Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D401/00—Heterocyclic compounds containing two or more hetero rings, having nitrogen atoms as the only ring hetero atoms, at least one ring being a six-membered ring with only one nitrogen atom
  • C07D401/14—Heterocyclic compounds containing two or more hetero rings, having nitrogen atoms as the only ring hetero atoms, at least one ring being a six-membered ring with only one nitrogen atom containing three or more hetero rings
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D209/00—Heterocyclic compounds containing five-membered rings, condensed with other rings, with one nitrogen atom as the only ring hetero atom
  • C07D209/56—Ring systems containing three or more rings
  • C07D209/80—[b, c]- or [b, d]-condensed
  • C07D209/82—Carbazoles; Hydrogenated carbazoles
  • C07D209/88—Carbazoles; Hydrogenated carbazoles with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to carbon atoms of the ring system

Definitions

• This invention relates to tertiary diamines containing heterocyclic groups, to organic electroluminescent devices incorporating them and to the use of such diamines as light emitting materials, hole injecting materials or hole transporting materials in such devices. These devices may be utilised in flat- panel displays.
• Flat-panel displays are the critical enabling technology for many current applications such as mobile and video telephones and lap-top and palm-top computers.
• organic electroluminescent also known as organic light emitting diode
• organic or organometallic molecules or semi-conducting polymers offer the potential for lower cost, improved viewing angles, better contrast and lower power consumption.
• organic electroluminescent displays have recently entered commercial production, there is still significant scope for enhancing performance parameters such as lifetime, efficiency and colour.
• a flat-panel device comprises a multi-layer assembly of structurally important films.
• an electroluminescent medium is sandwiched between two electrodes, at least one which is transparent.
• the electroluminescent medium emits light in response to the application of an electrical potential difference across the electrodes.
• the display incorporates patterned red, green and blue light emitters it can produce a colour image.
• the electroluminescent medium lying between the electrodes may itself comprise separate zones, e.g., a hole injecting and transporting zone and a luminescent electron injecting and transporting zone.
• the interface of these two organic zones constitutes an internal junction which allows the injection of holes into the luminescent electron injecting and transporting zone, so that recombination of holes and electrons can take place giving rise to luminescence, but which blocks electron injection into the hole injecting and transporting zone.
• organic electroluminescent devices In order to achieve a good charge balance in organic electroluminescent devices charge transport layers are included.
• the resulting devices which comprise a multi-layered structure generally exhibit improved performance compared to single layer devices which comprise an emitting material located between the electrodes of the device.
• the organic electroluminescent material sandwiched between the electrodes should exhibit thermal stability and operational durability if the device is to be useful in flat-panel displays. Therefore, the organic electroluminescent material needs to comprise compounds which perform well as charge transporters at higher temperatures as well as ones which meet the requirements for emission performance.
• NPB N,N'-di(1-naphthyl)-N,N'- diphenyl-[l, -biphenyl]-4,4'-diamine
• Tg glass transition temperature
• the present invention provides compounds which have good hole transporting, hole injection and emitting properties which are able to perform at relatively high temperatures. According to the present invention there is provided a compound having the formula I
• Ar is an aromatic group selected from:
• n 1 to 3;
• R 1 is a group selected from alkyl, alkenyl, cycloalkyl, cycloalkenyl, carbocyclic aryl optionally substituted by at least one group selected from halo, alkyl, cyano, nitro and cycloalkyl and an. aromatic heterocyclic group optionally substituted by at least one group selected from halo, cyano, nitro, alkyl, cycloalkyl and aryl optionally substituted by at least one halo group;
• R 2 is a fused bicyclic or tricyclic aromatic heterocyclic group selected from
• heterocyclic group may, optionally, be substituted by at least one group selected from halo, cyano, nitro, alkyl, cycloalkyl and aryl optionally substituted by at least one halo and wherein Q is O, S or N-R 5 where R 5 is H, alkyl, cycloalkyl or aryl optionally substituted by at least one group selected from halo, alkyl, cyano or nitro.
• R 3 is a group selected from alkyl, alkenyl, cycloalkyl, cycloalkenyl, carbocyclic aryl optionally substituted by at least one group selected from halo, alkyl, cyano, nitro and cycloalkyl, and an aromatic heterocyclic group optionally substituted by at least one group selected from halo, cyano, nitro, alkyl, cycloalkyl and aryl optionally substituted by at least one halo; and
• R 4 is a group selected from carbocyclic aryl optionally substituted by at least one group selected from halo, cyano, nitro and alkyl, and aromatic heterocyclic optionally substituted by at least one group selected from halo, cyano, nitro, alkyl, aryl optionally substituted by at least one halo, and cycloalkyl.
• an electroluminescent device comprising a compound of the formula I, as defined above.
• R 1 is a group selected from alkyl, alkenyl, cycloalkyl, cycloalkenyl, carbocyclic aryl optionally substituted by at least one group selected from alkyl, halo, cyano, nitro and cycloalkyl, and an aromatic heterocyclic group optionally substituted by at least one group selected from alkyl, halo, cycloalkyl, cyano, nitro and aryl optionally substituted by at least one halo group.
• Preferred groups for the group R 1 are 1 to 6C alkyl, 2 to 6C alkenyl, 5 or 6C cycloalkyl, 5 or 6C cycloalkenyl, 6 to 15C aryl which may be substituted by at least one 1 to 6C alkyl, halo (e.g., F, Cl, Br and I), cyano, nitro or 5 or 6C cycloalkyl and aromatic heterocyclic groups selected from mono, bi or tricyclic heterocyclic groups containing at least one ring heteroatom selected from O, S and N, which aromatic heterocyclic group may be substituted by one or more 1 to 6C alkyl, halo (e.g., F, Cl, Br and I), 5 or 6C cycloalkyl, cyano, nitro or phenyl optionally substituted by at least one halo group.
• halo e.g., F, Cl, Br and I
• R 1 examples include the alkyl groups methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl and tert-butyl, the aromatic groups phenyl, naphthyl, arthryl, phenanthryl and pyrenyl which are optionally, but preferably, substituted by 1-6C alkyl or an electron withdrawing group selected from F, -CN and -N0 2, and the heterocyclic groups pyridyl and quinolyl which are optionally substituted by 1-6C alkyl or an electron withdrawing group selected from F, -CN or -N0 2 .
• R 2 is a fused bicyclic or tricyclic aromatic heterocyclic group selected from
• heterocyclic group may, optionally, be substituted by at least one group selected from halo, cyano, nitro, alkyl, cycloalkyl and aryl optionally substituted by at least one halo and wherein Q is O, S or N-R 5 where R 5 is H, alkyl, cycloalkyl or aryl optionally substituted by at least one group selected from halo, alkyl, cyano or nitro.
• R 2 is a group selected from
• heterocyclic group may, optionally, be substituted as described above and wherein Q is O, S or N-R 5 where R 5 is H, alkyl, cycloalkyl or aryl optionally substituted by at least one group selected from alkyl, halo, cyano and nitro.
• heterocyclic aromatic groups include radicals derived from benzothiophene, benzofuran, indole, carbazole, chromene and xanthene.
• R 2 groups are carbazolyl groups of the formula
• R 5 is as defined above and R 6 is H, halo (i.e., F, Cl, Br, I), cyano, nitro, alkyl, cycloalkyl or aryl optionally substituted by at least one halo group.
• a carbazolyl group attached to the tertiary amine in the compound of formula I not only increases the Tg of the compound but, because a carbazolyl group is an electron donor to the tertiary amine group to which it is attached, it also has the effect of increasing the electron density at the tertiary amine group.
• a compound of the formula I having a carbazolyl group directly attached to a tertiary amine group has improved hole injection properties compared to the prior art compound NPB.
• the group R 3 is selected from alkyl, alkenyl, cycloalkyl, cycloalkenyl, carbocyclic aryl optionally substituted by at least one group selected from halo, nitro, alkyl and cycloalkyl, and an aromatic heterocyclic group optionally substituted by at least one group selected from halo, nitro, alkyl, cycloalkyl and aryl optionally substituted by at least one halo group.
• R 3 groups reference may be made to the list of groups provided above for R 1 .
• the identity of the group R 3 may be the same as or different from the identity of the group R 1 .
• the groups R 1 and R 3 are identical.
• the group R 4 in the formula I is selected from carbocyclic aryl groups optionally substituted by at least one group selected from halo, cyano, nitro and alkyl and aromatic heterocyclic groups optionally substituted by at least one group selected from halo, nitro, alkyl, cycloalkyl and aryl optionally substituted by at least one halo group.
• R 4 is a carbocyclic aryl group optionally substituted as described above it preferably will be a 6- 15C aryl optionally substituted by at least one 1 to 6C alkyl, halo (i.e., F, Cl, Br, I), cyano, nitro or 5 or 6C cycloalkyl group.
• aryl groups include phenyl, naphthyl, anthryl, phenanthryl and pyrenyl any of which may be substituted by a 1-6C alkyl group or an electron withdrawing group selected from F, -CN and -N0 2 .
• the group R 4 is a fused bicyclic or tricyclic aromatic heterocyclic group containing at least one ring heteroatom selected from N, O and S which heterocyclic group is optionally substituted by at least one group selected from halo (i.e. F, Cl, Br or I), cyano, nitro, alkyl, cycloalkyl and aryl which may, itself, be substituted by at least one halo group.
• R 4 is an aromatic heterocyclic group, which is optionally substituted as described above, selected from
• R 4 is identical to the group R 2 .
• R 4 are carbazolyl groups as described above in connection with the discussion of R 2 group. It is particularly preferred that the groups R 2 and R 4 are identical carbazolyl groups in view of the effects the carbazolyl groups have on the hole transporting properties of the compound, as mentioned above.
• Ar is the biphenylyl group.
• Examples of compounds of the invention include N,N'-bis(9-ethylcarbazoI- 3-yl)-N,N'-diphenylbenzidine which is a blue emitting compound, N,N'-bis(9- ethylcarbazol-3-yl)-N,N'-di(1-naphthyl)benzidine which is a cyan emitting compound and N,N'-bis(9-ethyIcarbazol-3-yl)-N,N'-di(6-quinolyI)benzidine which is a green emitting compound.
• two moles of R 1 NH 2 and one mole of Br-Ar-Br are refluxed in an anhydrous aromatic solvent for several hours in the presence of palladium acetate, tri- tert-butyl phosphine and sodium tert-butoxide.
• the product secondary amine is then refluxed for several hours with two equivalents of R 2 -X also in an anhydrous aromatic solvent and also in the presence of palladium acetate, tri(t-butyl)phosphine and sodium tert-butoxide to give the desired tertiary amine.
• the aromatic solvent used in the coupling reaction between the aromatic halide and the amine may, for instance, be toluene or deuterated benzene, as is described by F.E. Goodson et al., J. Am. Chem. Soc. 1999, 121 , 7527-7539, or o-xylene, as is described by M. Watanabe et al., Tetrahedron Letters 41 (2000) 481-483.
• Asymmetrical triarylamines of the formula I above, wherein the group R 1 ⁇ R 3 and/or R 2 ⁇ R 4 may be prepared by reacting the compound Br-Ar-I with the secondary amine R 1 R 2 NH in the presence of a copper catalyst, such as Cu Cl to give the compound
• the compounds of the formula I have hole transporting properties which make them potentially useful in organic light emitting devices.
• the compound can be used as either hole injecting or hole transporting layers in such devices, or as the emitting layer or as a component of the emitting layer in such devices.
• an organic electroluminescent device comprises an anode and a cathode separated from each other by an organic luminescent material.
• the organic luminescent material in its simplest form, comprises a hole injecting and transporting zone adjacent to the anode and an electron injecting and transporting zone adjacent to the cathode. More usually, however, the organic luminescent material will comprise several layers or zones, each performing as is well known in the art a different function from its neighbouring zone. In this respect, reference is made to US-A-5,061 ,569.
• the compounds of the present invention have utility, in such devices, in a hole transporting zone and/or a hole injection zone as mentioned above.
• reaction mixture was cooled to ambient and then filtered, washed with toluene (50ml) and the filtrate was saturated with hexane (300ml) to crash out the product.
• the yellow precipitate was filtered off, washed with hexane (200ml) and finally suction dried for 3 hours to give 11.2g of crude product.
• the product was purified by sublimination at 360°C and 1 x 10 "7 mbar to give 3.7g (79%) as bright yellow amorphous material.
• the reaction mixture was cooled to ambient temperature and then saturated with hexane (200 ml) to crash out the product.
• the yellow precipitate was filtered off, washed with water (50 ml) followed by hexane (200 ml) and finally suction dried for 5 hours to give 2.3 g of crude product.
• the product was purified by sublimation at 430°C and 1 x 10 "7 mbar to give 1.6g (61 %) as bright yellow amorphous material.
• ITO coated glass substrates which can be purchased from several suppliers, for example Applied Films, USA or Merck Display Technology, Taiwan, are cleaned and patterned using a standard detergent and standard photolithography processes.
• the substrates used in the following examples measured 4" x 4" and 0.7mm thick, the ITO was 120nm thick, and the ITO is patterned to produce 4 devices on each substrate each with an active light emitting area of 7.4 cm 2 .
• the substrates are cleaned in a detergent (3 vol.% Decon 90), thoroughly rinsed in deionised water, dried and baked at 105°C until required.
• the treated substrate is oxidised in an oxygen plasma etcher.
• an oxygen plasma etcher By way of example an Emitech K1050X plasma etcher operated at 100 Watts for two minutes is adequate.
• the substrate and shadow mask is then immediately transferred to a vacuum deposition system where the pressure is reduced to below 10 "6 mbar.
• the organic layers are evaporated at rates between 0.5-1.5A/S.
• the mask is changed to form a cathode with a connection pad and no direct shorting routes.
• the cathode is deposited by evaporating 1.5nm of LiF at a rate of 0.2A/s followed by 150nm of aluminium evaporated at a rate of 2A/s.
• Some devices were encapsulated at this stage using an epoxy gasket around the edge of the emissive area and a metal lid. This procedure was carried out in dry nitrogen atmosphere.
• the epoxy was a UV curing epoxy from Nagase, Japan.
• the photoluminescence (PL) measurements were carried out using a CCD spectrograph for light detection while excitation was provided by a UV lamp at 365nm.
• the devices were prepared using the standard method described above.
• the structures of the devices were as follows:
• the devices were excited and the emitted light measured thorough the glass substrate.
• the device was positioned in such a way to avoid direct reflection of the UV light onto the detector.
• the device was placed on top of a hot plate that was used to vary the temperature of the device.
• a schematic diagram of the experimental set-up is shown in Figure 1.
• Figure 2 shows the PL spectra of device 1 measured at different temperatures.
• the metal cathode will reflect any remaining UV light and further absorption and emission can occur as the reflected UV light travels back through the device.
• the PL spectrum measured at 106°C shows a different emission profile to the PL spectra measured at lower temperatures.
• the spectrum at 106°C consists of only Alq 3 emission; the NPD emission has completely disappeared.
• the emission profile consists of emission from TLB1 (peak emission at approximately 460 nm) and a shoulder at lower energy due to Alq 3 emission.
• the PL spectrum was then measured at 69°, 96°, 118°C and showed no temperature dependence up to 118°C. However at 136°C the emission spectrum shows only contribution from Alq 3 .
• the emission of device 1 (device 2), as previously explained, is expected to show contribution of both hole transporting layer, HTL, and Alq 3 . This is true up to certain temperatures where both materials are thermally stable.
• the organic material of the lowest Tg is NPD (TLB1).
• the thermal instability of the device is expected to be in the range of the Tg of the HTL. This is reflected in the emission spectra of both device 1 and device 2 as major change in their profiles occur in the range 59-106°C and 118-136°C respectively.
• the Tg of NPD and TLB1 are 96°C and 136°C, respectively.
• the HTL material starts diffusing into the Alq 3 layer forming a blend where molecules of the HTL can be very close to those of Alq3.
• both molecules absorb light.
• an efficient energy transfer from NPD's excited states to the lower lying energy states of Alq 3 occurs giving emission only from Alq 3 .
• TLB1 gives blue emission
• CuPc phthalocyanine
• BCP acts as a hole-blocking layer so that hole and electron recombination occurs principally on the TLB1 layer.
• the thicknesses of the layers are as follows:
• TLB1 300 A
• TLB2 The CIE co-ordinates from this TLB1 device are approximately (0.15, 0.14) and the peak in the emission spectrum is at approximately 442 nm. However, the spectrum shows a 'shoulder' of significant emission at wavelengths higher than the peak, which results in emission over a wavelength range. This feature is due to exciplex formation with the neighbouring BCP layer. TLB2 has bulkier substituents and therefore shows reduced exciplex formation; results for TLB2 emission devices are given below. Emission characteristics TLB2:
• TLB2 500 A
• the CIE co-ordinates from this TLB2 device are approximately (0.16, 0.29) and the peak in the emission spectrum is at approximately 486 nm.
• a device with a hole-injection layer between the ITO and TLB2 layers was found to be more efficient.
• An example of such a device structure is ITO/CuPc/TLB2/BCP/Alq/LiF/AI, where the thicknesses of the layers are as follows:
• the CIE co-ordinates from this TLB2 device with a hole-injection layer are approximately (0.15, 0.30) and the peak in the emission spectrum is at approximately 488 nm.
• the normalised EL spectrum from the TLB2 emission device with a CuPc hole-injection layer is shown in Figure 4.
• the current density of this device as a function of the supply voltage is shown in Figure 5.
• the luminance of the device as a function of the supply voltage is shown in Figure 6.
• TLB2 acts as a hole- injection layer.
• the thicknesses of the layers are as follows: TLB2: 400 A; BCP: 70 A Alq: 500 A LiF: 15 A Al: 1500 A
• the CIE co-ordinates from this TLB2 device in which the emission is principally due to the Alq layer are approximately (0.32, 0.56) and the peak in the emission spectrum is at approximately 522 nm.
• the normalised EL spectrum from the TLB2 hole-injection device is shown in Figure 8.
• FIGS 9 and 10 show the current density and luminance of this device as functions of the supply voltage. This device is more efficient than the non-optimized TLB2 emission device described above. Hole-transporting properties of TLB2:
• ITO/TLB2/Alq/LiF/AI ITO/TLB2/Alq/LiF/AI, where TLB2 acts as a hole- transporting layer.
• the thicknesses of the layers are as follows:
• Figure 12 shows a comparison between the hole-injection properties of TLB1 and MTDATA.
• Two devices of each structure are shown, i.e. two ITO/TLB1/NBP/Alq/LiF/AI and two ITO/MTDATA/NBP/Alq/LiF/AI.
• MTDATA (4, 4 , 4 " -tris[3-methylphenyl(phenyl)amino]triphenylamine) is a compound that is commonly used as a good hole injection layer, placed between the ITO and NPB.
• MTDATA has a very low Tg of about 65°C and, thus, is not suitable for commercial products. From the comparison shown in Figure 12 it can be seen that TLB1 (which has the benefit of a significantly higher Tg) is as effective as MTDATA at aiding hole injection.

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• 2001
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