Polymer containing aldehyde groups, reaction and crosslinking of this polymer, crosslinked polymer, and electroluminescent device comprising this polymer

Abstract

The present invention relates to a polymer which comprises at least one structural unit which contains at least one aldehyde group, and to a process for the preparation of a crosslinkable or crosslinked polymer including a polymer which contains aldehyde groups. The present invention thus also relates to a crosslinkable polymer and a crosslinked polymer which is prepared by the process according to the invention, and to the use of this crosslinked polymer in electronic devices, in particular in organic electroluminescent devices, so-called OLEDs (OLED=organic light emitting device).

Claims

1. A polymer which comprises at least one structural unit of formula (II): ##STR00025## where the symbols and indices used have the following meanings: Ar.sup.1 to Ar.sup.6 are identical or different and represent, independently of one another, a substituted or unsubstituted, mono- or polycyclic, aromatic or heteroaromatic ring system having 5 to 25 ring atoms; and wherein Ar.sup.a and/or Ar.sup.6 contains an aldehyde group in its para-position, m is 0 or 1; n is 0, 1 or 2; the dashed lines represent bonds to the next structural unit of the polymer; with the proviso that, if n=1, the two N atoms bond to different C atoms of the same aromatic ring system, wherein the polymer comprises 1-30 mol % of at least one structural unit according to formula (II), and wherein the polymer comprises at least one further structural unit which is different from the structural unit of the formula (II) which is selected from the group consisting of structural units having hole-injection and/or hole-transport properties, structural units having electron-injection and/or electron-transport properties, structural units capable to emitting light from the triplet state, structural units which are not organometallic complexes or do not influence singlet-triplet transfer selected from the group consisting of 1,4-phenylene, 1,4-naphthylene, 1,4- or 9,10-anthrylene, 1,6, 2,7- or 4,9-pyrenylene, 3,9- or 3,10-perylenylene, 4,4′-biphenylylene, 4,4″-terphenylylene, 4,4′ bi 1,1′-naphthylylene, 4,4′-tolanylene, 4,4′-stilbenylene, 4,4″-bisstyrylarylene, benzothiadiazole and corresponding oxygen derivatives, quinoxaline, phenothiazine, phenoxazine, dihydrophenazine, bis(thiophenyl)arylene, oligo(thiophenylene), phenazine, rubrene, pentacene and perylene derivatives, optionally substituted, or structural units selected from the group consisting of 4,5-dihydropyrene derivatives, 4,5,9,10-tetrahydropyrene derivatives, 9,9′-spirobifluorene derivatives, phenanthrene derivatives, 9,10-dihydrophenanthrene derivatives, 5,7-dihydro-dibenzoxepine derivatives and cis- and trans-indenofluorene derivatives.

2. The polymer according to claim 1, wherein Ar.sup.3 or Ar.sup.6 is a substituted or unsubstituted unit selected from the group consisting of phenylene, biphenylene, triphenylene, 1,1′: 3′,1″-terphenyl-2′-ylene, naphthylene, anthracene, binaphthylene, phenanthrene, dihydrophenanthrene, pyrene, dihydropyrene, chrysene, perylene, tetracene, pentacene, benzo[a]pyrene, fluorene, indene, indenofluorene, spirobifluorene, pyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, tetrazole, furan, thiophene, selenophene, oxazole, isoxazole, 1,2-thiazole, 1,3-thiazole, 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,5-thiadiazole, 1,3,4-thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, 1,3,5-triazine, 1,2,4-triazine, 1,2,3-triazine, 1,2,4,5-tetrazine, 1,2,3,4-tetrazine, 1,2,3,5-tetrazine, indole, isoindole, indolizine, indazole, benzimidazole, benzotriazole, purine, naphthimidazole, phenanthrimidazole, pyridimidazole, pyrazinimidazole, quinoxalinimidazole, benzoxazole, naphthoxazole, anthroxazole, phenanthroxazole, isoxazole, benzothiazole, benzofuran, isobenzofuran, dibenzofuran, quinoline, isoquinoline, pteridine, benzo-5,6-quinoline, benzo-6,7-quinoline, benzo-7,8-quinoline, benzoisoquinoline, acridine, phenothiazine, phenoxazine, benzopyridazine, benzopyrimidine, quinoxaline, phenazine, naphthyridine, azacarbazole, benzocarboline, phenanthridine, phenanthroline, thieno[2,3b]thiophene, thieno[3,2b]thiophene, dithienothiophene, isobenzothiophene, dibenzothiophene and benzothiadiazothiophene.

3. The polymer according to claim 1, wherein Ar.sup.1, Ar.sup.2, Ar.sup.4 and Ar.sup.5 in the formula (II) is (are) a substituted or unsubstituted unit selected from the group consisting of 4,5-dihydropyrene, 4,5,9,10-tetrahydrofluorene, 9,9′-spirobifluorene, fluorene, phenanthrene, 9,10-dihydrophenanthrene, 5,7-dihydrodibenzoxepine, cis-indenofluorene, trans-indenofluorene, phenylene, thiophene, benzanthracene, carbazole, benzimidazole, oxepine and triazine.

4. The polymer according to claim 1, wherein the further structural unit is a structural unit of the formula (II) which does not contain an aldehyde group.

5. The polymer according to claim 1, wherein the structural unit of the formula (II) is selected from the group consisting of the following structural units: ##STR00026##

6. A mixture of one or more polymer(s) according to claim 1 with further polymeric, oligomeric, dendritic and/or low-molecular-weight substances.

7. A formulation comprising one or more polymer(s) according to claim 1 in one or more solvents.

8. A formulation comprising the mixture according to claim 7 in one or more solvents.

9. A process for the preparation of a crosslinked polymer which comprises the following steps: (a) providing a polymer according to claim 1 which contains aldehyde groups; (b) conversion of the aldehyde groups into vinyl groups or alkenyl groups; and (c) crosslinking of the polymer.

10. A crosslinked polymer which is obtainable by the process according to claim 9.

11. An organic electronic device which comprises the crosslinked polymer according to claim 10.

12. The organic electronic device according to claim 11, wherein the device is an organic or polymeric organic electroluminescent device (OLED, PLED), organic integrated circuit (O-IC), organic field-effect transistor (OFET), organic thin-film transistor (OTFT), organic solar cell (O-SC), organic laser diode (O-laser), organic photovoltaic (OPV) element or device or organic photoreceptor (OPC).

13. A polymer which comprises 1-30 mol % of at least one structural unit selected from the group consisting of the following structural units: ##STR00027## and wherein the polymer comprises at least one further structural unit which is different from ##STR00028## which is selected from the group consisting of structural units having hole-injection and/or hole-transport properties, structural units having electron-injection and/or electron-transport properties, structural units capable to emitting light from the triplet state, structural units which are not organometallic complexes or do not influence singlet-triplet transfer selected from the group consisting of 1,4-phenylene, 1,4-naphthylene, 1,4- or 9,10-anthrylene, 1,6, 2,7- or 4,9-pyrenylene, 3,9- or 3,10-perylenylene, 4,4′-biphenylylene, 4,4″-terphenylylene, 4,4′ bi 1,1′-naphthylylene, 4,4′-tolanylene, 4,4′-stilbenylene, 4,4″-bisstyrylarylene, benzothiadiazole and corresponding oxygen derivatives, quinoxaline, phenothiazine, phenoxazine, dihydrophenazine, bis(thiophenyl)arylene, oligo(thiophenylene), phenazine, rubrene, pentacene and perylene derivatives, optionally substituted, or structural units selected from the group consisting of 4,5-dihydropyrene derivatives, 4,5,9,10-tetrahydropyrene derivatives, 9,9′-spirobifluorene derivatives, phenanthrene derivatives, 9,10-dihydrophenanthrene derivatives, 5,7-dihydro-dibenzoxepine derivatives and cis- and trans-indenofluorene derivatives.

14. A process for the preparation of a crosslinked polymer which comprises the following steps: (a) providing a polymer comprising at least one structural unit of the following formula (I): ##STR00029## wherein at least one representative from Ar and Ar′ contains an aldehyde group, where the symbols and indices used have the following meanings: Ar and Ar′ represent, independently of one another, a substituted or unsubstituted, mono- or polycyclic, aromatic or heteroaromatic ring system; X represents a covalent single bond or a straight-chain, branched or cyclic C.sub.1-10-alkylene, C.sub.1-10-alkenylene or C.sub.1-10-alkynylene group, in which one or more H atoms is optionally replaced by F and in which one or more CH.sub.2 groups is optionally replaced by O, NH or S; and n is 1, 2, 3 or 4; and the dashed lines represent bonds to the next structural unit of the polymer, wherein the polymer comprises 1-30 mol % of at least one structural unit according to formula (I), and wherein the polymer comprises at least one further structural unit which is different from the structural unit of the formula (I) which is selected from the group consisting of structural units having hole-injection and/or hole-transport properties, structural units having electron-injection and/or electron-transport properties, structural units capable to emitting light from the triplet state, structural units which are not organometallic complexes or do not influence singlet-triplet transfer selected from the group consisting of 1,4-phenylene, 1,4-naphthylene, 1,4- or 9,10-anthrylene, 1,6, 2,7- or 4,9-pyrenylene, 3,9- or 3,10-perylenylene, 4,4′-biphenylylene, 4,4″-terphenylylene, 4,4′ bi 1,1′-naphthylylene, 4,4′-tolanylene, 4,4′-stilbenylene, 4,4″-bisstyrylarylene, benzothiadiazole and corresponding oxygen derivatives, quinoxaline, phenothiazine, phenoxazine, dihydrophenazine, bis(thiophenyl)arylene, oligo(thiophenylene), phenazine, rubrene, pentacene and perylene derivatives, optionally substituted, or structural units selected from the group consisting of 4,5-dihydropyrene derivatives, 4,5,9,10-tetrahydropyrene derivatives, 9,9′-spirobifluorene derivatives, phenanthrene derivatives, 9,10-dihydrophenanthrene derivatives, 5,7-dihydro-dibenzoxepine derivatives and cis- and trans-indenofluorene derivatives, which contains aldehyde groups; (b) conversion of the aldehyde groups into vinyl groups or alkenyl groups; and (c) crosslinking of the polymer.

Description

EXAMPLES

Example 1

Preparation of a Monomer Used for the Preparation of an Interlayer Polymer According to the Invention

(1) ##STR00015##

(2) 5 g of 4-(N,N-diphenylamino)benzaldehyde (18.3 mmol) are dissolved in 270 ml of dried THF and cooled to 0° C. 6.5 g of N-bromosuccinimide (36.6 mmol) are added successively as solid, and the solution is left to stir at 0° C. for 4 hours.

(3) The solid is filtered off, and water and dichloromethane are added to the solution. The phases are separated. The organic phase is washed three times with water and dried over Na.sub.2SO.sub.4, then filtered and evaporated in a rotary evaporator. The product is recrystallised a number of times from heptane/toluene.

(4) .sup.1H NMR (CDCl.sub.3, δ (ppm), J (Hz)): 7.02 (d, 4H, J=8.8), 7.04 (d, 2H, J=8.8), 7.44 (d, 4H, J=8.9), 7.71 (d, 2H, J=8.8), 9.84 (s, 1H)

Example 2

Preparation of a Monomer Used for the Preparation of a Matrix Polymer According to the Invention

(5) ##STR00016##

(6) 4.9 g of N-(4-formylphenyl)carbazole (18.1 mmol) are dissolved in 270 ml of dried THF and cooled to 0° C. 6.4 g of N-bromosuccinimide (36.1 mmol) are added successively as solid, and the solution is left to stir at 0° C. for 4 hours.

(7) The solid is filtered off, and water and dichloromethane are added to the solution. The phases are separated. The organic phase is washed three times with water and dried over Na.sub.2SO.sub.4, then filtered and evaporated in a rotary evaporator. The product is recrystallised a number of times from ethyl acetate.

(8) .sup.1H NMR (C.sub.2D.sub.2Cl.sub.4, δ (ppm), J (Hz)): 7.34 (d, 2H, J=8.6), 7.55 (d, 2H, J=8.8), 7/1 (d, 2H, J=8.3), 8.13 (d, 2H, J=8.6), 8.21 (s, 2H), 10.10 (s, 1H)

Example 3a

Preparation of Polymers P1a, P1b and P1c, and P2a, P2b and P2c According to the Invention Using the Monomers Prepared in Examples 1 and 2

(9) Polymers P1 and P2 according to the invention are prepared from the three different structural units shown below by SUZUKI coupling by the process described in WO 03/048225. Polymers P1a, P1b and P1c, and P2a, P2b and P2c prepared in this way comprise the three structural units in the percentage proportions indicated (percent data=mol %) after removal of the leaving groups.

(10) ##STR00017## ##STR00018##

Example 3b

Preparation of Comparative Polymers C1 and C2 which Comprise the Two Structural Units Shown Below in the Percentage Proportions Indicated (PerCent Data=Mol %) after Removal of the Leaving Groups by the Same Process as Described in Example 3a

(11) ##STR00019## ##STR00020##

Example 4

Introduction of Crosslinkable Groups into Polymers P1 and P2 Prepared in Accordance with Example 3a

(12) Polymers P1a′, P1b′ and P1c′, and P2a′, P2b′ and P2c′ containing crosslinkable groups are prepared from polymers P1a, P1b and P1c, and P2a, P2b and P2c prepared in accordance with Example 3a by Wittig reaction in accordance with the following reaction schemes:

(13) Wittig Reaction of P1:

(14) ##STR00021##
Wittig Reaction of P2:

(15) ##STR00022##

(16) To this end, polymer P1a (1 g) is dissolved in 20 ml of dried THF at 50° C. under argon and subsequently cooled to room temperature.

(17) 2.86 g (8 mmol) of methyltriphenylphosphonium bromide are dissolved in 20 ml of dried THF at 0° C. under argon, and 0.90 g (8 mmol) of potassium tert-butoxide is added in portions at 0° C. The polymer solution is subsequently added slowly at 2° C. using a syringe, and the mixture is left to stir overnight at room temperature. The solution is extracted three times with water, and the organic phase is precipitated in methanol.

(18) Polymers P1b and P1c, and P2a, P2b and P2c are reacted analogously.

Example 5

Production of a Green-Emitting PLED Comprising Comparative Polymers C1 and C2 from Example 3b

(19) The production of a polymeric light-emitting diode has already been described a number of times in the patent literature (see, for example, WO 2004/037887). In order to explain the present invention by way of example, a PLED is produced by the process described in WO 2004/037887 using comparative polymer C1 by spin coating onto an ITO substrate which has been coated in advance with PEDOT (PEDOT is a polythiophene derivative (Baytron P, from H. C. Starck, Goslar)). The coated substrate is dried by heating at 180° C. for 10 minutes. The layer thickness of the resultant interlayer is 20 nm. 80 nm of an emitting layer consisting of a polymer matrix C2 and a green-phosphorescent triplet emitter T1 (about 20 mol %) are then applied by spin coating. A Ba/Al cathode (metals from Aldrich) is then applied by vapour deposition, and the PLED is encapsulated and characterised electro-optically. Table 1 shows the results obtained.

(20) ##STR00023##

Example 6

Production of Various Green-Emitting PLEDs Having Crosslinked Polymer Layers Using Polymers P1a′ and P2a′, P2b′ and P2c′ from Example 3a

(21) The production is carried out as described in Example 5, using polymer P1a′ instead of comparative polymer C1 and using polymers P2a′, P2b′ and P2c′ instead of comparative polymer C2. After the spin coating, the coating is in each case dried by heating at 180° C. for one hour in the case of P1′ and P2′ in order to crosslink the polymers. The layer thickness of the interlayer comprising polymer P1a′ is 20 nm, and the layer thickness of the emitting layer comprising polymers C2, P2a′, P2b′ and P2c′ is in each case 80 nm. The electro-optical characterisation of the PLEDs is carried out as in Example 5 and is described below. The results are summarised in Table 1.

(22) Electro-Optical Characterisation:

(23) For the electro-optical characterisation, the PLEDs produced in Examples 5 and 6 are clamped in holders manufactured specifically for the substrate size, and provided with spring contacts. A photodiode with eye response filter can be placed directly on the measurement holder in order to exclude influences from extraneous light.

(24) The voltages are typically increased from 0 to max. 20 V in 0.2 V steps and reduced again. For each measurement point, the current through the PLED and the photocurrent obtained are measured by the photodiode. In this way, the IUL data of the test PLED are obtained. Important parameters are the maximum efficiency measured (“eff.” in cd/A) and the voltage required for 100 cd/m.sup.2 (U.sub.100).

(25) In order, in addition, to know the colour and the precise electroluminescence spectrum of the test PLED, the voltage required for 100 cd/m.sup.2 is again applied after the first measurement, and the photodiode is replaced by a spectrum measurement head. This is connected to a spectrometer (Ocean Optics) by an optical fibre. The colour coordinates (CIE: Commission International de l'éclairage, standard observer from 1931) can be derived from the measured spectrum.

(26) TABLE-US-00001 TABLE 1 Results of electro-optical characterisation of green-emitting PLEDs. Interlayer Matrix Max. eff. U@100 cd/m.sup.2 CIE polymer polymer [cd/A] [V] [x/y] C1 C2 15.0 9.1 0.35/0.61 P1a′ C2 15.2 9.7 0.34/0.62 P1a′ P2a′ 15.4 9.5 0.35/0.63 P1a′ P2b′ 14.7 9.3 0.35/0.62 P1a′ P2c′ 14.5 9.5 0.36/0.61

(27) The efficiency of the PLEDs comprising crosslinked interlayer and/or matrix polymers P1a′ and P2a-c′ is comparable with the efficiency of the PLEDs comprising uncrosslinked comparative polymers C1 and C2. The voltage and colour coordinates are likewise comparable. This shows that crosslinking has no adverse effects on efficiency, voltage and colour coordinates. However, a major advantage is that crosslinking of the polymers according to the invention allows the layer thickness to be varied specifically and controlled precisely, since the crosslinked layer can no longer be partially dissolved and washed off, which is explained in greater detail in Example 8. Thus, a multilayered structure is achieved in a PLED in which all layers are processed from solution and have a defined layer thickness. In the present case, for example, it is also possible to apply a third layer of defined layer thickness to the crosslinked green-emitting layer (P2′ comprising 20 mol % of T1) before the cathode is applied by vapour deposition and the PLED is encapsulated. If the third layer is likewise crosslinkable, a fourth layer of defined layer thickness can be applied.

Example 7

Production of Various Blue-Emitting PLEDs Using Polymers P1a′, P1b′ and P1c′, and the Crosslinking Thereof

(28) The production is carried out analogously to Examples 5 and 6. Polymers C1, P1a′, P1b′ and P1c′ are applied by spin coating to ITO substrates which have been coated in advance with PEDOT. The substrates coated with P1a′, P1b′ and P1c′ are subsequently each dried by heating at 180° C. for one hour in order to crosslink the polymers. The thickness of the polymer layer is in each case 20 nm. A layer of a blue-emitting polymer B1 with a thickness of 65 nm is then applied by spin coating. (The preparation of B1 is carried out analogously to Example 3. B1 comprises the structural units shown below in the percentage proportions indicated (percent data=mol %) after removal of the leaving groups.)

(29) ##STR00024##

(30) A Ba/Al cathode is subsequently applied by vapour deposition, and the PLED is encapsulated. The electro-optical characterisation of the PLED is carried out as described in Example 6. The results are summarised in Table 2.

(31) TABLE-US-00002 TABLE 2 Results of electro-optical characterisation of blue-emitting PLEDs. Interlayer Max. eff. U@100 cd/m.sup.2 CIE polymer [cd/A] [V] [x/y] C1 6.04 2.9 0.15/0.23 P1a′ 5.92 2.8 0.15/0.23 P1b′ 5.68 2.9 0.15/0.26 P1c′ 5.69 2.9 0.15/0.24

(32) The efficiency of the PLEDs comprising crosslinked polymers P1a′, P1b′ and P1c′ is comparable with that of uncrosslinked comparative polymer C1. Voltage and colour coordinates are likewise comparable. This shows that crosslinking of the interlayer has no adverse effects on efficiency, voltage and colour coordinates of the PLED. However, a major advantage is that crosslinking of the polymers according to the invention allows the layer thickness to be varied specifically and controlled precisely, since the crosslinked layer can no longer be partially dissolved and washed off, which is explained in greater detail in Example 8. Thus, a multilayered structure comprising at least two layers is achieved in a PLED processed from solution in which the layers have a defined layer thickness.

Example 8

Control of the Layer Thicknesses

(33) Polymers C1, C2, P1a′, P1b′, P1c′, P2a′, P2b′ and P2c′ are spin-coated onto glass supports in layer thicknesses as described in Table 2. The layer thickness is measured by scratching the polymer layer with a needle, with the scratch extending down to the glass substrate. The depth of the scratch and thus the polymer layer thickness is subsequently measured twice at at least two points each with the aid of an AFM (atomic force microscopy) needle, and the average is formed (Table 3). In the case of polymers P1′ and P2′ according to the invention, the polymer film is dried by heating at 180° C. for one hour in order to crosslink the film. In the case of comparative polymers C1 and C2, the polymer film is dried by heating at 180° C. for 10 minutes. All polymer films are then washed with toluene for one minute on the spin coater (speed of rotation 1000 rpm), and the film is again dried by heating at 180° C. for 10 minutes in order to remove the solvent. The layer thickness is subsequently measured again as described above in order to check whether the layer thickness has changed (Table 3). If the layer thickness is not reduced, the polymer is insoluble and the crosslinking is thus adequate.

(34) TABLE-US-00003 TABLE 3 Layer-thickness measurements on crosslinked and uncrosslinked polymers before and after washing with toluene Measured layer Measured layer Remaining layer thickness before thickness after thickness after crosslinking* and crosslinking* and crosslinking* and washing process washing process washing process Polymer (nm) (nm) [%] P1a′ 20 19 95 P1a′ 39 33 85 P1b′ 21 20 95 P1c′ 20 19 95 P1c′ 43 40 93 P2a′ 80 70 88 P2b′ 80 73 92 P2c′ 80 76 95 C1 20 4 20 C1 40 5 13 C2 80 5 6 *Crosslinking only in the case of P1a-c′ and P2a-c′

(35) The results show that the crosslinking of the polymers according to the invention is virtually quantitative. The higher the proportion of crosslinking groups, the more insoluble the polymer after crosslinking. In the case of a small layer thickness of 20 nm, a crosslinkable monomer proportion in the polymer of only 10% is sufficient for the layer to be adequately crosslinked and not washed out. 95% of the layer thickness originally applied (P1′) remain, compared with 20% in the case of an uncrosslinkable polymer (C1). In the case of layer thicknesses of 80 nm, a proportion of 10% of crosslinkable monomer units in the polymer already exhibits a significant improvement. After washing, about 88% of the layer thickness of the crosslinked polymer (P2a′) remain instead of 6% in the case of the corresponding uncrosslinkable polymer (C2). In the case of 20% of crosslinkable monomer units in the polymer, >90% of the layer thickness originally applied remain (P2b′, P2c′). It is thus possible to control the layer thickness in the case of the crosslinkable polymers according to the invention.