D))
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`(19) 0
`
`soreenor
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`EuropeanPatentOffice
`Office européen des brevets
`
`AEMUA
`
`EP 1 238 981 A2
`
`(11)
`
`(12)
`
`EUROPEAN PATENT APPLICATION
`
`(43) Date of publication:
`11.09.2002 Bulletin 2002/37
`
`(51) Int cl.?; CO7F 15/00, HO1L 51/00
`
`(21) Application number: 02005112.4
`
`(22) Dateoffiling: 07.03.2002
`
`
`(84) Designated Contracting States:
`AT BE CH CY DE DK ES FI FR GB GRIEITLILU
`MC NL PT SE TR
`Designated Extension States:
`AL LT LV MK RO SI
`
`(30) Priority: 08.03.2001 JP 2001064254
`20.02.2002 JP 2002042522
`
`(71) Applicant: CANON KABUSHIKI KAISHA
`Ohta-ku, Tokyo (JP)
`
`* Tsuboyama, Akira
`Tokyo (JP)
`¢ Miura, Seishi
`Tokyo (JP)
`® Moriyama, Takashi
`Tokyo (JP)
`* Kamatani, Jun
`Tokyo (JP)
`* Furugori, Manabu
`Tokyo (JP)
`
`(74) Representative:
`Leson, Thomas JohannesAlois, Dipl.-Ing.
`(72) Inventors:
`Tiedtke-Buhling-Kinne & Partner GbR,
`¢ Takiguchi, Takao
`TBK-Patent,
`Tokyo (JP)
`Bavariaring 4
`¢ Okada, Shinjiro
`80336 Miinchen (DE)
`Tokyo (JP)
`
`
`(564) Metal coordination compound, luminescencedevice and display apparatus
`
`An electroluminescence device having a layer containing a specific metal coordination compound is provided.
`(57)
`The metal coordination compound is represented by formula (1) below:
`
`ML,,L',
`
`(1),
`
`wherein M is a metal atom of Ir, Pt, Rh or Pd; L and L' are mutually different bidentate ligands; m is 1, 2 or 3 and nis
`0,
`1 or 2 with the proviso that m+n is 2 or 3; a partial structure MLm is represented by formula (2) shown below anda
`partial structure ML’, is represented by formula (3) or (4) shown below:
`
`M
`
`CyN1i
`
`CyCl
`
`Jm
`
`(2)
`
`CyN2
`
`CyC2
`
`n
`
`(3)
`
`M
`
`0
`
`E
`
`>
`
`G
`
`(4)
`
`jn
`
`EP1238981A2
`
`at least one of the optional substituent(s) of the cyclic groups, and the cyclic groups CyC1 and CyC2include an
`aromatic group capable of having a substituent represented by the following formula (5):
`
`M.
`
`| \
`
`Printed by Jouve, 75001 PARIS (FR)
`
`(Cont. next page)
`
`

`

`The metal coordination compound having the aromatic group is effective in providing high-efficiency luminescence
`and long-term high luminance.
`
`EP 1 238 981 A2
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`

`

`EP 1 238 981 A2
`
`Description
`
`FIELD OF THE INVENTION AND RELATED ART
`
`[0001] The presentinvention relates to an organic luminescence device (also called an organic electroluminescence
`device or organic EL device) for use in a planar light source, a planar display, etc. Particularly, the present invention
`relates to a novel metal coordination compound and a luminescence device having a high luminescenceefficiency and
`causing little change with time by using a metal coordination compound represented by formula (1) appearing herein-
`after.
`
`[0002] An old example of organic luminescence deviceis, e.g., one using luminescence of a vacuum-deposited
`anthracene film (Thin Solid Films, 94 (1982) 171). In recent years, however, in view of advantages, such as easiness
`of providing a large-area device comparedwith an inorganic luminescence device, and possibility of realizing desired
`luminescence colors by developmentof various new materials and drivability at low voltages, an extensive study ther-
`eon for device formation as a luminescence device of a high-speed responsiveness and a high efficiency, has been
`conducted.
`
`20
`
`- 48 (1997), for example, an organic EL device generally
`1
`Asprecisely described in Macromol. Symp. 125,
`[0003]
`has an organization comprising a pair of upper and lower electrodes formed on a transparent substrate, and organic
`material layers including a luminescence layer disposed between the electrodes.
`[0004]
`In the luminescence layer, aluminum quinolinol complexes (inclusive of Alg3 shownhereinafter as a repre-
`sentative example) having an electron-transporting characteristic and a luminescence characteristic, are used for ex-
`ample. In a hole-transporting layer, a material having an electron-donative property, such as a tripohenyldiamine deriv-
`ative (inclusive of o-NPD shownhereinafter as a representative example), is used for example.
`[0005]
`Such a device shows a current-rectifying characteristic such that when an electric field is applied between
`the electrodes, holes are injected from the anode and electrons are injected from the cathode.
`[0006] The injected holes and electrons are recombined in the luminescence layer to form excitons, which emit
`luminescence when theyare transitioned to the ground state.
`
`[0007] In this process, the excited states include a singlet state andatriplet state and a transition from the former
`to the ground state is called fluorescenceand a transition from the latter is called phosphorescence. Materials in theses
`states are called singlet excitons and triplet excitons, respectively.
`[0008]
`In most of the organic luminescence devices studied heretofore, fluorescence caused by the transition of a
`singlet exciton to the ground state, has been utilized. On the other hand, in recent years, devices utilizing phospho-
`rescencevia triplet excitons have been studied.
`[0009] Representative publishedliterature may include:
`
`25
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`30
`
`Article 1: Improved energy transfer in electrophosphorescent device (D.F. O'Brien, et al., Applied Physics Letters,
`Vol. 74, No. 3, p. 422 (1999)}; and
`Article 2: Very high-efficiency green organic light-emitting devices based on electrophosphorescence (M.A. Baldo,
`et al., Applied Physics Letters, Vol. 75, No. 1, p. 4 (1999)).
`
`In these articles, a structure including four organic layers sandwiched between the electrodes, and the ma-
`[0010]
`terials used therein include carrier-transporting materials and phosphorescentmaterials, of which the namesand struc-
`tures are shown below together with their abbreviations.
`Alg3: aluminum quinolinol complex
`a-NPD: N4,N4'-di-naphthalene-1-yl-N4,N4'-diphenyl-biphenyl-4,4'-diamine
`CBP: 4,4'-N,N'-dicarbazole-biphenyl
`BCP: 2,9-dimethyl-4, 7-diphenyl-1,10-phenanthroline
`PtOEP: platinum-octaethylporphyrin complex
`Ir(ppy)s: iridium-phenylpyrimidine complex
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`EP 1 238 981 A2
`
`Rooke oo8
`
`Alq3
`
`a-NPD
`
`CBP
`
`
`
`3
`
`Ir(ppy) 3
`
`<
`
`2
`
`CH,
`
`BCP
`
`HAC
`
`CaHs
`
`(CoHs
`
`CoHs
`
`CaHs
`
`CoH.
`
`CaHs
`
`CoHs
`
`Cols
`
`PtOEP
`
`[0011] The above-mentioned Articles 1 and 2 both have reported structures, as exhibiting a high efficiency, including
`a hole-transporting layer comprising @-NPD, an electron-transporting layer comprising Alq3, an exciton diffusion-pre-
`venting layer comprising BCP, and a luminescencelayer comprising CBP as a host and ca. 6 % of PtOEP or Ir(ppy)3
`as a phosphorescent material dispersed in mixture therein.
`[0012]
`Such a phosphorescent material is particularly noted at present because it is expected to provide a high
`luminescenceefficiency in principle for the following reasons. More specifically, excitons formed by carrier recombina-
`tion comprise singlet excitons and triplet excitons in a probability ratio of 1:3. Conventional organic EL devices have
`utilized fluorescence of which the luminescenceefficiencyis limited to at most 25 %. On the other hand, if phospho-
`rescence generated from triplet excitons is utilized, an efficiency of at least three times is expected, and even an
`efficiency of 100 %, i.e., four times, can be expectedin principle, if a transition owing to intersystem crossing from a
`singlet state having a higher energyto a triplet state is taken into account.
`[0013] However,like a fluorescent-type device, such an organic luminescence device utilizing phosphorescenceis
`generally required to be further improved regarding the deterioration of luminescenceefficiency and device stability.
`[0014] The reason ofthe deterioration has not been fully clarified, but the present inventors consider as follows based
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`EP 1 238 981 A2
`
`on the mechanism of phosphorescence.
`[0015]
`In the case where the luminescence layer comprises a host material having a carrier-transporting function
`and a phosphorescent guest material, a process of phosphorescencevia triplet excitons may include unit processes
`as follows:
`
`Ooahan—
`
`. transportation of electrons and holes within a luminescencelayer,
`. formation of host excitons,
`. excitation energy transfer between host molecules,
`. excitation energy transfer from the hostto the guest,
`. formation of guesttriplet excitons, and
`. transition of the guesttriplet excitons to the ground state and phosphorescence.
`
`[0016] Desirable energy transfer in each unit process and luminescence are caused in competition with various
`energy deactivation processes.
`[0017] Needless to say, aluminescenceefficiency of an organic luminescence device is increased by increasing the
`luminescence quantum yield of a luminescence center material.
`[0018]
`Particularly, in a phosphorescent material, this may be attributable to a life of the triplet excitons which is
`longer by three or more digits than the life of a singlet exciton. More specifically, becauseit is held in a high-energy
`excited state for a longer period, it is liable to react with surrounding materials and cause polymer formation among
`the excitons, thus incurring a higher probability of deactivation process resulting in a material change or life deteriora-
`tion.
`
`20
`
`[0019] Aluminescence deviceis desired to exhibit high efficiency luminescence and showahigh stability. Particularly,
`it is strongly desired to provide a luminescence material compound which is less liable to cause energy deactivation
`in a long life of excited energy state and is also chemically stable, thus providing a longer devicelife.
`
`25
`
`SUMMARYOF THE INVENTION
`
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`
`[0020] Accordingly, principal objects of the present invention are to provide a luminescence material which exhibits
`a high luminescenceefficiency and retains a high luminancefor a long period, and also provide a luminescence device
`and a display apparatus using the same.
`[0021]
`Inthe present invention, a metal complex is used as a luminescence material, particularly a novel luminescent
`metal complex compound comprising iridium as a center metal and an aromatic group of formula (5) appearing here-
`inafter as a part of a ligand or as a substituentof a ligand.
`[0022] More specifically, the present invention provides as a luminescence material a metal coordination compound
`represented by formula (1) below:
`
`ML aL,
`
`(1),
`
`wherein M is a metal atom ofIr, Pt, Rh or Pd; L and L' are mutually different bidentate ligands; mis 1, 2 or 3 andnis
`0,
`1 or 2 with the proviso that m+n is 2 or 3; a partial structure MLm is represented by formula (2) shown below and a
`partial structure ML’, is represented by formula (3) or (4) shown below:
`
`M
`
`CyN1
`
`CyCl
`
`(2)
`
`Jm
`
`M
`
`CyN2
`
`CyC2
`
`Jn
`
`(3)
`
`O
`
`Oo
`
`M >
`
`E
`
`Gin
`
`(4)
`
`wherein CyN1 and CyN2 are each cyclic group capable of having a substituent, including a nitrogen atom and bonded
`to the metal atom M via the nitrogen atom; CyC1 and CyC2 are each cyclic group capable of having a substituent,
`including a carbon atom and bondedto the metal atom M via the carbon atom with the proviso that the cyclic group
`CyN1 and the cyclic group CyC1 are bonded to each other via a covalent bond and the cyclic group CyN2 and the
`cyclic group CyC2 are bondedto each other via a covalent bond;
`
`

`

`EP 1 238 981 A2
`
`the optional substituent of the eyclic groups is selected from a halogen atom, cyano group, a nitro group, a
`trialkylsilyl group of which the alkyl groups are independently a linear or branched alkyl group having 1
`to 8 carbon
`atoms, a linear or branched alkyl group having 1 to 20 carbon atoms of which the alkyl group can include one or non-
`neighboring two or more methylene groups that can be replaced with -O-, -S-, -CO-, -CO-O-, -O-CO-, -CH=CH- or
`-C=C-, and the alkyl group can include a hydrogen atom that can be optionally replaced with a fluorine atom, or an
`aromatic group capable of having a substituent(that is a halogen atom, a cyano atom, a nitro atom, a linear or branched
`alkyl group having 1 to 20 carbon atoms of which the alkyl group can include one or non-neighboring two or more
`methylene groups that can be replaced with -O-, -S-, -CO-, -CO-O-, -O-CO-, -CH=CH- or -C=C-, and the alkyl group
`can include a hydrogen atom that can be optionally replaced with a fluorine atom);
`E and G are independently a linear or branchedalkyl group having 1 to 20 carbon atomsof which the alkyl group
`can include a hydrogen atom that can be optionally replaced with a fluorine atom, or an aromatic group capable of
`having a substituent (that is a halogen atom, a cyano atom, a nitro atom, a trialkylsilyl group of which the alkyl groups
`are independently a linear or branched alkyl group having 1 - 8 carbon atoms, a linear or branched alkyl group having
`1 to 20 carbon atoms of which the alkyl group can include one or non-neighboring two or more methylene groupsthat
`can be replaced with -O-, -S-, -CO-, -CO-O-, -O-GO-, -GH=CH- or -C=C-, and the alkyl group can include a hydrogen
`atom that can be optionally replaced with a fluorine atom; and
`at least one of the optional substituent(s) of the cyclic groups, and the cyclic groups CyC1 and CyC2 include an
`aromatic group capable of having a substituent represented by the following formula (5):
`
`xS
`
`O
`
`wherein the aromatic group of the formula (5) is bonded to CyN1, CyN2, CyC1 or CyC2 via a single bond when the
`aromatic group is the optional substituent(s) of the cyclic groups, and the aromatic group of the formula (8) is bonded
`to CyN1 or CyN2 via a single bond and bonded to the metal atom M via a single bond when the aromatic group is
`CyC1 or CyC2;
`Y denotes C=O, CRR', C=C(CN)ps, O or S wherein R and R' are independently a hydrogen atom, a linear or
`branched alkyl group having 1 to 8 carbon atoms, a linear or branched alkyl group having 1
`to 20 carbon atoms of
`which the alkyl group can include one or non-neighboring two or more methylene groups that can be replaced with
`-O-, -S-,
`-COQ-, -CO-O-, -O-CO-, -CH=CH- or -C=C-, and the alkyl group can include a hydrogen atom that can be
`optionally replaced with a fluorine atom, or an aromatic group capable of having a substituent (that is a halogen atom,
`a cyano atom, a nitro atom, a trialkylsilyl group of which the alkyl groups are independently a linear or branched alkyl
`group having 1
`- 8 carbon atoms, a linear or branched alkyl group having 1 to 20 carbon atoms of which the alkyl group
`can include one or non-neighboring two or more methylene groups that can be replaced with -O-, -S-, -CO-, -CQ-O-,
`-O-CO-, -CH=CH- or -C=C-, and the alkyl group can include a hydrogen atom that can be optionally replaced with a
`fluorine atom); and
`the optional substituent of the aromatic group of the formula (5) is selected from a halogen atom, cyano group,
`a nitro group, a trialkylsilyl group of which the alkyl groups are independently a linear or branched alkyl group having
`1 to 8 carbon atoms, a linear or branched alkyl group having 1 to 20 carbon atomsof which the alkyl group can include
`one or non-neighboring two or more methylene groups that can be replaced with -O-, -S-, -CO-, -CO-O-, -O-CO-,
`-GH=GH- or -G=C-, and the alkyl group can include a hydrogen atom that can be optionally replaced with a fluorine
`atom, or an aromatic group capable of having a substituent (that is a halogen atom, a cyano atom, a nitro atom, a
`linear or branched alkyl group having 1 to 20 carbon atomsof which the alky! group can include one or non-neighboring
`two or more methylene groups that can be replaced with -O-, -S-, -CO-, -CO-O-, -O-CO-, -CH=CH- or -C=C-, and the
`alkyl group can include a hydrogen atom that can be optionally replaced with a fluorine atom) with the proviso that an
`adjacent pair of substituents can be bonded to form a cyclic structure.
`[0023]
`Preferred embodiments of the metal coordination compound of the formula (1) according to the present in-
`vention include the following:
`
`A metal coordination compound having a partial structure ML', represented by the formula (8) in the formula (1).
`A metal coordination compound having a partial structure ML‘, represented by the formula (4) in the formula (1).
`A metal coordination compound, wherein n is 0 in the formula (1).
`A metal coordination compound, wherein the group Y in the formula (5) is C=O or CRR'.
`A metal coordination compound wherein the cyclic groups CyC1 in the formula (1) and CyC2 in the formula (3)
`
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`

`

`EP 1 238 981 A2
`
`are independently selected from phenyl group, thieny! group, thianaphthyl group, naphthyl group, pyrenyl group,
`9-fluorenonyl group, fluorenyl group, dibenzofuryl group, dibenzothienyl group, or carbazolyl group, as an aromatic
`cyclic group capable of having a substituent with the proviso that the aromatic cyclic group can include one or two
`CH groups that can be replaced with a nitrogen atom, particularly selected from phenyl group or 2-fluorenyl group.
`A metal coordination compound, wherein the cyclic groups CyN1 in the formula (2) and CyN2 in the formula (3)
`are independently selected from pyridyl group, pyridazinyl group, and pyrimidinyl group, particularly pyridyl group,
`as an aromatic cyclic group capable of having a substituent.
`A metal coordination compound, wherein the cyclic groups CyN1, CyN2, CyC1 and CyC2 are independently non-
`substituted, or have a substituent selected from a halogen atom and a linear or branchedalkyl group having 1 to
`20 carbon atoms {of which the alkyl group can include one or non-neighboring two or more methylene groupsthat
`can be replaced with -O-, -S-, -CO-, -CO-O-, -O-CO-, -CH=CH-, -C=C-, or a divalent aromatic group capable of
`having a substituent (that is a halogen atom or a linear or branched alkyl group having 1 to 20 carbon atoms (of
`which the alkyl group can include one or non-neighboring two or more methylene groupsthat can be replaced with
`-O-, and the alkyl group can include a hydrogen atom that can be optionally replaced with a fluorine atom)), and
`the alkyl group can include a hydrogen atom that can be optionally replaced with a fluorine atom}.
`
`[0024] A metal coordination compound, whereinMin the formula (1) is iridium.
`
`[0025]
`A metal coordination compound represented bythe following formula (6):
`
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`
`Ir
`
`o~R
`
`
`
`Na
`2
`
`\
`
`f %*
`
`(6)
`
`Ra|3
`35
`
`40
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`
`wherein X denotes CRR’, O or S where R and R'are independentlyalinear or branched alkyl group of formula: C,Ha,,4-
`in which n is an integer of 1
`- 20, the alkyl group can include one or non-neighboring two or more methylene groups
`that can be replaced with -O- and also can include a hydrogen atom that can be optionally replaced with a fluorine atom;
`[0026] R2 denotes a hydrogen atom; a fluorine atom; a linear or branched alkyl group of formula: C,Ha,44- in which
`n is an integer of 1
`- 20, the alkyl group can include one or non-neighboring two or more methylene groups that can
`be replaced with -O- and also can include a hydrogen atom that can be optionally replaced with a fluorine atom; a
`phenyl group capable of having a substituent; a 9,9-dialkylfluoreny! group (of which the alkyl groups are independently
`a linear or branched alkyl group of formula: C,H»,,4- in which n is an integer of 1
`- 20, the alkyl group can include one
`or non-neighboring two or more methylene groupsthat can be replaced with -O- and also can include a hydrogen atom
`that can be optionally replaced with a fluorine atom); a dibenzofuranyl group capable of having a substituent; and a
`dibenzothienyl group capable of having a substituent; the optional substituent of phenyl group, 9,9-dialkylfluoreny|
`group, dibenzofuranyl group and dibenzothienyl group is a fluorine atom or a linear or branched alkyl group of formula:
`CyHoni in which n is an integer of 1 - 20, the alkyl group can include one or non-neighboring two or more methylene
`groups that can be replaced with -O- and also can include a hydrogen atom that can be optionally replaced with a
`fluorine atom.
`
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`
`[0027] The present invention also provides an electroluminescence device, comprising: a pair of electrodes disposed
`on a substrate, and a luminescenceunit comprising at least one organic compound disposed between the electrodes,
`wherein the organic compound comprises a metal coordination compound represented by the formula (1) described
`above.
`
`In the luminescence device, a voltage is applied between the electrodes to emit light.
`[0028]
`Ina preferred embodiment of the electroluminescence device, a voltage is applied between the electrodes
`[0029]
`to emit phosphorescence.
`[0030] The presentinvention further provides a picture display apparatus, comprising an electroluminescence device
`
`

`

`EP 1 238 981 A2
`
`described above and a means for supplying electric signals to the electroluminescence device.
`[0031] These and other objects, features and advantagesof the presentinvention will become more apparent upon
`a consideration of the following description of the preferred embodiments of the present invention taken in conjunction
`with the accompanying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0032]
`
`Figures 1A, 1B and 1C illustrate embodiments of the luminescence device according to the present invention,
`respectively.
`Figure 2 schematicallyillustrates a panel structure including an EL device and drive means.
`
`DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
`
`[0033] Basic structures of organic luminescence (EL) devices formed according to the present invention areillus-
`trated in Figures 1A, 1B and 1C.
`[0034] As shownin thesefigures, an organic luminescence device generally comprises, on a transparent substrate
`15, a 50 to 200 nm-thick transparent electrode 14, a plurality of organic film layers and a metal electrode 11 formed
`so as to cover the organic layers.
`[0035]
`Figure 1A shows an embodiment wherein the organic luminescence device comprises a luminescencelayer
`12 and a hole-transporting layer 13. The transparent electrode 14 may comprise ITO, etc., having a large workfunction
`so asto facilitate hole injection fram the transparent electrode 14 to the hole-transporting layer 13. The metal electrode
`11 comprises a metal material having a small work function, such as aluminum, magnesium or alloys of these elements,
`so as to facilitate electron injection into the organic luminescence device.
`[0036] The luminescence layer 12 comprises a compound (metal coordination compound) according to the present
`invention. The hole-transporting layer 13 may comprise, e.g., a triphenyldiamine derivative, as represented by a-NPD
`mentioned above, and also a material having an electron-donative property as desired.
`[0037]
`A device organized above exhibits a current-rectifying characteristic, and when an electric field is applied
`between the metal electrode 11 as a cathode and the transparent electrode 14 as an anode, electrons are injected
`from the metal electrode 11 into the luminescencelayer 12, and holes are injected from the transparent electrode 15.
`The injected holes and electrons are recombined in the luminescence layer 12 to form excitons having high energy
`potential, which cause luminescence during transition to the ground state. In this instance, the hole-transporting layer
`13 functions as an electron-blocking layer to increase the recombination efficiency at the boundary between the lumi-
`nescence layer layer 12 and the hole-transporting layer 13, thereby providing an enhanced luminescenceefficiency.
`[0038]
`Further, inthe structure of Figure 1B, an electron-transporting layer 16 is disposed between the metal electrode
`11 and the luminescence layer 12 in Figure 1A. As a result, the luminescencefunction is separated from the functions
`of electron transportation and hole transportation to provide a structure exhibiting more effective carrier blocking, thus
`increasing the luminescenceefficiency. The electron-transporting layer 16, may comprise, e.g., an oxadiazole deriva-
`tive.
`
`Figure 1C shows anotherdesirable form of a four-layer structure, including a hole-transporting layer 13, a
`[0039]
`luminescence layer 12, an exciton diffusion prevention layer 17 and an electron-transporting layer 16, successively
`from the side of the transparent electrode 14 as the anode.
`[0040] The luminescence materials used in the present invention are most suitably metal coordination compounds
`represented by the above-mentioned formulae (1) to (6), which are found to cause high-efficiency luminescence, retain
`high luminance for a long period and showlittle deterioration by current passage.
`[0041] The metal coordination compound of the present invention emits phosphorescence, and its lowest excited
`state is believed to be an MLCT* (metal-to-ligand charge transfer) excited state or n-n* excited state in a triplet state,
`and phosphorescenceis caused atthe time of transition from such a state to the ground state.
`[0042] Hereinbelow, methods for measurement of some properties and physical values described herein for char-
`acterizing the luminescence material of the present invention will be described.
`[0043]
`(1) Judgment between phosphorescence and fluorescence
`[0044]
`The identification of phosphorescence was effected depending on whether deactivation with oxygen was
`caused or not. A solution of a sample compound in chloroform after aeration with oxygen or with nitrogen is subjected
`to photoillumination to cause photo-luminescence. The luminescenceis judged to be phosphorescenceif almost no
`luminescenceattributable to the compound is observed with respect to the solution aerated with oxygen but photo-
`luminescence is confirmed with respect to the solution aerated with nitrogen. The phosphorescenceof all the com-
`pounds of the present invention has been confirmed by this method unless otherwise noted specifically.
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`(2) Phosphorescenceyield (a relative quantum yield, i.e., a ratio of an objective sample's quantum yield ©
`[0045]
`(sample) to a standard sample's quantum yield ®(st)) is determined according to the following formula:
`
`EP 1 238 981 A2
`
`@(sample)/®(st) =
`
`[Sem(sample)/labs(sample)|/[Sem(st)/labs(st)],
`
`wherein labs(st) denotes an absorption coefficient at an excitation wavelength of the standard sample; Sem(st), a
`luminescence spectral areal intensity when excited at the same wavelength: labs(sample), an absorption coefficient
`at an excitation wavelength of an objective compound; and Sem(sample), a luminescence spectral areal intensity when
`excited at the same wavelength.
`[0046]
`Phosphorescenceyield values described herein are relative values with respect to a phosphorescenceyield
`® = 1 of Ir(ppy)3 as a standard sample.
`[0047]
`(3) Amethod of measurement of phosphorescencelife is as follows.
`[0048]
`A sample compound is dissolved in chloroform and spin-coated onto a quartz substrate in a thickness of ca.
`0.1 um and is exposed to pulsative nitrogen laser light at an excitation wavelength of 337 nm at room temperature by
`using a luminescencelife meter (made by Hamamatsu Photonics K.K.). After completion of the excitation pulses, the
`decay characteristic of luminescence intensity is measured.
`[0049] Whenan initial luminescence intensity is denoted by Ip, a luminescence intensity after t(sec) is expressed
`according to the following formula with reference to a luminescencelife t(sec):
`
`|= Ip-exp(-t/t).
`
`[0050] The luminescence material (metal coordination compound) of the present invention exhibited high phospho-
`rescence quantum yields of 0.11 to 0.9 and short phosphorescencelives of 0.1 to 40 usec. A short phosphorescence
`life becomes a condition for causing little energy deactivation and exhibiting an enhanced luminescence efficiency.
`More specifically if the phosphorescencelife is long, the numberoftriplet state molecules maintained for luminescence
`is increased, and the deactivation processis liable to occur, thus resulting in a lower luminescenceefficiency particularly
`at the time of a high-current density. The material of the present invention has a relatively short phosphorescencelife
`thus exhibiting a high phosphorescence quantum yield, and is therefore suitable as a luminescence material for an EL
`device.
`
`[0051] Asaresult of various studies of ours, it has been found that an organic EL device using the metal coordination
`compound of the formula (1) as a principal luminescence material causes high-efficiency luminescence, retains high
`luminancefor a long period and showslittle deterioration by current passage.
`[0052]
`In the formula (1) representing the metal coordination compound of the present invention, n may preferably
`0 or 1, more preferably O. Further, the partial structure ML'n may preferably comprise the aromatic group represented
`by the above-mentioned formula (5).
`In the formula (5), Y may preferably comprise C=O or CRR'. When Y is CRR'
`where R and R' are CH, the metal coordination compound of the formula (I) may preferably have no substituent.
`Particularly, when CyC1 is FL2 (appearing hereinafter) where R and R' are CH, and CyN1 is Pi, R1 to R4 (as substituents
`for Pi and FL2) may preferably be hydregen atom at the same time.
`[0053]
`Inthe present invention, by incorporating the aromatic group of the formula (5) into the metal coordination
`compound of the formula (1), it becomes possible to control an emission wavelength (particularly to provide a long
`emission wavelength). The presence of the aromatic group of the formula (5) is effective in enhancing a solubility of
`the metal coordination compound of the present invention in an organic solvent, thus facilitating a purification thereof
`by recrystallization or column chromatography. As a result, the metal coordination compound of the present invention
`is suitable as a luminescence material for the organic EL device.
`[0054]
`Further, as shown in Examples appearing hereinafter, it has been substantiated that the metal coordination
`compound of the present invention exhibited an excellent stability in a continuous current passage test. This may be
`attributable to incorporation of the aromatic group of the formula (5) into the molecular structure of the metal coordination
`compound of the formula (1) according to the present invention. More specifically, achange in intermolecular interaction
`due to the introduction of the aromatic group of the formula (5) allows an intermolecular interaction of the metal coor-
`dination compound with, e.g., a host material to suppress formation of exciton associates causing thermal deactivation,
`thus reducing a quenching process thereby to improve phosphorescenceyield and device characteristics.
`[0055] The luminescence device according to the present invention may preferably be an electroluminescence device
`of the type wherein a layer of the metal coordination compound of the formula (1) is disposed between opposing two
`electrodes and a voltage is applied between the electrodes to cause luminescence, as shown in Figures 1A, 1BandiC.
`
`20
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`35
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`40
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`45
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`50
`
`55
`
`

`

`EP 1 238 981 A2
`
`For the application to a display, a drive system using a thin-film transistor (TFT) drive circuit according to an
`[0056]
`active matrix-scheme may be used. Hereinbelow, an embodiment of using a device of the present invention in combi-
`nation with an active matrix substrate is briefly described with reference to Figure 2.
`[0057]
`Figure2 illustrates an embodiment of panel structure comprising an EL device and drive means. The panel
`is provided with a scanning signal driver, a data signal driver and a current supply source which are connected to gate
`selection lines, data signal lines and current supply lines, respectively. At each intersection of the gate selection lines
`and the data signal lines, a display pixel electrode is disposed. The scanning signal drive sequentially selects the gate
`selection lines G1, G2, G3 ... Gn, and in synchronism herewith, picture signals are supplied from the data signal driver
`to display a picture (image).
`[0058]
`Bydriving a display panel including a luminescencelayer comprising a luminescence material of the present
`invention, it becomes possible to provide a display which exhibits a good picture quality and is stable even for a long
`period display.
`[0059]
`Some synthetic paths for providing a metal coordination compound represented by the above-mentioned
`formula (1) are illustrated below with referenceto an iridium coordination compound (m+n = 3) for example:
`
`20
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`55
`
`Ir(CH;COCHCOCH;);
`
`3XL
`
`
`Ir(L)s
`
`or
`
`IrCl,.XH,O
`eu
`or
`
`2XL
`
`
`.
`
`[Ir{L)eCl]
`
`L
`
`
`Ir(L);
`
`NajIrCl.2H,O
`
`Ir(L),(CH;COCHCOCH,)
`
`[0060] Other metal coordination compound (M = Pt, Rh and Pd) can also be synthesized in a similar manner.
`[0061]
`Some specific structural examples of metal coordination compounds usedin the presentinvention are shown
`in Tables 1 to Tables 42 appearing hereinafter, which are however only representative examples and are not exhaustive.
`
`Pi to Cz for CyN1, CyN2, CyC1 and CyC2 shownin Tables 1 to 42 repres