classes of compounds described above. P-nitroanilines with suitable substitution patterns are available commercially or can be produced in a known way. DMAP = 4-dimethylamino) pyridine In these schemes the single substituents have the meaning given above

These include molecules which themselves form SC* phases and can therefore be used as χ (((2) active waveguide material.

A second group consists of molecules which, although not themselves producing SC* phases, induce SC* phases in suitable SC matrix mixtures as chiral dopants.

Furthermore, compounds of formula I can also be used as monomers to form LC side chains of polymers having a ferroelectric phase. where X1, X2, R3, R4, R1 and A1 have the meanings above and R7 means a chiral or achiral alkyl in which, independently of one another, one or more of the -CH2 groups can be replaced by -O, -S, -COO, -HC=CH, -CC or 1,4-phenyls and which can be simply or repeatedly substituted with F, Cl, CN, niederalkyl and niederalcoxy.

Compounds of formula Ia are particularly preferred for the formation of polymeric χ(2) active materials, characterised by the fact that R7 is finitely polymerizable, e.g. by one of the following polymerizable groups: or The invention also covers LC side-chain polymers which can be produced, for example, by polymerization of acrylic acid derivatives, styryl derivatives and the like, or by polymer analogues reactions of alkenes to poly (methyl hydrogen siloxanes).

Surprisingly, among these nlo-active ferroelectric liquid crystal substances and mixtures, examples have been found which, at low temperatures, enter the glass state, freezing the dipolar order induced at higher temperatures in the SC* phase.

The LC side chain polymers produced from compounds of formula I, especially formula Ia, generally have the properties of monomers, i.e. they have a ferroelectric SC* phase and non-linear optical properties.

Another application of the presented substances and polymers is the exploitation of bistability in Surface Stabilized Ferroelectric (SSF) configurations. It is known that ferroelectric liquid crystals with sufficiently large helical height occupy bistable switching states in suitably prepared cells. The required large helical height can be realized by compensation in ferroelectric liquid crystal mixtures. In this case, a dipolar ordered homogeneous orientation favorable for the efficient generation of frequency conversion is obtained by the action of a short electrical pulse.

The same application is possible for the recently discovered Surface Bistable Ferroelectric (SBF) configuration, except that a small helical pitch is required, a condition that many of the above nlo substances meet.

Non-distable configurations, e.g. those of the so-called Deformed Helix Ferroelectric (DHF) type [see Beresnev L.A. et al., Liquid Crystals 5 (1989), 1171], are also considered for use as χ(2) active layers. Here, by applying a relatively low voltage, it is possible to orient the material dipolarly and thus make χ(2) active. This orientation is maintained only as long as the field is in motion.

The expert is aware that the above-described possibilities of use for the SC* phase are also applicable to the higher order ferroelectric phases (I*, F*, G*, H*, J*, K*).

The following illustrations describe the embodiments of the optical element of the invention. Fig. 1 a schematic cross-sectional representation of a waveguide element,Fig. 2 a schematic cross-sectional representation of an alternative waveguide configuration,

The optically nonlinear waveguide element shown in Fig. 1 has the structure of a liquid crystal cell consisting of two glass plates 1, 7 coated with transparent electrodes 2, 6. Above the electrode layers are polymer surface-treated cladding layers 3,5 with low refractive index. Between these two plates coated there is a ferroelectric liquid crystal 4. The thickness of the liquid crystal layer is fixed by (not shown) spacer holder. The cladding layers simultaneously cause the homogeneous orientation of the liquid crystal layer and allow the conduction of the optical waves in the liquid crystal. The Cladding layer 3 is a wide optical beam for the light to be reflected from the optical crystal 8 and 9 is a light source for the optical light to be reflected from the crystal into the fluid crystal.

In the manufacture, the space between the coated plates is filled with a ferroelectric liquid crystal mixture and oriented homogeneously in the electric field. In the ferroelectric phase, a dipole field is created which aligns the lateral dipoles of the ferroelectric liquid crystal molecules perpendicular to the plate plane. By cooling below the glass temperature of the mixture with an applied dipole field, the dipole oriented layer is frozen in the glass state.

In this waveguide, light from a long-wave laser diode is coupled to one of the grids embedded in the cladding layer in such a way that it propagates in a TE-like fashion as an extraordinary beam. With the correct choice of layer thickness and direction of propagation in the direction of the director, an effective propagation constant β (ω) of the TE-mode can be set so that the second harmonic wave produced by the nonlinear coefficient d21 passes through the layer in a TM-like phase. At the end of the cell, the base and the base wave frequencies are coupled via the second optical grid embedded in the cladding layer.

In addition to the lattice coupling described here, the methods known from the literature of prism and front coupling are also conceivable.

The optical waveguide element shown in Fig. 2 has a liquid crystal layer with a periodically polished structure. It also consists of two glass plates 1, 7 coated with transparent electrodes 2, 6. However, the electrodes have a lattice structure that allows the liquid crystal layer to be polished spatially by aging. Over the electrode layers are polymer surface-treated cladding layers with a low refractive index of 3.5. Between these coated plates is a ferroelectric liquid crystal 4.

The period is 2 lc = $\frac{\text{2π}}{\text{Δβ}}$ The light coupling is again done using the methods described in connection with Fig. 1. The light coupling is performed by using the most commonly used method of phase matching.

The optical antipodes of chiral compounds have the same phase conversion temperatures and absolutely the same values of entanglement but with opposite signs.

The abbreviations used to characterize the phase transitions have the following meanings: For crystalline, for chemical, for SA, SB, SC, etc. for chemical, A, B, C, etc.SC*, SF*-etc. for chiral, C, F, etc.N for nematic, for cholesterol, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for isotropic, for, for isotropic, for, for isotropic, for, for, for isotropic, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for, for,

Example 1

0,06 g 5-amino-2-nitro-4-[R]-2-octyloxy]benzoic acid, 0,1 g 4-heptyl-2-pyrimidinyl) phenol, 0,04 g 4-dimethylamino) pyridine were dissolved in 10 ml dichloromethane and the solution was stirred for 10 minutes with 0,07 g N,N'-dicyclohexylcarbodi triamid by portioning. The mixture was stirred, filtered and pressed at room temperature for 40 hours. Chromatography of the residue of silica gel with ethyl acetate/dichloromethane (vol.

The 5-amino-2-nitro-4-[R]-2-octyloxy]benzoic acid used as starting material was obtained as follows: (a) A solution of 10 g 4-hydroxy-3-nitrobenzoic acid and 370 ml of ethyl alcohol was presented and then hydrochloric gas was introduced for 5 hours. The reaction mixture was poured on 1300 ml of ice water and the resulting solid was filtered, washed and dried with 50% ethyl alcohol. This produced 8.5 g of ethyl 4-hydroxy-3-nitrobenzoic acid with a melting point of 68.5-69.5 °C as yellow crystals. (b) A mixture of 4 g ethyl 4-hydroxy-3-nitrobenzoic acid, 5.4 g of bolsulfonic acid (S) 2-octylester, 6.9 ml of calcium carbonate and 110 ml of ethyl ketone was heated overnight for return. The resulting reaction water was heated to 500 ml of diethyl alcohol and mixed with 500 ml of diethyl alcohol.Magnesium sulphate was dried, filtered and compressed. Chromatography of the silica gel residue with dichloromethane yielded 5.6 g ethyl 3-nitro-4-[R)-2-octyloxy) benzoate as yellow oil. c) A mixture of 1.7 g ethyl 3-nitro-4-[R)-2-octyloxy] benzoate and 50 ml ethyl alcohol was hydrated over 0.1 g platinum dioxide until the absorption of hydrogen was completed. The catalyst was filtered and the filter was heated. Chromatography of the silica gel residue with dichloromethane yielded 1.5 h ethyl 3-nitro-4-[R)-2-octyloxy] benzoate as yellow oil.The resulting solids were filtered and dried, yielding 0.20DThe resulting solid was separated from the refrigerated reaction mixture and dried, yielding 0.9 g of 3-acetylamino-4-[R]-2-octyloxy]benzoic acid. f) A solution of 0.4 ml hydrochloric acid and 0.3 ml acetic acid was portioned at 0 °C with 0.1 g of 3-acetylamino-4-[R]-2-octyloxy]benzoic acid, which was dissolved for 10 minutes at this temperature and then for 10 minutes at 20 °C, and then reduced to 6 ml of water without ice. The solid was then dissolved in 50 ml of concentrated 5-acetyl-4-octyloxy acid and mixed with the next 50 ml of the solution, and then dissolved in a 2-carbon phenol.

The following compounds can be produced by analogy: 4- (nonyloxy) -4-biphenylyl 5-amino-2-nitro-4-[R) 2-octyloxy) benzoate, Smp. (C-I) 140-142°C.4'-[4- (trans-4-pentylcyclohexyl) butyl]-4-biphenyl 5-amino-2-nitro-4-[R) 2-octyloxy] benzoatp-[trans-5-[R] 2-octyloxy] benzoatp-[trans-5-[E] 2-methyl-2-methyl-2-phenyl-2-m-dioxy-2-phenyl] 5-amino-2-nitroxy-4-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-methyl-benzoamino-benzoamino-benzoamino-benzoamino-benzoamino-benzoamino-benzoamino-benzoamino-benzoamino-benzoamino-benzoamino-benzoamino-benzoamino-benzoamino-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzoam-benzo

Example 2

A mixture of 5-dimethylamino-2-nitro-4-[R]-2-octyloxybenzoic acid, 4-dimethyl-2-pyrimidinyl) phenol, N,N'-dicyclohexylcarbodiimidine, 4-dimethylamino-pyridine and dichloromethane was analogically converted to example 1, resulting in 4-dimethyl-2-pyrimidinyl-phenyl 5-dimethylamino-2-nitro-4-[R]-2-octyloxybenzoate as yellow crystals with a melting point of 60-62 °C and [α] $\frac{\text{20}}{\text{D}}$ + 3° is equal to

The 5-dimethylamino-2-nitro-4-[R]-2-octyloxy]benzoic acid used as starting material was produced as follows: a) The esterification of 5-amino-2-nitro-2-[r]-2-octyloxy]benzoic acid was performed analogously to the synthesis of 4-heptyl-2-pyrimidinyl) phenyl 5-amino-2-nitro-4-[r]-octyloxy]benzoate, resulting in ethyl 5-amino-2-nitro-4-[r]-2-octyloxy-benzoate. b) The addition of 0.05 g of ethyl 5-amino-2-nitro-4-[r]-2-octyloxy]benzoate, 0.13 g of sodium hydrocarbonate, 2.5 ml of dimethyl alcohol and 0.5 ml of methyl methyl methidate was heated for 72 hours to return to the flow. The reaction table was filtered and then agglomerated.

The following compounds can be produced by analogy: The following substances are to be classified in the same category as the product:

Example 3

2-Amino-5-nitro-4-[R]-2-octyloxy]benzoic acid, 4-(5-heptyl-2-pyrimidinyl) phenol, N,N'-dicyclohexylcarbodiimid, 4-(dimethylamino) pyridine and dichloromethane were converted in an analogue manner to example 1, which yielded 4-(5-heptyl-2-pyrimidinyl) phenyl 2-amino-5-nitro-4-[R]-2-octyloxy]benzoate with a melting point of 105 °C with [α] $\frac{\text{20}}{\text{D}}$ This is + 19°.

The 2-amino-5-nitro-4-[r]-2-octyloxy]benzoic acid used as starting material was prepared as follows: (a) A solution of 20 g 4-toluidine and 400 g concentrated sulphuric acid (d = 1,84) was dripped at 0°C with a solution of 15 g hydrochloric acid (d = 1,48) and sulphuric acid (d = 1,84) and the reaction temperature was kept below 0°C. After completion of the addition, the reaction mixture was stirred for 1 hour at 0°C and then further diluted to 1200 ml of ice water so that the reaction temperature did not rise above 25°C. The reaction mixture was diluted with 4000 ml of water and then neutralized with sodium carbonate solution. The resulting solid was then portionly dried, hydrolyzed, crystallized and dehydrated with hydrogen peroxide.This produced 23 g 4-methyl-3-nitroaniline as yellow crystals. (b) A solution of 10 g 4-methyl-3-nitroaniline and 40 ml acetic anhydride was heated for 15 minutes to return. The cooled reaction mixture was added to 200 ml of water and cooled to 0°C, then stirred for 30 minutes at 0°C. The resulting solid was filtered and dried. This yielded 11 g 4-acetylamino-2-nitrotoluol. (c) A suspension of 10 g 4-acetylamino-2-nitrotoluol, 8 g magnesium sulfate and 500 ml of water was then heated for the return and served for 20 minutes with 24 g potassium permate and 8 g magnesium sulfate. The reaction triangle was then heated for 1.5 hours and returned to the flow,The result was 5.6 g 4-acetyllamino-2-nitrobenzoic acid with a melting point of 217-220°C.d) The dehydration of 4-acetyllamino-2-nitrobenzoic acid was carried out analogously to the synthesis of 5-amino-2-nitro-4-[r]-2-octyloxy]benzoic acid. This resulted in 4-amino-2-nitrobenzoic acid with a melting point of 244-245°C.e) A warm solution of 3 4-amino-2-nitrobenzoic acid, 5 ml of water and 3.6 ml of concentrated sulphuric acid was first cooled to 0°C, then mixed with 8.5 g of ice water and then mixed with 0.8 ml of sodium for 10 minutes and then mixed with water at 1.38°C. The solution was then cooled to 1.3 ml of water and then mixed with sodium for 1 hour.The resulting solid was filtered, yielding 1 g of 4-hydroxy-2-nitrobenzoic acid as yellow crystals with a melting point of 230 °C (decomposition).f) The esterification of 4-hydroxy-2-nitrobenzoic acid was performed to synthesize ethyl 4-hydroxy-3-nitrobenzoate. This yielded ethyl 4-hydroxy-2-nitrobenzoate.g) The esterification of 4-ethyl 2-hydroxy-2-nitrobenzoate was performed to synthesize ethyl 4-hydroxy-2-nitrobenzoate.[citation needed]20D=-9,4°.h) Hydration of ethyl 2-nitro-4-[(R)-2-octyloxy]benzoate was performed analogously to synthesis of ethyl 3-amino-4-[(R)-2-octyloxy]benzoate, resulting in ethyl 2-amino-4-[(R)-2-octyloxy]benzoate as a colourless oil.i) Hydration of ethyl 2-amino-4-[(R)-2-octyloxy]benzoate was performed analogously to synthesis of 3-amino-4-[(R)-2-octyloxy]benzoates. This resulted in 2-amino-4-[(R)-2-octyloxy]benzoates with melting point 94-95.5°C. The Acylic acid of 2-amino-4-[(R) 2-octyloxybenzoate was obtained analogously to 2-amino-4-[Amino-4-acetyloxy]benzoates.20D=-4.4°.k) The nitration of 2-acetylamino-4-[R)-2-octyloxy]benzoic acid was carried out in analogy to the synthesis of 5-acetylamino-2-nitro-4-[R)-2-octyloxy]benzoic acid. This resulted in 2-acetylamino-5-nitro-4-[R)-2-octyloxy]benzoic acid.l) The desulfurization of 2-acetylamino-5-nitro-4-[R)-2-octyloxy]benzoic acid was carried out in analogy to the synthesis of 5-amino-4-nitro-4-[R)-2-octyloxy]benzoic acid. These are 2-amino-5-nitro-4-[R]-2-octyloxy]benzoes.

The following compounds can be produced in an analogue manner: 4-nonyloxy) -4-biphenylyl 2-amino-5-nitro-4-[r) -2-octyloxy]benzoate with a melting point of 133-134°C.4-[5-trans-heptyl-m-dioxan-2-methyl) pyridine-2-phenyl-2-amino-4-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro-nitro

Example 4

The esterification of 4-[2-amino-5-nitro-4-[(R)-2-octyloxy]phenyl]benzoate with 4-hydroxy-4'-nonyloxybiphenyl was performed analogously to the synthesis of 4'-(5-heptyl-2-pyrimidinyl)phenyl-5-amino-2-nitro-4-[(R)-2-octyloxy]benzoate, resulting in 4'-(nonyloxyphenyl)phenyl 4-[2-amino-5-nitro-4-[(R)-2-octyloxy]phenyl]benzoate.

The 4-[2-Amino-5-nitro-4-[[[R]-2-octyloxy]phenyl]benzoic acid used as starting material was obtained as follows: (a) A gaseous mixture of carbon dioxide and bromine is introduced into a melt of 10,5 g m-nitrophenol heated to 120-140 °C until the calculated weight gain is reached. The introduction of pure carbon dioxide removes bromine residues from the reaction mixture. The product mixture is crystallized twice from 10% aqueous hydrochloric acid, yielding 8 g 4-bromine-3-nitrophenol. (b) The evaporation of 4-bromine-3-nitrophenol was carried out analogously to the synthesis of ethyl 3-nitro-4-[R]-2-octyloxybenzoate. This reaction yields 1-bromine-2-nitro-4-[R]-2-octyloxybenzoate. 25,2 g (2-bromine-2-dimethyl-2-phenol) was added to the solution in 100 ml of magnesium tetraethyl sulphate, which is extremely weak.After completion of the addition, the heat was returned for another 2 hours, reaching 95% (gas chromatography). 20 ml of the Grignard reagent solution was dripped at -70°C under nitrogen atmosphere and intense stirring to a mixture of 10 ml of triisopropyl borate and 0.5 ml of dry tetrahydrofuran. After completion of the addition, the reaction mixture was slowly heated to room temperature and stirred for another 30 minutes. The reaction mixture was then poured into 100 ml of 10% hydrochloric acid. The solution was set to pH = 9 with solid sodium carbonate and extracted three times with 100 ml of acetic acid ethyl ester. The combined organic phases were washed twice with 100 ml of water, filtered over sodium sulphate, dried and pressed.Chromatography of the silica gel residue with a mixture of acetic acid ethyl ester and ethanol (vol. 2:1) yielded 4-[2- ((4,4-dimethyl-2-oxazolyl) ]phenylhoronic acid. (d) A mixture of 0.684 g 1-bromo-2-nitro-4-[r]-2-octyloxy]benzole, 80 mg Pd[r]-pH3) 4 and 4.6 ml toluene was treated with 0.6 g 4-[2-[4,4-dimethyl-2-oxazolyl)]phenylboronic acid in 1.14 ml methanol and 2.28 ml 2M aqueous sodium carbonate solution. The reaction mixture was heated to 80°C under intense stirring for 48 hours. After cooling, 10 ml 2M aqueous Na2CO3 solution and 1 ml concentrated ammonia water were added and the reaction table was dried with 20 ml of methyleneglycerol. The organic phase is separated, thickened and pressed. Chromatography of the cycloacetyl cycloate with a residual solution of ammonium and oxalic acid (Voluminium).The reaction is carried out by heating the solution to a temperature of 95 °C. After cooling, the precipitate is filtered and given 10 ml. Subsequently, the precipitate is decomposed in 15 ml of 20% sodium hydroxide solution in methanol and water (vol. 1:1) The reaction is intensively heated for 40 minutes under neutral stirring at 70 °C. After cooling, the reaction is carried out with a concentrated solution of acetylated nitric acid. The reaction is carried out by a vacuum washing of 4-amino-4-amino-4-acetylated 2-amino-4-acetylated nitric acid. This reaction is carried out by the analogy of 4-amino-4-acetylated 4-amino-4-acetylated 2-acetylated nitric acid.This resulted in 4-[2-Acetylamino-4-nitro-[R) -octyloxy]phenyl]benzoic acid. (h) The nitration of 4-[2-Acetylamino-4-[R) -octyloxy-phenyl]benzoic acid was performed analogously to the synthesis of 5-Acetylamino-2-nitro-4-[R) -octyloxy]benzoic acid, which resulted in 4-[2-Acetylamino-5-nitro-4-[R) -octyloxy]phenyl]benzoic acid. (i) The absorption of the amide function of 4-[Acetylamino-5-nitro-4-[Rety) -octyloxy]benzoic acid was performed analogously to the synthesis of 5-[Amino-2-nitro-4-nitro-nitro-[R] -octyloxy-benzoic acid.

The following compounds can be produced by analogy: It consists of a mixture of hydrocarbons having carbon numbers predominantly in the range of C1 through C5 and boiling in the range of approximately -15 oC to -15 oC (- 40oF to -40oF).

Example 5

The esterification of 4-[5-amino-2-nitro-4-[(R)-2-octyloxy]phenyl]benzoic acid with 4-hydroxy-4'-octyloxybipbenyl is performed analogously to 4'- ((5-heptyl-2-pyrimidinyl) phenyl-5-amino-2-nitro-4-[(R)-2-octyloxy]benzoate, resulting in 4'- ((Octyloxy)-4-biphenylyl-4-[5-amino-2-nitro-4-[(R)-2-octyloxy]phenyl]benzoate. Smp. (C-I) 177.8-180.5°C, conversion (SA-Ch) 128°C, Klp. (Ch-I) 150°C.

The 4-[5-Amino-2-nitro-4-[[R]-2-octyloxy]phenyl]benzoic acid used as starting material was obtained as follows: a) 4-[4-hydroxyphenyl]benzoic acid was produced with ethanol analogous to the synthesis of 4-hydroxy-3-nitrobenzoic acid ethyl ester. This resulted in ethyl 4-[4-hydroxyphenyl]benzoate. b) The evaporation of ethyl 4-[4-hydroxyphenyl]benzoate was performed analogous to the synthesis of ethyl 3-nitro-4-[(R)-2-octyloxy]benzoate. This resulted in ethyl[4-[(R) 4-[(2-octyloxy]phenyl]benzoate. c) The evaporation of ethyl 4-[4-[R)-2-octyloxy]benzoate was performed analogously to the synthesis of 3-[4-hydroxyphenyl]benzoate.Reduction of 4-[3-Nitro-4-[R]-2-octyloxyphenyl]benzoic acid was carried out analog to the synthesis of ethyl 3-amino-4-[R]-2-octyloxy]benzoate at a temperature of 2 °C. This was followed by 4-[3-acetyl-4-[R]-2-octyloxy-acetyl]acetyl. Further reduction of the amine from 4-[3-nitro-4-[Amino-4-acetyl]benzoic acid is carried out in a series of 20 ml of 2-acetyl-4-[R]-2-octyloxy-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acetyl-acThe resulting 4-[5-acetylamino-2-nitro-4-[R]-2-octyloxy]phenyl]benzoic acid is incorporated into the subsequent reaction without further purification. (h) The acetylamine group of 4-[5-acetylamino-2-nitro-4-[R]-2-octyloxy]phenyl]benzoic acid was dehydrated by analogy to the synthesis of 5-amino-2-nitro-4-[R]-2-octyloxy]benzoic acid, resulting in 160 4-[5-amino-2-mgnitro-4-[R]-2-octyloxy]phenyl]benzoates.

The following compounds can be produced by analogy: The total value of all the materials of Chapter 9 used does not exceed 20% of the ex-works price of the product

Example 6

For the manufacture of poly{4-(11-Acryloyloxyundecanoxy)phenyl 4-[2-amino-5-nitro-4-[(R)-2-octyloxy]phenyl]benzoate}: a solution of 1 g 4- ((11-Acryloyloxyundecanoxy)phenyl 4-[2-amino-5-nitro4-[(R)-2-octyloxy]phenylbenzoate and 2.4 mg α,α'-Azo-isobutyronitrile in 2,8 ml toluene is passed through argon at 0 °C for 10 minutes and then heated to 70 °C in a closed vessel for 48 hours. After cooling the polymerisation mixture to room temperature, the failed polymerisation polymers are again removed and converted into 10 ml of glass hydride. The solution is dissolved in 300 ml of methanol, which is then converted into 4- (acryloxydeoxy) methanol (I/SC) at a further conversion step of 109 °C. This process takes place:

The monomer 4- ((11-Acryloyloxyundecanoxy)phenyl 4-[2-amino-5-nitro-4-[((R)-2-octyloxy]phenyl]benzoate used as starting material was produced as follows: a) 4- ((11-hydroxyundecanoxy) phenol: a mixture of 5 g of 11-bromundecanool and 5 g of hydroquinone in 200 ml of 2-butanone and 4 g of potassium carbonate is heated for 48 hours under reflux. The reaction mixture is filtered and the solvent is distilled. The residue dissolved in 400 ml of acetic acid is washed four times with 100 ml of 10% (w/v) of potassium carbonate and then twice with water. The solution is dried over sodium sulphate, filtered and evaporated.After the reaction mixture is heated for 48 hours in a water separator under reflux, the reaction mixture is washed twice with 100 ml of a 10% (w/v) sodium hydrocarbonate solution and then three times with 100 ml of water. After drying the organic phase with sodium sulphate, the chloroform is distilled to yield 5.2 g of 4-11-acryloxydecanoxyphenol. Smp. 72 - 74°Cc) 4- ((11-acryloxydecanoxy) 4-phenyl[2-amino-5-nitro-4-[R) 2-octyloxyphenyl] benzenyl] benzoate: The conversion of 4-amino-5-nitro-4-benzyl[[R] 2-nitro-4-nitro-4-benzyl[R] 2-nitro-4-nitro-4-benzyl[R] 2-benzyloxyphenyl-4-benzyloxyphenyl[R] 4-benzyloxyphenyl[R] 4-benzyloxyphenyl[R] 4-benzyloxyphenyl[R] 4-benzyloxyphenyl[R] benzyloxy-4-benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzyloxy[R] benzylo] benzyloxy[R2[R] benzylo] benzylo] benzylo[R5[R5[R] benzylo] benzylo] benzylo[R5[R5[R] benzylo] benzylo[R5[R] benzylo] benzylo[R5[R] benzylo] benzylo[R5[R] benzylo] benzylo[R5[R] benzylo[R] benzylo[R] benzylo[R5[R] benzylo] benzylo[R5[R]

The following momomers can be produced by analogy: 4-[11-acryloyl-nitroxyundecanoxy)phenyl 4-[2-amino-5-nitro-4-[(R)-2-octyloxy]phenyl]benzoate4- (((11-Methacryloyl-nitroxyundecanoxy)phenyl 4-[2-amino-5-nitro-4-[(R)-2-octyloxyphenyl]phenyl 4-[2-amino-5-nitro-4-[(R)-2-octyloxyphenyl]phenyl-benzoatePolyzoam4-[(10-fluoroxydecanoxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxydehydroxyde

It can be used to produce the following polymers by analogy: It consists of a mixture of hydrocarbons having carbon numbers predominantly in the range of C1 through C5 and boiling in the range of approximately -15oC to -15oC.

Example 7

The polymerisation of 4'- (((11-acryloxyundecanoxy) -4-biphenyl 4-[2-amino-5-nitro-4-[(R)-2-octyloxy]phenyl]benzoate} was carried out analogously to the polymerisation of 4- ((11-acryloxyundecanoxy) 4-[2-amino-5-nitro-4-[(R)-2-octyloxy]phenyl]benzoate} which yielded 0,63 g{4'-(11-acryloxyundecanoxy) -4-biphenyl[2-amino-5-nitro-4-nitro-4-[(R)-2-octyloxy]phenyl]benzoate. Conversion rate: ca. 140°C. (SCT): 270°C. (SCT):

The monomer 4'- ((11-Acryloyloxyundecanoxy) -4-biphenyl 4-[2-amino-5-nitro-4-[(R)-2-octyloxy]phenyl]benzoate used as starting material was produced as follows: a) 4-Hydroxy-4'- ((11-Hydroxyundecanoxy) biphenyl: The synthesis of 4-Hydroxy-4'- ((11-Hydroxyundecanoxy) biphenyl was carried out analogously to the synthesis of 4-Hydroxyundecanoxy) phenol (Example 6a). This resulted in 4-Hydroxy-4'- ((11-Hydroxyundecanoxy) biphenyl. Smp: 144 -146°Cb) 4'- ((11-Hydroxyundecanoxy) 4-Hydroxydephenyl: The conversion of 4-Hydroxyde-4'- ((11-Hydroxyundecanoxy) biphenyl was carried out analogously to the synthesis of 4-Hydroxyundecanoxy) phenol (Example 6b). This resulted in 4-Hydroxy-4'- ((11-Hydroxyundecanoxy) biphenyl. Smp: 144 -146°Cb) 4'- ((11-Hydroxydeoxy-acetyl) 4-nitroxy-acetyl) 4-Hydroxydephenyl: The conversion of 4-Hydroxydephenyl to 4-Hydroxydephenyl (Acetoxydephenyl) 4-Hydroxy) 4- (Acetoxydephenyl) 4-Hydroxy-4-acetyl) 4-Hydroxy (Acetoxydephenyl) 4-Hydroxy) 4-Hydroxy (Acetoxydephenyl) 4-Hydroxy) 4-Hydroxy-acetyl (Acetoxy) 4-Hydroxy) 4-Hydroxy-acetyl (Acetoxy) 4-Hydroxy) 4-Hydroxy-acetyl (Acetyl) 4-Hydroxy) 4-Hydroxy-acetyl (Acetyl) 4-Hydroxy) 4-Hydroxy-acetyl (Acetyl) 4-Hydroxy) 4-Hydroxy-acetyl (Acetyl) 4-Hydroxy) 4-Hydroxy-acetyl (Acetyl) 4-Hydroxy-acetyl) 4-Hydroxy-

The following monomers can be produced by analogy: It consists of a mixture of hydrocarbons having carbon numbers predominantly in the range of C1 through C5 and boiling in the range of approximately -15oC to -15oC at temperatures of -15oC to -15oC and boiling in the range of approximately -15oC to -15oC.

By analogy, the following polymers can be produced from the monomers mentioned above: It consists of a mixture of hydrocarbons having carbon numbers predominantly in the range of C1 through C5 and boiling in the range of approximately -15oC to -15oC at temperatures of -15oC to -15oC.

Claims (19)

1. An optical element for efficient generation of short-wave laser light by frequency conversion by means of a wave-guiding layer of a liquid crystalline material having a periodic structure which permits a quasi-phase matching of a guided laser beam, the period length of the three-dimensional structure being defined by the coherence length l_C = π/Δβ of the material, where Δβ = β₀(2ω)-2β₀(ω), where ω = the angular frequency of the fundamental wave, 0 is zero-order mode and β = propagation constant of the mode, characterised in that the period length of the three-dimensional structure is equal to twice the coherence length l_C and in that the liquid crystalline material

   contains either a ferroelectric X⁽²⁾-active mixture of chiral molecules with an nlo molecule group, whose X⁽²⁾-active axis is directed substantially transversely of the longitudinal axis of the chiral molecule, and SC-phase-forming liquid crystal molecules,

   or an X⁽²⁾-active, SC*-forming side-chain copolymer, which has chiral side chains with an nlo molecule group, whose X⁽²⁾-active axis is directed substantially transversely of the longitudinal axis of the side chain.
2. An optical element according to claim 1, characterised in that the material, owing to its birefringent properties, can be used for phase matching of the d₂₁ component of the nlo tensor.
3. An optical element according to claim 1 or 2, characterised in that the nlo-molecule group incorporated transversely to the longitudinal axis is a nitroaniline derivative.
4. An optical element according to any of claims 1 to 3, characterised in that the ferroelectric liquid crystal material forms an S_C* phase or a higher-order ferroelectric phase which can be dipolar oriented in the electric field.
5. An optical element according to any of claims 1 to 3, characterised in that the ferroelectric LC material forms an S_C* phase which is homogeneously oriented in bistable manner by boundary forces.
6. An optical element according to claim 4, characterised in that the dipolar orientation is fixed by cooling below the glass temperature.
7. An optical element according to claim 1 or 2, characterised in that, by using the Pockels' effect, it operates as an electro-optical switch or light modulator in the spectral range from 1300 to 430 nm.
8. An optical element according to any of claims 1 to 3, characterised in that the mixture has the phase sequence I-Chol-Sm_A-S_C*-glass.
9. An optical element according to claim 1 or 2, characterised in that the element is operated in the S_C* phase so that, when an electric field is applied, the X⁽²⁾ property becomes operative but disappears when the electric field is switched off.
10. An optical element according to claim 1 or 2 characterised in that it is usable for doubling the frequency of laser light having a wavelength of 850 - 1300 nm.
11. An optical element according to any of claims 4 - 6, characterised in that the dipolar orientation is at right angles to the waveguide plane.
12. A frequency-doubling module comprising a laser diode emitting in the range from 850-1300 nm and optically coupled to an optical element according to any of the preceding claims.
13. Compounds having the general formula: where

    X¹, X² denote -NO₂ and -NR⁵R⁶ respectively, where R⁵ and R⁶ independently of one another stand for H or lower alkyl;

    R³, R⁴ independently denote H, F, Cl, Br, NH₂, NO₂, CN, lower alkyl or lower alkoxy, with the proviso that X¹ is different from R⁴ and X² is different from R³;

    R¹ denotes chiral alkyl or cycloalkyl where, independently of one another, one or two non-neighbouring -CH₂ groups can be substituted by O, S, -COO-, -OOC-, -HC=CH-, or by -C≡C- in the aliphatic radical, and which can be substituted one or more times by F, Cl, CN, lower alkyl or lower alkoxy, with the proviso that the chirality centre is in an alkyl chain on the first or second C atom, or on a C atom in the ring, in the case of a cycloalkyl radical;

    A¹ denotes 1 to 4 six-member rings which are directly linked to one another or to the p-nitro-aniline ring and/or at one or optionally a number of places via -CH₂-CH₂-, -CH₂O-, -OCH₂-, -COO-, -OOC-, -COS-, -SOC-, -CH=CH-, -C≡C-, -N=N-, -N=NO-, -ON=N-, -CH=N-, -N=CH-, or butylene, in which a -CH₂CH₂- group can be substituted by -COO-, -OOC-, -HC=CH-, or -C≡C- and/or a -CH₂ group can be substituted by O or S. The six-member rings in A¹, independently of one another, stand for 1,4-phenylene, unsubstituted or optionally mono-, di- or polysubstituted with F, Cl, lower alkyl or lower alkoxy and in which one or two -CH- groups can be replaced by nitrogen, or 1,4-cylclohexylene in which one or two -CH₂- groups (preferably not neighbouring) can be substituted by O or S or a -CH₂CH₂- group can be subtituted by -CH=CH-, or naphthalene-2,5-diyl, decalin-2,6-diyl, tetralin-2,6-diyl, thiadiazolyl or oxodiazolyl;

    Z1 denotes a simple covalent bond, -CH₂-CH₂-, -CH₂O-, -OCH₂-, -COO-, -OOC-, -COS-, -SOC-, -CH=CH-, -C≡C-, -N=N-, -N=NO-, -ON=N-, -CH=N, -N=CH-, or butylene, where a -CH₂CH₂- group can be substituted by -COO-, -OOC-, -HC=CH-, or -C≡C- and/or a -CH₂- group can be substituted by O or S;

    A¹ denotes the structural element where X¹, X², R³ and R⁴ have the meanings given previously;

    n = 0 or 1;

    R² denotes chiral or achiral alkyl or cycloalkyl in which, independently of one another, one or more -CH₂- groups can be substituted by O, S, -COO-, -HC=CH- or by -C≡C- or 1,4 phenylene in the aliphatic radical, and which be substituted one or more times by F, Cl, CN, lower alkyl or lower alkoxy, with the proviso that any chirality centre present will be in an alkyl chain on the first or second C atom or, in the case of a cylcoalkyl radical, will be on a carbon atom in the ring, or if n = O, also the group where X¹, X², R¹. R³, R⁴ and A¹ have the meanings given previously, and M denotes an integer 6-16, where one or two non-neighbouring -CH₂- groups, independently of one another, can be substituted by O, S, -COO-, -CH=CH- or -C≡C-.
14. Formula I compounds according to claim 13, characterised in that R² denotes chiral or achiral alkyl or cycloalkyl in which, independently of one another, one or two non-neighbouring -CH₂- groups can be substituted by O, S, -COO-, -HC=CH- or can be substituted by -C≡C- in the aliphatic radical, and which can be substituted one or more times by F, Cl, CN, lower alkyl or lower alkoxy, with the proviso that any chirality centre present will be in an alkyl chain on the first or second C atom and, in the case of a cylcoalkyl radical, will be on a carbon atom in the ring, or if n = O, also the group where X¹, X², R¹. R³, R⁴ and A¹ have the meanings given previously, and m denotes an integer 6-16, where one or two non-neighbouring -CH₂- groups, independently of one another, can be substituted by -O-, -S-, -COO-, -CH=CH- or -C≡C-.
15. Non-linear optical compounds according to claim 13 of the general formula Ia wherein R⁷ denotes chiral or achiral alkyl in which, independently of one another, one or more -CH₂-groups can be substituted by -O-, -S-, -COO-, -HC=CH-, -C≡C- or 1,4-phenylene, and which can be substituted one or more times by F, Cl, CN, lower alkyl or lower alkoxy.
16. Non-linear optical compounds according to claim 13 or 15, characterised in that R² or R⁷ bears one of the following polymerisable groups in the terminal position: or
17. Use of the non-linear optical compounds according to claim 15 or 16 to form non-linear optical polymers.
18. Use of the non-linear optical compounds according to any of the claims 13 to 16 in an optical element according to any of claims 1 to 11.
19. Use of the non-linear optical polymers according to claim 17 in an optical element according to any of claims 1 to 11.