Polymers, their preparation and uses

Abstract

A polymer containing an optionally substituted repeat unit of formula (I) wherein each R is the same or different and represents H or an electron withdrawing group, and each R.sup.1 is the same or different and represents a substituent. ##STR00001##

Claims

1. A monomer of formula (II): ##STR00041## wherein each R is H; each R1 is the same or different and represents a substituent that is not aryl or heteroaryl; and each X is the same or different and is selected from the group consisting of boronic acid groups, boronic ester groups, borane groups and halide functional groups.

2. A monomer according to claim 1 wherein at least one R1 is a solubilizing group.

3. A monomer according to claim 1 wherein each R1 is the same or different and is independently selected from the group consisting of optionally substituted C1-20 alkyl, and optionally substituted C1-20 alkoxy.

4. A method of forming a polymer comprising the step of polymerizing a monomer according to claim 1.

5. A method according to claim 4 wherein the polymer is a copolymer formed by polymerizing the monomer with one or more co-monomers.

6. A method according to claim 5 wherein the monomer is polymerized with a co-monomer for forming an optionally substituted aryl or heteroaryl repeat unit.

7. A method according to claim 5 wherein the co-monomer is a co-monomer for forming an optionally substituted fluorene repeat unit.

8. A method according to claim 5 wherein the copolymer is an alternating copolymer.

9. A method according to claim 5 wherein the copolymer is a random copolymer.

10. A method according to claim 5 wherein the copolymer is a block copolymer.

11. A method according to claim 4 wherein each X is the same or different and is a halide functional group, and the polymerization is performed in the presence of a nickel complex catalyst.

12. A method according to claim 4 comprising the step of polymerizing : (a) a monomer of formula (II) wherein each X is a boron the same or different and is a boron derivative functional group selected from a boronic acid, a boronic ester and a borane, and an aromatic monomer having at least two reactive halide functional groups; or (b) a monomer of formula (II) wherein each X is the same or different and is a reactive halide functional group, and an aromatic monomer having at least two boron derivative functional group selected from a boronic acid, a boronic ester and a borane; or (c) a monomer of formula (II) wherein one X is a reactive halide functional group and the other X is a boron derivative functional group selected from a boronic acid, a boronic ester and a borane, wherein the reaction mixture comprises a catalytic amount of a palladium catalyst suitable for catalyzing the polymerization of the aromatic monomers, and a base in an amount sufficient to convert the boron derivative functional groups into boronate anionic groups.

13. A monomer of formula (II): ##STR00042## wherein each R is H; each R1 is the same or different and represents a substituent; and each X is the same or different and is selected from the group consisting of boronic acid groups, boronic ester groups, borane groups and halide functional groups, wherein each R1 is the same or different and is independently selected from the group consisting of optionally substituted C1-20 alkyl, and optionally substituted C1-20 alkoxy.

14. A monomer according to claim 13 wherein at least one R1 is a solubilizing group.

15. A method of forming a polymer comprising the step of polymerizing a monomer according to claim 13.

16. A method according to claim 15 wherein the polymer is a copolymer formed by polymerizing the monomer with one or more co-monomers.

17. A method according to claim 16 wherein the monomer is polymerized with a co-monomer for forming an optionally substituted aryl or heteroaryl repeat unit.

18. A method according to claim 16 wherein the co-monomer is a co-monomer for forming an optionally substituted fluorene repeat unit.

19. A method according to claim 16 wherein the copolymer is an alternating copolymer.

20. A method according to claim 16 wherein the copolymer is a random copolymer.

21. A method according to claim 16 wherein the copolymer is a block copolymer.

22. A method according to claim 15 wherein each X is the same or different and is a halide functional group, and the polymerization is performed in the presence of a nickel complex catalyst.

23. A method according to claim 15 comprising the step of polymerizing : (a) a monomer of formula (II) wherein each X is a boron the same or different and is a boron derivative functional group selected from a boronic acid, a boronic ester and a borane, and an aromatic monomer having at least two reactive halide functional groups; or (b) a monomer of formula (II) wherein each X is the same or different and is a reactive halide functional group, and an aromatic monomer having at least two boron derivative functional group selected from a boronic acid, a boronic ester and a borane; or (c) a monomer of formula (II) wherein one Xis a reactive halide functional group and the other X is a boron derivative functional group selected from a boronic acid, a boronic ester and a borane, wherein the reaction mixture comprises a catalytic amount of a palladium catalyst suitable for catalyzing the polymerization of the aromatic monomers, and a base in an amount sufficient to convert the boron derivative functional groups into boronate anionic groups.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be described in further detail, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 shows a prior art electroluminescent device

(3) FIG. 2(a) shows a plot of photoluminescent wavelength over time for a prior art polyfluorene

(4) FIG. 2(b) shows a plot of photoluminescent wavelength over time for a co-polymer according to the invention

(5) FIG. 2(c) shows a plot of photoluminescent wavelength over time for a homopolymer according to the invention

(6) FIG. 3 shows a plot of electroluminescent wavelength for polymers according to the invention as compared to a prior art polyfluorene

DETAILED DESCRIPTION OF THE INVENTION

(7) A polymer according to the present invention may comprise a homopolymer or copolymers (including terpolymers or higher order polymers).

(8) Copolymers according to the present invention include regular alternating, random and block polymers where the percentage of each monomer used to prepare the polymer may vary.

(9) Preferred co-repeat units include triarylamines, arylenes and heteroarylenes.

(10) Examples of arylene repeat units are fluorene, particularly 2,7-linked 9,9 dialkyl fluorene or 2,7-linked 9,9 diaryl fluorene; spirofluorene such as 2,7-linked 9,9-spirofluorene; indenofluorene such as a 2,7-linked indenofluorene; or phenyl such as alkyl or alkoxy substituted 1,4-phenylene. Each of these groups may optionally be substituted.

(11) Particularly preferred triarylamine repeat units derived from triarylamine monomers include units of formulae 1-6:

(12) ##STR00015##

(13) A and B may be the same or different and are substituent groups. It is preferred that one or both of A and B is independently selected from the group consisting of alkyl, aryl, perfluoroalkyl, thioalkyl, cyano, alkoxy, heteroaryl, alkylaryl and arylalkyl groups. One or more of A and B also may be hydrogen. It is preferred that one or more of A and B is independently an unsubstituted, isobutyl group, an n-alkyl, an n-alkoxy or a trifluoromethyl group because they are suitable for helping to select the HOMO level and/or for improving solubility of the polymer.

(14) Particularly preferred heteroaryl repeat units include units of formulae 7-21:

(15) ##STR00016##

(16) wherein R.sub.6 and R.sub.7 are the same or different and are each independently hydrogen or a substituent group, preferably alkyl, aryl, perfluoroalkyl, thioalkyl, cyano, alkoxy, heteroaryl, alkylaryl or arylalkyl. For ease of manufacture, R.sub.6 and R.sub.7 are preferably the same. More preferably, they are the same and are each a phenyl group.

(17) ##STR00017## ##STR00018## ##STR00019##

(18) Further suitable Ar groups are known in this art, for example as disclosed in WO 00/55927 and WO 00/46321, the contents of which are incorporated herein by reference.

(19) For ease of processing, it is preferred that the polymer is soluble. Substituents such as C.sub.1-10 alkyl or C.sub.1-10alkoxy may usefully be selected to confer on the polymer solubility in a particular solvent system. Typical solvents include mono- or poly-alkylated benzenes such as toluene and xylene or tetrahydrofuran. Techniques for solution deposition of the polymer according to the invention include inkjet printing as disclosed in EP 0880303, spin-coating, dip-coating, doctor blade coating and screen printing.

(20) The polymers according to the invention may carry cross-linkable groups such as oxetanes, azides, acrylates, vinyl and ethynyl groups in order that the polymer may be deposited in a soluble form followed by cross-linking to render the polymer insoluble. Cross-linking may be achieved through thermal treatment or exposure of the polymer to radiation, in particular UV radiation. Cross-linking may be employed to allow deposition of multiple layers from solution as disclosed in WO 96/20253. Alternatively, photo-initiated cross-linking may be used by exposure of a polymer layer through a mask to form a pattern of insoluble material from which unexposed, soluble polymer may be removed by solvent treatment as disclosed in Nature 421, 829-833, 2003.

(21) Two polymerisation techniques that are particularly amenable to preparation of conjugated polymers from aromatic monomers such as dibenzosilole monomers according to the invention are Suzuki polymerisation as disclosed in, for example, WO 00/53656 and Yamamoto polymerisation as disclosed in, for example, “Macromolecules”, 31, 1099-1103 (1998). Suzuki polymerisation entails the coupling of halide and boron derivative functional groups; Yamamoto polymerisation entails the coupling of halide functional groups. Accordingly, it is preferred that each monomer is provided with two reactive functional groups wherein each functional group is independently selected from the group consisting of (a) boron derivative functional groups selected from boronic acid groups, boronic ester groups and borane groups and (b) halide functional groups.

(22) The transmetallating agents used to prepare monomers of the invention include alkyl- and aryl-lithium compounds such as methyllithium, n-butyllithium, t-butyllithium, phenyllithium and lithium di-isopropyl amine.

(23) Examples of monomers of formula (VI) preparable according to the method of the invention include the following:

(24) ##STR00020## ##STR00021## ##STR00022##

(25) With reference to FIG. 1, the standard architecture of an optical device according to the invention, in particular an electroluminescent device, comprises a transparent glass or plastic substrate 1, an anode of indium tin oxide 2 and a cathode 4. The polymer according to the invention is located in layer 3 between anode 2 and cathode 4. Layer 3 may comprise the polymer according to the invention alone or a plurality of polymers. Where a plurality of polymers are deposited, they may comprise a blend of at least two of a hole transporting polymer, an electron transporting polymer and, where the device is a PLED, an emissive polymer as disclosed in WO 99/48160. Alternatively, layer 3 may be formed from a single polymer that comprises regions selected from two or more of hole transporting regions, electron transporting regions and emissive regions as disclosed in, for example, WO 00/55927 and U.S. Pat. No. 6,353,083. Each of the functions of hole transport, electron transport and emission may be provided by separate polymers or separate regions of a single polymer. Alternatively, more than one function may be performed by a single region or polymer. In particular, a single polymer or region may be capable of both charge transport and emission. Each region may comprise a single repeat unit, e.g. a triarylamine repeat unit may be a hole transporting region. Alternatively, each region may be a chain of repeat units, such as a chain of polyfluorene or dibenzosilole units as an electron transporting region. The different regions within such a polymer may be provided along the polymer backbone, as per U.S. Pat. No. 6,353,083, or as groups pendant from the polymer backbone as per WO 01/62869.

(26) In addition to layer 3, a separate hole transporting layer and/or an electron transporting layer may be provided.

(27) The polymers according to the invention may be used as the host for a fluorescent dopant as disclosed in, for example, J. Appl. Phys. 65, 3610, 1989 or as the host for a phosphorescent dopant as disclosed in, for example, Nature (London), 1998, 395, 151.

(28) Preferred metal complexes comprise optionally substituted complexes of formula (XI):
M.sup.1L.sup.1.sub.qL.sup.2.sub.rL.sup.3.sub.s   (XI)

(29) wherein M.sup.1 is a metal; each of L.sup.1, L.sup.2 and L.sup.3 is a coordinating group; q is an integer; r and s are each independently 0 or an integer; and the sum of (a. q)+(b. r)+(c.s) is equal to the number of coordination sites available on M, wherein a is the number of coordination sites on L.sup.1, b is the number of coordination sites on L.sup.2 and c is the number of coordination sites on L.sup.3.

(30) Heavy elements M induce strong spin-orbit coupling to allow rapid intersystem crossing and emission from triplet states (phosphorescence). Suitable heavy metals M include:

(31) lanthanide metals such as cerium, samarium, europium, terbium, dysprosium, thulium, erbium and neodymium; and

(32) d-block metals, in particular those in rows 2 and 3 i.e. elements 39 to 48 and 72 to 80, in particular ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum and gold.

(33) Suitable coordinating groups for the f-block metals include oxygen or nitrogen donor systems such as carboxylic acids, 1,3-diketonates, hydroxy carboxylic acids, Schiff bases including acyl phenols and iminoacyl groups. As is known, luminescent lanthanide metal complexes require sensitizing group(s) which have the triplet excited energy level higher than the first excited state of the metal ion. Emission is from an f-f transition of the metal and so the emission colour is determined by the choice of the metal. The sharp emission is generally narrow, resulting in a pure color emission useful for display applications.

(34) The d-block metals form organometallic complexes with carbon or nitrogen donors such as porphyrin or bidentate ligands of formula (XII):

(35) ##STR00023##

(36) wherein Ar.sup.1 and Ar.sup.2 may be the same or different and are independently selected from optionally substituted aryl or heteroaryl; Z.sup.1 and Z.sup.2 may be the same or different and are independently selected from carbon or nitrogen; and Ar.sup.1 and Ar.sup.2 may be fused together. Ligands wherein Z.sup.1 is carbon and Z.sup.2 is nitrogen are particularly preferred.

(37) Examples of bidentate ligands are illustrated below:

(38) ##STR00024##

(39) Each of Ar.sup.1 and Ar.sup.2 may carry one or more substituents. Particularly preferred substituents include fluorine or trifluoromethyl which may be used to blue-shift the emission of the complex as disclosed in WO 02/45466, WO 02/44189, US 2002-117662 and US 2002-182441; alkyl or alkoxy groups as disclosed in JP 2002-324679; carbazole which may be used to assist hole transport to the complex when used as an emissive material as disclosed in WO 02/81448; bromine, chlorine or iodine which can serve to functionalise the ligand for attachment of further groups as disclosed in WO 02/68435 and EP 1245659; and dendrons which may be used to obtain or enhance solution processability of the metal complex as disclosed in WO 02/66552.

(40) Other ligands suitable for use with d-block elements include diketonates, in particular acetylacetonate (acac); triarylphosphines and pyridine, each of which may be substituted.

(41) Main group metal complexes show ligand based, or charge transfer emission. For these complexes, the emission color is determined by the choice of ligand as well as the metal. A wide range of fluorescent low molecular weight metal complexes are known and have been demonstrated in organic light emitting devices [see, e. g., Macromol. Sym. 125 (1997) 1-48, U.S. Pat. No. 5,150,006, U.S. Pat. No. 6,083,634 and U.S. Pat. No. 5,432,014], in particular tris-(8-hydroxyquinoline)aluminium. Suitable ligands for di or trivalent metals include: oxinoids, e. g. with oxygen-nitrogen or oxygen-oxygen donating atoms, generally a ring nitrogen atom with a substituent oxygen atom, or a substituent nitrogen atom or oxygen atom with a substituent oxygen atom such as 8-hydroxyquinolate and hydroxyquinoxalinol-10-hydroxybenzo (h) quinolinato (II), benzazoles (III), Schiff bases, azoindoles, chromone derivatives, 3-hydroxyflavone, and carboxylic acids such as salicylato amino carboxylates and ester carboxylates. Optional substituents include halogen, alkyl, alkoxy, haloalkyl, cyano, amino, amido, sulfonyl, carbonyl, aryl or heteroaryl on the (hetero) aromatic rings which may modify the emission color.

(42) The metal complex may be incorporated into the host polymer of the invention, either as a substituent on the main chain of the polymer or incorporated into the main chain of the polymer, as disclosed in, for example, EP 1245659, WO 02/31896, WO 03/18653 and WO 03/22908. In this case, the polymer may provide the functions of emission and at least one of hole transport and electron transport.

(43) The host polymer of the invention may be a homopolymer or a copolymer. In the case of copolymers, suitable co-repeat units include carbazoles, such as 2,7-linked carbazole repeat units. Alternatively, 3,6-linked carbazole repeat units as disclosed in J. Am. Chem. Soc. 2004, 126, 6035-6042 may also be used.

(44) It is reported in J. Am. Chem. Soc. 2004, 126, 6035-6042 that shorter poly paraphenylene chains within the host backbone increases the triplet energy level of the host. It will therefore be appreciated that a higher triplet energy level for copolymers comprising a repeat unit according to the invention is achieved using a 3,6-linked carbazole repeat unit and a 3,6-linked dibenzosilole repeat unit according to the eighth aspect of the invention, as compared to a copolymer with units linked through 2,7-positions. Similarly, see “Carbazole Compounds as Host Materials for Triplet Emitters in Organic Light Emitting Diodes: Polymer Hosts for High Efficiency Light Emitting Diodes” Addy van Dijken, Jolanda J. A. M. Bastiaansen, Nicole M. M. Kiggen, Bea M. W. Langeveld, Carsten Rothe, Andy Monkman, Ingrid Bach, Philipp Stössel, and Klemens Brunner, J. Am. Chem. Soc. ASAP Articles, Web Release Date: 28 May 2004. Accordingly, a preferred host material has formula (XIII):

(45) ##STR00025##

(46) wherein R.sup.1 is as defined in the first aspect of the invention. Polymers of this type may comprise blocks of the illustrated dibenzosilole and carbazole units, however in a particularly preferred embodiment the polymer (XIII) is a 1:1 copolymer of alternating dibenzosilole and carbazole units.

(47) Other suitable co-repeat units for host co-polymers according to the invention include triarylamine repeat units of formulae 1-6 described above. Accordingly, another preferred host polymer has formula (XIV):

(48) ##STR00026##

(49) wherein R.sup.1 is as defined in the first aspect of the invention and A is as defined above. Polymers of this type may comprise blocks of the illustrated dibenzosilole and triarylamine units, however in a particularly preferred embodiment the polymer (XIV) is a 1:1 copolymer of alternating dibenzosilole and carbazole units.

(50) Although not essential, a layer of organic hole injection material (not shown) between the anode 2 and the polymer layer 3 is desirable because it assists hole injection from the anode into the layer or layers of semiconducting polymer. Examples of organic hole injection materials include poly(ethylene dioxythiophene) (PEDT/PSS) as disclosed in EP 0901176 and EP 0947123, or polyaniline as disclosed in U.S. Pat. No. 5,723,873 and U.S. Pat. No. 5,798,170.

(51) Cathode 4 is selected from materials that have a workfunction allowing injection of electrons into the electroluminescent layer. Other factors influence the selection of the cathode such as the possibility of the adverse interactions between the cathode and the electroluminescent material. The cathode may consist of a single material such as a layer of aluminium. Alternatively, it may comprise a plurality of metals, for example a bilayer of calcium and aluminium as disclosed in WO 98/10621, elemental barium disclosed in WO 98/57381, Appl. Phys. Lett. 2002, 81(4), 634 and WO 02/84759 or a thin layer of dielectric material to assist electron injection, for example lithium fluoride disclosed in WO 00/48258 or barium fluoride, disclosed in Appl. Phys. Lett. 2001, 79(5), 2001.

(52) A typical electroluminescent device comprises an anode having a workfunction of 4.8 eV. Accordingly, the HOMO level of the hole transporting region is preferably around 4.8-5.5 eV. Similarly, the cathode of a typical device will have a workfunction of around 3 eV. Accordingly, the LUMO level of the electron transporting region is preferably around 3-3.5 eV.

(53) The polymers according to the invention may also be used in current switching devices for an integrated circuit as disclosed in, for example, WO 99/54936. In particular, the polymer may be a component of a field effect transistor comprising an insulator with a gate electrode located on one side of the insulator; a polymer according to the invention located on the other side of the insulator; and a drain electrode and a source electrode located on the polymer.

(54) Electroluminescent devices may be monochrome devices or full colour devices (i.e. formed from red, green and blue electroluminescent materials).

EXAMPLES

A) 2,7-Linked Dibenzosilole Monomers and Repeat Units

Monomer Example

(55) Monomers 1 and 2 according to the second aspect of the invention was synthesised according to the following reaction scheme.

(56) ##STR00027##

(57) a) Cu, DMF, 125° C., 3 h, 75%; b) Sn, HCl, EtOH, 110° C., 2 h, 72%; c) (i) NaNO.sub.2, HCl, 0° C., 1 h (ii) KI, −10 to 50° C., 2 h, 15%; d) (i) t-BuLi, THF, −90 to −78° C., 2 h (ii) Si(n-hexyl).sub.2Cl.sub.2, 24 h, 52%; e) (i) t-BuLi, diethyl ether, −78° C., 1 h (ii) 2-isopropoxy-4,4′,5,5′-tetramethyl-1,3,2-dioxaboralane, room temperature, 24 h, 74%.

4,4′-Dibromo-2,2′-dinitro-biphenyl

(58) ##STR00028##

(59) Reference: R. G. R. Bacon and S. G. Pande, J. Chem. Soc., 1970, 1967.

(60) To a solution of 2,5-dibromonitrobenzene (50.0 g, 179 mmol) in DMF (200 cm.sup.3) was added copper powder (27.0 g, 424 mmol) and the reaction mixture heated to 125° C. After 3 h, the mixture was allowed to cool to room temperature and then treated with toluene (200 cm.sup.3). The insoluble inorganic salts were removed by filtration through celite and the filtrate was evaporated to dryness. The crude material was vigorously washed with methanol (500 cm.sup.3) and redissolved in toluene (200 cm.sup.3). The remaining inorganic salts were again removed by filtration through celite, and the filtrate was evaporated to yield the title compound (27.1 g, 75%) as yellow crystals (Found: C, 35.8; H, 1.5; N, 6.7. C.sub.12H.sub.6Br.sub.2N.sub.2O.sub.4 requires C, 35.9; H, 1.5; N, 7.0%); ν.sub.max/cm.sup.−1 (Neat solid) 730, 829, 1004, 1103, 1344, 1526; δ.sub.H(500 MHz, CDCl.sub.3) 7.18 (2H, d, J 8.2, ArH), 7.85 (2H, dd, J 8.2, 2.0, ArH), 8.39 (2H, d, J 2.0, ArH); δ.sub.C(100 MHz, CDCl.sub.3) 122.9, 128.1, 131.9, 132.0, 136.6, 147.4.

4,4′-Dibromo-biphenyl-2,2′-diamine

(61) ##STR00029##

(62) Reference: Patrick, D. A.; Boykin, D. W.; Wilson, W. D.; Tanious, F. A.; Spychala, J.; Bender, B. C.; Hall, J. E.; Dykstra, C. C.; Ohemeng, K. A.; Tidwell, R. R., Eur. J. Med. Chem., 1997, 32(10), 781.

(63) To a solution of 4,4′-Dibromo-2,2′-dinitro-biphenyl (15.0 g, 37.3 mmol) in ethanol (abs., 186 cm.sup.3) was added 32% w/w aqueous HCl (124 cm.sup.3). Tin powder (17.6 g, 147 mmol) was added portion-wise over 10 minutes and the reaction mixture was heated to reflux at 100° C. for 2 hours. After cooling, the mixture was poured into ice water (ca. 400 cm.sup.3) and then basified with 20% w/w aqueous NaOH solution (150 cm.sup.3). The product was extracted with diethyl ether and the organic layer washed with brine, dried over anhydrous MgSO.sub.4 and evaporated to dryness. Purification by recrystallization from ethanol afforded the title compound (9.2 g, 72%) as light brown crystals (Found: C, 42.1; H, 3.0; N, 8.0. C.sub.12H.sub.10Br.sub.2N.sub.2 requires C, 42.2; H, 3.0; N, 8.2%); ν.sub.max/cm.sup.−1 (Neat solid) 792, 994, 1406, 1477, 1608, 3210, 3357, 3443; δ.sub.H (400 MHz, CDCl.sub.3) 6.92 (6H, s, ArH), 3.78 (4H, brs, NH.sub.2); δ.sub.C(100 MHz, CDCl.sub.3) 118.1, 121.7, 122.0, 122.7, 132.2, 145.4; m/z (ES) 340.9283 ([M+H).sup.+. C.sub.12H.sub.11Br.sub.2N.sub.2 requires 340.9284), 343.1 (100%), 263.1 (80), 185.1 (25).

4,4′-Dibromo-2,2′-diiodo-biphenyl

(64) ##STR00030##

(65) 4,4′-Dibromo-biphenyl-2,2′-diamine (5.0 g, 14.6 mmol) was suspended in 16% w/w aqueous. HCl (16 cm.sup.3) at 0° C. Sodium nitrite (2.2 g, 31.9 mmol) was added dropwise whilst maintaining the temperature at 0° C. After a further 60 minutes of stirring at 0° C., KI solution (5.0 g, 30.1 mmol in 5 cm.sup.3 H.sub.2O) was added dropwise to the reaction mixture at −10° C. The reaction mixture was allowed to warm to room temperature, and then to 50° C. for 2 h. The crude reaction mixture was allowed to cool to room temperature and then basified with 10% w/w aqueous NaOH (90 cm.sup.3). The product was extracted into diethyl ether and the organic layer washed with brine, dried with anhydrous MgSO.sub.4 and evaporated. Purification by column chromatography (hexane) yielded the title compound (1.45 g, 15%) as an off-white solid (Found: C, 25.8; H, 1.0. C.sub.12H.sub.6Br.sub.2I.sub.2 requires C, 25.6; H, 1.1%); mp 89° C.; ν.sub.max/cm.sup.−1 (Neat solid) 710, 817, 993, 1086, 1448, 1565; δ.sub.H(400 MHz, CDCl.sub.3) 7.03 (2H, d, J 8.2, ArH), 7.55 (2H, dd, J 8.2 1.9, ArH), 8.08 (2H, d, J 1.9, ArH); δ.sub.C(100 MHz, CDCl.sub.3) 99.8, 122.5, 130.7, 131.4, 141.0, 146.8.

2,7-Dibromo-9,9′-dihexyl-9H-9-dibenzosiloledibenzosilole

(66) ##STR00031##

(67) t-Butyllithium (6.26 cm.sup.3, 10.6 mmol, 1.7 M in Pentane) was added over 2 h to a solution of 4,4′-dibromo-2,2′-diiodo-biphenyl (1.5 g, 2.66 mmol) in dry THF (30 cm.sup.3) at −90° C. under nitrogen atmosphere. The mixture was stirred for a further 1 h at −90° C. Dichlorodihexylsilane was subsequently added and the mixture was stirred at room temperature overnight. The reaction was quenched with distilled water, and the THF was removed by vacuum. The product was then extracted into diethyl ether and the organic layer washed with brine, dried with anhydrous MgSO.sub.4 and evaporated. Purification by column chromatography (hexane) yielded the title compound (0.7 g, 52%) as a colorless oil; ν.sub.max/cm.sup.−1 (Neat liquid) 720, 813, 1001, 1072, 1384, 2855, 2923, 2956; δ.sub.C (500 MHz, CDCl.sub.3) 0.84-0.97 (10H, m, CH.sub.2+CH.sub.3), 1.22-1.36 (16H, m, CH.sub.2), 7.55 (2H, dd, J 8.3 2.0, ArH), 7.64 (2H, d, J 8.3, ArH), 7.70 (2H, d, J 2.0, ArH); δ.sub.C(100 MHz, CDCl.sub.3) 12.0, 14.0, 22.5, 23.7, 31.3, 32.9, 122.2, 122.5, 133.0, 140.4, 146.0; δ.sub.Si (100 MHz, CDCl.sub.3) 4.1.

2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)-9,9-dihexyl-9H-9-dibenzosiloledibenzosilole

(68) ##STR00032##

(69) t-Butyllithium (1.19 cm.sup.3, 2.02 mmol, 1.7 M in Pentane) was added over 30 minutes to a solution of 2,7-dibromo-9,9′-dihexyl-9H-9-dibenzosilole (0.25 g, 0.49 mmol) in dry THF (3 cm.sup.3) at −78° C. under nitrogen atmosphere. The mixture was stirred for a further 1 h at −78° C. 2-Isopropoxy-4,4′, 5,5′-tetramethyl-1,3,2-dioxaboralane (0.25 cm.sup.3, 2.02 mmol) was then added dropwise to the mixture and stirring continued overnight at room temperature. The reaction was quenched with distilled water, and the THF was removed by vacuum. The product was then extracted into diethyl ether and the organic layer washed with brine, dried with anhydrous MgSO.sub.4 and evaporated. Purification by column chromatography (hexane) using florisil yielded the title compound (0.22 g, 74%) as a white solid (Found: C, 71.2; H, 9.5. C.sub.36H.sub.56Br.sub.2O.sub.4Si requires C, 71.8; H, 9.4%); ν.sub.max/cm.sup.−1 (Neat liquid) 1093, 1143, 1345, 1597, 2922; δ.sub.C(100 MHz, CDCl.sub.3) 12.3, 14.1, 22.6, 23.8, 24.9, 31.3, 33.0, 83.7, 120.5, 136.8, 137.5, 139.7, 151.0; δ.sub.Si (100 MHz, CDCl.sub.3) 3.2.

(70) Monomers according to the second aspect of the invention may alternatively be prepared according to the process set out below wherein the intermediate compound 2,2′-dibromo-4,4′-di(trimethylsilyl)-1,1′-biphenyl is firstly prepared according to the reaction scheme shown below:

(71) ##STR00033##

(72) The monomer according to the second aspect of the invention may be derived from this biphenyl intermediate by one of two routes:

(73) ##STR00034##

(74) Surprisingly, it is possible to perform selective transalkylation of the dimethylsilyl group obtained through Route B above without affecting the trimethylsilyl end groups.

(75) This allows for a wide number of substituents to be formed on the silicon atom, for example hexyl and undecyl as illustrated in the above scheme.

Polymer Examples

Polymer Example 1

(76) A homopolymer according to the first aspect of the invention was prepared by Suzuki polymerization of Monomer 1 and Monomer 2 followed by end-capping with bromobenzene and phenylboronic acid according to the following scheme to afford dibenzosilole polymer PS6:

(77) ##STR00035##

(78) To a dried Schlenk tube was added 2,7-dibromo-9,9-dihexyl-9H-9-dibenzosilole (84 mg, 0.17 mmol, 1.0 equiv.), 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)-9H,9-dihexyldibenzosilole (100 mg, 0.17 mmol, 1.0 equiv.), palladium(II) acetate (1.0 mg, 45 μmol, 2.7%) and tricyclohexylphosphine (5 mg, 178 μmol, 10.7%) under nitrogen atmosphere. Dry toluene (2.5 cm.sup.3) was added and the mixture was stirred at 90° C. for 5 min. 20% w/w Tetraethylammonium hydroxide aqueous solution (1.0 cm.sup.3) was then added. The mixture was stirred for a further 2 h. To the mixture was then added phenylboronic acid (20.3 mg, 17 mmol, 1.0 equiv.), and after stirring for 1 h, bromobenzene (26.1 mg, 17 mmol, 1.0 equiv.) was added. After stirring for a further 1 h, the mixture was cooled to room temperature and poured into stirring methanol (30 cm.sup.3). The precipitate was dissolved in toluene (10 cm.sup.3) and reprecipitated in stirring methanol (50 cm.sup.3). The precipitated product was filtered and then dried in vacuo to yield the title compound (90 mg, 78%) as a pale grayish green solid. GPC assay in CHCl.sub.3 vs. narrow polystyrene standards revealed M.sub.w=8.7×10.sup.4, M.sub.n=1.4×10.sup.4, M.sub.p=1.0×10.sup.5, PDI=7.41; ν.sub.max/cm.sup.−1 (Neat solid) 731, 820, 1062, 1248, 1408, 1447, 2854, 2920, 2955; δ.sub.H (400 MHz, CDCl.sub.3) 0.50-1.60 (m, CH.sub.2+CH.sub.3), 6.40-7.00 (brm, ArH), 7.40-8.10 (brm, ArH); δ.sub.C(125 MHz, CDCl.sub.3) 11.2, 14.1, 22.6, 24.6, 31.4, 33.1, 121.2, 129.0, 131.8, 138.8, 139.9, 147.2; δ.sub.Si (100 MHz, CDCl.sub.3) 3.07.

Polymer Example 2

(79) A copolymer according to the invention was prepared by Suzuki polymerization as disclosed in WO 00/53656 with a diboronic acid of di(n-hexyl)fluorene followed by end-capping with bromobenzene and phenyl boronic acid to afford Polymer PS6F6 as shown below:

(80) ##STR00036##

Polymer PS6F6

Poly(9,9-dihexyl-2,7-fluorenyl-alt-9,9-dihexyl-2,7-silafluorenyl)

(81) ##STR00037##

(82) To a dried Schlenk tube was added 9,9-dihexyl-2,7-dibromo-9H-9-dibenzosilole (84 mg, 0.17 mmol, 1.0 equiv.), 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)-9,9-dihexylfluorene (97 mg, 0.17 mmol, 1.0 equiv.), palladium(II) acetate (1.0 mg, 45 μmol, 2.7%) and tricyclohexylphosphine (5 mg, 178 μmol, 10.7%) under nitrogen atmosphere. Dry toluene (2.5 cm.sup.3) was added and the mixture was stirred at 90° C. for 5 min. 20% w/w Tetraethylammonium hydroxide aqueous solution (1.0 cm.sup.3) was then added. After 1 hour, the mixture became very viscous and additional dry toluene (1.0 cm.sup.3) was added. The mixture was stirred for a further 1 h. To the mixture was then added phenylboronic acid (20.3 mg, 17 mmol, 1.0 equiv.), and after stirring for 1 h, bromobenzene (26.1 mg, 17 mmol, 1.0 equiv.) was added. After stirring for a further 1 h, the mixture was cooled to room temperature and poured into stirring methanol (30 cm.sup.3). The precipitate was dissolved in toluene (10 cm.sup.3) and reprecipitated in stirring methanol (50 cm.sup.3). The precipitated product was filtered and then dried in vacuo to yield the title compound (100 mg, 93%) as a pale grayish green solid; GPC assay in CHCl.sub.3 vs. narrow polystyrene standards revealed M.sub.w=4.24×10.sup.5, M.sub.n=1.09×10.sup.5, M.sub.p=4.96×10.sup.5, PDI=4.55; ν.sub.max/cm.sup.−1 (Neat solid) 734, 815, 1064, 1252, 1378, 1426, 1452, 2854, 2923, 2954; δ.sub.H(500 MHz, CDCl.sub.3) 0.74-0.89 (m, CH.sub.2+CH.sub.3), 1.00-1.20 (m, CH.sub.2), 1.20-1.55 (m, CH.sub.2), 2.10 (brs, CCH.sub.2), 7.50-8.00 (m, ArH); δ.sub.C (125 MHz, CDCl.sub.3) 12.4, 14.0, 14.1, 22.56, 22.59, 23.8, 24.0, 29.7, 31.4, 31.5, 33.1, 40.4, 55.3, 120.0, 121.2, 121.4, 125.3, 128.2, 129.2, 131.9, 138.9, 140.1 (2 signals), 140.3, 147.1, 151.7; δ.sub.Si (100 MHz, CDCl.sub.3) 3.02.

(83) Device Example

(84) General Method:

(85) Onto indium tin oxide supported on a glass substrate (available from Applied Films, Colorado, USA) was deposited a layer of PEDT/PSS, available from H C Starck of Leverkusen, Germany as Baytron P®, by spin coating. A layer of electroluminescent polymer was deposited over the PEDT/PSS layer by spin-coating from xylene solution. Onto the layer of electroluminescent polymer was deposited by evaporation a cathode consisting of a first layer of calcium and a second, capping layer of aluminium.

(86) Devices according to the invention were made according to the above method using Polymer PS6 and Polymer PS6F6.

(87) For the purpose of comparison, a device was made according to the above method comprising a layer of poly-9,9-di(n-hexyl)-2,7-fluorene (hereinafter referred to as Polymer PF6).

(88) As can be seen from the table below, the PS6 homopolymer according to the invention has a deeper LUMO level, i.e. it has a higher electron affinity, than the corresponding polyfluorene homopolymer PF6. At the same time, a wide HOMO-LUMO bandgap similar to that of PF6 is preserved. Furthermore, data for the PF6S6 polymer shows that a deep LUMO level is preserved when the dibenzosilole units of the invention are conjugated with units having a shallower LUMO level.

(89) TABLE-US-00001 Polymers E.sub.onset(ox) (V).sup.a E.sub.g.sup.opt (eV).sup.b HOMO (eV).sup.c LUMO (eV).sup.d PF6 1.41 2.93 −5.84 −2.91 PF6S6 1.48 2.92 −5.91 −2.99 PS6 1.52 2.93 −5.95 −3.02 .sup.aOxidative onset potential. .sup.bOptical band gap energy determined by the onset absorption (UV-Vis). .sup.cDetermined from E.sub.onset(ox) (taking energy level of ferrocene to be −4.8 eV under vacuum). .sup.dDetermined from adding E.sub.g.sup.opt to the HOMO energy level.

(90) As can be seen from FIG. 2(a), photoluminescence of the prior art PF6 polymer suffers from very significant color shift over time towards the red end of the visible spectrum. Incorporation of dibenzosilole repeat units into the PF6 polymer, as shown in FIG. 2(b), results in a very significant reduction in this color shift, and color shift for the S6 homopolymer, as shown in FIG. 2(c), is negligible.

(91) As can be seen from FIG. 3, devices comprising PS6 or PS6F6 give sustained blue emission with emission maxima being identical to that of photoluminescence at 426 nm. The PF6 device on the other hand degraded very rapidly under current and showed a green emission upon operation, displaying a broad peak at about 540 nm.

B) 3,6-Linked Dibenzosilole Monomers and Repeat Units

(92) A monomer according to the ninth aspect of the invention was synthesised according to the following reaction scheme. Again, as with the 2,7-linked dibenzosiloles described above, transalkylation of the dimethylsilyl group (step e) does not affect the trimethylsilyl end groups and so this route again provides a means for introducing a wide range of substituents on the silicon atom.

(93) ##STR00038##

(94) Scheme Synthesis of dibenzosilole monomers: a) n-BuLi, THF, −78° C. to rt, 24 h, 88%; b) I.sub.2, NaIO.sub.4, conc. H.sub.2SO.sub.4, AcOH, Ac.sub.2O, 24 h, 40%; c) n-BuLi, TMSCl, −78° C. to rt, 24 h, 84%; d) (i) t-BuLi, −78° C. to rt, 24 h (ii) SiMe.sub.2Cl.sub.2, −78° C. to rt, 24 h, 81%; e) n-HexLi, −78° C., 15 min, 95%; f) ICl, DCM, r.t., 1 h, 90%; g) t-BuLi, 2-isopropoxy-4,4′,5,5′-tetramethyl-1,3,2-dioxaboralane, −78° C. to rt, 24 h.

(95) ##STR00039##

(96) Scheme a) (i) P(OAc).sub.2, P(Cy).sub.3, Et.sub.4NOH, Toluene, 90° C., 24 h (ii) phenylboronic acid, 2 h (iii) bromobenzene, 2 h, 51%.

(97) For the purpose of comparison, the 2,7-linked polymer poly(9,9-dihexyl-2,7-fluorenyl-alt-9,9-dihexyl-2,7-dibenzosilyl) (Polymer B) was prepared.

(98) Poly(9,9-dihexyl-2,7-fluorenyl-alt-9,9-dihexyl-3,6-dibenzosilyl) (Polymer A) was prepared according to the following method:

(99) ##STR00040##

(100) Scheme a) (i) P(OAc).sub.2, P(Cy).sub.3, Et.sub.4NOH, Toluene, 90° C., 24 h (ii) phenylboronic acid, 2 h (iii) bromobenzene, 2 h, 90%.

(101) UV-Vis Absorption Spectra

(102) The table below shows the absorption maxima and optical band gaps of the copolymers. The solution UV-Vis absorption spectra of the copolymers were measured in hexane.

(103) TABLE-US-00002 λ.sub.max (nm).sup.a E.sub.g.sup.opt (eV, nm).sup.b Polymer solution film solution film PF6 394 390 2.98 (416) 2.93 (423) Polymer A 332 334 3.30 (376) 3.23 (383) Polymer B 400 394 2.87 (432) 2.92 (425) .sup.aOptical band gap, E.sub.g.sup.opt (eV) = 1240/absorption edge (nm). .sup.bBand gaps of the polymers, measured from the UV absorption onsets.

(104) As can be seen from the table, Polymer A comprising a 3,7-linked dibenzosilole according to the eighth aspect of the invention is significantly blue shifted and has a wider bandgap as compared to the 2,7-linked poly-dibenzosilole Polymer B and the 2,7-linked polyfluorene PF6.

(105) Cyclic Voltammetry

(106) The films of the copolymers were prepared by spin-coating the samples (1.0 wt % solution in toluene) on the gold working electrode. Measurements were then taken in a solution of Bu.sub.4N.sup.+ClO.sub.4.sup.− (0.10 M) in acetonitrile at a scan rate of 50 mV/s at room temperature, using a platinum wire as the counter electrode and a Ag/AgCl electrode as the reference electrode. Both measurements were calibrated against ferrocene which has an ionization potential of 4.8 eV.

(107) As can be seen from the table below, the 3,6-linked poly-dibenzosilole of Polymer A according to the eighth aspect of the invention has a wider HOMO-LUMO bandgap as compared to 2,7-linked Polymer A.

(108) TABLE-US-00003 Polymers E.sub.onset(ox) (V).sup.a E.sub.g.sup.opt (eV).sup.b HOMO (eV).sup.c LUMO (eV).sup.d Polymer A 1.57 3.23 −6.00 −2.77 Polymer B 1.48 2.92 −5.91 −2.99 .sup.aOxidative onset potential. .sup.bOptical band gap energy determined by the onset absorption (UV-Vis). .sup.cDetermined from E.sub.onset(ox) (taking energy level of ferrocene to be −4.8 eV under vacuum). .sup.dDetermined from adding E.sub.g.sup.opt to the HOMO energy level.

(109) Although the present invention has been described in terms of specific exemplary embodiments, it will be appreciated that various modifications, alterations and/or combinations of features disclosed herein will be apparent to those skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims.