PYRAMIDAL LIQUID CRYSTALS

Abstract: Dodeca-substituted derivatives of macrocyclic tetramers, obtained by acid-catalyzed condensation of pyrogallol and an aliphatic aldehyde, wherein the substituents are alkanoyl groups, are described. These substituted tetramers are optically anisotropic in the molten state and, in particular, show mesophases of the pyramidal type.

Description: The present invention relates to liquid crystalline macrocyclic tetramers. More particularly, the present invention relates to thermotropic dodeca-substituted macrocyclic tetramers which show mesophases of the pyramidal type. The term "pyramidal mesophase", as used in the present description and in the claims, denotes a two-dimensional structure wherein the molecules are arranged in the form of columns. The molecules making up the columns are formed by a central nucleus of pyramidal shape with twelve substituent chains symmetrically distributed around the base (centre) of the pyramid. In such a column, the central nuclei are piled on each other and show the same orientation. This type of monophase is described, for instance, in Journal de Physique, 47 (1986), page 351 and in Zeitschrift für Naturforschung, 40A (1985), page 149. Liquid crystals and their use as electronic components (for example, in the optoelectronic field), for the non-destructive analysis of materials or in medical diagnosis and, more generally, as "displays", have been known for many years and are described in many publications such as, for example, US-A-4 430 650. In US-A-4 619 788, hexa-substituted derivatives of tribenzocyclononatriene, showing monophases of the pyramidal type, are described. These are molecules provided with a rigid central nucleus having a pyramidal structure wherein the chains of the substituents are symmetrically linked to the base of the pyramid. These compounds have an electric dipolar moment which makes them particularly suitable for use as "memory devices" or as displays in optoelectronics. It has now been found that dodeca-substituted derivatives of the cyclic tetramer, which are obtainable by acid-catalyzed condensation of pyrogallol and an aliphatic (alkyl) aldehyde and wherein the substituents are alkanoyl chains, are stable products, anisotropic in the molten state, and show monophases of the pyramidal type. Therefore, object of the present invention are thermotropic dodeca-substituted macrocyclic tetramers of the general formula: wherein the groups R are alkyl radicals containing 1 or 2 carbon atoms and the groups R′, the same or different from each other, represent a radical of the general formula: -CO-C n H 2n+1 (II) wherein n is an integer greater than or equal to 12. Among the compounds of general formula (I) those, wherein n is an integer of from 12 to 30, are the preferred ones. Although the groups R′ can be the same or different from each other, compounds wherein all of the radicals R′ have the same meaning are preferred. In the thermotropic macrocylic tetramers of the present invention the groups R are arranged in axial position, as shown in Fig. 1, which represents a perspective view of the molecule. This type of structure tends to form hexagonal columns of pyramidal shape in the mesophase. The tetramers of general formula (I) usually have melting temperatures of from about 30 to about 100°C. The clearing points of the molten products generally range from about 60 to about 120°C. The pyramidal-column liquid crystalline structure can be inferred from differential scanning calorimetry (DSC), analysis with a polarized light optical microscope and X-ray diffraction. In particular, for all of the mesogens of the present class, a mesophase of the "broken fan" type is observed under the microscope, said mesophase being typical for highly organized column-shaped liquid crystals. By slow cooling (starting from the isotropic state), an omeotropic organization of the mesophase is obtained, wherein the columns are oriented perpendicularly to the surface of the slide. In contrast thereto, by allowing the mesophase to slide on a rigid support, a planar arrangement of the columns with respect to the surface of the slide is observed. The X-ray diffraction of the non-oriented mesophase shows two diffraction rings: The first one is very wide with great angles, characteristic for the molten aliphatic chains; The second one is intense and narrow with small angles, representing the two-dimensional organization in the plane. Said observations allow the mesophase to be defined as hexagonal column-shaped and belonging to the symmetry group (D ho ). In Fig. 2 the transition temperatures of the different phases of a macrocyclic tetramer of the general formula (I), wherein R is CH₃ are shown for exemplary purposes. In said figure, the temperatures are given on the ordinate, whereas the values of n of the radical R′ are indicated on the abscissa. The letters I, P and K denote the isotropic phase, the pyramidal liquid crystalline phase and the crystalline phase, respectively. In particular, in Fig. 2, the circles represent the "clearing points", whereas squares represent the transition crystal-pyramidal mesophase. The thermotropic macrocylic tetramers of the present invention may be prepared by reacting a macrocyclic tetramer of the general formula: wherein R is as defined above, with acyl halides of the general formula R′-X, wherein X represents a halogen atom, preferably chlorine, and R′ has the meanings given above. Examples of suitable acyl halides are: myristoyl chloride, palmitoyl chloride, stearoyl chloride, tridecanoyl chloride, etc. The above reaction may, for instance, be carried out as a conventional bulk esterification under normal pressure and at temperatures of from about +50°C to about +200°C. The macrocyclic tetramers of general formula (III) may be obtained by acid-catalyzed condensation at room temperature of pyrogallol and the acetal of an aliphatic (alkyl) aldehyde in a polar solvent, preferably an alcohol such as methanol or ethanol. The catalyst may, for instance, be selected from hydrochloric acid, sulfuric acid, phosphoric acid, para-toluene sulfonic acid, etc. These catalysts are generally used in amounts of from 1 to 20% by weight, based on the total amount of the reagents. The substrates of general formula (III) may, for instance, be prepared according to the following reaction scheme: wherein R is an alkyl radical containing 1 or 2 carbon atoms and R″ is an alkyl, cycloalkyl, aryl or alkylaryl radical containing from 1 to 30 carbon atoms. Preferably, the groups R″ are the same. Examples of radicals R″ include linear or branched alkyl groups having 1 to 30, preferably 1 to 12 and, particularly, 1 to 6 carbon atoms (for example, methyl, ethyl, n- and i-propyl and butyl); cycloalkyl groups having 3 to 8 carbon atoms (for example, cyclopentyl and cyclohexyl); aryl groups having 6 to 14 carbon atoms (for example, phenyl, naphthyl and biphenylyl); alkylaryl groups having 7 to 15 carbon atoms. Furthermore, the groups R″ may be combined to form an alkylene group of preferably 2 or 3 carbon atoms. Particularly preferred are alkyl groups R″ as defined above. With the above process, only one of the many possible configurational isomers is obtained, namely the isomer called "crown" (Fig. 3), wherein all of the groups R are in the axial position. Because of their pyramidal shape, the macrocyclic tetramers of the present invention have an intrinsic electric dipole moment, oriented in the direction of the symmetry axis C₄ of the molecules. This characteristic, together with the arrangement of the pyramidal mesophase in columns wherein the central nuclei are piled on each other and all show the same orientation, makes the columns polar. The polar axis coincides with the symmetry axis of the column. This is why the pyramidal mesophase formed by the macrocyclic tetramers of the present invention can be ferroelectric if all of the columns assume the same direction of polarization at macroscopic level (see Fig. 4). Generally, the column-shaped mesophases of the hexagonal type tend to favour the ferroelectric orientation over the anti-ferroelectric orientation. Furthermore, the same result can be obtained by orienting the columns under the influence of an external electric field. The above properties make the thermotropic macrocyclic tetramers of the present invention particularly suitable for use in "memory devices", in optoelectronic displays, in phototonics as components for "non-linear optical devices" and, in general, in all fields wherein liquid crystals can be employed. The following examples are given in order to illustrate the present invention without, however, limiting it. EXAMPLE 1 Preparation of 3.4.5.10.11.12.17.18.19.24.25.26-dodecahydroxy-c-1,c-8,c-15,c-22-tetramethyl-[1₄]metacyclophane 12.61 g (0.1 mol) of pyrogallol were dissolved, under argon, in 50 ml of ethanol and 10 ml of 37% HCl. The solution was cooled to 0°C by means of an ice bath and 14.22 ml of 1,1-diethoxyethane were added dropwise within 1 hour. Thereafter, the solution was kept at room temperature under agitation fo 48 hours, whereupon it was heated to reflux for 6 hours. The resulting mixture was cooled to room temperature, water was added thereto and the formed precipitate was filtered off and repeatedly washed until neutral. The product was dried under vacuum (1 x 10⁻³ torr/25°C) to afford 11.0 g of pure product (yield 72%). Mass (DCI⁺): MH⁺=609 ¹H-NMR (DMSO-d₆): δ 1.55 (d, 12H, J=7.5 Hz, CH₃); 4.56 (q, 4H, J=7.5 Hz, CH); 6.79 (s, 4H, Ar-H); 8.02 (bs, 4H, OH); 8.22 (s, 8H, OH). Elemental analysis for C₃₂H₃₂O₃₂: Calculated: C= 63.15% H = 5.30% Found: C = 63.01% H = 5.43% EXAMPLE 2 Preparation of 3.4.5.10.11.12.17.18.19.24.25.26-dodecatridecanoyloxy-c-1,c-8,c-15,c-22-tetramethyl-[1₄]metacyclophane 0.609 g (1 mmol) of the tetramer obtained in example 1 and 10.1 ml (40 mmol) of tridecanoyl chloride were heated for 10 hours at 140°C under agitation. After completion of the reaction, the excess chloride was distilled off under vacuum (10⁻² torr). The residue was dissolved in methylene chloride and the resulting solution was first extracted with 0.1N NaOH, then washed with water until neutral and, thereupon, dried over sodium sulfate. The solvent was evaporated and the crude product thus obtained was purified on a silica gel column using methylene chloride/hexane (8:2) as eluent. 1.72 g of pure product were obtained (yield 58%). Mass (DCI⁻): M⁻=2960 ¹H-NMR (CDCl₃): δ 0.89 [t, 36H, (CH₂) n - CH ₃]; 1.30 [bs, 216H, (CH₂)₉]; 1.45 (d, 12H, J=7.4 Hz, CH- CH ₃); 1.55 (bm, 12H, CO-CH₂- CH ₂); 1.71 (bm, 12H, CO-CH₂- CH ₂′); 2.28 (bm, 12H, CO-CH₂); 2.50 (bm, 12H, CO-CH₂′); 4.22 (q, 4H, J=7.4 Hz, CH); 6.03 (s, 2H, Ar-H); 7.31 (s, 2H, Ar-H′). Elemental analysis for C₁₈₈H₃₂₀O₂₄: Calculated: C = 76.17% H = 10.88% Found: C = 76.17% H = 11.08% EXAMPLE 3 to 5 By following the procedure of example 2, using myristoyl chloride, palmitoyl chloride and stearoyl chloride respectively, the following were obtained: 3.4.5.10.11.12.17.18.19.24.25.26-dodecatetradecanoyloxy-c-1,c-8,c-15,c-22-tetramethyl-[1₄]metacyclophane (yield 54% after purification on a silica gel column, using methylene chloride/hexane (9:1) as eluent. Mass (DCI⁻): M⁻= 3128. ¹H-NMR (CDCl₃): δ 0.89 [t, 36H, (CH₂) n - CH ₃]; 1.30 [bs, 240H, (CH₂)₁₀]; 1.47 (d, 12H, J = 7.4 Hz, CH- CH ₃); 1.53 (bm, 12H, CO- CH ₂); 1.72 (bm, 12H, CO-CH₂- CH ₂′); 2.29 (bm, 12H, CO-CH₂); 2.51 (bm, 12H, CO-CH₂′); 4.22 (q, 4H, J=7.4 Hz, CH); 6.02 (s, 2H, Ar-H); 7.31 (s, 2H, Ar-H′). Elemental analysis for C₂₀₀H₃₄₄O₂₄ Calculated: C = 76.67% H = 11.07% Found: C = 76.71% H = 11.26% ) 3.4.5.10.11.12.17.18.19.24.25.26-dodeca-hexadecanoyloxy-c-1,c-8,c-15,c-22-tetramethyl-[1₄]metacyclophane (yield 50% after two crystallizations from methylene chloride/ethyl ether. Mass (DCI⁻): M⁻=3464 ¹H-NMR (CDCl₃): δ 0.89 [t, 36H, (CH₂) n - CH ₃]; 1.29 [bs, 288H, (CH₂)₁₂]; 1.45 (d, 12H, J=7.4 Hz, CH- CH ₃); 1.49-1.80 (m, 24H, CO-CH₂- CH ₂); 2.28 (bm, 12H, CO-CH₂); 2.51 (bm, 12H, CO-CH₂′); 4.22 (q, 4H, J=7.4 Hz, CH); 6.01 (s, 2H, Ar-H); 7.30 (s, 2H, Ar-H′). Elemental analysis for C₂₂₄H₃₉₂O₂₄: Calculated: C = 77.55% H = 11.39% Found: C = 77.52% H = 11.58% ) 3.4.5.10.11.12.17.18.19.24.25.26-dodeca-octadecanoyloxy-c-1,c-8,c-15,c-22-tetramethyl-[l₄]metacyclophane (yield 53% after two crystallizations from methylene chloride/ethyl ether. Mass (DCI⁻): M⁻= 3800 ¹H-NMR (CDCl₃): δ 0.89 [t, 36H, (CH₂) n - CH ₃]; 1.30 [bs, 336H, (CH₂)₁₄]; 1.46 (d, 12H, J=7.4 Hz, CH- CH ₃); 1.70 (m, 24H, CO-CH₂- CH ₂); 2.30 (bm, 12H, CO-CH₂); 2.51 (bm, 12H, CO-CH₂′); 4.23 (q, 4H, J=7.4 Hz, CH); 6.03 (s, 2H, Ar-H); 7.30 (s, 2H, Ar-H′). Elemental analysis for C₂₄₈H₄₄₀O₂₄: Calculated: C = 78.26% H = 11.65% Found: C = 78.30% H = 11.70% ) EXAMPLES 6 and 7 (Comparative Examples) By following the procedure of example 2, using decanoyl chloride and lauroyl chloride, respectively, two non-liquid crystalline products were obtained, namely: 3.4.5.10.11.12.17.18.19.24.25.26-dodeca-decanoyloxy-c-1,c-8,c-15,c-22-tetramethyl[1₄]metacyclophane (yield 52% after purification on a silica gel column, using methylene chloride/hexane (9:1) as eluent. Mass (DCI⁻): M⁻=2456 ¹H-NMR (CDCl₃): δ 0.89 [t, 36H, (CH₂) n ]; 1.25 (bs, 144H, (CH₂)₆]; 1.48 (d, 12H, J=7.4 Hz, CH- CH ₃); 1.52 (bm, 12H, CO-CH₂-CH₂); 1.71 (bm, 12H, CO-CH₂- CH ₂′); 2.30 (bm, 12H, CO-CH₂); 2.50 (bm, 12H, CO-CH₂′); 4.22 (q, 4H, J=7.4 Hz, CH); 6.02 (s, 2H, Ar-H); 7.30 (s, 2H, Ar-H′). Elemental analysis for C₁₅₂H₂₄₈O₂₄: Calculated: C = 74.22% H = 10.16% Found: C = 74.13% H = 10.45% ) 3.4.5.10.11.12.17.18.19.24.25.26-dodeca-dodecanoyloxy-c-1,c-8,c-15,c-22-tetramethyl[1₄]metacyclophane (yield 58% after purification on a silica gel column, using methylene chloride/hexane (9:1) as eluent. Mass (DCI⁻): M⁻=2792. ¹H-NMR (CDCl₃): δ 0.89 [t, 36H, (CH₂) n CH ₃]; 1.24 [bs, 192H, (CH₂)₈]; 1.45 (d, 12H, J=7.4 Hz, CH- CH ₃); 1.54 (bm, 12H, CO-CH₂- CH ₂); 1.71 (bm, 12H, CO-CH₂- CH ₂′); 2.30 (bm, 12H, CO-CH₂); 2.52 (bm, 12H, CO-CH₂′); 4.22 (q, 4H, J=7.4 Hz, CH); 6.04 (s, 2H, Ar-H); 7.32 (s, 2H, Ar-H′). Elemental analysis for C₁₇₆H₂₉₆O₂₄: Calculated: C = 75.60% H = 10.67% Found: C = 75.69% H = 10.90% ) The following Table 1 lists the transition temperatures and the enthalpies of the products described in examples 2 to 7.

Claims: Thermotropic dodeca-substituted macrocyclic tetramers of the general formula: wherein the groups R are alkyl radicals containing 1 or 2 carbon atoms and the groups R′, the same or different from each other, represent a radical of the general formula -CO-C n H 2n+1 (II) wherein n is an integer greater than or equal to 12. Tetramers according to claim 1, wherein n is an integer of from 12 to 30. Tetramers according to claim 1 or 2, wherein all of the radicals R′ are the same. Tetramers according to any one of the preceding claims having melting temperatures of from about 30°C to about 100°C and isotropization temperatures in the molten state (clearing points) of from about 60°C to about 120°C. Tetramers according to any one of the preceding claims, wherein the monophase is of the hexagonal column shaped type with pyramidal arrangement. Use of the tetramers according to any one of the preceding claims as components of "memory devices", in optoelectronic displays and in the field of phototonics as components of non-linear optical devices. Process for the preparation of macrocyclic tetramers of the general formula: wherein R is defined as in claim 1, comprising the reaction, at room temperature, of pyrogallol and an acetal of an aliphatic aldehyde in the presence of an acidic catalyst and in a polar solvent, preferably an alcohol. Process according to claim 7, wherein the acetal of the aliphatic aldehyde has the general formula: wherein R is a C₁-C₂ alkyl radical and R″ is an alkyl, cycloalkyl, aryl or alkylaryl radical containing from 1 to 30 carbon atoms. Process according to claim 7 or 8, wherein the catalyst is selected from hydrochloric acid, sulfonic acid, phosphoric acid and p-toluene sulfonic acid.

Inventors: BONSIGNORE, STEFANIO, COMETTI, GIUSEPPE, DALCANALE, ENRICO, DU VOSEL, ANNICK
Applicants: MONTEDISON S.P.A.
Application year: 1989
Main classification: C09K19
IPC codes: C07C39, G02F1, C07C37, C09K19, C07B61, C07C69