GB2168372A

GB2168372A - Alkoxyphthalocyanines

Info

Publication number: GB2168372A
Application number: GB08530799A
Authority: GB
Inventors: Kenneth John Harrison; Michael John Cook; Steven Dennis Howe; Andrew James Thomson
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1984-12-13
Filing date: 1985-12-13
Publication date: 1986-06-18
Also published as: GB8431446D0; GB8530799D0

Abstract

New alkoxyphthalocyanines are of general formula (I): <IMAGE> wherein R1 to R8 are the same or different and each is an optionally substituted C1 to C6 alkyl group, and X and Y, when taken separately, are the same or different and each is a halo substituent or, when taken together, are an optionally-substituted benzo group. Alkoxyphthalocyanines (I) may be used in smectic liquid crystal materials for laser-addressed devices.

Description

SPECIFICATION Alkoxyphthalocyanines The present invention relates to certain novel alkoxyphthalocyanines, to methods for their preparation and to certain uses thereof.

In recent years several materials have been proposed for laser addressed applications in which laser beams are used to scan across the surface of the material to leave a written impression thereon. For various reasons, many of these materials have consisted of organic solvents which are at least partially transparent in the visible region. The technique relies upon localised absorption of laser energy which causes localised heating and in turn alters the optical properties of the otherwise transparent material in the region of contact with the laser beam. Thus as the beam traverses the material, a written impression of its path is left behind. The most important of these applications is currently in laser addressed storage devices, and in laser addressed projection displays in which light is directed through a cell containing the material and is projected onto a screen.Such devices have been described by F J Khan (Appl. Phys. Lett.

Vol. 22, p. 111, 1973) and by Harold and Steele (Proceedings of Euro Display 84, pages 29-31, September 1984, Paris, France) in which the material in the device was a smectic liquid crystal material.

The use of semiconductor lasers, especially GaxAi1-xAs lasers (where x is from 0 to 1 as is preferably 1), has proven particularly popular in the above applications because they can provide laser energy at a range of wavelengths in the near infra-red which cannot be seen (and thus cannot interfere with the visible display), and yet can provide a useful source of well-defined, intense heat energy. Gallium arsenide lasers provide laser light at a wavelength of about 850 nm, and are most useful for the above applications. With increasing Al content (x < 1), laser wavelength may be reduced down to about 750 nm.

One of the main problems associated with the use of the above materials is that it has hitherto proved difficult to provide materials which are transparent in the visible region and yet are strong absorbers in either the uv or ir region (preferably in the near uv region). The use of dyes within these materials can provide strong absorption at certain wavelengths, but few dyes are transparent in the visible region and many are insoluble in the type of materials used for laser addressed applications.

It is an object of the present invention to provide a dye compound in which the above problems are overcome or at least mitigated in part.

According to the present invention there is provided a group of alkoxyphthalocyanines of general formula I

wherein R,-R8 are the same or different and each is an optionally substituted C, to C6 alkyl group and X and Y, when taken separately, are the same or different and each is a halo substituent or, when taken together, are an optionally substituted benzo group.

Preferably, each of R,-R8 is an optionally substituted C2 to C6 alkyl group, whilst X and Y, when taken separately, are chloro substituents. In one particularly preferred embodiment of the present invention R, R8 represent the same C3-C6 alkyl group.

Most preferably, X and Y are taken together and are an optionally substituted benzo group.

These phthalocyanines exhibit a number of useful properties. First they are moderately soluble in nonpolar organic solvents such as dichloromethane and toluene. This solubility increases, for a given X and Y and, where appropriate, for a given substitution of R1-R8 as the size of R,-R8 increases.

More importantly, however, the absorption properties of the present phthalocyanines are characterised by strong absorption bands in the UV region between about 250 to 360 nm, and in the near IR (infra red) region between about 7 0 and 900 nm, with a broad "window" between the two regions. Their absorption bands in the near IR region are especially pronounced. This especially strong absorption in the near IR, together with the broad window in the visible region of very much lower absorption, allows the pres ent phthalocyanines when dissolved in organic solvents (especially liquid crystal materials) to provide absorption of laser energy from near-IR lasers such as GaxAilxAs lasers, This, in turn, allows such solvent phthalocyanine mixtures to be used in laser address applications.The present phthalocyanines where X and Y are taken together and are optionally substituted benzo are especially preferred, because they exhibit strong absorption bands at or near the wavelength of galluim arsenide (x = 1) lasers of about 850 nm.

The present phthalocyanines may most readily be prepared, in a second aspect of the present invention, by reacting a benzenedicarbonitrile of general formula II

wherein R9 is an optionally substituted C, to Cg, especially Q to C8, alkyl group, and X and Y, when taken separately, are the same or different and each is a halo substituent or, when taken together, are an optionally substituted benzo group, with an alkali metal alkoxide of general formula ROM wherein R is an optionally substituted C, to C6, especially C3 to C6, alkyl group and M is an alkali metal, especially lithium or sodium.

Preferably the conversion of the benzenedicarbonitrile to the phthalocyanine is effected in the alcohol (ROH) corresponding to the alkoxide (ROM) employed, ie ethoxide in ethanol, pentoxide in pentanol.

In one embodiment of the present process R and Rg are the same alkyl group, in which case the resultant phthalocyanine contains only one type of alkoxy group.

In another embodiment of the present process R and R6 are different, in which case, and this is a surprising feature of the present process, not only is a phthalocyanine formed by cyclisation of four benzenedicarbonitrile molecules but also the groups OR6 are totally or partially replaced by alkoxide (OR) groups In this case, R preferably represents a higher alkyl group than R9 According to a third aspect of the present invention there is provided an organic solvent having a phthalocyanine according to the first aspect dissolved therein. The solvent is preferably a liquid crystal material.

Any liquid crystal material may be used, provided it possesses at least two metastable states at different temperatures, one highly transparent to visible light and one highly scattering. Thus when addressed by a laser the material will absorb energy through the phthalocyanine and will pass from the one state to the other.

The liquid crystal material preferably exhibits a metastable state which is a smectic phase, most preferably a smectic A phase. Materials when in a smectic, especially a smectic A phase, are generally highly viscous which is important when a long term memory effect in the material is desired. The material most preferably exhibits a smectic phase and, at a higher temperature, a nematic phase. The material preferably contains at least one cyanobiphenyl compound, because such materials are typical of those known in the art which exhibit smectic or smectic - and - nematic phases at useful temperatures.

The organic solvent, especially liquid crystal material, preferably contains from 0.01% to 5%, most preferably from 0.05 to 2%, by weight phthalocyanine according to the present invention.

For a typical laser addressed projection display application, a useful liquid crystal material is one which exhibits a smectic phase up to, for example, 45"C, a nematic phase from, for example, 48"C to 49"C, and an isotropic phase above 49"C. Such a material will be well known to those skilled in the art, and these properties are not altered to any significant degree by small amounts of the present phthalocyanines dissolved in the material.

According to a fourth aspect of the present invention, there is provided a liquid crystal electro-optical device including two electrically-insulating, optically transparent substrates, electrodes on the inner surfaces of the substrates, and a film of a dielectric material contained between the substrates which material comprises a liquid crystal material according to the third aspect of the present invention.

The device is preferably a smectic to nematic phase change device.

The device may be used in a laser addressed, particularly a Ga,AI,,As (where x is preferably 1) laser addressed projection smectic storage display. The device preferably has an absorbance to incident laser energy of greater than 0.2, most preferably greater than 0.5, by providing a suitable film thickness and phthalocyanine concentration. The thickness of the film is preferably between 5 and 30 microns.

The use of the above device, containing the useful smectic/nematic/isotropic liquid crystal (LC) material described above, in a projection display application will now be described.

"Total erase" of any image on the device is achieved by applying a strong AC electric field between the conducting layers which aligns all molecules perpendicular to the device walls producing the overall clear state. To "write" information on to this clear background, the scanning laser beam heats the LC locally into the totally disordered, isotropic phase. The heated regions then lose heat very rapidly to the surroundings, cooling almost instantly back to the smectic phase and "freezing in" a large portion of the random molecular alignment of the isotropic phase. This leave lines of the strongly scattering texture wherever the laser scans. To "selectively erase" a piece of written information requires the laser to scan again over the same path while a weak electric field is applied.The scanned material is once again heated into the isotropic phase, but as it cools through the low viscosity, nematic phase the electric field is strong enough to realign the molecules perpendicular to the cell walls.

The present invention will now be described by way of Example only with reference to the accompanying Figure 1, which illustrates an electro-optical device containing a liquid crystal material having an alkoxyphthalocyanine compound dissolved therein.

Example 1 Preparation of Tetra (3, 6 - dip en toxy - 4,5 - dichloro benzo) tetraazaporphin (octapentoxy, octachlorophthalocynanine) a. 1, 4 - Dimethoxy - 2, 3 - dichloro - 5, 6 - dicyanobenzene was prepared by the action of methyl sulphate and potasium carbonate on 2, 3 - dichloro - 5, 6 - dicyano - 1, 4 -benzo quinol in acetone.

b. 1, 4 - Dimethoxy - 2, 3 - dichloro - 5, 6 - dicyanobenzene (4.3 g.) was added to a solution of lithium 1 - pentoxide, prepared by dissolving lithium (0.4 g.) in 1 - pentanol (50 ml.). The reaction mixture was heated under reflux with stirring for 0.5 hr. The pentanol was then removed under vacuum and the residue was treated with acetic acid (100 ml) and stirred for 10 min. The acetic acid was in turn removed in vacuo and the residue was dissolved in dichloro-methane (100 ml.), washed consecutively with a saturated sodium bicarbonate solution (2 x 100 ml.) and water (100 ml) and then dried (MgSO4). Finally the dichloromethane was removed and the residue was chromatographed over silica using dichloromethane as eluent.Tetra (3,6 - dipentoxy -4, 5 - dichloro benzo) tetraazoporphin was collected as a mixture with other phthalocyanines of general formula I wherein each of R, to R6 is either methoxy or pentoxy. Tetra (3,6 - dipentoxy - 4,5 - dichlorobenzo) tetraazaporphin NMREH (60MH,, CDCI3); 0.9 (t, 3H), 1.0 - 2.4 (m, 6H), 5.0 (t, 2H). X max (CHCl3) 325 nm (E = 6.2 x 104); 668 nm (sh) (E = 3.6 x 104); 750 nm (E = 1.3 x 105).

(E = extinction coefficient) Example 2 Preparation of Tetra (1, 4 - dip entoxy - 2, 3 - naphtho) tetraazaporphin (octapentoxynaphtnalocyanine) a. 1, 4 - Dimethoxy - 2, 3 - dicyanonaphthalene was prepared by reacting 2, 3 - dichloro - 1, 4 - naphthoquinone with metal cyanides followed by methylation. (G.A. Reynolds 35metal, J. Org. Chem., 1964, 86, 3591; H. von Pracejus et al, Tetrahadron, 1965, 21, 2257) b. 1, 4 - Dimethoxy - 2, 3 - dicyanonaphthalene (4 g) was added to a solution of lithium 1-pentoxide, prepared by dissolving lithium (0.4 g) in 1-pentanol (50 ml). The reaction mixture was heated under reflux with stirring for 0.5 h. The pentanol was then removed under vacuum and the residue was treated with acetic acid (100 ml) and stirred for 10 min.The acetic acid was in turn removed in vacuo and the residue was dissolved in dichloromethane (100 ml), washed consecutively with a saturated sodium bicarbonate solution (2 x 100 ml) and water (100 ml), and then dried (MgSO4). Finally the dichloromethane was removed and the residue was chromatographed over silica using dichloromethane as eluent. Tetra (1, 4-dipentoxy-2,3-naphtho) tetraazaporphin (1.7 g, 30%) was collected as a dark powder m.p. 265".

(Found: C, 74.96; H, 7.70; N, 7.79. C66H166O6N6 requires C, 75.29; H, 7.61; N, 7.98%.) N.M.R. 5H (60 MHz; CDCl3); 1.0. (t, 3H); 1.1-2.9 (m, 6H); 5.1 (t, 2H); 7.8 (m, 1H); 8.9 (m,1H). Xmax (CDCl3) 324 nm (E = 6.83 x 104); 760 nm (E = 4.55 x 104); 813 nm (E = 4.36 x 104); 846 nm (E = 3 x 105). XmaX (CHCl3) 326 nm (E = 7.4 x 104); 758 nm (E = 4.5 x 104); 852 nm (E = 1.7 x 105); 864 nm (E = 1.8 x 105).

Example 3 Preparation of Tetra (3, 6- dimethoxy - 4, 5 dichlorobenzo) tetraazaporphin (octamethoxy, octachlorophthalocyanine) a. 1, 4 - Dimethoxy - 2, 3 - dichloro - 5, 6 - dicyanobenzene was prepared as described in Example 1.

b. 1, 4 - Dimethoxy - 2, 3 - dichloro - 5, 6 - dicyanobenzene (4.3g) was added to a solution of lithium 1 methoxide, prepared by dissolving lithium (0.4g) in methanol (50 ml). The reaction was heated under reflux with stirring for 0.5 hr. The methanol was then removed under vacuum and the residue was treated with acetic acid (100 ml) and stirred for 10 min. The acetic acid was in turn removed in vacuo and the residue dissolved in dichloromethane (100 ml), washed consecutively with a saturated sodium bicarbonate solution (2 x 100 ml) and water (100 ml) and then dried (MgSO4).Finally the dichloromethane was removed and the residue was chromatographed over silica using dichloromethane as eluent to afford Tetra (3, 6 - dimethoxy - 4, 5 -dichlorobenzo) tetraazaporphin. bH (CDCl3) 4.9 (s). Xmax (CDCl3) 347 nm (e = 5.0 x 104); 641 nm (E = 2.2 x 104); 673 nm (E = 2.5 x 104); 710 nm (E = 9.8 x 104); 739 nm (E = 1.1 x 105).

Example 4 Preparation of Tetra (3, 6 - diethoxy - 4, 5 dichlorobenzo tetraazaporphin (octaethoxy, octachlorophthalocyanine) 1, 4 - Dimethoxy - 2, 3 - dichloro - 5, 6 - dicyanobenzene (0.5g) was added to a solution of lithium ethoxide, prepared by dissolving lithium (0.05g) in ethanol (4 ml). The reaction mixture was heated in a sealed tube at 150tC for 45 minutes. On cooling, acetic acid (10 ml) was added, the reaction mixture stirred for 10 minutes and the solvent removed. The residual solid was washed with 1 molar potassuim hydroxide solution (50 ml), water (50 ml) and dried.

The residue was chromatographed over silica using dichloromethane as eluent. Tetra (3, 6 - diethoxy 4, 5 dichlorobenzo) tetraazaporphin was collected as a mixture with other phthalocyanines of general formula I wherein each of R to R6 is either methoxy or ethoxy. Tetra (3, 6 -diethoxy - 4, 5 dichlorobenzo) tetraazaporphin (Found: C, 49.74; H, 3.34; N, 9.83; Cl, 24.25. CH42N6Cl6O6 requires C, 50.46; H, 3.71; N, 9.81; Cl, 24.82). h,,, (CHCl3) 320 nm (E = 5.4 x 104); 672 nm (E = 4.0 x 109); 710 nm (E = 1.2 x 105); 738 nm (E = 1.5 x 105).

Example 5 Preparation of Tetra (1,4 - dibutoxy - 2, 3 - naphtho) tetraazaporphin (octabutoxynaphthalocyanine) 1, 4 - Demethoxy - 2, 3 - dicyanonaphthalene (49) was added to a solution of lithium 1- butoxide prepared by dissolving lithium (0.4g) in 1-butanol (50 ml). The reaction mixture was heated under reflux with stirring for 0.5 h. The butanol was then removed under vacuum and the residue was treated with acetic acid (30 ml) and stirred for 10 min. The acetic acid was in turn removed in vacuo and the residue was dissolved in dichloromethane (100 ml), washed consecutively with 0.5 Molar potassium hydroxide (100 ml) and water (100 ml), and then dried (Mg2SO4). Finally the dichloro-methane was removed and the residue was chromatographed over silica using dichloromethane as eluent.Tetra (1, 4 -dibutoxy - 2, 3 - naphtho) tetraazaporphin (1.2 g. 22%) was collected m.p. 296 - 300"C. (Found: C, 73.91; H, 6.84; N, 8.68. C60 H93 N6 O6 requires C, 74.39; H, 7.02; N, 8.67).

rH N.M.R.âH (60 MHz; CDCI3); 0.9 (+, 6H, Me); 1.3 - 2.8 (m, 8H, alkyl); 5.1 (+, 4H, O-CH2); 7.8 (m, 2H, Ar); 8.9 (m, 2H, Ar). h,,, (CHCI3) 262 nm (E = 9.9 x 104); 320 nm (E = 6.6 x 104); 352 nm (E = 4.8 x 104); 758 nm (E = 5.2 x 104); 858 nm (E = 1.0 x 105).

Example 6 The alkoxyphthalocyanine of Example 1 was dissolved in liquid crystal material E7. Material E7 is a nematic liquid crystal material supplied by BDH Chemicals of Poole, Dorset, UK, and consists of a mixture of cyanobiphenyls and cyanoterphenyls. Material E7 has a similar solvent power to that of the smectic liquid crystal material S2, also supplied by BDH Chemicals. However the lower viscosity of E7 make it more suitable for the determination of alkoxyphthalocyanine solubility than S2. S2 is a mixture of cyanobiphenyls exhibiting a smectic and a nematic phase.

The solubility at 20"C of the alkoxyphthalocyanine was found to be 0.72% by weight of E7.

Example 7 The alkoxyphthalocyanine of Example 2 was dissolved in material E7, and was found to have a solubility at 20"C of 0.33% by weight of E7.

Example 8 The alkoxyphthalocyanine of Example 4 was dissolved in material E7, and was found to have a solubility at 20"C of 0.14% by weight of E7.

Example 9 The alkoxyphthalocyanine of Example 5 was dissolved in material E7, and was found to have a solubility at 20"C of 0.19% by weight of E7.

The liquid crystal material product of Example 9 was disposed within the liquid crystal cell 1 illustrated in Figure 1 in the form of a 12 microns thick film 2 between two transparent glass slides 3, 4. The internal faces of both slides are coated with thin layers 5,6 of indium tin oxide, a transparent electrical conductor.

Electric fields may thus be applied across the film 2.

The cell 1 exhibited maximum absorbance at a wavelength of 866 nm to incident optical radiation, and an absorbance at about 850 nm of 0.62.

Claims

1. An alkoxyphthalocyanine of general formula I

characterised in that R, to R6 are the same or different and each is an optionally-substituted C, to C6 alkyl group, and X and Y, when taken separately, are the same or different and each is a halo substituent or, when taken together, are an optionally substituted benzo group.

2. An alkoxyphthalocyanine according to claim 1 characterised in that each of R1 to R6 is an optionally substituted C3 to C6 alkyl group.

3. An alkoxyphthalocyanine according to claim 2 characterised in that R, to R6 are the same and each is a C3 to C6 alkyl group.

4. An alkoxyphthalocyanine according to any one of the preceding claims characterised in that X and Y, when taken separately, are chloro substituents.

5. An alkoxyphthalocyanine according to any one of claims 1 to 4 characterised in that X and Y are taken together and are an optionally substituted benzo group.

6. A method of preparing an alkoxyphthalocyanine which comprises reacting a benzenedicarbonitrile of general formula II

wherein R6 is an optionally substituted C, to C6 alkyl group and X and Y, when taken separately, are the same or different and each is a halo substituent or, when taken together, are an optionally-substituted benzo group, with an alkali metal hydroxide of general formula ROM wherein R is an optionally substituted C, to C6 alkyl group and M is an alkali metal.

7. A method according to claim 6, characterised in that R9 is an optionally substituted C3 to C6 alkyl group.

8. A method according to claim 6 or claim 7 characterised in that R is an optionally substituted C3 to C6 alkyl group.

9. A method according to any one of the preceding claims 6 to 8 characterised in that M is lithium or sodium.

10. A method according to any one of the preceding claims 6 to 9 characterised in that the reaction of the benzenedi-carbonitrile with the alkoxide is performed in an alcohol of general formula ROH which corresponds to the alkoxide of general formula ROM.

11. A method according to any one of the preceding claims 6 to 10 characterised in that Rand R6 are the same alkyl group.

12. A method according to any one of the preceding claims 6 to 10 characterised in that R and R9 are different alkyl groups.

13. A method according to claim 12 characterised in that R represent a higher alkyl group than R6.

14. A method according to any one of the preceding claims 6 to 13 characterised in that X and Y are taken together and are an optionally substituted benzo group.

15. An organic solvent having dissolved therein at least one alkoxyphthalocyanine according to any one of the preceding claims 1 to 5.

16. A liquid crystal material having dissolved therein at least one alkoxyphthalocyanine according to any one of the preceding claims 1 to 5.

17. A material according to claim 16 characterised in that the material contains at least one cyanobiphenyl compound.

18. A material according to claim 16 or claim 17 characterised in that the material exhibits a smectic phase.

19. A material according to claim 18 characterised in that the material exhibits a smectic and a nematic phase.

20. A material according to claim 18 or claim 19 characterised in that the material exhibits a smectic A phase.

21. A liquid crystal electro-optical device including two electrically-insulating, optically transparent substrates, electrodes on the inner surfaces of the substrates and a film of dielectric material contained between the substrates, characterised in that the dielectric material is a liquid crystal material according to any one of the preceding claims 16 to 20.

22. A device according to claim 21 characterised in that the device is a smectic to nematic phase change device.

23. A device according to claim 21 or claim 22 characterised in that the thickness of the film is between 5 and 30 microns.

24. An alkoxyphthalocyanine substantially as hereinbefore described with reference to any one of the Examples 1 to 5.

25. A method of preparing an alkoxyphthalocyanine substantially as hereinbefore described with reference to any one of the Examples 1 to 5.

26. A liquid crystal material containing an alkoxyphthalo-cyanine substantially as herein before described with reference to any one of the Examples 6 to 9.