Liquid crystal photoalignment materials

Abstract

A charge transporting, liquid crystal photoalignment material comprising a charge transporting moiety connected through covalent chemical bonds to a surface derivatising moiety, and a photoalignment moiety connected through covalent chemical bonds to a surface derivatising moiety.

Claims

1. A charge transporting, liquid crystal photoalignment material comprising hole transporting moiety and a liquid crystal photoalignment moiety wherein both the hole transporting moiety and the liquid crystal photoalignment moiety form at least one single fused aromatic ring system which constitutes a combined hole transporting and liquid crystal photoalignment moiety and wherein the hole transporting moiety and the liquid crystal photoalignment moiety of the at least one single fused aromatic ring system are not separated by one or more linkages, and wherein the combined hole transporting and liquid crystal photoalignment moiety is connected through a covalent chemical bond to a surface derivatising moiety.

2. The charge transporting, liquid crystal photoalignment material of claim 1, wherein the combined hole transporting and liquid crystal photoalignment moiety includes a hole transporting moiety having the following structure: ##STR00010##

3. The charge transporting, liquid crystal photoalignment material of claim 1, wherein the combined hole transporting and liquid crystal photoalignment moiety comprises a photoalignment moiety including one or more of a cinnamate ester, a coumarin, a quinolinone, or a benzo[b]thiinone.

4. The charge transporting, liquid crystal photoalignment material of claim 1, wherein the combined hole transporting and liquid crystal photoalignment moiety is chosen from: ##STR00011##

5. The charge transporting, liquid crystal photoalignment material of claim 1, wherein the surface derivatising moiety comprises a trihalosilanyl group, a trialkoxysilanyl group, or a Werner complex of transition metals.

6. The charge transporting, liquid crystal photoalignment material of claim 5, wherein the surface derivatising moiety is selected from the group consisting of a trichlorosilanyl group, a triethoxysilanyl group, a trimethoxysilanyl group, a -carboxylato--hydroxido-bis[aquadichloridoethanolchromium(III)] group, an alkali metal enolate salt of a 1,3-dialkyl substituted pentane-1,3-dione, an alkaline earth metal enolate salt of a 1,3-dialkyl substituted pentane-1,3-dione, and an alkali metal salt of a dialkylamine.

7. The charge transporting, liquid crystal photoalignment material of claim 1, wherein the surface derivatising moiety is connected to the combined hole transporting and liquid crystal photoalignment moiety by a flexible linkage, wherein the flexible linkage is a flexible ethylene, a flexible trimethylene, or a flexible hexamethylene linkage.

8. A charge transporting layer fabricated by first forming a layer comprising the charge transporting, liquid crystal photoalignment material of claim 1, then coating a layer of a charge transporting reactive mesogen material onto the charge transporting, liquid crystal photoalignment layer, then crosslinking the charge transporting reactive mesogen.

9. The charge transporting layer of claim 8, wherein the charge transporting layer has a uniformly aligned liquid crystalline structure.

10. The charge transporting layer of claim 8, wherein the charge transporting layer has a uniformly aligned nematic structure.

Description

(1) The invention comprises a charge transporting, liquid crystal photoalignment material comprising a charge-transporting moiety connected through covalent chemical bonds to a surface derivatising moiety, and a photoalignment moiety connected through covalent chemical bonds to a surface derivatising moiety.

(2) The invention also comprises a method for forming charge transporting, liquid crystal photoalignment layer comprising the immersion of a glass or similar substrate into a solvent solution of material comprising a charge transporting moiety connected through covalent chemical bonds to surface derivatising moiety and a liquid crystal photoalignment moiety connected through covalent chemical bonds to a surface derivatising moiety and then withdrawing and drying said substrate.

(3) The invention also comprises a charge transporting liquid crystal photoalignment layer produced by such a method.

(4) The invention also comprises an electronic device incorporating such a layer.

(5) The invention also comprises a light emitting polymer layer formulated by first forming a charge transporting liquid crystal photoalignment layer by a method aforesaid, then coating a layer of a luminescent reactive mesogen material onto the liquid crystal photoalignment layer, then crosslinking the luminescent reactive mesogen.

(6) The invention also comprises an electronic device that comprises a charge transporting layer or a light emitting polymer layer as aforesaid.

(7) The invention also comprises a light emitting diode that comprises a light emitting polymer layer as aforesaid.

(8) Examples of surface derivatising materials of the invention that are intended to be used to form hole transporting photoalignment layers of this type are portrayed in FIGS. 5-9. In the molecules in these figures chemical functional units that fulfill the hole transporting role are labelled A, chemical functional units that fulfill the photoalignment role are labelled B, and surface derivatising functional units are labelled C. The hole transporting functional units (A) utilized in these examples include one or more functional sub-units that are chosen from a set including thieno[3,2-b]thiophene, dithieno[3,2-b:2,3-d]thiophene, thieno[3,2-d]thieno[3,2-b:4,5-b]dithiophene, 2,2-bithiophene, 2,2:5,2-terthiophene, 2,2:5,2:5,2quaterthiophene, benzo[1,2-b:4,5-b]dithiophene, benzo[1,2-b:3,4-b:5,6-b]trithiophene, naphthol[2,3-b:6,7-b]dithiophene, benzo[4,5]thieno[3,2-d]benzo[b]thiophene, triphenylamine, 1,4-bis(diphenylamino)benzene, 1,3,5-tris(diphenylamino)benzene, 4,4-bis(diphenylamino)biphenyl, N,N-diphenyl-N-naphth-1-ylamine, N-phenyl-N,N-dinaphth-1-ylamine, trinaphth-1-ylamine, thiazolo[4,5-d]thiazole, 2,2-bithiazole, 2,2:5,2-terthiazole, N,N,N-tris(benzo[b]thiophene-5-yl)amine, thiazolo[4,5-b]thiophene, N,N,N-tris(benzo[d]thiazole-5-yl)amine, or other thiophene containing sub-units, triarylamine containing sub-units, thiazole containing sub-units, or sub-units that combine more than one of these three functionalities.

(9) ##STR00001## ##STR00002## ##STR00003##

(10) The photoalignment functional units (B) utilized in these examples include one or more functional sub-units that are chosen from a set including cinnamate esters, coumarins, quinolones (quinolin-2-ones), and thiocoumarins (benzo[b]thiin-2-ones).

(11) ##STR00004##

(12) An example of a functional sub-unit that combines the hole transporting and photoalignment functionalities is the thieno[23:4,5]thieno[2,3-b]thiine-6-one functional sub-units found in the molecule in FIG. 9.

(13) ##STR00005##

(14) Other similar sub-units with combined functionalities may be funned, for instance:

(15) ##STR00006##

(16) These sub-units are similar to the thiocoumarin and coumarin ring systems in that they have similar ,-unsaturated thiolactone and lactone six-membered rings fused to aromatic systems. In these cases the fused aromatic, ring systems are hole transporting in nature.

(17) In the case of the material portrayed in FIG. 9, the two thieno[23:4,5]thieno[2,3-b]thiin-6-one functional sub-units are connected by a 1,4 phenylene nucleus to form combination hole transporting and photoalignment functional units within the material's molecules (labelled A&B, in the figure).

(18) The surface derivatising functional units labelled C in FIGS. 5-9 may be chosen from a set including trihalosilanyl groups (especially trichlorosilanyl groups), trialkoxysilanyl groups (especially methoxy and ethoxy), and Werner complexes of transition metals. In particular if metal complexes are used, dinuelear carboxyl to complexes of transition metals of the type

(19) ##STR00007##

(20) are preferred. Here R represents the remainder of the inventive, surface derivatising, hole transporting, photoalignment material molecule; M represents a transition metal (preferably with oxidation state+3 and most preferably CrIII; X represents an anionic ligand chosen from halido (e.g., chlorido), pseudo halide (e.g., cyanido, cyanato, etc.) or an oxoacid derived anion (e.g. nitrato); and R represents an organic radical, preferably an alkyl radical and most preferably methyl or ethyl. The example shown in FIG. 7 utilises as surface derivatising functional units -carboxylato--hydroxido-bis[aquadichloridoethanolchromium(III)] groups (R taken as ethyl).

(21) It may be useful, in terms of sterically freeing the surface derivatising functional units to interact with substrate surfaces, or freeing photoalignment groups to assume random orientations, to introduce into the molecules of inventive materials flexible linkages between one or another of the hole transporting or photoalignment or surface derivatising functional units. For instance, in the example shown in FIG. 7 the coumarin-containing photoalignment functional units (B) are linked with the hole transporting nucleus of the molecules through flexible trimethylene linkages. In the molecule portrayed in FIG. 5 the photoaligning cinnamate functional units are connected to the hole transporting molecular nucleus through flexible ethylene linkages while the surface derivatising trichlorosilyl groups are connected to the same nucleus through flexible hexamethylene linkages.

(22) A further embodiment of the invention consists of surface derivatising materials that are intended to be used to form electron transporting photoalignment layers. All example of this type of material is shown in FIG. 10. These materials differ from the hole transporting materials exemplified by the structures in FIG. 5-9 in that the molecular functional units labelled A are electron transporting rather than hole transporting. The electron transporting functional units may be built of from a set of sub-units including, selected independently from, but not limited to, aryl 1,2,4-triazoles (especially triaryl 1,2,4-triazoles), 1,3-oxazoles, 2,2-bi-1,3-oxazoles, 1,2,4-oxadiazoles, 3,3-bi-1,2,4-oxadiazoles, imidazo[4,5-d]-imidazoles, benzo[1,2-d:4,5-d]dioxazoles, benzo[1,2-d2,3-d:4,5-d]trioxazoles, bathocuproines, and bathophenanthrolines.

(23) ##STR00008##

(24) The photoalignment functional units B used in the molecules of this embodiment are the same as those that are used in the hole-transporting embodiment.

(25) The surface derivatising functional units used in this embodiment are of necessity different from those used in the hole-transporting embodiment. Since the electron transporting, photoalignment materials must surface derivatise an active metal cathode the chemistry involved is different. The surface derivatising functional groups of this embodiment may be chosen from a set including, but not limited to, alkali metal and alkaline earth metal enolate salts of 1,3-dialkyl substituted pentane-1,3-diones (preferably calcium salts) and alkali metal salts of dialkylamines that are chemically bonded to the electron transporting and photoalignment functional units of the molecules of the embodiment materials, trihalosilyl groups, and trialkoxysilyl groups.

(26) A further embodiment of the invention consists of a process for forming hole transporting or electron transporting photoalignment layers formed by contacting device substrates with solutions containing materials whose molecules comprise at least one or more of each of a charge transporting functional unit, a photoalignment functional unit, surface derivatising functional unit. These layers may be formed by one or more cycles of applying said solutions and heat curing said solutions. Preferred hole transporting or electron transporting functional layers may be harmed carrying out between 3 and 7 application and cure cycles. The structure of the photoalignment layer formed by two application and cure cycles of the material in FIG. 5 is shown in FIG. 11.

(27) Yet a further embodiment of the patent consists of forming a hole transporting or electron transporting photoalignment layer by contacting device substrates with solutions containing a mixture of at least two materials at least one of which is a first material that comprises molecules containing at least one or more of each of a charge transporting functional unit and a surface derivatising functional unit, and at least one of which is a second material that comprises molecules containing at least one or more of each of a liquid crystal photoalignment functional unit and a surface derivatising functional unit.

(28) An example of a hole transporting photoalignment layer formed from such a mixture is the following. A solution of 0.8 grams/liter of compound 1200 (FIG. 12) and 1.6 grams/liter of compound 1300 (FIG. 13) in toluene is puddled onto the surface of an indium-tin oxide OLED anode for two minutes. The device is then spun at 2500 rpm, rinsed with toluene to remove excess material, and then cured at 90 C. for one hour. This deposition and thermal cure cycle is repeated three more times. The coated part is rinsed in deionised water for 15 minutes to remove ionic impurities. And then dried at 120 C. in a vacuum oven for 15 minutes. The resultant alignment film coated substrates are then exposed to polarized 325 nm. wavelength radiation from HeCd laser to induce the anisotropic surface energy required for liquid crystal alignment. After this exposure the films are ready to be overcoated with reactive mesogen emitter or reactive mesogen charge transporting material. After the coated reactive mesogen is annealed above its nematic to isotropic transition temperature and cooled it will be uniformly aligned by the underlying photoalignment material.

(29) A farther improvement on the mixture-based charge transporting layers consists of changing the ratio of the number of photoalignment functional units to charge transporting functional units within the photoalignment material film from one monomolecular layer to the next. As an example, using the material deposition technique outlined in the preceding paragraph a first mono-molecular layer is deposited using a solution of 2.4 grams/liter of material 1200 in toluene. Next mono-molecular layers are deposited from a solution 1.8 grams/liter of material 1200 and 0.6 grams/liter of material 1300 in toluene. Finally a fourth mono-molecular layer is deposited from a solution of 0.6 grams/liter of material 1200 and 1.8 grams/liter of material 1300 in toluene. A bole transporting photoalignment layer of this type with a varying concentration photoalignment functional unit from one mono-molecular layer to the next may be used advantageously to maximize hole transporting characteristics while maintaining good liquid crystal alignment.

(30) In these examples the molecules of the first, hole transporting, material may be chosen from a group of materials whose molecules combine one or more hole transporting functional units with one or more surface derivatising functional units. In turn, the hole transporting functional units comprise one or more functional sub-units that are chosen from a set including:

(31) ##STR00009##

(32) or triarylamines as was the ease in the work described in U.S. Pat. No. 5,834,100.

(33) The photoalignment functional units utilized in the second materials include one or more functional sub-units that are chosen from a set including cinnamate esters, coumarins, quinolones (quinolin-2-ones), and thiocoumarins (benzo[b]thiin-2-ones).

(34) The surface derivatising functional units in both the first and second materials may be chosen from a set including trihalosilanyl groups (especially trichlorosilanyl groups), trialkoxysilanyl groups (especially methoxy and ethoxy), and Werner complexes of transition metals. In particular if metal complexes are used, dinuclear carboxylato complexes of transition metals of the type discussed above are preferred.

(35) Further examples of the first, hole transporting, materials are shown in FIGS. 14-16. Further examples of the second, photoalignment, materials are shown in FIGS. 17-18.

BRIEF DESCRIPTION OF THE DRAWINGS

(36) A full and enabling disclosure of the present disclosure is provided in the specification, including reference to the accompanying figures, in which:

(37) FIG. 1 illustrates a prior art electroluminescent device;

(38) FIG. 2 illustrates the structure of tris[4-(trichlorosilyl)phenyl]amine;

(39) FIG. 3 illustrates monolayer structure on a substrate after curing;

(40) FIG. 4 illustrates a structure containing multiple molecular layers obtained after several cycles;

(41) FIGS. 5-9 illustrate examples of surface derivatising, materials that can be used to form hole transporting photoalignment layers;

(42) FIG. 10 illustrates an example of a surface derivatising, materials that can be used to form an electron transporting photoalignment layer;

(43) FIG. 11 illustrates the structures of the photoalignment layer formed by two application and cure cycles of the material of FIG. 5;

(44) FIGS. 12 and 13 illustrate two compounds used to form a hole transporting photoalignment layer;

(45) FIGS. 14-16 illustrate examples of hole transporting materials; and

(46) FIGS. 17-18 illustrate examples of photoalignment materials.

(47) Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention,