Oligomeric organic light emitting diode (OLED) materials containing multiple crosslinking functions

Abstract

OLED materials having the formula: T-A(-S-B(-P-B)m-S-A)n-T where A are independently selected rod-shaped, rigid molecular core units, S are independently selected flexible spacer units, B are polymerisable crosslinking groups independently selected, P are spacer groups independently selected, T are independently selected end groups, m are independently selected from values of from 1 to 4, n is equal to I to 3.

Claims

1. An OLED comprising materials having the formula:
T-A(-S-B(-P-B(-P-B).sub.m-S-A).sub.n-T where A are independently selected rod-shaped, rigid molecular core units having the general structure:
-E-F-(E-F).sub.X-E- wherein E is independently chosen from a single bond or an aromatic diradical disubstituted so as to maintain the linear nature of rigid molecular core A, wherein F is a diradical containing a fluorene, an azafluorene or a polyazafluorene aromatic ring system and which is disubstituted so as to maintain the linear nature of the rigid molecular core A, and wherein x is between 0 and 7, S are independently selected flexible spacer units which are branched, straight chain, or cyclic alkyl groups with 3 to 12 carbon atoms, which are unsubstituted or mono- or poly-substituted by F, Cl, Br, l, or CN or wherein one or more nonadjacent CH.sub.2 groups are replaced by —O—, —S—, —NH—, —NR—, —SiRR—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CH═CH—, —C≡C— such that O and S atoms are not directly linked to other O or S atoms, B are independently selected polymerisable crosslinking groups, P are independently selected spacer groups, T are independently selected end groups which are chosen from hydrogen, an alkyl chain, an alkoxy chain, a cyano group or a fluorine, or where the T group comprises an alkyl chain or an alkoxy chain, the chain is optionally terminated with terminal crosslinking groups, m are independently selected from values of from 1 to 4, n is equal to 1 to 3.

2. The OLED according to claim 1, wherein the materials display liquid crystalline order.

3. The OLED according to claim 1, wherein the materials display nematic order.

4. The OLED according to claim 1, in which x is between 0 and 4.

5. The OLED according to claim 1, wherein each B is independently selected from: ##STR00044## ##STR00045##

6. The OLD according to claim 1, wherein each P is independently selected from: ##STR00046## ##STR00047## ##STR00048##

7. The OLED according to claim 1, wherein the crosslinking (B) and spacer (P) functionalities are combined in a single structural sub-unit of the molecule to form a structure selected from: ##STR00049## ##STR00050##

8. The OLED according to claim 1, wherein the terminal cross linking groups are selected from: ##STR00051##

9. An OLED device comprising the OLED materials according to claim 1.

10. An OLED device formed by crosslinking the OLED materials according to claim 1 wherein the crosslinking groups are polymerized by exposure to UV light.

Description

(1) The present invention provides liquid crystalline, photopolymerisable host materials having suitable electronic properties, but which are relatively inexpensive to make

(2) The invention, in one aspect, comprises materials having the formula:
T-A(-S-B(-P-B).sub.m-S-A).sub.n-T
where A are independently selected rod-shaped, rigid molecular core units, S are independently selected flexible spacer units, B are polymerisable crosslinking groups independently selected, P are spacer groups independently selected, T are independently selected end groups, m are independently selected from values of from 1 to 4, n is equal to 1 to 3.

(3) The crosslinking groups may be chosen so as to allow the molecules to be polymerised into a polymer matrix, particularly by exposure to UV. The molecular nucleus or core units and also the spacer units may be chosen such that the material displays liquid crystalline order and most preferably that it displays nematic order. It is also preferred that the core units are chosen so as to promote either light emitting or charge transporting properties, or both, in the product polymer matrix.

(4) The rod-shaped, rigid molecular core units (A) may be any conjugated aromatic ring systems, but it is preferred that they have the general structure:
-E-F-(E-F).sub.n-E-
wherein E may be independently chosen from a single bond or an aromatic diradical disubstituted so as to maintain the linear nature of rigid molecular core A, and wherein F is a diradical containing a fluorene, azafluorene or polyazafluorene aromatic ring system and which is disubstituted so as to maintain the linear nature of the rigid molecular core A, and wherein n is between 0 and 7, preferably between 0 and 4.

(5) Examples of E sub-units are:

(6) ##STR00003## ##STR00004## ##STR00005## ##STR00006## ##STR00007## ##STR00008##
wherein R may be hydrogen, alkyl or fluoroalkyl. Further examples of E sub-units are:

(7) ##STR00009## ##STR00010##
wherein R may be an alkyl or fluorinated alkyl group.

(8) Examples of F sub-units are:

(9) ##STR00011## ##STR00012## ##STR00013## ##STR00014##
wherein X are chosen independently from CH, N, CR′, or CF, and R′═C.sub.nH.sub.2n+1 where n has a value chosen independently from 1 to 5; Y and Z are chosen independently from CH.sub.2, CHR″, CR″.sub.2, NH, NR″, O, S, S═O, O═S═O, and C═O and R″═C.sub.nH.sub.2n+1 where n has a value chosen independently from 1 to 5; R are independently chosen from H or C.sub.nH.sub.2n+1 where n has a value chosen independently from 1 to 10, and m has a value between 3 and 7.

(10) Other examples of F sub-units are:

(11) ##STR00015## ##STR00016##
wherein the substituents may independently be one of structures:

(12) ##STR00017## ##STR00018## ##STR00019##
and wherein R is an alkyl group and may be chosen from methyl, ethyl, propyl, butyl, isopropyl, sec-butyl, isobutyl, tert-butyl, 2-amyl, 3-amyl, 2-methyl-2-butyl, 3-methyl-3-amyl, 3-ethyl-3-amyl, neo-pentyl, hexyl, heptyl, octyl, nonyl, or decyl and X may be independently selected from ═CH—, ═N—, CR′, or CF, and R′═C.sub.nH.sub.2n+1 where n has a value chosen independently from 1 to 5.

(13) The flexible spacer units S may be branched, straight chain, or cyclic alkyl groups with 3 to 12 carbon atoms, which are unsubstituted, or mono- or poly-substituted by F, Cl, Br, I, or CN or wherein one or more nonadjacent CH.sub.2 groups are replaced by —O—, —S—, —NH—, —NR—, —SiRR—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CH═CH—, —C≡C— such that O and S atoms are not directly linked to other O or S atoms.

(14) The spacer units P separate the crosslinking groups B from each other and help determine the stiffness of the polymer matrix formed after the molecules have been crosslinked. More rigid P units, for instance those composed of aromatic rings, will lead to a stiffer, more rigid polymer. More flexible P spacers, for instance simple alkyl chains, will result in a softer more deformable polymer matrix. Altering the characteristics of the P spacers can be used to “tune” the characteristic of the resulting polymer matrix film.

(15) A further aspect of the invention is that mixtures of materials with varying length spacers may be used to destabilise the more highly ordered smectic phases in favour of the nematic phase if that is desired.

(16) Examples of spacer groups (P) are:

(17) ##STR00020##

(18) Crosslinking group (B) may be any crosslinking group so long as it is difunctionalised such that it may be incorporated in the backbone of the molecule, for instance:

(19) ##STR00021##

(20) Mixtures may be used of two or more molecules in at least one of which the crosslinking units are electron deficient and in at least another one of which the crosslinking units are electron rich. In mixtures of this type crosslinking proceeds by way of electron transfer polymerization. Crosslinking liquid crystalline materials using this technique for use in OLEDs and other organic electronics has previously been described in patent application WO2007064721.

(21) Examples of electron deficient crosslinking groups that may serve as the B group in the invention are:

(22) ##STR00022## ##STR00023## ##STR00024##

(23) Examples of electron rich crosslinking groups that may serve as the B group in the invention are:

(24) ##STR00025##

(25) The end groups T may be chosen from hydrogen, an alkyl chain, an alkoxy chain, a cyano group or a fluorine. The alkyl and alkoxy chains may comprise branched, straight chain, or cyclic alkyl groups with 1 to 12 carbon atoms, which are unsubstituted, or mono- or poly-substituted by F, Cl, Br, I, or CN or wherein one or more nonadjacent CH.sub.2 groups are replaced by —O—, —S—, —NH—, —NR—, —SiRR—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S—, —CH═CH—, —C≡C— such that O and S atoms are not directly linked to other O or S atoms. The alkyl or alkoxy chains may be terminated with crosslinking groups. Examples of these terminal crosslinking groups are:

(26) ##STR00026##

(27) Examples of molecular structures of the inventive materials are:

(28) ##STR00027## ##STR00028## ##STR00029## ##STR00030## ##STR00031##

(29) Compounds with structures 29, 30, 31, 33, and 34 in which m=n=1 are, in general preferred because they are simpler and less expensive to prepare.

(30) Since the -S-B-P-B-S- structure will, in general, be easily prepared and therefore less expensive than adding on additional aromatic rings in the molecular core units, the inventive compounds provide a method to increase molecular weight and to enhance the film forming characteristics of solutions of the materials with minimal impact to the cost of manufacture. In addition, the length of the molecule is increased without substantially altering chromophoric properties of the molecular core. The capability can prove most useful when developing host materials that require relatively short wavelength luminescence bands to be compatible with guest emitter materials.

(31) In another embodiment of the invention the crosslinking (B) and spacer (P) functionalities can be combined in a single structural sub-unit of the molecule. Some examples of these sorts of structures are:

(32) ##STR00032## ##STR00033##

(33) In another embodiment of the invention, materials having the formula:
T-A(-S-B(-P-B).sub.m-S-A).sub.n-T
may be mixed with the prior art materials having the formulae B-S-A-S or B-S-A-S-B.

(34) For instance one equivalent of material having the structure 29 from above:

(35) ##STR00034##
could be mixed with two equivalents of material consisting of 3 mole % of a compound with formula:

(36) ##STR00035##
and 97 mole % of a compound with formula:

(37) ##STR00036##

(38) The material is then coated down and polymerized to form the copolymer.

(39) In yet a further embodiment of the invention, material having structure 29, for example, may be copolymerised with a non-liquid crystalline monomer, for instance:

(40) ##STR00037##

(41) This provides a method of producing a polymer matrix film by the electron transfer polymerization method while only using only single liquid crystalline material of the invention.

(42) An exemplary synthesis follows:

Compounds Used for Exemplary Synthesis

(43) ##STR00038##

Synthesis of Compound 1

(44) ##STR00039## ##STR00040## ##STR00041## ##STR00042##

Synthesis of Compound 2

(45) ##STR00043##