Patent Application
20060152144
The present invention relates to a blue light-emitting polymer, processes of preparing the blue light-emitting polymer, and luminescent elements including the blue light-emitting polymer. More specifically, this invention relates to a blue light-emitting polymer capable of emitting blue light at a high luminance for a long time upon the application of electric energy, processes of producing the polymer and luminescent elements including the blue light-emitting polymer.
For luminescent compounds that may be utilized for organic electroluminescent elements, which are often abbreviated to “organic EL elements”, have been proposed various low molecular weight organic luminescent compounds.
When a low molecular weight organic luminescent compound is utilized for a luminescent element, the luminescent compound has to be deposited on the light-emitting layer or dispersed in a fixative substance such as polymer. Therefore a process to produce an organic electroluminescent element including a low molecular weight organic luminescent compound requires a step of vapor deposition or a step of high polymer film formation that comprises the application of a high polymer solution including the low molecular weight organic luminescent compound. Generally, the step of high polymer film formation is easier than that of vapor deposition.
Another piece of information about the background art is that luminescent polymers, capable of emitting blue light for a long time and excellent in durability, have not been developed.
[Problems to be Solved by the Invention]
The objective of the present invention is to provide a blue light-emitting polymer capable of emitting blue light at a high luminance for a long time, and further excellent in durability. This invention also aims for providing processes for producing the blue light-emitting polymer and luminescent elements including the blue light-emitting polymer.
[Means to Solve the Problems]
The first means to achieve the objective is a blue light-emitting polymer having a repeating unit represented by formula (1):
wherein each of Ar1 and Ar2 denotes a group represented by formula (2), (3), (4) or (5), wherein Ar1 and Ar2 may be the same or different from each other; and Z is a single bond or a group represented by formula (6).
Formula (2) is:
wherein R1 is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 14 carbon atoms; and “n” denotes an integer from 1 to 4.
Formula (3) is:
wherein each of R2 and R3 denotes a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 14 carbon atoms, wherein R2 and R3 may be the same or different from each other; “m” denotes an integer of 1 or 2; and “n” means the same as the above.
Formula (4) is:
wherein each of R4, R5 and R6 denotes a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 14 carbon atoms, wherein R4, R5 and R6 may be the same or different from one another; “m” and “n” respectively mean the same as the above.
Formula (5) is:
wherein each of R7 and R8 denotes a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 14 carbon atoms, wherein R7 and R8 may be the same or different from each other; and “n” means the same as the above.
Formula (6) is:
wherein R10 denotes a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and two R10s may be the same or different from each other.
The second means to achieve the objective is a process of producing a blue light-emitting polymer having the repeating unit represented by formula (1), comprising dehydrohalogenating an aromatic compound represented by formula (7) and an aromatic compound with a halogen atom represented by formula (8) to obtain a compound; acetylating the obtained compound; oxidizing the acetylated compound; hydrolyzing the oxidized compound to produce a dicarboxylic acid represented by formula (9); and condensation-polymerizing the dicarboxylic acid (9) and a hydrazinium salt.
Formula (7) is:
H—Ar1—H (7)
wherein Ar1 denotes the same as that defined in relation to the first means.
Formula (8) is:
H—Ar2—CH2X (8)
wherein Ar2 denotes the same as that defined in relation to the first means, and X denotes a halogen atom.
Formula (9) is:
HOOC—Ar1—CH2—Ar2—COOH (9)
The third means to achieve the objective of the present invention is another process of producing a blue light-emitting polymer having the repeating unit represented by formula (1), comprising acetylating a fluorene represented by formula (10); oxidizing the acetylated fluorene; hydrolyzing the oxidized acetylated fluorene to obtain a compound represented by formula (11); and condensation-polymerizing the compound (11) and the compound represented by formula (9) shown hereinbefore in the presence of a hydrazinium salt.
Formula (10) is:
wherein R10 denotes a hydrogen atom or an alkyl group with 1-10 carbon atoms; and two R10s may be the same or different from each other.
Formula (11) is:
The fourth means is a luminescent element which has a light-emitting layer including a blue light-emitting polymer having the repeating unit represented by formula (1) between a pair of electrodes.
[Advantages of the Invention]
The present invention can provide a blue light-emitting polymer capable of emitting light at a high luminance for a long time, and furthermore processes of producing the blue light-emitting polymer and a luminescent element including the polymer.
A, B, C . . . blue light-emitting element, 1 . . . substrate, 2 . . . transparent electrode, 3 . . . light-emitting layer, 4 . . . electrode layer
The blue light-emitting polymer of the present invention has a repeating unit represented by formula (1):
The repeating unit of the blue light-emitting polymer is composed of an oxadiazole ring, a methylene group, a first substituent Ar1, a second substituent Ar2, and a third substituent Z.
The oxadiazole ring has two carbon atoms. One of them is bonded with the second substituent Ar2 and the other with the first substituent Ar1 that belongs to the next repeating unit through the third substituent Z.
The second substituent Ar2 is bonded with the oxadiazole ring and with the first substituent Ar1 through the methylene group. The first substituent Ar1 is also bonded with a carbon atom of the oxadiazole ring that belongs to the preceding repeating unit through the third substituent Z of the preceding repeating unit. Each of Ar1 and Ar2 denotes one of the following formulas (2)-(5), and Ar1 and Ar2 may be the same or different from each other.
Each of Ar1 and Ar2 may be the group represented by formula (2) below.
The group represented by formula (2) has a benzene ring as its basic skeleton. One of a pair of p-positioned carbon atoms of the benzene ring is bonded with a carbon atom of the oxadiazole ring, and the other is bonded with the carbon atom of the methylene group. The other carbon atoms of the benzene ring may be bonded with R1.
R1 is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 14 carbon atoms.
The alkyl group having 1 to 10 carbon atoms for R1 includes methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, sec-pentyl group, tert-pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, etc. Among those are preferred an alkyl group having 1 to 5 carbon atoms, such as methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, sec-pentyl group, or tert-pentyl group. The most preferable are alkyl groups having 1 to 3 carbon atoms.
The alkyl group having 1 to 10 carbon atoms may be a fluorine atom-including alkyl group where at least one of the hydrogen atoms is replaced with a fluorine atom.
For the fluorine atom-including alkyl group with 1 to 10 carbon atoms is preferred a fluorine atom-including alkyl group with 1 to 3 carbon atoms. Examples of the preferred are fluoromethyl group, difluoromethyl group, trifluoromethyl group, fluoroethyl group, 1,1-difluoroethyl group, 1,2-difluoroethyl group, 1,1,1-trifluoroethyl group, 1,1,2-trifluoroethyl group, 1,2,2-trifluoroethyl group, 1,1,2,2-tetrafluoroethyl group, 1,1,2,2,2-pentafluoroethyl group, 1-fluoropropyl group, 2-fluoropropyl group, 1,1-difluoropropyl group, 1,2-difluoropropyl group, 1,3-difluoropropyl group, 2,2-difluoropropyl group, 1,1,1-trifluoropropyl group, 1,1,2-trifluoropropyl group, 1,2,3-trifluoropropyl group, 1,2,2-trifluoropropyl group, and 1,3,3-trifluoropropyl group.
Examples of the alkoxyl group with 1 to 5 carbon atoms include ethoxyl group, methoxyl group, propoxyl group, isopropoxyl group, butoxyl group, s-butoxyl group, t-butoxyl group, a pentoxyl group.
The aryl group with 6 to 14 carbon atoms includes, for example, phenyl group, a tolyl group, a naphtyl group, a biphenyl group, and an anthryl group.
“n” in formula (1) denotes an integer from 1 to 4. When n is 2, 3, or 4, R1s bonded to the benzene ring may be the same or different from each other.
Also, Ar1 and Ar2 may be a group represented by formula (3).
The group represented by formula (3) has a naphthalene ring as its basic skeleton. One of the 1-positioned and 4-positioned carbons of the naphthalene ring is bonded with a carbon atom of the oxadiazole ring and the other with the carbon atom of the methylene ring. The other carbon atoms of the naphthalene ring are bonded with one or two R2s and up to four R3s.
Each of R2 and R3 means a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxyl group having 1 to 5 carbon atoms, or an aryl having 6 to 14 carbon atoms.
The alkyl group, the alkoxyl group and the aryl group are the same as those explained above.
“m” in formula (3) denotes an integer of 1 or 2, and “n” means the same as that explained above.
Up to two R2s and up to four R3s may be the same or different from each other.
Ar1 and Ar2 may also be a group represented by formula (4).
The group represented by formula (4) has an anthracene ring as its basic skeleton. One of the 1-positioned and 4-positioned carbons of the anthracene ring is bonded with a carbon atom of the oxadiazole ring and the other with the carbon atom of the methylene ring. The other carbon atoms of the anthracene ring are bonded with R4(s), R5(s) and R6(s).
Each of R4, R5, and R6 means a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxyl group having 1 to 5 carbon atoms, or an aryl having 6 to 14 carbon atoms.
The alkyl group, the alkoxyl group and the aryl group are the same as those explained above.
“m” and “n” mean the same as those explained above.
Up to two R4s and R5s, and up to four R6s may be the same or different from each other.
Furthermore, Ar1 and Ar2 may be a group represented by formula (5).
The group represented by formula (5) has an anthracene ring as its basic skeleton. One of the 9-positioned and 10-positioned carbons of the anthracene ring is bonded with a carbon atom of the oxadiazole ring and the other with the carbon atom of the methylene ring. The other carbon atoms of the anthracene ring are bonded with R7 (s) or R8 (s).
Each of R7 and R8 means a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxyl group having 1 to 5 carbon atoms, or an aryl having 6 to 14 carbon atoms.
The alkyl group, the alkoxyl group and the aryl group are the same as those explained above.
“n” in formula (5) means the same as that explained above.
Up to four R7s and R8s of the anthracene ring may be the same or different from each other.
“Z” in formula (1) denotes a single bond or a group represented by formula (6) below.
The group represented by formula (6) is composed of a fluorene and an oxadiazole ring.
The 2-positioned carbon atom of the fluorene is bonded with one of the carbon atoms of the oxadiazole ring, and the 7-positioned carbon atom thereof with a carbon atom of Ar2 in formula (1). Also, the other carbon atom of the oxadiazole ring is bonded with the Ar1 in the next repeating unit.
R10 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms.
Examples of the alkyl group having 1 to 10 carbon atoms are methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, sec-pentyl group, tert-pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, etc. Among those are preferred an alkyl group having 1 to 5 carbon atoms, such as methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, sec-pentyl group, or tert-pentyl group. Alkyl groups having 1 to 3 carbon atoms are particularly preferable.
The alkyl group having 1 to 10 carbon atoms may be a fluorine atom-including alkyl group where at least one of the hydrogen atoms is replaced with a fluorine atom.
For the fluorine atom-including alkyl group with 1 to 10 carbon atoms is preferred a fluorine atom-including alkyl group with 1 to 3 carbon atoms. Examples of the preferred are fluoromethyl group, difluoromethyl group, trifluoromethyl group, fluoroethyl group, 1,1-difluoroethyl group, 1,2-difluoroethyl group, 1,1,1-trifluoroethyl group, 1,1,2-trifluoroethyl group, 1,2,2-trifluoroethyl group, 1,1,2,2-tetrafluoroethyl group, 1,1,2,2,2-pentafluoroethyl group, 1-fluoropropyl group, 2-fluoropropyl group, 1,1-difluoropropyl group, 1,2-difluoropropyl group, 1,3-difluoropropyl group, 2,2-difluoropropyl group, 1,1,1-trifluoropropyl group, 1,1,2-trifluoropropyl group, 1,2,3-trifluoropropyl group, 1,2,2-trifluoropropyl group, and 1,3,3-trifluoropropyl group.
Also, the average molecular weight of the blue light-emitting polymer of the present invention is preferably 10000 to 500000, particularly 20000 to 300000.
Because the repeating unit represented by formula (1) has an oxadiazole ring that has a large π electron cloud, the density of the π electron cloud in each repeating unit increases and the π electron cloud becomes stabilized. In these circumstances, it is surmised that blue light can be emitted by the application of a small energy. The blue light-emitting polymer of the present invention is characterized by its repeating unit having the oxadiazole ring with a large π electron cloud, the carbon atoms of which oxadiazole ring are bonded with the groups Ar1 and Ar2. Because this blue light-emitting polymer has a repeating unit that includes aromatic rings and an oxadiazole ring in its backbone chain, it becomes chemically stable, which leads to its special property; it does not easily deteriorate even under severe conditions.
The blue light-emitting polymer of the present invention may be prepared in the following manners.
Specifically, an aromatic compound represented by formula (7) and an aromatic compound with a halogen atom represented by formula (8), which are the starting substances, are heated in a solvent to be subjected to a dehydrohalogenating reaction.
Formula (7) is:
H—Ar1—H (7)
wherein Ar1 denotes the same as the above.
Formula (8) is:
H—Ar2—CH2X (8)
wherein Ar2 denotes the same as the above, and “X” denotes a halogen atom. For the halogen atom may be used a chlorine atom, a fluorine atom, a bromine atom, an iodine atom, etc. A chlorine atom is preferable.
The aromatic compound includes, for example, benzene, toluene, o-dimethylbenzene, m-dimethylbenzene, p-dimethylbenzene, o-diethylbenzene, m-diethylbenzene, p-diethylbenzene, naphthalene, 1,2-dimethylnaphthalene, 1,3-dimethylnaphthalene, 1,4-dimethylnaphthalene, 1,2-diethylnaphthalene, 1,3-diethylnaphthalene, 1,4-diethylnaphthalene, and anthracene.
The aromatic compound with a halogen atom includes, for example, benzyl chloride, 1-chloromethylnaphthalene, 2-chloromethylnaphthalene, 1-chloromethylanthracene, 2-chloromethylanthracene, 5-chloromethylanthracene, benzyl bromide, 1-bromomethylnaphthalene, 2-bromomethylnaphthalene, 1-bromomethylanthracene, 2-bromomethylanthracene, and 5-bromomethylanthracene.
The solvent includes an inorganic solvent such as hydrochloric acid, sulfuric acid, or nitric acid, and an organic solvent such as ethanol, methanol, acetic acid, acetic anhydride, dimethyl ether, diethyl ether, acetone, phthalic acid, phthalic anhydride, n-hexane, benzene, toluene, pyridine, tetrahydrofuran, dimethylformamide, which may sometimes be abbreviated to “DMF” hereinafter, and N,N-dimethylacetamide, which may sometimes be abbreviated to “DMAC” hereinafter.
A catalyst may also be employed in this reaction.
For the catalyst may be used, for example, iron, zinc, nickel, copper, platinum, aluminum oxide, or aluminum chloride.
The temperature for the dehydrohalogenation reaction should be from 80 to 100° C., preferably from 85 to 95° C.
The dehydrohalogenation reaction produces a compound represented by formula (12) below.
H—Ar1—CH2—Ar2—H (12)
The compound represented by formula (12) is heated with an acyl halide represented by formula (13) in a solvent, so that the compound is acetylated.
R11CO—X (13)
wherein R11 in formula (13) denotes an alkyl group with 1 to 5 carbon atoms.
Examples of the alkyl group with 1 to 5 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, sec-pentyl group, and tert-pentyl group. Among them, an alkyl group with 1 to 3 carbon atoms is preferable.
“X” in formula (13) denotes a halogen atom, which includes a chlorine atom, a fluorine atom, a bromine atom, and an iodine atom. A chlorine atom is preferable.
For the acyl halide may be used acetyl chloride, propionyl chloride, butyryl chloride, isobutyryl chloride, acetyl bromide, propionyl bromide, butyryl bromide, isobutyryl bromide, etc.
Examples of the solvent include inorganic solvents such as carbon sulfide or carbon disulfide, and organic solvents such as ethanol, methanol, acetic anhydride, phthalic anhydride, diethyl ether, dimethyl ether, acetone, benzene, toluene, pyridine, tetrahydrofuran, DMF, and DMAC.
A catalyst may also be employed in this reaction.
For the catalyst may be used aluminum chloride, antimony chloride, lead chloride, titanium chloride, bismuth chloride, or zinc chloride.
The temperature for the acetylating reaction is typically from 20 to 50° C., preferably from 30 to 40° C.
The acetylating reaction produces a compound represented by formula (14).
R11CO—Ar1—CH2—Ar2—COR11 (14)
Then, the compound represented by formula (14) is subjected to an oxidization reaction by heating it with an oxidizing agent in a solvent.
The solvent includes, for example, non-polar solvents such as benzene, carbon tetrachloride, hexane, diethyl ether, and dimethyl ether, and polar solvents such as methanol, ethanol, pyridine, tetrahydrofuran, DMF, and DMAC. It is preferable if the solvent for this oxidization reaction is the same as that used for the acetylating reaction. If so, the oxidization can be carried out directly after the completion of the acetylation, by adding the oxidizing agent to the product liquid of the acetylation and heating the obtained mixture.
Examples of the oxidizing agent include sodium hypochlorite are potassium hypochlorite.
The reaction temperature for the oxidization reaction is typically from 40 to 80° C., preferably from 60 to 70° C.
The oxidization reaction produces a carbonyl compound represented by formula (15).
MCO—Ar1—CH2—Ar2—COM (15)
“M” in formula (15) denotes the element originating from the oxidizing agent. Therefore “M” is, for example, sodium or potassium.
Hydrolysis of the carbonyl compound represented by formula (15) in the presence of an acid or an alkali produces a dicarboxylic acid represented by formula (9).
HOOC—Ar1—CH2—Ar2—COOH (9)
For the acid may be employed hydrochloric acid, sulfuric acid, or nitric acid. For the alkali, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, or ammonia may be used.
Then, the dicarboxylic acid and a hydrazinium salt are subjected to condensation-polymerization by heating them in the presence of a dehydrating agent.
Examples of the dehydrating agent include sulfuric acid, zinc chloride, phosphoric acid anhydride, boric acid, oxalic acid, or polyphosphoric acid.
Examples of the hydrazinium salt include hydrazine hydrochloride, hydrazine sulfate and hydrazine nitrate.
The reaction temperature for the condensation-polymerization is typically from 100 to 150° C., preferably from 110 to 130° C.
This reaction results in the blue light-emitting polymer of the present invention represented by formula (1).
Another process of producing the blue light-emitting polymer of the present invention is as follows.
A fluorene represented by formula (10) and an acyl halide represented by formula (13) are heated in a solvent, so that the fluorene is acetylated.
In formula (10), R10 denotes a hydrogen atom, or an alkyl group with 1 to 10 carbon atoms, preferably with 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms. The alkyl group includes those examples that have been mentioned above.
R11—CO—X (13)
In formula (13), R11 denotes a hydrogen atom, or an alkyl group with 1 to 5 carbon atoms.
Examples of the alkyl group with 1 to 5 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, sec-pentyl group, and tert-pentyl group. Among them are preferred alkyl groups with 1 to 3 carbon atoms.
“X” in formula (13) denotes a halogen atom, which includes a chlorine atom, a fluorine atom, a bromine atom, and an iodine atom. A chlorine atom is preferable.
For the acyl halide may be used acetyl chloride, propionyl chloride, butyryl chloride, isobutyryl chloride, acetyl bromide, propionyl bromide, butyryl bromide, isobutyryl bromide, etc. An acyl chloride is preferable. More preferable is an acyl chloride with 1 to 3 carbon atoms.
Examples of the solvent include inorganic solvents such as carbon sulfide or carbon disulfide, and organic solvents such as ethanol, methanol, acetic anhydride, phthalic anhydride, diethyl ether, dimethyl ether, acetone, benzene, toluene, pyridine, tetrahydrofuran, DMF, and DMAC.
A catalyst may also be employed in this reaction.
For the catalyst may be used, for example, aluminum chloride, antimony chloride, lead chloride, titanium chloride, bismuth chloride, or zinc chloride.
The temperature for the acetylating reaction is typically from 20 to 50° C., preferably from 30 to 40° C.
The acetylating reaction produces a compound represented by formula (16).
Then, the compound represented by formula (16) is subjected to an oxidization reaction by heating it with an oxidizing agent in a solvent.
The solvent includes, for example, non-polar solvents such as benzene, carbon tetrachloride, hexane, diethyl ether, and dimethylether, and polar solvents such as methanol, ethanol, pyridine, tetrahydrofuran, DMF, and DMAC.
Examples of the oxidizing agent include sodium hypochlorite are potassium hypochlorite.
The reaction temperature for the oxidization reaction is typically from 40 to 80° C., preferably from 60 to 70° C.
The oxidization reaction produces a carbonyl compound represented by formula (17).
“M” in formula (17) denotes the element originating from the oxidizing agent. Therefore “M” is, for example, sodium or potassium.
Hydrolysis of the carbonyl compound represented by formula (17) in the presence of an acid or an alkali produces a dicarboxylic acid represented by formula (11).
For the acid may be employed hydrochloric acid, sulfuric acid, or nitric acid. For the alkali, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, or ammonia may be used.
Then, the dicarboxylic acid and a hydrazinium salt are subjected to condensation-polymerization by heating them in the presence of a dehydrating agent.
Examples of the dehydrating agent include sulfuric acid, zinc chloride, phosphoric acid anhydride, boric acid, oxalic acid, or polyphosphoric acid.
Examples of the hydrazinium salt include hydrazine hydrochloride, hydrazine sulfate and hydrazine nitrate.
The reaction temperature for the condensation-polymerization is typically from 100 to 150° C., preferably from 110 to 130° C.
This reaction results in the blue light-emitting polymer of the present invention represented by formula (1).
The luminescent element utilizing the blue light-emitting polymer of the present invention will be explained in the followings.
When the luminescent element shown in
For the red-light emitting compound is suitable the Nile Red luminescent compound emitting red light represented by formula (18).
For the green light-emitting compound is suitable a coumarone compound emitting green light, an indophenol compound emitting green light and an indigo compound emitting green light. The coumarin compound represented by the formula (19) is preferable among them.
When an electric field is applied between the transparent electrode 2 and the electrode layer 4, electrons are injected from the electrode layer 4 and positive holes are injected from the transparent electrode 2. In the light-emitting layer 3, the electrons are recombined with positive holes, which causes the energy level to return to the valence band from the conduction band. This transition of the energy level is accompanied by emission of the energy differential as light.
The luminescent element A shown in
As understood from the foregoing, when the light-emitting layer of the luminescent element A includes a blue light-emitting polymer of the present invention and not a red light-emitting compound or a green light-emitting compound, the luminescent element A emits clear blue light.
The luminescent element A may also be shaped into a tubular light emitter comprising a tubularly shaped substrate 1, a transparent electrode 2 placed on the internal surface of the substrate 1, a light emitting layer 3 and an electrode layer 4 placed on the transparent electrode 2 in this order. Because the luminescent element A does not include mercury, it is an ecological light source and may be a substitute for conventional fluorescent lamps.
For the substrate 1 may be used any known substrate, as long as the transparent electrode 2 can be formed on the surface of the substrate. Examples of the substrate 1 are a glass substrate, a plastic sheet, a ceramic substrate, and a metal substrate whose surface is insulated, for example, by forming thereon a layer of an insulating paint.
When the substrate 1 is opaque, the luminescent element, which includes a red light-emitting compound, a green light-emitting compound and a blue light-emitting polymer of the present invention, is a single-faced illuminator that emits white light from the surface layer opposite to the substrate. On the other hand, when the substrate 1 is transparent, the luminescent element is a double-faced illuminator that emits white light from both of the substrate and the surface layer opposite to the substrate.
For the transparent electrode 2, various materials may be employed, as long as their work functions are large, they are transparent, and they can function as a cathode and inject holes to the light-emitting layer 3 when voltage is applied thereto. Specifically, the transparent electrode 2 may be made of a transparent inorganic conductive material of ITO, In2O3, SnO2, ZnO, CdO, etc. and derivatives thereof, or an electrically conductive high polymer such as polyaniline.
The transparent electrode 2 may be formed on the substrate 1 by chemical vapor phase deposition, spray pyrolysis, high-vacuum metal deposition, electron beam deposition, sputtering, ion beam sputtering, ion plating, ion-assisted deposition, and other methods.
When the substrate is made of an opaque material, the electrode formed on the substrate need not be transparent.
The light-emitting layer 3 is a layer that includes a blue light-emitting polymer according to the present invention when the layer 3 is intended to emit blue light. It includes a red light-emitting compound and a green light-emitting compound in addition to a blue light-emitting polymer of the present invention when it is intended to emit white light. A film of a blue light-emitting polymer of the present invention, or a film of a red light-emitting compound, a green light-emitting compound, and a blue light-emitting polymer of the present invention may be formed on the transparent electrode 2.
A typical way of forming a film of the blue light-emitting polymer on the transparent electrode 2 may be the application of a solution of the polymer dissolved in a suitable solvent onto the transparent electrode. The application method includes, for example, a spin cast method, a brush-coating method, etc.
The thickness of the light-emitting layer 3 ranges, typically between 30 nm and 500 nm, preferably between 100 nm and 300 nm. When the thickness is too small, the amount of the emitted light may be insufficient. On the other hand, when the thickness is too large, the voltage required to drive the element may be too high, which is not desirable. Besides, the large thickness may reduce the flexibility of the film necessary to be shaped into a planar, tubular, curved, or ring article.
For the electrode layer 4 may be employed a material having a small work function. Examples of the material are elementary metals and metallic alloys, such as MgAg, aluminum alloy, metallic calcium, etc. A preferable electrode layer 4 is made of an alloy of aluminum and a small amount of lithium. This electrode layer 4 may easily be formed on the surface of light-emitting layer 3, which, in turn, has been formed on substrate 1, by the technique of metal deposition.
When the light-emitting layer is formed, a buffer layer should be inserted between each electrode and the light-emitting layer.
Materials for the buffer layer are, for example, an alkaline metal compound such as lithium fluoride, an alkaline earth metal compound such as magnesium fluoride, an oxide such as an aluminum oxide, and 4,4′-biscarbazole biphenyl (Cz-TPD). Also, materials for forming the buffer layer between the cathode made of, for example, ITO, and the organic layer include m-MTDATA (4,4′,4″-tris(3-methylphenyl-phenylamino)triphenylamine), phthalocyanine, polyaniline, and polythiophene derivatives, and inorganic oxides such as molybdenum oxide, ruthenium oxide, vanadium oxide, and lithium fluoride. When the materials are appropriately selected, these buffer layers can lower the driving voltage of the organic EL element, improve the quantum efficiency of luminescence, and achieve an increase in the luminance of the emitted light.
Next, the second example of the luminescent element according to the present invention is shown in
As shown in
The substrate 1, the transparent electrode 2 and the electrode layer 4 are the same as those explained for the luminescent element A in
The light-emitting layer of the luminescent element B comprises light-emitting sublayers 3a and 3b. The light-emitting sublayer 3a is a deposited film formed by depositing a light-emitting compound on the hole-transporting layer 5. The light-emitting sublayer 3b functions as a host material.
Examples of the hole-transporting substance included in the hole-transporting layer 5 are a triphenylamine compound such as N,N′-diphenyl-N,N′-di(m-tolyl)-benzidine (TPD) and α-NPD, a hydrazon compound, a stilbene compound, a heterocyclic compound, a π electron star burst positive hole transporting substance, etc.
Examples of the electron-transporting substance included in the electron-transporting layer 6 are an oxadiazole derivative such as 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole and 2,5-bis(1-naphthyl)-1,3,4-oxadiazole (BND), and 2,5-bis(5′-tert-butyl-2′-benzoxazolyl)thiophene. Also, a metal complex material such as quinolinol aluminum complex (Alq3), benzoquinolinol beryllium complex (Bebq2) may be used suitably.
The electron-transporting layer 6 of the luminescent element B shown in
The thickness of each layer is the same as that in a known multi-layer organic EL element.
The luminescent element B in
The third example of the luminescent element of this invention is shown in
The luminescent element C shown in
The luminescent element C functions in the same way as the luminescent element B.
Another example of the luminescent element of this invention is shown in
An example of the luminescent elements, other than those shown in
Also, it is preferred if the light-emitting layer includes, as a sensitizing agent, rubrene, especially rubrene together with Alq3.
A blue light-emitting element utilizing a blue light-emitting polymer of the present invention, or a white light-emitting element utilizing a red light-emitting compound, a green light-emitting compound and a blue light-emitting polymer of the present invention may generally be used for an organic EL element driven by direct current, and also by pulses and alternating current.
Synthesis of a Blue Light-Emitting Polymer
<Dehydrohalogenation>
In a 2 L three-necked flask were placed 100 g of naphthalene, 148.14 g of benzyl chloride, and 40.82 g of zinc. The flask containing the mixture was placed in a water bath and the mixture was heated to 90° C. The mixture was stirred for 1.5 hours at around the temperature and allowed to react. After the termination of the reaction, the product was cooled with ice. The cooled product was subjected to extraction with benzene. The extraction/separation was carried out four times. 375 ml of benzene was used each time. The extract was washed with water four times, which was followed by a filtration. The solids collected were dissolved in 2 L of benzene, and the resulting solution was vacuum distilled for an hour at 80° C. with an evaporator. After the distillation, ethanol was added to the obtained concentrate. The resultant was heated to 60° C., then cooled naturally, and filtered. 62.38 g of white crystals were obtained.
An NMR spectrum chart of the white crystals is shown in
<Acetylation>
In a 1 L three-necked flask were placed 32.55 g of the compound obtained in the step of dehydrohalogenation, 116.35 g of acetyl chloride, 197.7 g of aluminum chloride, and 167 ml of carbon disulfide. The flask containing the mixture was placed in a water bath and the mixture was heated to 35° C. The mixture was stirred for 2.5 hours at around the temperature and allowed to react. After the termination of the reaction, the product was cooled naturally. The cooled product was subjected to extraction with chloroform. The extraction/separation was carried out three times. 80 ml of chloroform was used each time. Then, the extract was washed with water four times. The solvent was distilled away from the washed extract and the remaining was dried up to solids. The solids were introduced into 75 ml of dioxane, and the resulting mixture was filtered. The solids collected were dissolved in a mixed solvent of dioxane and petroleum ether, and the resultant solution was dried up. 26.77 g of yellow crystals were obtained.
An NMR spectrum chart of the yellow crystals is shown in
<Oxidation and Hydrolysis>
In a 2 L three-necked flask were placed 26.77 g of the compound produced in the step of acetylation and 40 ml of methanol. The flask containing the mixture was placed in a water bath and the mixture was heated up to 65° C. step by step. A 0.7 mol/L aqueous solution of sodium hypochlorite was gradually added to the mixture during the stepwise process of heating. The total amount of the added was 500 ml. The resulting mixture was stirred for 2 hours at 65° C. and allowed to react. After the termination of the reaction, the product was cooled naturally. The cooled product was filtered, and the solids collected were washed with water and then with 25 ml of methanol. The washed was dried. 21.44 g of white crystals were obtained.
An NMR spectrum chart of the obtained crystals is shown in
<Condensation-Polymerization>
In a 2 L three-necked flask were placed 3.0 g of the dicarboxylic acid produced through the oxidation and hydrolysis, 49 g of polyphosphoric acid, and 1.27 g of hydrazine sulfate. The flask containing the mixture was placed in an oil bath and the mixture was heated to 120° C. The mixture was stirred for 6.5 hours at around the temperature and allowed to react. After the termination of the reaction, the product was cooled with ice. The cooled product was subjected to extraction with DMAC using a Soxhlet abstractor. The resulting extract was concentrated, and the concentrate was filtered. The filtrate was taken, and the solvent was removed from the filtrate. A film having stringiness was obtained.
An NMR spectrum chart of the obtained film is shown in
The obtained film was loaded in a model F-4500 spectrofluorophotometer, a product by Hitachi, Ltd., and the fluorescence spectrum of the film was measured under the following conditions. The measured spectrum is shown in
Conditions of Measurement
Measuring mode: Wavelength scanning
Exciting wavelength: 365 nm
Wavelength at which the emission of fluorescence started: 380 nm
Wavelength at which the emission of fluorescence ended: 700 nm
Scanning speed: 2400 nm/min.
Slit on the side of excitation: 5.0 nm
Slit on the side of fluorescence emission: 5.0 nm
Photomal voltage: 700 V
As understood from
Synthesis of a Blue Light-Emitting Polymer
<Condensation-Polymerization>
In a 2 L three-necked flask were placed 1.0 g of the dicarboxylic acid represented in formula (22), which had been prepared in Example 1, 0.92 g of a commercial fluorene represented by formula (25) below, 0.84 g of hydrazine sulfate, and 60 g of polyphosphoric acid.
The flask containing the mixture was placed in an oil bath and the mixture was heated to 107° C. The mixture was stirred for 48 hours at around the temperature and allowed to react. After the termination of the reaction, the product solution was poured into pH-9 water so that solids were formed. From the solids only white solids were taken, and the white solids were dissolved in 150 ml of DMAC, which is the abbreviation of N,N-dimethylacetamide. The resultant solution was heated to 180° C. and refluxed at around the temperature for 12 hours. Then, the refluxed was cooled naturally and filtered. The filtrate obtained was vacuum dried. A film was obtained.
An IR spectrum chart of the obtained film is shown in
A sample solution was prepared by dissolving 100 mg of the obtained film in 5 ml of DMAC. This sample solution was loaded in a model F-4500 spectrofluorophotometer, a product by Hitachi, Ltd., and the fluorescence spectrum of the film was measured under the same conditions as that of the film produced in Example 1 was measured. The measured spectrum is shown in
As understood from
The present invention provides a blue light-emitting polymer capable of emitting blue light at a high luminance for a long time, processes of producing the polymer and luminescent elements including the blue light-emitting polymer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-188390 | Jun 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/08872 | 6/24/2004 | WO | 12/30/2005 |
