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  • C07D491/02—Heterocyclic compounds containing in the condensed ring system both one or more rings having oxygen atoms as the only ring hetero atoms and one or more rings having nitrogen atoms as the only ring hetero atoms, not provided for by groups C07D451/00 - C07D459/00, C07D463/00, C07D477/00 or C07D489/00 in which the condensed system contains two hetero rings
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  • C07D471/02—Heterocyclic compounds containing nitrogen atoms as the only ring hetero atoms in the condensed system, at least one ring being a six-membered ring with one nitrogen atom, not provided for by groups C07D451/00 - C07D463/00 in which the condensed system contains two hetero rings
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  • C07D471/02—Heterocyclic compounds containing nitrogen atoms as the only ring hetero atoms in the condensed system, at least one ring being a six-membered ring with one nitrogen atom, not provided for by groups C07D451/00 - C07D463/00 in which the condensed system contains two hetero rings
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  • H10K85/631—Amine compounds having at least two aryl rest on at least one amine-nitrogen atom, e.g. triphenylamine
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  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/917—Electroluminescent

Definitions

• This invention relates to an electroluminescent (EL) device comprising a light-emitting layer comprising a boron complex that can provide a wide range of hues.
• an organic EL device is comprised of an anode for hole injection, a cathode for electron injection, and an organic medium sandwiched between these electrodes to support charge recombination that yields emission of light. These devices are also commonly referred to as organic light-emitting diodes, or OLEDs.
• organic EL devices are Gurnee et al. U.S. Pat. No. 3,172,862, issued Mar. 9, 1965; Gurnee U.S. Pat. No. 3,173,050, issued Mar. 9, 1965; Dresner, "Double Injection
• organic EL elements include an organic EL element consisting of extremely thin layers (e.g. ⁇ 1.0 ⁇ m ) between the anode and the cathode.
• organic EL element encompasses the layers between the anode and cathode.
• one organic layer of the EL element adjacent to the anode is specifically chosen to transport holes, and therefore, it is referred to as the hole-transporting layer, and the other organic layer is specifically chosen to transport electrons, and is referred to as the electron-transporting layer. Recombination of the injected holes and electrons within the organic EL element results in efficient electroluminescence.
• LEL organic light-emitting layer
• the light-emitting layer commonly consists of a host material doped with a guest material, also known as a dopant.
• HIL hole-injecting layer
• HTL hole-transporting layer
• LEL light- emitting layer
• ETL electron transport/injection layer
• a device can emit white light by emitting a combination of colors, such as blue-green light and red light or a combination of blue light and orange light.
• White EL devices can be used with color filters in full-color display devices. They can also be used with color filters in other multicolor or functional- color display devices. White EL devices for use in such display devices are easy to manufacture, and they produce reliable white light in each pixel of the displays.
• the OLEDs are referred to as white and can appear white or off-white, for this application, the CIE coordinates of the light emitted by the OLED are less important than the requirement that the spectral components passed by each of the color filters be present with sufficient intensity in that light.
• the devices must also have good stability in long-term operation. That is, as the devices are operated for extended periods of time, the luminance of the devices should decrease as little as possible.
• Boron complexes have been used as labeling dyes in analytical and biological applications; for example, see EP 4,774,339, EP 747,448 and EP 46, 861. However, boron complexes have found only limited application as dopants in electroluminescent devices.
• a useful class of dopants is derived from the 5,6,5-tricyclic pyrromethene-BF complexes and disclosed in US 5,683,823; JP 09 289,081 A; and JP 11 097,180A. These materials are characterized by typically narrow emission spectra, which may result in attractively high color purity. However, the green emitting unsubstituted or alkyl substituted pyrromethene-BF 2 complexes exhibit relatively low quantum efficiencies of electroluminescence. In order to achieve highly efficient OLEDs, one needs to use phenyl rings as substituents thereby extending the conjugated ⁇ - system.
• the emission wavelength typically becomes red-shifted yielding a reddish amber color, which is the shortest wavelength light that can be emitted by pyrromethene-BF2 complexes with good efficiency.
• luminance efficient green or blue-green OLEDs do not appear to be conveniently obtained with pyrromethene BF complexes used as dopants.
• JP2001294851 A describes boron complexes of heterocycles used in an electroluminescent device. For example, it describes materials in which one ring includes a cyclic amide or sulfonamide. However, these materials are reported to afford a narrow emission spectrum, which would not necessarily be desirable for use in a white-light-emitting device, which must emit a broad spectrum of light.
• US6661023 B2 describes electroluminescent (EL) device containing a boron dopant compound containing a bis(azinyl)methene boron complex. Such compounds, however, can be inefficient in their quantum efficiency of emission. The use of these materials is also limited by the difficulty in tuning the emission wavelengths, for example, to obtain a blue-green emission.
• Certain boron complex containing devices are described in US 6,661,023 B2 to Benjamin P. Hoag et al. and in patent publication US 2003-0198829 Al to Benjamin P. Hoag et al.
• the invention provides an electroluminescent device comprising a light emitting layer comprising a boron complex wherein the boron is bonded to a nitrogen atom of a 6-membered heteroaromatic ring group and to a nitrogen atom of a 5-membered heteroaromatic ring group, provided that the 5- and 6-membered heteroaromatic ring groups are further connected by a methene bridge, and provided further that the 5-membered heteroaromatic ring contains at least one additional heteroatom that is divalent or trivalent.
• the invention also provides a device containing the electroluminescent device and a process for emitting light using the device. The invention device exhibits improve efficiency and emission hue
• FIG. 1 shows a schematic cross-section of a typical OLED device in which this invention may be used.
• An electroluminescent device of the invention maybe a multilayer device comprising a cathode, an anode, charge-injecting layers (if necessary), charge-transporting layers, and a light-emitting layer (LEL) comprising a host and at least one light-emitting material.
• LEL light-emitting layer
• the light emitting layer comprises a boron complex wherein the boron is bonded to a nitrogen atom of a 6-membered heteroaromatic ring group and a nitrogen atom of a 5-membered heteroaromatic ring group and provided that the 5- and 6-membered rings are further connected by a methene group which may be referred to as a bridge, and provided the 5- membered ring contains at least one additional heteroatom that is divalent or trivalent.
• the additional heteroatom is a N, O, S, Se, or Te atom.
• the additional heteroatom is an N, O or S atom.
• the five-membered ring is fused to an additional aromatic ring group, such as a benzene ring group.
• the five- membered ring is fused to an additional aromatic ring group and the six- membered ring is also fused to an additional, independently selected, aromatic ring group
• the methene bridge may be substituted or unsubstituted.
• the methene bridge is substituted with cyano substituent, a trifluoromethyl substituent, an aryl group, such as a phenyl group or a tolyl group, a heteroaryl group, such as a pyridine group, or an alkyl group, such as a methyl group.
• the boron complex is represented by
• Ar 1 represents the atoms necessary to form a six- membered heteroaromatic ring group.
• ring groups are pyridine ring groups, pyrazine ring groups, pyridazine ring groups, quinoline ring groups, and isoquinoline ring groups.
• Ar 2 represents the atoms necessary to form a five-membered heteroaromatic ring that contains, in addition to the nitrogen atom, at least one additional heteroatom that is divalent or trivalent.
• Suitable ring groups are a thiazole ring group, a selenazole ring group, an imidazole ring group, an oxazole ring group, a pyrazole ring group, a benzothiazole ring group, a benzoselenazole ring group, a benzimidazole ring group, and a benzoxazole ring group.
• the rings formed by Ar and Ar may contain additional fused rings.
• Ar 1 and Ar 2 may be fused with independently selected benzene ring groups.
• the substituents of Formula (1) are chosen so that at least six rings are present.
• L 1 and L 2 represent independently selected substituents.
• L and L can each independently represent a halogen substituent, an alkyl group, an aryl group, an alkoxy group, an alkylthio group, an arylfhio group, a sulfamoyl group, an acetamido group, a diarylamino group, and an aryloxy group.
• L and L represent independently a fluoro substituent or an alkyl carboxylate group, such as an acetate group or propionate group.
• L 1 and L 2 both represent a fluoro substituent.
• Y represents hydrogen or a substituent.
• Y may represent a cyano substituent, an aryl group, such as a phenyl group or a tolyl group, a heteroaryl group, such as a pyridine group, or an alkyl group, such as a methyl group.
• substituents of Formula (1) are selected to prevent or limit exciplex formation. That is, substituents are chosen that inhibit the formation of excited state complexes involving one or more compounds of Formula (1). Particularly useful substituents introduce steric interactions, such as one or more t-butyl groups, 5-pentyl groups, or mesityl groups.
• Formula (2) represents the boron complex.
• W represents O, S, Se, Te or N-R a , wherein R a is a substituent, such as a methyl group or a phenyl group.
• R a is a substituent, such as a methyl group or a phenyl group.
• V and V independently represent hydrogen or an independently selected substituent, for example an alkyl group, such as a methyl group, or an aryl group, such as a phenyl group.
• V may join together to form a ring group such as a benzene ring group.
• Ar , L L 2 , and Y were described previously.
• the boron complex is represented by Formula (3).
• V 3 -V 10 independently represent hydrogen or an independently selected substituent, such as a phenyl group or a methyl group. Adjacent substituents may join together to form a ring group, such as a benzene ring group.
• W, L 1 , L 2 , and Y were described previously.
• the substituents of Formula (1) are selected to provide an emission in the range of 450 - 500 nm. In one desirable embodiment the substituents of Formula (1) are selected to provide an emission in the range of 460 - 490 nm. In one suitable embodiment the substituents of Formula (1) are selected to provide an emission that has a primary maximum and a secondary maximum.
• the light-emitting layer of the device comprises a host and one or more light-emitting materials where the light-emitting material(s) is present in an amount of up to 10 wt % of the host, more typically from 0.1-5.0 wt % of the host.
• At least one light-emitting material is suitably a boron complex comprising a ring system of Formula (1).
• Desirable hosts include those based on a chelated oxinoid compound or an anthracene compound. In one desirable embodiment the host is represented by Formula (4).
• W ⁇ -W ⁇ 0 independently represent hydrogen or an independently selected substituent, provided that two adjacent substituents can combine to form rings.
• W 9 and W 10 independently represent naphthyl groups.
• W 9 and W 10 represent a naphthyl group and a biphenyl group.
• hosts are tris(8-quinolinolato)aluminum (III), 9, 10-di-(2-naphthyl)anthracene, 2-tert-butyl-9,l 0-di-(2-naphthyl)anthracene, 9-(4-biphenyl)- 10-(2-naphthyl)anthracene and 9-(4-biphenyl)- 10-( 1 - naphthyl)anthracene.
• the host is selected such that the host absorbs light at a shorter wavelength than the dopant and the emission spectrum of the host overlaps with the absorption spectrum of the dopant.
• Ebodiments of the dopants useful in the invention can provide a wide range of hues. Embodiments of the dopants especially useful in the invention provide an emitted light having a blue hue, a green hue or a blue-green hue. In another preferred embodiment, dopants useful in the invention are used in an electroluminescent device that emits white light.
• Useful boron complexes can be synthesized by methods known in the literature. Desirably a suitable ligand is prepared and the ligand is then complexed to boron. For examples of boron complexation reactions see G, Sathyamoorthi, M. Soong, T. Ross, J. Boyer, Heteroatom Chem., 4, 603 (1993) and J. Douglass, P. Barelski, R. Blankenship, J. HeterocycL Chem., 10, 255 (1973). Illustrative examples of boron complexes useful in the present invention include the following compounds.
• Embodiments of the invention provide not only improved luminance efficiency but also a desirable blue or blue-green hue as evidenced by the location and shape of the emission curve of the emitted light.
• substituted or substituteduent means any group or atom other than hydrogen .
• group when the term “group” is used, it means that when a substituent group contains a substitutable hydrogen, it is also intended to encompass not only the substituent's unsubstituted form, but also its form further substituted with any substituent group or groups as herein mentioned, so long as the substituent does not destroy properties necessary for device utility.
• a substituent group may be halogen or may be bonded to the remainder of the molecule by an atom of carbon, silicon, oxygen, nitrogen, phosphorous, sulfur, selenium, or boron.
• the substituent may be, for example, halogen, such as chloro, bromo or fluoro; nitro; hydroxyl; cyano; carboxyl; or groups which may be further substituted, such as alkyl, including straight or branched chain or cyclic alkyl, such as methyl, trifluoromefhyl, ethyl, t-butyl, 3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such as ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecy
• the substituents may themselves be further substituted one or more times with the described substituent groups.
• the particular substituents used may be selected by those skilled in the art to attain the desired desirable properties for a specific application and can include, for example, electron-withdrawing groups, electron-donating groups, and steric groups.
• the substituents may be joined together to form a ring such as a fused ring unless otherwise provided.
• the above groups and substituents thereof may include those having up to 48 carbon atoms, typically 1 to 36 carbon atoms and usually less than 24 carbon atoms, but greater numbers are possible depending on the particular substituents selected.
• the present invention can be employed in many EL device configurations using small molecule materials, oligomeric materials, polymeric materials, or combinations thereof. These include very simple structures comprising a single anode and cathode to more complex devices, such as passive matrix displays comprised of orthogonal arrays of anodes and cathodes to form pixels, and active-matrix displays where each pixel is controlled independently, for example, with thin film transistors (TFTs).
• TFTs thin film transistors
• the essential requirements of an OLED are an anode, a cathode, and an organic light-emitting layer located between the anode and cathode. Additional layers may be employed as more fully described hereafter.
• FIG. 1 A typical structure according to the present invention and especially useful for a small molecule device, is shown in FIG. 1 and is comprised of a substrate 101, an anode 103, a hole-injecting layer 105, a hole-transporting layer 107, a light-emitting layer 109, an electron-transporting layer 111, and a cathode 113. These layers are described in detail below. Note that the substrate 101 may alternatively be located adjacent to the cathode 113, or the substrate 101 may actually constitute the anode 103 or cathode 113.
• the organic layers between the anode 103 and cathode 113 are conveniently referred to as the organic EL element.
• the total combined thickness of the organic layers is desirably less than 500 nm.
• a hole-blocking layer located between the light-emitting layer and the electron-transporting layer, may be present.
• the anode 103 and cathode 113 of the OLED are connected to a voltage/current source through electrical conductors. The OLED is operated by applying a potential between the anode 103 and cathode 113 such that the anode
• the OLED device of this invention is typically provided over a supporting substrate 101 where either the cathode 113 or anode 103 can be in contact with the substrate.
• the electrode in contact with the substrate 101 is conveniently referred to as the bottom electrode.
• the bottom electrode is the anode 103, but this invention is not limited to that configuration.
• the substrate 101 can either be light transmissive or opaque, depending on the intended direction of light emission.
• the light transmissive property is desirable for viewing the EL emission through the substrate 101.
• Transparent glass or plastic is commonly employed in such cases.
• the substrate 101 can be a complex structure comprising multiple layers of materials. This is typically the case for active matrix substrates wherein TFTs are provided below the OLED layers. It is still necessary that the substrate 101, at least in the emissive pixelated areas, be comprised of largely transparent materials such as glass or polymers.
• the transmissive characteristic of the bottom support is immaterial, and therefore the substrate can be light transmissive, light absorbing or light reflective.
• Substrates for use in this case include, but are not limited to, glass, plastic, semiconductor materials such as silicon, ceramics, and circuit board materials.
• the substrate 101 can be a complex structure comprising multiple layers of materials such as found in active matrix TFT designs. It is necessary to provide in these device configurations a light-transparent top electrode.
• the anode 103 should be transparent or substantially transparent to the emission of interest.
• Common transparent anode materials used in this invention are indium-tin oxide (ITO), indium-zinc oxide (IZO) and tin oxide, but other metal oxides can work including, but not limited to, aluminum- or indium-doped zinc oxide, magnesium-indium oxide, and nickel-tungsten oxide.
• ITO indium-tin oxide
• IZO indium-zinc oxide
• tin oxide other metal oxides can work including, but not limited to, aluminum- or indium-doped zinc oxide, magnesium-indium oxide, and nickel-tungsten oxide.
• metal nitrides such as gallium nitride
• metal selenides such as zinc selenide
• metal sulfides such as zinc sulfide
• the transmissive characteristics of the anode 103 are immaterial and any conductive material can be used, transparent, opaque or reflective.
• Example conductors for this application include, but are not limited to, gold, iridium, molybdenum, palladium, and platinum.
• Typical anode materials, transmissive or otherwise, have a work function of 4.1 eN or greater. Desired anode materials are commonly deposited by any suitable means such as evaporation, sputtering, chemical vapor deposition, or electrochemical means.
• Anodes can be patterned using well-known photolithographic processes. Optionally, anodes may be polished prior to application of other layers to reduce surface roughness so as to minimize short circuits or enhance reflectivity.
• the cathode 113 used in this invention can be comprised of nearly any conductive material. Desirable materials have good film-forming properties to ensure good contact with the underlying organic layer, promote electron injection at low voltage, and have good stability. Useful cathode materials often contain a low work function metal ( ⁇ 4.0 eN) or metal alloy.
• One useful cathode material is comprised of a Mg:Ag alloy wherein the percentage of silver is in the range of 1 to 20 %, as described in U.S. Patent No. 4,885,221.
• cathode materials include bilayers comprising the cathode and a thin electron-injection layer (EIL) in contact with an organic layer (e.g., an electron transporting layer (ETL)), the cathode being capped with a thicker layer of a conductive metal.
• EIL electron transporting layer
• the EIL preferably includes a low work function metal or metal salt, and if so, the thicker capping layer does not need to have a low work function.
• One such cathode is comprised of a thin layer of LiF followed by a thicker layer of Al as described in U.S. Patent No. 5,677,572.
• An ETL material doped with an alkali metal, for example, Li-doped Alq is another example of a useful EIL.
• cathode material sets include, but are not limited to, those disclosed in U.S. Patent Nos. 5,059,861, 5,059,862, and 6,140,763.
• the cathode 113 When light emission is viewed through the cathode, the cathode 113 must be transparent or nearly transparent. For such applications, metals must be thin or one must use transparent conductive oxides, or a combination of these materials.
• Cathode materials are typically deposited by any suitable method such as evaporation, sputtering, or chemical vapor deposition. When needed, patterning can be achieved through many well known methods including, but not limited to, through-mask deposition, integral shadow masking as described in US 5,276,380 and EP 0 732 868, laser ablation, and selective chemical vapor deposition.
• a hole-injecting layer 105 may be provided between anode 103 and hole-transporting layer 107.
• the hole-injecting layer can serve to improve the film formation property of subsequent organic layers and to facilitate injection of holes into the hole-trarlsporting layer 107.
• Suitable materials for use in the hole-injecting layer 105 include, but are not limited to, porphyrinic compounds as described in US 4,720,432, plasma-deposited fluorocarbon polymers as described in US 6,208,075, and some aromatic amines, for example, MTDATA (4,4',4"-tris[(3- methylphenyl)phenylamino]triphenylamine).
• a hole-injection layer is conveniently used in the present invention, and is desirably a plasma-deposited fluorocarbon polymer.
• the thickness of a hole-injection layer containing a plasma-deposited fluorocarbon polymer can be in the range of 0.2 nm to 15 nm and suitably in the range of 0.3 to 1.5 nm.
• Hole-Transporting Layer While not always necessary, it is often useful to include a hole- transporting layer in an OLED device.
• the hole-transporting layer 107 of the organic EL device contains at least one hole-transporting compound such as an aromatic tertiary amine, where the latter is understood to be a compound containing at least one trivalent nitrogen atom that is bonded only to carbon atoms, at least one of which is a member of an aromatic ring.
• the aromatic tertiary amine can be an arylamine, such as a monoarylamine, diarylamine, triarylamine, or a polymeric arylamine. Exemplary monomeric triarylamines are illustrated by Klupfel et al. US 3,180,730.
• triarylamines substituted with one or more vinyl radicals and/or comprising at least one active hydrogen containing group are disclosed by Brantley et al US 3,567,450 and US 3,658,520.
• a more preferred class of aromatic tertiary amines is those which include at least two aromatic tertiary amine moieties as described in US 4,720,432 and US 5,061,569.
• Such compounds include those represented by structural formula (A).
• a Qi. . Q2 A Qi. . Q2
• Qi and Q 2 are independently selected aromatic tertiary amine moieties and G is a linking group such as an arylene, cycloalkylene, or alkylene group of a carbon to carbon bond.
• G is a linking group such as an arylene, cycloalkylene, or alkylene group of a carbon to carbon bond.
• at least one of Qi or Q 2 contains a polycyclic fused ring structure, e.g., a naphthalene.
• G is an aryl group, it is conveniently a phenylene, biphenylene, or naphthalene moiety.
• a useful class of triarylamines satisfying structural formula (A) and containing two triarylamine moieties is represented by structural formula (B): R2 I R Ri— C— R 3 u I R where Ri and R 2 each independently represents a hydrogen atom, an aryl group, or an alkyl group or Ri and R 2 together represent the atoms completing a cycloalkyl group; and R 3 and R 4 each independently represents an aryl group, which is in turn substituted with a diaryl substituted amino group, as indicated by structural formula (C): R5 c
• R 5 and R 6 are independently selected aryl groups.
• at least one of R 5 or R contains a polycyclic fused ring structure, e.g., a naphthalene.
• Another class of aromatic tertiary amines is the tetraaryldiamines. Desirable tetraaryldiamines include two diarylamino groups, such as indicated by formula (C), linked through an arylene group.
• Useful tetraaryldiamines include those represented by formula (D).
• each Are is an independently selected arylene group, such as a phenylene or anthracene moiety
• n is an integer of from 1 to 4
• Ar, R , R , and R are independently selected aryl groups.
• at least one of Ar, R 7 , R 8 , and R is a polycyclic fused ring structure, e.g., a naphthalene.
• the various alkyl, alkylene, aryl, and arylene moieties of the foregoing structural formulae (A), (B), (C), (D), can each in turn be substituted.
• Typical substituents include alkyl groups, alkoxy groups, aryl groups, aryloxy groups, and halide such as fluoride, chloride, and bromide.
• the various alkyl and alkylene moieties typically contain from about 1 to 6 carbon atoms.
• the cycloalkyl moieties can contain from 3 to about 10 carbon atoms, but typically contain five, six, or seven ring carbon atoms ⁇ e.g., cyclopentyl, cyclohexyl, and cycloheptyl ring structures.
• the aryl and arylene moieties are usually phenyl and phenylene moieties.
• the hole-transporting layer can be formed of a single tertiary amine compound or a mixture of such compounds. Specifically, one may employ a triarylamine, such as a triarylamine satisfying the formula (B), in combination with a tetraaryldi amine, such as indicated by formula (D).
• a triarylamine such as a triarylamine satisfying the formula (B)
• a tetraaryldi amine such as indicated by formula (D).
• Illustrative of useful aromatic tertiary amines are the following: 1 , 1 -Bis(4-di-p-tolylaminophenyl)cyclohexane (TAPC) 1 , 1 -Bis(4-di-p-tolylaminophenyl)-4-methylcyclohexane 1 ,1 -Bis(4-di-/?-tolylaminophenyl)-4-phenylcyclohexane 1,1 -Bis(4-di- ?-tolylaminophenyl)-3-phenylpropane (TAPPP) N,N,N',N , -tetraphenyl-4,4'"-diamino- 1 , 1 ':4', 1 ":4", 1 "'-quaterphenyl Bis(4-dimethylamino-2-methylphenyl)phenylmethane 1 ,4-bis[2-[4-[N,N
• Tertiary aromatic amines with more than two amine groups may be used including oligomeric materials.
• polymeric hole-transporting materials can be used such as poly(N-vinylcarbazole) (PNK), polythiophenes, polypyrrole, polyaniline, and copolymers such as poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate) also called PEDOT/PSS.
• PNK poly(N-vinylcarbazole)
• PNK polythiophenes
• polypyrrole polyaniline
• copolymers such as poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate) also called PEDOT/PSS.
• the hole-transporting layer can comprise two or more sublayers of differing compositions, the composition of each sublayer being as described above.
• the thickness of the hole-transporting layer can be between 10 and about 500 nm and suitably
• Light-Emitting Layer In addition to the light-emitting materials of this invention, additional light emitting materials may be used in the EL device, including other fluorescent materials. Other fluorescent materials may be used in the same layer as the boron complex material, in adjacent layers, in adjacent pixels, or any combination. As more fully described in U.S. Patent Nos. 4,769,292 and 5,935,721, the light-emitting layer (LEL) of the organic EL element includes a luminescent material where electroluminescence is produced as a result of electron-hole pair recombination.
• the light-emitting layer can be comprised of a single material, but more commonly consists of a host material doped with a guest emitting material or materials where light emission comes primarily from the emitting materials and can be of any color.
• the host materials in the light-emitting layer can be an electron-transporting material, as defined below, a hole- transporting material, as defined above, or another material or combination of materials that support hole-electron recombination.
• Fluorescent emitting materials are typically incorporated at 0.01 to 10 % by weight of the host material.
• the host and emitting materials can be small non-polymeric molecules or polymeric materials such as polyfluorenes and polyvinylarylenes (e.g., poly(p-phenylenevinylene), PPN).
• small-molecule emitting materials can be molecularly dispersed into a polymeric host, or the emitting materials can be added by copolymerizing a minor constituent into a host polymer.
• Host materials may be mixed together in order to improve film formation, electrical properties, light emission efficiency, operating lifetime, or manufacturability.
• the host may comprise a material that has good hole- transporting properties and a material that has good electron-transporting properties.
• An important relationship for choosing a fluorescent material as a guest emitting material is a comparison of the excited singlet-state energies of the host and the fluorescent material. It is highly desirable that the excited singlet-state energy of the fluorescent material be lower than that of the host material.
• the excited singlet-state energy is defined as the difference in energy between the emitting singlet state and the ground state.
• the lowest excited state of the same electronic spin as the ground state is considered the emitting state.
• Host and emitting materials known to be of use include, but are not limited to, those disclosed in US 4,768,292, US 5,141,671, US 5,150,006, US 5,151,629, US 5,405,709, US 5,484,922, US 5,593,788, US 5,645,948, US 5,683,823, US 5,755,999, US 5,928,802, US 5,935,720, US 5,935,721, and US 6,020,078.
• Metal complexes of 8-hydroxyquinoline and similar derivatives also known as metal-chelated oxinoid compounds (Formula E), constitute one class of useful host compounds capable of supporting electroluminescence, and are particularly suitable for light emission of wavelengths longer than 500 nm, e.g., green, yellow, orange, and red.
• the metal can be monovalent, divalent, trivalent, or tetravalent metal.
• the metal can, for example, be an alkali metal, such as lithium, sodium, or potassium; an alkaline earth metal, such as magnesium or calcium; a trivalent metal, such aluminum or gallium, or another metal such as zinc or zirconium.
• alkali metal such as lithium, sodium, or potassium
• alkaline earth metal such as magnesium or calcium
• trivalent metal such aluminum or gallium, or another metal such as zinc or zirconium.
• any monovalent, divalent, trivalent, or tetravalent metal known to be a useful chelating metal can be employed.
• Z completes a heterocyclic nucleus containing at least two fused aromatic rings, at least one of which is an azole or azine ring. Additional rings, including both aliphatic and aromatic rings, can be fused with the two required rings, if required. To avoid adding molecular bulk without improving on function the number of ring atoms is usually maintained at 18 or less.
• CO-1 Aluminum trisoxine [alias, tris(8-quinolinolato)aluminum(III)]
• CO-2 Magnesium bisoxine [alias, bis(8-quinolinolato)magnesium(II)]
• CO-3 Bis[benzo ⁇ f ⁇ -8-quinolinolato]zinc (II)
• CO-4 Bis(2-methyl-8-quinolinolato)aluminum(III)- ⁇ -oxo-bis(2-methyl-8- quinolinolato) aluminum(III)
• CO-6 Aluminum tris(5-mefhyloxine) [alias, tris(5-methyl-8-quinolinolato) aluminum(III)]
• CO-7 Lithium oxine [alias, (8-quinolinolato)lithium(I)
• R , R , R , R , and R represent one or more substituents on each ring where each substituent is individually selected from the following groups: Group 1 : hydrogen, or alkyl of from 1 to 24 carbon atoms; Group 2: aryl or substituted aryl of from 5 to 20 carbon atoms; Group 3: carbon atoms from 4 to 24 necessary to complete a fused aromatic ring of anthracenyl; pyrenyl, or perylenyl; Group 4: heteroaryl or substituted heteroaryl of from 5 to 24 carbon atoms as necessary to complete a fused heteroaromatic ring of furyl, thienyl, pyridyl, quinolinyl or other heterocyclic systems; Group 5: alkoxylamino, alkylamino, or arylamino of from 1 to 24 carbon atoms; and Group 6: fluorine, chlorine, bromine or cyano.
• Illustrative examples include 9,10-di-(2-naphthyl)anthracene and 2- t-butyl-9,10-di-(2-naphthyl)anthracene.
• Other anthracene derivatives can be useful as a host in the LEL, including derivatives of 9,10-bis[4-(2,2- diphenylethenyl)phenyl]anthracene.
• Benzazole derivatives (Formula G) constitute another class of useful host materials capable of supporting electroluminescence, and are particularly suitable for light emission of wavelengths longer than 400 nm, e.g., blue, green, yellow, orange or red.
• n is an integer of 3 to 8;
• Z is O, NR or S; and
• R and R' are individually hydrogen; alkyl of from 1 to 24 carbon atoms, for example, propyl, t-butyl, heptyl, and the like; aryl or hetero-atom substituted aryl of from 5 to 20 carbon atoms for example phenyl and naphthyl, furyl, thienyl, pyridyl, quinolinyl and other heterocyclic systems; or halo such as chloro, fluoro; or atoms necessary to complete a fused aromatic ring; and
• L is a linkage unit consisting of alkyl, aryl, substituted alkyl, or substituted aryl, which connects the multiple benzazoles together.
• L may be either conjugated with the multiple benzazoles or not in conjugation with them.
• An example of a useful benzazole is 2,2 2"-(l,3,5-phenylene)tris[l-phenyl-lH-benzimidazole].
• Styrylarylene derivatives as described in U.S. Patent 5,121,029 and JP 08333569 are also useful hosts for blue emission.
• 9,10-bis[4-(2,2- diphenylethenyl)phenyl]anthracene and 4,4'-bis(2,2-diphenylethenyl)-l,r-biphenyl (DPNBi) are useful hosts for blue emission.
• Useful fluorescent emitting materials include, but are not limited to, derivatives of anthracene, tetracene, xanthene, perylene, rubrene, coumarin, rhodamine, and quinacridone, dicyanomethylenepyran compounds, thiopyran compounds, polymethine compounds, pyrylium and thiapyrylium compounds, fluorene derivatives, periflanthene derivatives, indenoperylene derivatives, bis(azinyl)amine boron compounds, bis(azinyl)methane compounds, and carbostyryl compounds.
• Illustrative examples of useful materials include, but are not limited to, the following:
• the phosphorescent complex guest material may be referred to herein as a phosphorescent material.
• the phosphorescent material typically includes one or more ligands, for example monoanionic ligands that can be coordinated to a metal through an sp carbon and a heteroatom.
• the ligand can be phenylpyridine (ppy) or derivatives or analogs thereof.
• Examples of some useful phosphorescent organometallic materials include tris(2-phenylpyridinato- N,C 2 )iridium(III), bis(2-phenylpyridinato-N,C 2 )iridium(III)(acetylacetonate), and bis(2-phenylpyridinato-N,C 2 )platinum(II).
• phosphorescent organometallic materials emit in the green region of the spectrum, that is, with a maximum emission in the range of 510 to 570 nm.
• Phosphorescent materials may be used singly or in combinations other phosphorescent materials, either in the same or different layers.
• Phosphorescent materials and suitable hosts are described in WO 00/57676, WO 00/70655, WO 01/41512 Al, WO 02/15645 Al, US 2003/0017361 Al, WO 01/93642 Al, WO 01/39234 A2, US 6,458,475 Bl, WO 02/071813 Al, US 6,573,651 B2, US 2002/0197511 Al, WO 02/074015 A2, US 6,451,455 Bl, US 2003/ 0072964 Al, US 2003 / 0068528 Al, US 6,413,656 Bl, US 6,515,298 B2, US 6,451,415 Bl, US 6,097,147, US 2003/0124381 Al, US 2003/0059646 Al, US 2003/0054198 Al, EP 1 239 526 A2, EP 1 238 981 A2, EP 1 244 155 A2, US 2002/0100906 Al, US 2003 / 0068526 Al, US 2003/0068535 Al, J
• the emission wavelengths of cyclometallated Ir(III) complexes of the type IrL 3 and IrL 2 L7 such as the green-emittingy ⁇ c-tris(2-phenylpyridinato- N,C 2 )iridium(III) and bis(2-phenylpyridinato-N,C 2 )iridium(III)(acetylacetonate) may be shifted by substitution of electron donating or withdrawing groups at appropriate positions on the cyclometallating ligand L, or by choice of different heterocycles for the cyclometallating ligand L.
• the emission wavelengths may also be shifted by choice of the ancillary ligand L7
• red emitters are the bis(2-(2'-benzothienyl)pyridinato-N,C )iridium(III)(acetylacetonate) and tris(2-phenylisoquinolinato-N,C)iridium(III).
• a blue-emitting example is bis(2- (4,6-difluorophenyl)-pyridinato-N,C 2 )iridium(III)(picolinate).
• phosphorescent materials include cyclometallated Pt(II) complexes such as cis-bis(2-phenylpyridinato-N,C )platinum(II), cis-bis(2- (2'-thienyl)pyridinato-N,C 3' ) platinum(II), cis-bis(2-(2'-thienyl)quinolinato-N,C 5' ) platinum(II), or (2-(4,6-difluorophenyl)pyridinato-N,C 2 ') platinum (II)
• cyclometallated Pt(II) complexes such as cis-bis(2-phenylpyridinato-N,C )platinum(II), cis-bis(2- (2'-thienyl)pyridinato-N,C 3' ) platinum(II), cis-bis(2-(2'-thienyl)quinolinato-N,C 5'
• Pt (II) porphyrin complexes such as 2,3,7,8,12,13,17,18- octaethyl-21H, 23H-porphine platinum(II) are also useful phosphorescent materials. Still other examples of useful phosphorescent materials include coordination complexes of the trivalent lanthanides such as Tb 3+ and Eu 3+ (J. Kido et al., Appl. Phys. Lett., 65, 2124 (1994)). Suitable host materials for phosphorescent materials should be selected so that transfer of a triplet exciton can occur efficiently from the host material to the phosphorescent material but cannot occur efficiently from the phosphorescent material to the host material.
• the triplet energy of the phosphorescent material be lower than the triplet energy of the host.
• a large triplet energy implies a large optical bandgap.
• the band gap of the host should not be chosen so large as to cause an unacceptable barrier to injection of charge carriers into the light-emitting layer and an unacceptable increase in the drive voltage of the OLED.
• Suitable host materials are described in WO 00/70655 A2; 01/39234 A2; 01/ 93642 Al ; 02/074015 A2; 02/15645 Al, and US 20020117662.
• Suitable hosts include certain aryl amines, triazoles, indoles and carbazole compounds.
• Desirable hosts are 4,4'- N,N'-dicarbazole-biphenyl, otherwise known as 4,4'-bis(carbazol-9-yl)biphenyl or CBP; 4,4'-N,N'-dicarbazole-2,2'-dimethyl-biphenyl, otherwise known as 2,2'- dimethyl-4,4'-bis(carbazol-9-yl)biphenyl or CDBP; 1 ,3-bis(N,N'- dicarbazole)benzene, otherwise known as l ,3-bis(carbazol-9-yl)benzene, and poly(N-vinylcarbazole), including their derivatives. Desirable host materials are capable of forming a continuous film.
• HBL Hole-Blocking Layer
• an OLED device employing a phosphorescent material often requires at least one hole-blocking layer placed between the electron-transporting layer 111 and the light-emitting layer 109 to help confine the excitons and recombination events to the light-emitting layer comprising the host and phosphorescent material.
• there should be an energy barrier for hole migration from the host into the hole-blocking layer while electrons should pass readily from the hole-blocking layer into the light-emitting layer comprising a host and a phosphorescent material.
• the first requirement entails that the ionization potential of the hole-blocking layer be larger than that of the light-emitting layer 109, desirably by 0.2 eN or more.
• the second requirement entails that the electron affinity of the hole-blocking layer not greatly exceed that of the light-emitting layer 109, and desirably be either less than that of light- emitting layer or not exceed that of the light-emitting layer by more than about 0.2 eN.
• the requirements concerning the energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the material of the hole-blocking layer frequently result in a characteristic luminescence of the hole-blocking layer at shorter wavelengths than that of the electron-transporting layer, such as blue, violet, or ultraviolet luminescence.
• the characteristic luminescence of the material of a hole- blocking layer be blue, violet, or ultraviolet. It is further desirable, but not absolutely required, that the triplet energy of the hole-blocking material be greater than that of the phosphorescent material.
• Suitable hole-blocking materials are described in WO 00/70655 A2 and WO 01/93642 Al.
• Two examples of useful hole-blocking materials are bathocuproine (BCP) and bis(2-methyl-8- quinolinolato)(4-phenylphenolato)aluminum(III) (BAlq).
• BCP bathocuproine
• BAlq bis(2-methyl-8- quinolinolato)(4-phenylphenolato)aluminum(III)
• BAlq bis(2-methyl-8- quinolinolato)(4-phenylphenolato)aluminum(III)
• BAlq bis(2-methyl-8- quinolinolato)(4-phenylphenolato)aluminum(III)
• BAlq bis(2-methyl-8- quinolinolato)(4-phenylphenolato)aluminum(III)
• the characteristic luminescence of BCP is in the ultraviolet, and that of BA
• Desirable thin film- forming materials for use in forming the electron- transporting layer 111 of the organic EL devices of this invention are metal-chelated oxinoid compounds, including chelates of oxine itself (also commonly referred to as 8-quinolinol or 8-hydroxyquinoline). Such compounds help to inject and transport electrons, exhibit high levels of performance, and are readily fabricated in the form of thin films. Exemplary of contemplated oxinoid compounds are those satisfying structural formula (E), previously described.
• Other electron-transporting materials suitable for use in the electron-transporting layer 111 include various butadiene derivatives as disclosed in US 4,356,429 and various heterocyclic optical brighteners as described in US 4,539,507.
• Benzazoles satisfying structural formula (G) are also useful electron transporting materials. Triazines are also known to be useful as electron transporting materials. If both a hole-blocking layer and an electron-transporting layer 111 are used, electrons should pass readily from the electron-transporting layer 111 into the hole-blocking layer. Therefore, the electron affinity of the electron- transporting layer 111 should not greatly exceed that of the hole-blocking layer. Desirably, the electron affinity of the electron-transporting layer should be less than that of the hole-blocking layer or not exceed it by more than about 0.2 eN. If an electron-transporting layer is used, its thickness may be between 2 and 100 nm and suitably between 5 and 20 nm.
• layers 109 through 111 can optionally be collapsed into a single layer that serves the function of supporting both light emission and electron transportation.
• the hole-blocking layer, when present, and layer 111 may also be collapsed into a single layer that functions to block holes or excitons, and supports electron transport.
• emitting materials may be included in the hole-transporting layer 107. In that case, the hole- transporting material may serve as a host.
• Multiple materials may be added to one or more layers in order to create a white-emitting OLED, for example, by combining blue- and yellow-emitting materials, cyan- and red-emitting materials, or red-, green-, and blue-emitting materials.
• White-emitting devices are described, for example, in EP 1 187 235, US 20020025419, EP 1 182 244, US 5,683,823, US 5,503,910, US 5,405,709, and US 5,283,182 and can be equipped with a suitable filter arrangement to produce a color emission.
• This invention may be used in so-called stacked device architecture, for example, as taught in US 5,703,436 and US 6,337,492.
• Deposition of Organic Layers The organic materials mentioned above are suitably deposited by any means suitable for the form of the organic materials. In the case of small molecules, they are conveniently deposited through sublimation or evaporation, but can be deposited by other means such as coating from a solvent together with an optional binder to improve film formation.
• the material to be deposited by sublimation or evaporation can be vaporized from a sublimator "boat" often comprised of a tantalum material, e.g., as described in US 6,237,529, or can be first coated onto a donor sheet and then sublimed in closer proximity to the substrate. Layers with a mixture of materials can utilize separate sublimator boats or the materials can be pre-mixed and coated from a single boat or donor sheet.
• Patterned deposition can be achieved using shadow masks, integral shadow masks (US 5,294,870), spatially-defined thermal dye transfer from a donor sheet (US 5,688,551, US 5,851,709 and US 6,066,357) or an inkjet method (US 6,066,357).
• OLED devices are sensitive to moisture or oxygen, or both, so they are commonly sealed in an inert atmosphere such as nitrogen or argon, along with a desiccant such as alumina, bauxite, calcium sulfate, clays, silica gel, zeolites, alkaline metal oxides, alkaline earth metal oxides, sulfates, or metal halides and perchlorates.
• a desiccant such as alumina, bauxite, calcium sulfate, clays, silica gel, zeolites, alkaline metal oxides, alkaline earth metal oxides, sulfates, or metal halides and perchlorates.
• Methods for encapsulation and desiccation include, but are not limited to, those described in U.S. Patent No. 6,226,890.
• barrier layers such as SiO x , Teflon, and alternating inorganic/polymeric layers are known in the art for encapsulation. Any
• Optical Optimization OLED devices of this invention can employ various well-known optical effects in order to enhance their emissive properties if desired. This includes optimizing layer thicknesses to yield maximum light transmission, providing dielectric mirror structures, replacing reflective electrodes with light- absorbing electrodes, providing anti-glare or anti-reflection coatings over the display, providing a polarizing medium over the display, or providing colored, neutral density, or color-conversion filters over the display. Filters, polarizers, and anti-glare or anti-reflection coatings may be specifically provided over the EL device or as part of the EL device. Embodiments of the invention can provide advantageous features such as higher luminous yield, lower drive voltage, and higher power efficiency.
• Embodiments of the compounds useful in the invention can provide a wide range of hues including those useful in the emission of white light (directly or through filters to provide multicolor displays). Embodiments of the invention can also provide an area lighting device. The invention and its advantages can be better appreciated by the following examples.
• the emission spectra were obtained at room temperature in ethyl acetate solution at concentrations of 10 "5 to 10 "6 M and expressed as quanta per unit time per unit wavelength interval against wavelength.
• a fluorescence procedure is well known to those skilled in the art [see, for example, CA. Parker and W.T. Rees, Analyst, 85, 587 (I960)].
• the maximum of emission spectra is defined as the wavelength corresponding to the highest point of such spectrum. The results are shown in the following table.
• Example 1 - EL Device Fabrication of Samples 1 -5 An EL device (Sample 1) satisfying the requirements of the invention was constructed in the following manner: 1. A glass substrate coated with an 85 nm layer of indium-tin oxide (ITO) as the anode was sequentially ultrasonicated in a commercial detergent, rinsed in deionized water, degreased in toluene vapor and exposed to oxygen plasma for about 1 min. 2. Over the ITO was deposited a 1 nm fluorocarbon (CFx) hole-injecting layer (HIL) by plasma-assisted deposition of CHF 3 . 3.
• ITO indium-tin oxide
• HIL hole-injecting layer
• a hole-transporting layer (HTL)ofNN'-di-l -naphthyl- NN'-diphenyl-4, 4'-diaminobiphenyl ( ⁇ PB) having a thickness of 75 nm was then evaporated from a tantalum boat. 4.
• a 20 nm light-emitting layer (LEL) of 2-tert-butyl-9, 10-di- (2-naphthyl)anthracene (TBAD ⁇ ) and Inv-27 (0.50 wt%) were then deposited onto the hole-transporting layer. These materials were also evaporated from tantalum boats. 5.
• a 35 nm electron- transporting layer (ETL) of tris(8- quinolinolato)aluminum (III) (AlOj) was then deposited onto the light-emitting layer. This material was also evaporated from a tantalum boat. 6. On top of the A1Q 3 layer was deposited a 220 nm cathode formed of a 10:1 volume ratio of Mg and Ag. The above sequence completed the deposition of the EL device. The device was then hermetically packaged in a dry glove box for protection against ambient environment. EL devices, Samples 2, 3, and 4, incorporating Inv-27 were fabricated in an identical manner as Sample 1 but Inv-27 was used at the levels indicated in the Table 2.
• Sample 5 was constructed in the same manner as Sample 1 except Inv-27 was omitted.
• the cells thus formed were tested for efficiency and color at an operating current of 20 mA/cm 2 and the results are reported in Table 2 in the form of output efficiency (W/A), luminance yield (cd/A), maximum wavelength ( ⁇ max) of emission and CIE (Commission Internationale de L'Eclairage) coordinates.
• Table 2 Evaluation Results for EL devices.
• the EL devices offer a range of hues including blue, blue-green, and green electroluminescence.
• An EL device satisfying the requirements of the invention was constructed in the following manner: 1. A glass substrate coated with an 85 nm layer of indium-tin oxide (ITO) as the anode was sequentially ultrasonicated in a commercial detergent, rinsed in deionized water, degreased in toluene vapor and exposed to oxygen plasma for about 1 min. 2. Over the ITO was deposited a 1 nm fluorocarbon (CFx) hole-injecting layer (HIL) by plasma-assisted deposition of CHF 3 . 3.
• ITO indium-tin oxide
• HIL hole-injecting layer
• a hole-transporting layer (HTL)of NN'-di- 1 -naphthyl- NN'-diphenyl-4, 4'-diaminobiphenyl ( ⁇ PB) having a thickness of 150 nm was then evaporated from a tantalum boat. 4.
• a 20 nm first light-emitting layer (LEL- 1 ) of 2-tert-butyl- 9,10-di-(2-naphthyl)anth ⁇ acene (TBAD ⁇ ) and Inv-3 (1.0 wt.%) were then deposited onto the hole-transporting layer. These materials were also evaporated from tantalum boats. 5.
• ETL electron-transporting layer
• HIL Hole- Injecting layer
• HTL Hole-Transporting layer
• LEL Light-Emitting layer
• ETL Electron-Transporting layer

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