Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/731—Liquid crystalline materials
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
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  • C09K11/00—Luminescent materials, e.g. electroluminescent or chemiluminescent
  • C09K11/06—Luminescent materials, e.g. electroluminescent or chemiluminescent containing organic luminescent materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/60—Organic compounds having low molecular weight
  • H10K85/615—Polycyclic condensed aromatic hydrocarbons, e.g. anthracene
  • H10K85/622—Polycyclic condensed aromatic hydrocarbons, e.g. anthracene containing four rings, e.g. pyrene
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K50/00—Organic light-emitting devices
  • H10K50/10—OLEDs or polymer light-emitting diodes [PLED]
  • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/917—Electroluminescent

Definitions

• This invention relates to organic light emitting diode (OLED) electroluminescent (EL) device comprising a light-emitting layer containing a rubrene dopant compound containing a branched alkyl or a non-aromatic carbocyclic group attached to the end rings of the naphthacene nucleus.
• OLED organic light emitting diode
• EL electroluminescent
• 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.
• organic EL devices include an organic EL element consisting of extremely thin layers (e.g. ⁇ 1.0 ⁇ m ) between the anode and the cathode.
• the organic EL element encompasses the layers between the anode and cathode electrodes.
• one organic layer of the EL element adjacent to the anode is specifically chosen to transport holes, therefore, it is referred to as the hole-transporting layer, and the other organic layer is specifically chosen to transport electrons, referred to as the
• the interface between the two layers provides an efficient site for the recombination of the injected hole/electron pair and the resultant electroluminescence.
• organic light-emitting layer LEL
• the light-emitting layer commonly consists of a host material doped with a guest material - dopant , which results in an efficiency improvement and allows color tuning.
• the solution spectra of these materials are typically characterized by wavelength of maximum emission, also referred to as emission ⁇ max , in a range of 550-560nm and are useful in organic EL devices in combination with dopants in other layers to produce white light.
• emission ⁇ max wavelength of maximum emission
• the range of light emitted by rubrene derived dopants limits the purity of the white light produced in such OLEDs.
• emission ⁇ max the range of maximum emission
• Useful dopants are those that emit light in solution in the 563- 650nm range and particularly in the 565-600nm range, also have good efficiency and sublime readily.
• Yellow light is generally defined as having a wavelength range in the visible region of the electromagnetic spectrum of 570-590nm, orange light 590-630nm and red light 630-700nm, as defined by Dr. R.W.G.Hunt in The Reproduction of Colour in Photography, Printing & Television, 4 th Edition 1987, Fountain Press, page 4.
• light has a spectral profile that overlaps these ranges, to whatever degree, it is loosely referred to as yellow-orange or orange- red.
• An OLED device comprising a light-emitting layer (LEL) containing a host and a dopant located between a cathode and an anode wherein the emitter is an orange-red light emitting rubrene derivative represented by formula (I): Formula (I)
• the invention also provides a display including such a device and a method of imaging using such a device.
• a display including such a device and a method of imaging using such a device.
• Such a device exhibits long wavelength electroluminescence desirable in the production of high purity white light.
• FIG. 1 shows a cross-section of a typical OLED device in which this invention may be used.
• DETAILED DESCRIPTION OF THE INVENTION The invention is generally as described above.
• An OLED device of the invention is a multilayer electroluminescent 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 dopant, a rubrene derivative.
• LEL light-emitting layer
• rubrene refers to a 5,6,11,12-tetraphenylnaphthacene as defined by the Grant &hackh's Chemical Dictionary, Fifth Edition, McGraw-Hill Book Company, page 512 and Dictionary of Organic Compounds, Fifth Edition, Chapman and Hall, Volume 5, page 5297.
• the tenn naphthacene is the chemical name used to describe four linearly fused benzene rings as defined by the Grant &hackh's Chemical Dictionary, Fifth Edition, McGraw-Hill Book Company, page 383.
• the light-emitting layer of the device comprises a host and dopant where the dopant is present in an amount of up to 10%- wt of the host, more typically from 0.1 -5.0%-wt of the host.
• The' dopant is suitably a 5,6, 11 , 12- tetraphenylnaphthacene with branched alkyl groups at the 2,8-positions of the naphthacene, and usefully a 5,6,11,12-tetraphenylnaphthacene with non-aromatic carbocyclic groups at the 2,8-positions of the naphthacene.
• Useful dopants of the invention are those that emit light in ethyl acetate solution such that 563nm ⁇ ⁇ max ⁇ 650nm and preferable 565nm ⁇ ⁇ max ⁇ 625nm and have good efficiency. Combined with other light emitting dopants, the dopants of the invention can be used to produce white light. The other light emitting dopants are usefully dopants that emit blue or blue-green light.
• Blue light is generally defined as having a wavelength range in the visible region of the electromagnetic spectrum of 450-480nm, blue-green 480-5 lOnm, green 510-550, green-yellow 550-570nm, yellow 570-590nm, orange 590-630nm and red 630-700nm, as defined by Dr. R. W.G.Hunt in The Reproduction of Colour in Photography, Printing & Television, 4" Edition 1987, Fountain Press, page 4. Suitable combinations of these components produce white light.
• Another embodiment of the invention comprises additional layers incorporating dopants the light from which in combination with the orange-red light of the rubrene derivative combine to give white light. Such additional dopants can be chosen so that they emit blue or blue-green light.
• each light- emitting layer of the device comprises a host and dopant where the dopant is present in an amount of up to 10%-wt of the host, more typically from 0.1-5.0%- wt of the host
• hosts include those based on amine compounds but not limited to such compounds.
• a host is NN'-di-l-naphthalenyl- NN'-di ⁇ henyl-4, 4'-diaminobiphenyl ( ⁇ PB)
• ⁇ PB 4'-diaminobiphenyl
• Formula (II) suitably represents compounds useful in the invention: Formula (II) wherein Ri is represented by the formula;
• each of R 3 , R 4 and R 5 is hydrogen or an independently selected substituent with no more than one being hydrogen or R 3 , R 4 and R 5 taken together can form a mono- or multi-cyclic ring system;
• R 2 is a substituent group; n is 1-5; provided that all Rj groups are the same; and provided further, that the R 2 groups, their location and n value on one ring are the same as those on the second ring.
• R 2 is a substituent group; n is 1-5; and provided that the R 2 groups, their location and n value on one ring are the same as those on the second ring.
• W represents the atoms necessary to complete a non-aromatic heterocyclic or non-aromatic carbocyclic ring group;
• R 2 is a substituent group;
• n is 0-5; and provided that the R 2 groups, their location and n value on one ring are the same as those on the second ring.
• Ri groups are the same and are conveniently branched alkyl, non-aromatic carbocyclic or non- aromatic heterocyclic groups.
• R ⁇ is a branched alkyl group
• particularly useful Ri groups are tert-butyl or tert-amyl groups and can be further substituted with additional substituents.
• Particularly useful additional substituents for the alkyl groups are fluorine or fluorine containing groups such as trifluoromethyl, pentafluoroethyl or fluorinated phenyl groups.
• Ri is a non-aromatic carbocyclic group
• the R 3 , I t and R 5 groups taken together can form a monocycle such as cyclohexyl, or may be multi-cyclic such as adamantyl.
• the R 2 groups on one phenyl group are the same as those on the diagonally opposite phenyl group, in terms of location and number.
• the term "diagonally opposite phenyl group” refers to the location of the phenyl groups on the naphthacene nucleus.
• the phenyl groups in the 5- and 11 -positions or the 6- and 12-positions are diagonally opposite each other.
• the R 2 groups are selected from the group consisting of halide, alkyl, aryl, alkoxy, and aryloxy groups. In one useful embodiment, the R 2 groups are selected from the group consisting of fluorine, alkyl, and aryl groups.
• R 2 is fluorine or a fluorine-containing group such as trifluoromethyl, pentafluoroethyl or fluorinated phenyl groups.
• the R 2 groups may be located in the ortho, meta and para positions on the phenyl ring, but preferably in the meta and para positions. When R 2 is fluorine it can be located in either of the ortho, meta or para positions, or it may be located in any combination of these positions or in all of these positions.
• the emission wavelength of these compounds may be adjusted to some extent by appropriate changes to the Ri, R 2 , R 3 , R 4 , R 5 and W groups to meet a color aim, namely orange-red.
• the rubrene compound is usually doped into a host compound, which represents the light-emitting layer between the hole-transporting and electron-transporting layers.
• the host is chosen such that there is efficient energy transfer from the host to the rubrene compound.
• the rubrene compound emits from the excited state to afford a bright, highly-efficient, stable EL device.
• the EL device of the invention is useful in any device where light emission is desired such as a lamp or a component in a static or motion imaging device, such as a television, cell phone, DVD player, or computer monitor.
• Illustrative examples of rubrene compounds useful in the present invention are the following: Inv-1
• Embodiments of the invention provide not only emission ⁇ max shifted to longer wavelength but also high luminance efficiency and a more desirable orange-red hue as evidenced by the location and shape of the absorption curve of the emitted light.
• substituted or “substituent” 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, trifluoromethyl, ethyl, t-butyl, 3-(2,4-di-t- ⁇ entylphenoxy) propyl, and tetradecyl; alkenyl, such as ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy; aryl such as phenyl, 4-t-butylphenyl
• 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 most OLED device configurations. 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 a thin film transistor (TFT).
• TFT thin film transistor
• FIG. 1 A more typical structure is shown in Figure 1 and contains a substrate 101, an anode 103, an optional 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 may alternatively be located adjacent to the cathode, or the substrate may actually constitute the anode or cathode. Also, the total combined thickness of the organic layers is preferably less than 500 nm.
• 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.
• Transparent glass or organic materials are commonly employed in such cases.
• the transmissive characteristic of the bottom support is immaterial, and therefore 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, ceramics, and circuit board materials. Of course it is necessary to provide in these device configurations a light-transparent top electrode.
• the conductive anode layer 103 is commonly formed over the substrate and, when EL emission is viewed through the anode, should be transparent or substantially transparent to the emission of interest.
• Common transparent anode materials used in this invention are indium-tin oxide (ITO) and tin oxide, but other metal oxides can work including, but not limited to, aluminum- or indium-doped zinc oxide (IZO), magnesium-indium oxide, and nickel-tungsten oxide.
• ITO indium-tin oxide
• IZO aluminum- or indium-doped zinc oxide
• IZO aluminum- or indium-doped zinc oxide
• nickel-tungsten oxide 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 layer 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 eV 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.
• hole-Injecting Layer While not always necessary, it is often useful that a hole-injecting layer 105 be provided between anode 103 and hole-transporting layer 107.
• the hole-injecting material can serve to improve the film formation property of subsequent organic layers and to facilitate injection of holes into the hole- transporting layer.
• Suitable materials for use in the hole-injecting layer include, but are not limited to, porphyrinic compounds such as those described in US 4,720,432, and plasma-deposited fluorocarbon polymers such as those described in US 6,208,075.
• Alternative hole-injecting materials reportedly useful in organic EL devices are described in EP 0 891 121 Al and EP 1 029 909 Al.
• 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 group. 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 are 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).
• Q 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 Q or Q contains a polycyclic fused ring group, e.g., a naphthalene.
• G is an aryl group, it is conveniently a phenylene, biphenylene, or naphthalene group.
• a useful class of triarylamine groups satisfying structural formula (A) and containing two triarylamine groups is represented by structural formula (B): R2 B I Rl — C — R 3 R
• 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):
• R 5 and R 6 are independently selected aryl groups.
• at least one of R 5 or R 6 contains a polycyclic fused ring group, e.g., a naphthalene.
• Another class of aromatic tertiary amine groups is the tetraaryldiamines. Desirable tetraaryldiamines groups include two diarylamino groups, such as indicated by formula (C), and 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 group
• n is an integer of from 1 to 4
• Ar, R 7 , R 8 , and R 9 are independently selected aryl groups.
• at least one of Ar, R 7 , Rg, and R is a polycyclic fused ring group, e.g., a naphthalene
• the various alkyl, alkylene, aryl, and arylene groups 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 halogen such as fluoride, chloride, and bromide.
• the various alkyl and alkylene groups 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 groups are usually phenyl and phenylene moieties.
• the hole-transporting layer can be formed of a single or a mixture of aromatic tertiary amine compounds.
• a triarylamine such as a triarylamine satisfying the formula (B)
• a tetraaryldiamine such as indicated by formula (D).
• a triarylamine is employed in combination with a tetraaryldiamine, the latter is positioned as a layer interposed between the triarylamine and the electron injecting and transporting layer.
• Illustrative of useful aromatic tertiary amines are the following: 1 , 1 -Bis(4-di- >-tolylaminophenyl) cyclohexane 1 , 1 -Bis(4-di- 7-tolylaminophenyl)-4-phenylcyclohexane 4,4'-Bis(diphenylamino)quadriphenyl
• hole-transporting materials includes polycyclic aromatic compounds as described in EP 1 009 041.
• polymeric hole-transporting materials can be used such as poly(N-vinylcarbazole) (PVK), polythiophenes, polypyrrole, polyaniline, and copolymers such as poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate) also called PEDOT/PSS.
• the light- emitting layer (LEL) 109 of the organic EL element comprises a luminescent or fluorescent material where electroluminescence is produced as a result of electron- hole pair recombination in this region.
• the light-emitting layer can be comprised of a single material, but more commonly consists of a host material doped with a guest compound or compounds where light emission comes primarily from the dopant 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.
• the dopant is usually chosen from highly fluorescent dyes, but phosphorescent compounds, e.g., transition metal complexes as described in WO 98/55561, WO 00/18851, WO 00/57676, and WO 00/70655 are also useful. Dopants are typically coated as 0.01 to 10 % by weight into the host material.
• An important relationship for choosing a dye as a dopant is a comparison of the bandgap potential which is defined as the energy difference between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the molecule. For efficient energy transfer from the host to the dopant molecule, a necessary condition is that the band gap of the dopant is smaller than that of the host material.
• Host and emitting molecules 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 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; an earth metal, such aluminum or gallium, or a transition metal such as zinc or zirconium.
• alkali metal such as lithium, sodium, or potassium
• alkaline earth metal such as magnesium or calcium
• earth metal such aluminum or gallium, or a transition 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-methyloxine) [alias, tris(5-methyl-8-quinolinolato) aluminum(III)]
• CO-7 Lithium oxine [alias, (8-quinolinolato)lithium(I)] CO
• Form F Derivatives of 9,10-di-(2-naphthyl)anthracene (Formula F) constitute one class of useful hosts 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.
• R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 represent hydrogen or one or more substituents selected from the following groups: Group 1 : hydrogen, alkyl and alkoxy groups typically having from 1 to 24 carbon atoms; Group 2: a ring group, typically having from 6 to 20 carbon atoms; Group 3: the atoms necessary to complete a carbocyclic fused ring group such as naphthyl, anthracenyl, pyrenyl, and perylenyl groups, typically having from 6 to 30 carbon atoms; Group 4: the atoms necessary to complete a heterocyclic fused ring group such as furyl, thienyl, pyridyl, and quinolinyl groups, typically having from 5 to 24 carbon atoms; Group 5: an alkoxylamino, alkylamino, and arylamino group typically having from 1 to 24 carbon atoms; and Group 6: fluorine, chlorine, bromine and 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, and phenylanthracene derivatives as described in EP 681,019.
• Benzazole derivatives constitute another class of useful hosts 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 where R is H or a substituent; and R 1 represents one or more optional substituents where R and each R' are H or alkyl groups such as propyl, t-butyl, and heptyl groups typically having from 1 to 24 carbon atoms; carbocyclic or heterocyclic ring groups such as phenyl and naphthyl, furyl, thienyl, pyridyl, and quinolinyl groups and atoms necessary to complete a fused aromatic ring group typically having from 5 to 20 carbon atoms; and halo such as chloro, and fluoro; L is a linkage unit usually comprising an alkyl or ary group which conjugately or unconjugately connects the multiple benzazoles together.
• Benzazole is 2, 2', 2"-(l,3,5- phenylene)tris[ 1 -phenyl- 1 H-benzimidazole] .
• Distyrylarylene derivatives as described in US 5,121,029 are also useful host materials in the LEL.
• Desirable fluorescent dopants include groups derived from fused ring, heterocyclic and other compounds such as anthracene, tetracene, xanthene, perylene, rubrene, coumarin, rhodamine, quinacridone, dicyanomethylenepyran, thiopyran , polymethine, pyrilium thiapyrilium, and carbostyryl compounds.
• useful dopants include, but are not limited to, the following:
• Electron-Transporting Layer Preferred 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 and exhibit both 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 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.
• layers 109 and 111 can optionally be collapsed into a single layer that serves the function of supporting both light emission and electron transportation.
• the cathode layer 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 eV) or metal alloy. One preferred 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 US 4,885,221. Another suitable class of cathode materials includes bilayers comprised of a thin layer of a low work function metal or metal salt capped with a thicker layer of conductive metal.
• cathode is comprised of a thin layer of LiF followed by a thicker layer of Al as described in US 5,677,572.
• Other useful cathode materials include, but are not limited to, those disclosed in US 5,059,861, US 5,059,862, and US 6,140,763.
• metals When light emission is viewed through the cathode, the cathode must be transparent or nearly transparent.
• metals must be thin or one must use transparent conductive oxides, or a combination of these materials.
• Optically transparent cathodes have been described in more detail in US 5,776,623.
• Cathode materials can be deposited by 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.
• the organic materials mentioned above are suitably deposited through sublimation, but can be deposited from a solvent with an optional binder to improve film formation. If the material is a polymer, solvent deposition is usually preferred.
• the material to be deposited by sublimation 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 5,851 ,709 and US 6,066,357) and inkjet method (US 6,066,357).
• OLED devices are sensitive to moisture and/or oxygen 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.
• the product may be further purified by sublimation (250 °C @ 200 millitorr) with a N 2 carrier gas.
• Example 2 Wavelength of maximum emission.
• ⁇ max of the compounds of the invention and comparative examples Comp-1 through Comp-4 were obtained by dissolving the compounds in ethyl acetate and recording the emission spectra in a fluorimeter.
• Table 1 shows that the comparison compounds have emission ⁇ max values in the range 545-562nm, whereas compounds of the invention show a desirable shift to longer wavelength and are in the range 566-572nm.
• the comparative compounds used in the invention are as follows: Comp-1
• Comp-1 is the parent rubrene. It is well known to those in the art and has no substituents at the 2- and 8-positions on either of the end rings of the naphthacene nucleus, nor on the four phenyl rings located on the center rings of the naphthacene.
• Comp-2 has tert-butyl substituents located on two of the four central phenyl rings of the naphthacene, diagonally opposite to each other, but falls outside the scope of the current invention because it has no tert-butyl groups on the end rings of the naphthacene.
• Comp-3 appears in the art and is disclosed as TBRb in "A New Yellow Fluorescent Dopant for High-Efficiency OLEDs", 11 th International Workshop on Inorganic and Organic Electroluminescence & 2002 International Conference on the Science and Technology of Emissive Displays and Lighting, September 2002, Session 4, E12002 Ghent, Ghent
• Comp-3 also falls outside the scope of the current invention. It has tert-butyl groups in the 2-and 8-positions of the naphthacene nucleus and in the para-position of the phenyl groups in the 5- and 11 -positions but has no substituent on the phenyl groups in the 6- and 12-positions.
• ⁇ max wavelength of maximum emission
• ethyl acetate solution 562nm, which falls short of the emission range of 563nm ⁇ ⁇ max ⁇ 650nm of the current invention.
• Comp-4 was selected to show that not all substituents on the end rings of the naphthacene are capable of shifting the emission ⁇ max to longer wavelength.
• An EL device satisfying the requirements of the invention was constructed as Sample 10 in the following manner: 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. a) Over the ITO was deposited a 1 nm fluorocarbon (CFx) hole-injecting layer (HIL) by plasma-assisted deposition of CHF 3 .
• ITO indium-tin oxide
• HIL hole-injecting layer
• a 37.5 nm electron-transporting layer (ETL) of tris(8-quinolinolato)aluminum (III) (A1Q 3 ) was then deposited onto the light- emitting layer. This material was also evaporated from a tantalum boat.
• ETL electron-transporting layer
• A1Q 3 tris(8-quinolinolato)aluminum
• e) 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.
• Samples 11, 12 and 13 were EL devices incorporating Inv-2, Inv-3 and Inv-5 fabricated in an identical manner and at the same level, 3%-wt, as the example incorporating Inv-1.
• Samples 14 through 17 are the comparative EL devices that were prepared from comparative compounds Comp-1 through Comp-4 maintaining the same device architecture and level as in the inventive examples.
• Samples 18 through 22 were El devices incorporating Inv-1 through Inv-5 and samples 23 through 25 were El devices incorporating Comp-2, Comp- 3 and Comp-4, respectively, fabricated in an identical manner as the example incorporating Inv-1 but at 5%-wt.
• the cells thus formed were tested for emission ⁇ max and efficiency (in the form of luminance yield), and the results are listed in Tables 2 and 3.
• Luminance yields reported at 20 mA/cm Table 3 shows all tested EL devices incorporating the dopants of the invention at 5%-wt of the host. At this level dopants of the invention also show good luminance yields and an average ⁇ max value of 578nm. In contrast, the EL devices incorporating the comparative dopants at 5%-wt exhibited an average ⁇ m value of 572nm. The dopants of the invention consistently show both improved luminescence and longer wavelength emission at both the 3 and 5%-wt levels. The comparative dopants do not show these improvements.
• HIL Hole-Injecting layer
• HTL Hole-Transporting layer
• ETL Electron-Transporting layer

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