JP2006022089A - Benzidine derivative, hole transporting material and derivative thereof or light emitting element, light emitting device and electronic equipment each using hole transporting material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substance having good heat resistance and capable of being used as a hole transporting material. <P>SOLUTION: The benzidine derivative is represented by N,N'-bis(spiro-9,9'-bifluoren-2-yl)-N,N'-diphenylbenzidine. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a substance that can be used as a material for manufacturing a light-emitting element.

  In recent years, many light-emitting elements used for displays and the like have a structure in which a layer containing a light-emitting substance is sandwiched between a pair of electrodes. In such a light-emitting element, excitons formed by recombination of electrons injected from one electrode and holes injected from the other electrode emit light when returning to the ground state.

  In the field of light-emitting elements, in order to obtain a light-emitting element with high emission efficiency, good chromaticity, and little deterioration and long life, various studies have been conducted on substances that are materials for manufacturing light-emitting elements. Yes.

By the way, as a cause of deterioration of the light emitting element, crystallization of a substance constituting the light emitting element can be given. For this reason, materials that are difficult to crystallize have been developed. For example, Patent Document 1 discloses an organic material having a high glass transition temperature and good heat resistance.
WO00 / 27946

  An object of the present invention is to provide a substance that has good heat resistance and can be used as a hole transport material. It is another object of the present invention to provide a substance that can be easily maintained in an amorphous state and can be used as a hole transport material.

  One aspect of the present invention is a benzidine derivative represented by the general formula (1).

一般式（１）において、Ｒ¹は、水素または炭素数１〜４のアルキル基のいずれか一を表す。

In the general formula (1), R ¹ represents any one of hydrogen, an alkyl group having 1 to 4 carbon atoms.

  One aspect of the present invention is a hole transport material including the benzidine derivative represented by the general formula (1).

  One aspect of the present invention relates to N, N′-diphenylbenzidine and 2-bromo-spiro-9,9′-bifluorene or 2-bromo-2 ′, 7′-dialkyl-spiro-9,9′-bifluorene. It is a compound obtained by a coupling reaction and having a melting point of 323 ° C. to 324 ° C.

  One aspect of the present invention relates to N, N′-diphenylbenzidine and 2-bromo-spiro-9,9′-bifluorene or 2-bromo-2 ′, 7′-dialkyl-spiro-9,9′-bifluorene. It is a hole transport material containing a compound obtained by a coupling reaction and having a melting point of 323 ° C. to 324 ° C.

  One embodiment of the present invention is a light-emitting element including a layer containing a benzidine derivative represented by the general formula (1).

  One aspect of the present invention relates to N, N′-diphenylbenzidine and 2-bromo-spiro-9,9′-bifluorene or 2-bromo-2 ′, 7′-dialkyl-spiro-9,9′-bifluorene. A light-emitting element having a layer containing a compound obtained by a coupling reaction.

  According to the present invention, a benzidine derivative having good heat resistance can be obtained. Further, according to the present invention, a benzidine derivative that can easily maintain an amorphous state can be obtained.

  According to the present invention, a hole transport material having good heat resistance can be obtained. Further, according to the present invention, a hole transport material that can easily maintain an amorphous state can be obtained.

  Since the benzidine derivative of the present invention has good heat resistance, the use of the benzidine derivative of the present invention makes it possible to obtain a light-emitting element with little characteristic change due to heat. Further, since the benzidine derivative of the present invention is easily maintained in an amorphous state, a light-emitting element with little deterioration due to crystallization can be obtained by using the benzidine derivative of the present invention.

  Hereinafter, one embodiment of the present invention will be described. However, the present invention can be implemented in many different modes, and those skilled in the art can easily understand that the modes and details can be variously changed without departing from the spirit and scope of the present invention. Is done. Therefore, the present invention is not construed as being limited to the description of the embodiment.

(Embodiment 1)
One embodiment of the present invention is a benzidine derivative represented by Structural Formulas (2) to (5).

  The benzidine derivatives represented by structural formulas (2) to (5) have a high glass transition temperature and good heat resistance. Moreover, the benzidine derivatives represented by structural formulas (2) to (5) are difficult to crystallize.

  The method for synthesizing the benzidine derivative of the present invention is not particularly limited. As shown in the synthesis scheme (a-1), N, N′-diphenylbenzidine and 2-bromo-spiro-9,9 ′ are used. It can be synthesized by a coupling reaction with bifluorene or 2-bromo-2 ′, 7′-dialkyl-spiro-9,9′-bifluorene.

In Synthesis Scheme (a-1), R ¹⁰ represents hydrogen or an alkyl group having 1 to 4 carbon atoms. Here, the alkyl group having 3 or 4 carbon atoms is preferably branched.

  The benzidine derivative of the present invention described above can be used as a material for forming a hole transport layer, that is, a hole transport material.

(Embodiment 2)
An embodiment of a light-emitting element using the benzidine derivative of the present invention as a hole transport material will be described with reference to FIG.

  FIG. 1 shows a light-emitting element having a light-emitting layer 113 between the first electrode 101 and the second electrode 102.

  In such a light-emitting element, holes injected from the first electrode 101 and electrons injected from the second electrode 102 are recombined in the light-emitting layer 113 to bring the light-emitting substance into an excited state. The excited luminescent material emits light when returning to the ground state. Note that in the light-emitting element of this embodiment mode, the first electrode 101 functions as an anode and the second electrode 102 functions as a cathode. A light-emitting substance is a substance that has good emission efficiency and can emit light with a desired emission wavelength.

  Here, there is no particular limitation on the light-emitting layer 113, but the light-emitting substance is preferably a layer that is dispersed and included in a layer formed of a substance having an energy gap larger than that of the light-emitting substance. Accordingly, it is possible to prevent light emitted from the light emitting substance from being quenched due to the concentration. Note that the energy gap is an energy gap between the LUMO level and the HOMO level.

There is no particular limitation on the light-emitting substance, and a substance that has favorable emission efficiency and can emit light with a desired emission wavelength may be used. For example, to obtain red light emission, 4-dicyanomethylene-2-isopropyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran ( Abbreviation: DCJTI), 4-dicyanomethylene-2-methyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran (abbreviation: DCJT), 4 -Dicyanomethylene-2-tert-butyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran (abbreviation: DCJTB), periflanthene, 2,5 -Dicyano-1,4-bis [2- (10-methoxy-1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] benzene, etc., emission spectrum from 600 nm to 680 nm It can be used and a substance which exhibits emission with a peak. When green light emission is desired, N, N′-dimethylquinacridone (abbreviation: DMQd), coumarin 6, coumarin 545T, tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), etc. emits light from 500 nm to 550 nm. A substance exhibiting light emission having a spectral peak can be used. When blue light emission is desired, 9,10-bis (2-naphthyl) -tert-butylanthracene (abbreviation: t-BuDNA) 9,9′-bianthryl, 9,10-diphenylanthracene (abbreviation: DPA), 9,10-bis (2-naphthyl) anthracene (abbreviation: DNA), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-gallium (BGaq), bis (2-methyl-8- A substance exhibiting light emission having an emission spectrum peak from 420 nm to 500 nm, such as quinolinolato) -4-phenylphenolato-aluminum (BAlq), can be used.

There is no particular limitation on a substance used for bringing the light-emitting substance into a dispersed state, for example, an anthracene derivative such as 9,10-di (2-naphthyl) -2-tert-butylanthracene (abbreviation: t-BuDNA), In addition to carbazole derivatives such as 4,4′-bis (N-carbazolyl) biphenyl (abbreviation: CBP), bis [2- (2-hydroxyphenyl) pyridinato] zinc (abbreviation: Znpp ₂ ), bis [2- ( 2-hydroxyphenyl) benzoxazolate] zinc (abbreviation: ZnBOX) or the like can be used.

  Although there is no particular limitation on the first electrode 101, it is preferable that the first electrode 101 be formed using a substance having a high work function when functioning as an anode as in this embodiment. Specifically, indium tin oxide (ITO), indium tin oxide containing silicon oxide, indium oxide containing 2 to 20% zinc oxide, gold (Au), platinum (Pt), nickel (Ni ), Tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), or the like. Note that the first electrode 101 can be formed using, for example, a sputtering method, an evaporation method, or the like.

  There is no particular limitation on the second electrode 102, but when it functions as a cathode as in this embodiment mode, the second electrode 102 is preferably formed using a substance having a low work function. Specifically, it is preferable to use aluminum containing an alkali metal such as lithium (Li) or magnesium or an alkaline earth metal. However, it may be formed using indium tin oxide (ITO) described above. Note that the second electrode 102 can be formed by, for example, a sputtering method, an evaporation method, or the like.

  In order to extract the emitted light to the outside, either one or both of the first electrode 101 and the second electrode is an electrode made of indium tin oxide or the like, or several An electrode formed with a thickness of several tens of nm is preferable.

  In addition, a hole transport layer 112 is provided between the first electrode 101 and the light emitting layer 113 as shown in FIG. Here, the hole transport layer is a layer having a function of transporting holes injected from the first electrode 101 to the light-emitting layer 113. In this manner, by providing the hole-transport layer 112 and separating the first electrode 101 and the light-emitting layer 113, it is possible to prevent the light emission from being quenched due to the metal.

  Note that the hole transport layer 112 is not particularly limited, but the hole transport layer 112 formed of the benzidine derivative of the present invention represented by any of the general formula (1) or the structural formulas (2) to (4) is used. It is preferable. The benzidine derivative of the present invention has high heat resistance. Therefore, by using the benzidine derivative of the present invention as a hole transport material, the hole transport layer 112 with little change in characteristics due to heat can be formed. Further, the benzidine derivative of the present invention is difficult to crystallize. Therefore, by using the benzidine derivative of the present invention as a hole transport material, the hole transport layer 112 that is difficult to crystallize can be formed.

  The hole transport layer 112 has a multilayer structure formed by combining two or more layers made of the benzidine derivative of the present invention represented by the general formula (1) or any one of the structural formulas (2) to (4). It may be a layer.

  Further, an electron transport layer 114 may be provided between the second electrode 102 and the light emitting layer 113 as shown in FIG. Here, the electron transporting layer is a layer having a function of transporting electrons injected from the second electrode 102 to the light emitting layer 113. In this manner, by providing the electron-transport layer 114 and separating the second electrode 102 and the light-emitting layer 113, it is possible to prevent the light emission from being quenched due to the metal.

Note that there is no particular limitation on the electron-transport layer 114, and tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (5-methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ ), bis (10-hydroxybenzo) [H] -quinolinato) beryllium (abbreviation: BeBq ₂ ), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq), metal complexes having a quinoline skeleton or a benzoquinoline skeleton, etc. Can be used. In addition, bis [2- (2-hydroxyphenyl) -benzoxazolate] zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2-hydroxyphenyl) -benzothiazolate] zinc (abbreviation: Zn (BTZ) ₂ ) The metal complex having an oxazole or thiazole ligand such as ₂ ) may be used. In addition, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis [5- (p-tert- Butylphenyl) -1,3,4-oxadiazol-2-yl] benzene (abbreviation: OXD-7), 3- (4-tert-butylphenyl) -4-phenyl-5- (4-biphenylyl)- 1,2,4-triazole (abbreviation: TAZ), 3- (4-tert-butylphenyl) -4- (4-ethylphenyl) -5- (4-biphenylyl) -1,2,4-triazole (abbreviation) : P-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproin (abbreviation: BCP), or the like. The electron transport layer 114 is preferably formed using a substance having a higher electron mobility than the hole mobility described above. The electron transport layer 114 is more preferably formed using a substance having an electron mobility of 10 ⁻⁶ cm ² / Vs or higher. Further, the electron transport layer 114 may be a multilayer structure formed by combining two or more layers made of the above-described substances.

  Further, a hole injection layer 111 may be provided between the first electrode 101 and the hole transport layer 112 as shown in FIG. Here, the hole injection layer is a layer having a function of assisting injection of holes from the electrode functioning as an anode into the hole transport layer 112.

The hole injection layer 111 is not particularly limited, and metal oxides such as molybdenum oxide (MoOx), vanadium oxide (VOx), ruthenium oxide (RuOx), tungsten oxide (WOx), and manganese oxide (MnOx) Can be used. In addition, phthalocyanine compounds such as phthalocyanine (abbreviation: H ₂ Pc) and copper phthalocyanine (CuPC), 4,4-bis (N- (4- (N, N-di-m-tolylamino) phenyl) -N -Hole injection by aromatic amine compounds such as phenylamino) biphenyl (abbreviation: DNTPD) or polymers such as poly (ethylenedioxythiophene) / poly (styrenesulfonic acid) aqueous solution (PEDOT / PSS) Layer 111 can be formed.

  Further, an electron injection layer 115 may be provided between the second electrode 102 and the electron transport layer 114 as shown in FIG. Here, the electron injection layer is a layer having a function of assisting injection of electrons from the electrode functioning as a cathode to the electron transport layer 114. Note that in the case where an electron transport layer is not particularly provided, an electron injection layer may be provided between the electrode functioning as a cathode and the light emitting layer to assist the injection of electrons into the light emitting layer.

The electron injection layer 115 is not particularly limited, and is formed using an alkali metal or alkaline earth metal compound such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF ₂ ), or the like. Things can be used. In addition, a substance having a high electron transporting property such as Alq ₃ or 4,4-bis (5-methylbenzoxazol-2-yl) stilbene (BzOs), and an alkali metal or alkali such as magnesium or lithium A material mixed with an earth metal can also be used as the electron injection layer 115.

  In the light-emitting element of the present invention described above, the hole injection layer 111, the hole transport layer 112, the light-emitting layer 113, the electron transport layer 114, and the electron injection layer 115 are formed by an evaporation method, an inkjet method, or a coating method, respectively. Or any other method. Further, the first electrode 101 or the second electrode 102 may be formed by any method such as a sputtering method or an evaporation method.

  As described above, by forming a hole transport layer using the benzidine derivative of the present invention, a light-emitting element with little change in element characteristics due to change in characteristics of the hole transport layer due to heat can be obtained. . In addition, by forming a hole transport layer using the benzidine derivative of the present invention, a light-emitting element with little deterioration due to crystallization of the hole transport layer can be obtained.

(Embodiment 3)
The light-emitting element of the present invention described in Embodiment Mode 2 can be applied to a pixel portion of a light-emitting device having a display function or an illumination portion of a light-emitting device having a lighting function. Since the light-emitting element of the present invention has little deterioration due to characteristic change or crystallization due to heat, light emission with less defects of images and illumination light due to deterioration of the light-emitting element is achieved by using the light-emitting element of the present invention. A device can be obtained.

  In this embodiment, a circuit configuration and a driving method of a light-emitting device having a display function will be described with reference to FIGS.

  FIG. 3 is a schematic view of a light emitting device to which the present invention is applied as viewed from above. In FIG. 3, a pixel portion 6511, a source signal line driver circuit 6512, a write gate signal line driver circuit 6513, and an erase gate signal line driver circuit 6514 are provided over a substrate 6500. The source signal line driver circuit 6512, the writing gate signal line driver circuit 6513, and the erasing gate signal line driver circuit 6514 are respectively FPC (flexible printed circuit) 6503 which is an external input terminal through a wiring group. Connected. The source signal line driver circuit 6512, the writing gate signal line driver circuit 6513, and the erasing gate signal line driver circuit 6514 receive a video signal, a clock signal, a start signal, a reset signal, and the like from the FPC 6503, respectively. . A printed wiring board (PWB) 6504 is attached to the FPC 6503. Note that the driver circuit portion is not necessarily provided over the same substrate as the pixel portion 6511 as described above. For example, an IC chip mounted on an FPC on which a wiring pattern is formed (TCP) or the like is used. It may be used and provided outside the substrate.

  In the pixel portion 6511, a plurality of source signal lines extending in the column direction are arranged side by side in the row direction. In addition, current supply lines are arranged side by side in the row direction. In the pixel portion 6511, a plurality of gate signal lines extending in the row direction are arranged side by side in the column direction. In the pixel portion 6511, a plurality of sets of circuits including light-emitting elements are arranged.

  FIG. 4 is a diagram illustrating a circuit for operating one pixel. The circuit illustrated in FIG. 4 includes a first transistor 901, a second transistor 902, and a light emitting element 903.

  Each of the first transistor 901 and the second transistor 902 is a three-terminal element including a gate electrode, a drain region, and a source region, and has a channel region between the drain region and the source region. Here, since the source region and the drain region vary depending on the structure and operating conditions of the transistor, it is difficult to limit which is the source region or the drain region. Therefore, in this embodiment, regions functioning as a source or a drain are referred to as a first electrode of a transistor and a second electrode of the transistor, respectively.

  The gate signal line 911 and the writing gate signal line driving circuit 913 are provided so as to be electrically connected or disconnected by a switch 918. The gate signal line 911 and the erasing gate signal line driver circuit 914 are provided so as to be electrically connected or disconnected by a switch 919. The source signal line 912 is provided so as to be electrically connected to either the source signal line driver circuit 915 or the power source 916 by the switch 920. The gate of the first transistor 901 is electrically connected to the gate signal line 911. The first electrode of the first transistor is electrically connected to the source signal line 912, and the second electrode is electrically connected to the gate electrode of the second transistor 902. The first electrode of the second transistor 902 is electrically connected to the current supply line 917, and the second electrode is electrically connected to one electrode included in the light-emitting element 903. Note that the switch 918 may be included in the write gate signal line driver circuit 913. The switch 919 may also be included in the erase gate signal line driver circuit 914. Further, the switch 920 may also be included in the source signal line driver circuit 915.

  There is no particular limitation on the arrangement of transistors, light-emitting elements, and the like in the pixel portion. For example, they can be arranged as shown in the top view of FIG. In FIG. 5, the first electrode of the first transistor 1001 is connected to the source signal line 1004, and the second electrode is connected to the gate electrode of the second transistor 1002. The first electrode of the second transistor is connected to the current supply line 1005, and the second electrode is connected to the electrode 1006 of the light emitting element. Part of the gate signal line 1003 functions as a gate electrode of the first transistor 1001.

  Next, a driving method will be described. FIG. 6 is a diagram for explaining the operation of a frame over time. In FIG. 6, the horizontal direction represents the passage of time, and the vertical direction represents the number of scanning stages of the gate signal line.

  When image display is performed using the light emitting device of the present invention, the screen rewriting operation and the display operation are repeatedly performed during the display period. The number of rewrites is not particularly limited, but is preferably at least about 60 times per second so that a person viewing the image does not feel flicker. Here, a period during which one screen (one frame) is rewritten and displayed is referred to as one frame period.

As shown in FIG. 6, one frame is time-divided into four subframes 501, 502, 503, and 504 including a writing period 501a, 502a, 503a, and 504a and a holding period 501b, 502b, 503b, and 504b. . A light emitting element to which a signal for emitting light is given is in a light emitting state in the holding period. The ratio of the length of the holding period in each subframe is as follows: first subframe 501: second subframe 502: third subframe 503: fourth subframe 504 = 2 ³ : 2 ² : 2 ¹ : 2 ⁰ = 8: 4: 2: 1. As a result, 4-bit gradation can be expressed. However, the number of bits and the number of gradations are not limited to those described here. For example, eight subframes may be provided so that 8-bit gradation can be performed.

  An operation in one frame will be described. First, in the subframe 501, the write operation is performed in order from the first row to the last row. Therefore, the start time of the writing period differs depending on the row. From the row in which the writing period 501a ends, the storage period 501b is started in order. In the holding period, the light-emitting element to which a signal for emitting light is given is in a light-emitting state. Further, the processing proceeds to the next subframe 502 in order from the row in which the holding period 501b ends, and the writing operation is performed in order from the first row to the last row as in the case of the subframe 501. The operation as described above is repeated until the holding period 504b of the subframe 504 ends. When the operation in the subframe 504 is completed, the process proceeds to the next frame. Thus, the accumulated time of the light emission in each subframe is the light emission time of each light emitting element in one frame. Various display colors having different brightness and chromaticity can be formed by changing the light emission time for each light emitting element and combining them in various ways within one pixel.

  When it is desired to forcibly end the holding period in the row that has already finished writing and has shifted to the holding period before the writing up to the last row is completed as in the subframe 504, after the holding period 504b. It is preferable to provide an erasing period 504c and control to forcibly enter a non-light emitting state. Then, the row that is forcibly set to the non-light emitting state is kept in the non-light emitting state for a certain period (this period is referred to as a non-light emitting period 504d). Then, as soon as the writing period of the last row ends, the next (or frame) writing period starts in order from the first row. Accordingly, it is possible to prevent the writing period of the subframe 504 and the writing period of the next subframe from overlapping.

  In this embodiment, the subframes 501 to 504 are arranged in order from the longest holding period. However, the subframes 501 to 504 are not necessarily arranged as in the present embodiment. For example, the subframes 501 to 504 may be arranged in order from the shortest holding period. Alternatively, a long holding period and a short holding period may be arranged at random. In addition, the subframe may be further divided into a plurality of frames. That is, the gate signal line may be scanned a plurality of times during the period when the same video signal is applied.

  Here, the operation of the circuit shown in FIG. 4 in the writing period and the erasing period will be described.

  First, the operation in the writing period will be described. In the writing period, the gate signal line 911 in the n-th row (n is a natural number) is electrically connected to the writing gate signal line driving circuit 913 via the switch 918 and is connected to the erasing gate signal line driving circuit 914. Is disconnected. The source signal line 912 is electrically connected to the source signal line driver circuit through the switch 920. Here, a signal is input to the gate of the first transistor 901 connected to the gate signal line 911 in the n-th row (n is a natural number), and the first transistor 901 is turned on. At this time, video signals are simultaneously input to the source signal lines from the first column to the last column. Note that the video signals input from the source signal lines 912 in each column are independent from each other. The video signal input from the source signal line 912 is input to the gate electrode of the second transistor 902 through the first transistor 901 connected to each source signal line. At this time, the light-emitting element 903 determines whether to emit light or not according to a signal input to the second transistor 902. For example, in the case where the second transistor 902 is a p-channel transistor, the light-emitting element 903 emits light by inputting a low level signal to the gate electrode of the second transistor 902. On the other hand, when the second transistor 902 is an n-channel transistor, the light emitting element 903 emits light when a high level signal is input to the gate electrode of the second transistor 902.

  Next, the operation in the erasing period will be described. In the erasing period, the gate signal line 911 in the n-th row (n is a natural number) is electrically connected to the erasing gate signal line driving circuit 914 via the switch 919, and is connected to the writing gate signal line driving circuit 913. Not connected. The source signal line 912 is electrically connected to the power source 916 through the switch 920. Here, a signal is input to the gate of the first transistor 901 connected to the gate signal line 911 in the n-th row, and the first transistor 901 is turned on. At this time, the erase signal is simultaneously input to the source signal lines from the first column to the last column. The erase signal input from the source signal line 912 is input to the gate electrode of the second transistor 902 through the first transistor 901 connected to each source signal line. At this time, current supplied from the current supply line 917 to the light-emitting element 903 is blocked by a signal input to the second transistor 902. Then, the light emitting element 903 is forced to emit no light. For example, in the case where the second transistor 902 is a p-channel transistor, the light-emitting element 903 does not emit light when a high level signal is input to the gate electrode of the second transistor 902. On the other hand, in the case where the second transistor 902 is an n-channel transistor, the light emitting element 903 does not emit light by inputting a low level signal to the gate electrode of the second transistor 902.

  In the erasing period, for the nth row (n is a natural number), a signal for erasing is input by the operation as described above. However, as described above, the nth row may be an erasing period and the other row (mth row (m is a natural number)) may be a writing period. In such a case, it is necessary to input a signal for erasure to the n-th row and a signal for writing to the m-th row using the source signal line in the same column. It is preferable to operate as described above.

  The gate signal line 911 and the erasing gate signal line driving circuit 914 are immediately disconnected after the light emitting element 903 in the n-th row does not emit light by the operation in the erasing period described above. The switch 920 is switched to connect the source signal line 912 and the source signal line driver circuit 915. Then, the source signal line and the source signal line driver circuit 915 are connected, and the gate signal line 911 and the writing gate signal line driver circuit 913 are connected. Then, a signal is selectively input from the writing gate signal line driving circuit 913 to the m-th signal line, the first transistor is turned on, and the source signal line driving circuit 915 receives the final signal from the first column. A signal for writing is input to the source signal lines up to the column. By this signal, the m-th row light emitting element emits light or does not emit light.

  Immediately after the writing period for the m-th row is completed as described above, the erasing period for the (n + 1) -th row is started. For this purpose, the gate signal line 911 and the writing gate signal line driving circuit 913 are disconnected, and the switch 920 is switched to connect the source signal line to the power source 916. Further, the gate signal line 911 and the writing gate signal line driving circuit 913 are disconnected, and the gate signal line 911 is connected to the erasing gate signal line driving circuit 914. Then, a signal is selectively input from the erasing gate signal line driving circuit 914 to the gate signal line of the (n + 1) th row to turn on the signal to the first transistor, and an erasing signal is input from the power supply 916. In this way, immediately after the erasing period of the (n + 1) th row is completed, the writing period of the (m + 1) th row is started. Thereafter, similarly, the erasing period and the writing period may be repeated until the erasing period of the last row is operated.

  In this embodiment, the mode in which the m-th writing period is provided between the n-th erasing period and the (n + 1) -th erasing period has been described. An m-th writing period may be provided between the period and the n-th erasing period.

  Further, in this embodiment, when the non-light emission period 504d is provided as in the subframe 504, the erasing gate signal line driver circuit 914 and a certain gate signal line are brought into a non-connected state, and writing is performed. The operation of connecting the gate signal line driving circuit 913 and the other gate signal lines is repeated. Such an operation may be performed particularly in a frame in which a non-light emitting period is not provided.

(Embodiment 4)
One mode of a cross-sectional view of a light-emitting device including the light-emitting element of the present invention is described with reference to FIGS.

  In FIG. 7, a transistor 11 provided for driving the light emitting element 12 of the present invention is surrounded by a dotted line. The light emitting element 12 is the light emitting element of the present invention having the light emitting layer 15 between the first electrode 13 and the second electrode 14. The drain of the transistor 11 and the first electrode 13 are electrically connected by a wiring 17 penetrating the first interlayer insulating film 16 (16a, 16b, 16c). The light emitting element 12 is separated from another light emitting element provided adjacent thereto by a partition wall layer 18. The light-emitting device of the present invention having such a structure is provided over the substrate 10 in this embodiment.

  Note that the transistor 11 illustrated in FIG. 7 is a top-gate transistor in which a gate electrode is provided on the side opposite to a substrate with a semiconductor layer as a center. However, the structure of the transistor 11 is not particularly limited, and may be, for example, a bottom gate type. In the case of a bottom gate, the semiconductor layer forming a channel may be formed with a protective film (channel protection type), or the semiconductor layer forming the channel may be partially concave ( Channel etch type).

  Further, the semiconductor layer included in the transistor 11 may be either crystalline or non-crystalline. Moreover, a semi-amorphous etc. may be sufficient.

The semi-amorphous semiconductor is as follows. A semiconductor having an intermediate structure between amorphous and crystalline (including single crystal and polycrystal) and having a third state that is stable in terms of free energy, has a short-range order, and has a lattice distortion. It contains a crystalline region. Further, at least a part of the region in the film contains crystal grains of 0.5 to 20 nm. The peak related to the L-O phonon in the Raman spectrum is shifted to a lower wavenumber side than 520 cm ⁻¹ . In X-ray diffraction, diffraction peaks of (111) and (220) that are derived from the Si crystal lattice are observed. In order to terminate dangling bonds (dangling bonds), hydrogen or halogen is contained at least 1 atomic% or more. It is also called a so-called microcrystalline semiconductor (microcrystal semiconductor). A silicide gas is formed by glow discharge decomposition (plasma CVD). As the silicide gas, SiH ₄ , Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF ₄ or the like can be used. This silicide gas may be diluted with H ₂ , or H ₂ and one or more kinds of rare gas elements selected from He, Ar, Kr, and Ne. The dilution ratio is in the range of 2 to 1000 times, the pressure is in the range of approximately 0.1 Pa to 133 Pa, the power supply frequency is 1 MHz to 120 MHz, preferably 13 MHz to 60 MHz, and the substrate heating temperature may be 300 ° C. or less, preferably 100 to 250 ° C. As an impurity element in the film, impurities of atmospheric components such as oxygen, nitrogen, and carbon are desirably 1 × 10 ²⁰ cm ⁻³ or less, and in particular, the oxygen concentration is 5 × 10 ¹⁹ / cm ³ or less, preferably 1 × 10 ¹⁹ / cm ³ or less. Note that the mobility of a TFT (thin film transistor) using a semi-amorphous semiconductor is approximately 1 to 10 cm ² / Vsec.

  Further, specific examples of the crystalline semiconductor layer include those made of single crystal or polycrystalline silicon, silicon germanium, or the like. These may be formed by laser crystallization, or may be formed by crystallization by a solid phase growth method using nickel or the like, for example.

  Note that in the case where the semiconductor layer is formed of an amorphous material, for example, amorphous silicon, the transistor 11 and other transistors (transistors constituting a circuit for driving a light emitting element) are all configured by N-channel transistors. It is preferable that the light-emitting device have a structured circuit. Other than that, a light-emitting device having a circuit including any one of an N-channel transistor and a P-channel transistor, or a light-emitting device including a circuit including both transistors may be used.

  Furthermore, the first interlayer insulating film 16 (16a, 16b, 16c) may be a multilayer as shown in FIGS. 7A to 7C, or may be a single layer. Note that 16a is made of an inorganic material such as silicon oxide or silicon nitride, and 16b is acrylic or siloxane (siloxane has a skeleton structure formed by a bond of silicon (Si) and oxygen (O). An organic group containing hydrogen (for example, an alkyl group or an aromatic hydrocarbon) is used.A fluoro group may be used as a substituent, or an organic group containing at least hydrogen and a fluoro group are used as a substituent. Or made of silicon oxide or the like that can be coated. Further, 16c is made of a silicon nitride film containing argon (Ar). In addition, there is no limitation in particular about the substance which comprises each layer, You may use things other than what was described here. Moreover, you may further combine the layer which consists of substances other than these. As described above, the first interlayer insulating film 16 may be formed using both an inorganic material and an organic material, or may be formed using any one of an inorganic material and an organic material.

  The partition layer 18 preferably has a shape in which the radius of curvature continuously changes at the edge portion. The partition layer 18 is formed using acrylic, siloxane, resist, silicon oxide, or the like. The partition wall layer 18 may be formed of any one of an inorganic material and an organic material, or may be formed using both.

  In FIGS. 7A and 7C, only the first interlayer insulating film 16 is provided between the transistor 11 and the light emitting element 12, but as shown in FIG. 7B, the first interlayer insulating film 16 is provided. In addition to the insulating film 16 (16a, 16b), the second interlayer insulating film 19 (19a, 19b) may be provided. In the light emitting device shown in FIG. 7B, the first electrode 13 penetrates through the second interlayer insulating film 19 and is connected to the wiring 17.

  Similar to the first interlayer insulating film 16, the second interlayer insulating film 19 may be a multilayer or a single layer. 19a is made of acrylic, siloxane, silicon oxide that can be formed by coating, or the like. Further, 19b is made of a silicon nitride film containing argon (Ar). In addition, there is no limitation in particular about the substance which comprises each layer, You may use things other than what was described here. Moreover, you may further combine the layer which consists of substances other than these. As described above, the second interlayer insulating film 19 may be formed using both an inorganic material and an organic material, or may be formed using any one of an inorganic material and an organic material.

  In the light-emitting element 12, when each of the first electrode 13 and the second electrode 14 is formed using a light-transmitting substance, the first electrode 13 and the second electrode 14 are formed as illustrated by the white arrows in FIG. Light emission can be extracted from both the first electrode 13 side and the second electrode 14 side. In addition, in the case where only the second electrode 14 is formed using a light-transmitting substance, light emission is extracted only from the second electrode 14 side as represented by a white arrow in FIG. 7B. be able to. In this case, it is preferable that the first electrode 13 is made of a material having a high reflectivity, or a film (reflective film) made of a material having a high reflectivity is provided below the first electrode 13. In addition, in the case where only the first electrode 13 is formed using a light-transmitting substance, light emission is extracted only from the first electrode 13 side as represented by a white arrow in FIG. be able to. In this case, it is preferable that the second electrode 14 is made of a highly reflective material, or a reflective film is provided above the second electrode 14.

  The light-emitting element 12 may have a configuration in which the first electrode 13 functions as an anode and the second electrode 14 functions as a cathode, or the first electrode 13 functions as a cathode, and the second The electrode 14 may function as an anode. However, in the former case, the transistor 11 is a P-channel transistor, and in the latter case, the transistor 11 is an N-channel transistor.

(Embodiment 5)
By mounting the light-emitting device of the present invention, an electronic device that can perform favorable display over a long period of time or an appliance that can be well illuminated over a long period of time can be obtained.

  One embodiment of an electronic device mounted with a light emitting device to which the present invention is applied is shown in FIG.

  FIG. 8A illustrates a laptop personal computer manufactured by applying the present invention, which includes a main body 5521, a housing 5522, a display portion 5523, a keyboard 5524, and the like. A personal computer can be completed by incorporating a light-emitting device having the light-emitting element of the present invention as a display portion.

  FIG. 8B illustrates a cellular phone manufactured by applying the present invention, which includes a main body 5552 which includes a display portion 5551, an audio output portion 5554, an audio input portion 5555, operation switches 5556 and 5557, an antenna 5553, and the like. Has been. A mobile phone can be completed by incorporating a light-emitting device having the light-emitting element of the present invention as a display portion.

  FIG. 8C illustrates a television set manufactured by applying the present invention, which includes a display portion 5531, a housing 5532, a speaker 5533, and the like. A television receiver can be completed by incorporating a light-emitting device having the light-emitting element of the present invention as a display portion.

  As described above, the light-emitting device of the present invention is very suitable for use as a display portion of various electronic devices.

  Note that in this embodiment, a light-emitting device having the light-emitting element of the present invention may be mounted on a car navigation device, a lighting device, or the like in addition to the electronic devices described above.

(Synthesis Example 1)
A method for synthesizing the benzidine derivative represented by the structural formula (2) will be described.

[Step 1]
A method for synthesizing 2-bromo-spiro-9,9′-bifluorene will be described.

  Into a 100 ml three-necked flask, 1.26 g (0.052 mol) of magnesium was put, the inside of the system was put under vacuum, and the mixture was heated and stirred for 30 minutes to activate. After cooling to room temperature, the system is placed under a nitrogen stream, 5 ml of diethyl ether and a few drops of dibromoethane are added, and 11.65 g (0.050 mol) of 2-bromobiphenyl dissolved in 15 ml of diethyl ether is slowly added dropwise to complete the addition. Thereafter, the mixture was refluxed for 3 hours to obtain a Grignard reagent. In a 200 ml three-necked flask, 11.7 g (0.045 mol) of 2-bromofluorenone and 40 ml of diethyl ether were placed. The synthesized Grignard reagent was slowly added dropwise to the reaction solution, refluxed for 2 hours after completion of the addition, and further stirred overnight at room temperature. After completion of the reaction, the reaction solution was washed twice with a saturated aqueous ammonium chloride solution, the aqueous layer was extracted twice with ethyl acetate, and the organic layer was washed with saturated brine. After drying with magnesium sulfate, suction filtration and concentration were performed to obtain 18.76 g of solid 9- (2-biphenylyl) -2-bromo-9-fluorenol in a yield of 90%.

Next, the synthesized 9- (2-biphenylyl) -2-bromo-9-fluorenol (18.76 g, 0.045 mol) and glacial acetic acid (100 ml) were placed in a 200 ml three-necked flask, and a few drops of concentrated hydrochloric acid were added and refluxed for 2 hours. did. After completion of the reaction, the precipitate was collected by suction filtration, and washed by filtration with a saturated aqueous sodium hydrogen carbonate solution and water. The obtained brown solid was recrystallized with ethanol to obtain 10.24 g of a light brown powdery solid in a yield of 57%. This light brown powdery solid was confirmed to be 2-bromo-spiro-9,9′-bifluorene by nuclear magnetic resonance ( ¹ H-NMR).

¹ H-NMR of this compound is shown below.
¹ H-NMR (300 MHz, CDCl ₃ ) δ ppm: 7.86-7.79 (m, 3H), 7.70 (d, 1H, J = 8.4 Hz), 7.47-7.50 (m , 1H), 7.41-7.34 (m, 3H), 7.12 (t, 3H, J = 7.7 Hz), 6.85 (d, 1H, J = 2.1 Hz), 6.74. -6.70 (m, 3H)

  Moreover, the synthesis scheme (b-1) of the synthesis method described above is shown below.

[Step 2]
A method for synthesizing N, N′-bis (spiro-9,9′-bifluoren-2-yl) -N, N′-diphenylbenzidine (abbreviation: BSPB) will be described.

  In a 100 ml three-necked flask, 1.00 g (0.0030 mol) of N, N′-diphenylbenzidine, 2.49 g (0.0062 mol) of 2-bromo-spiro-9,9′-bifluorene synthesized by the synthesis method of Step 1 , 170 mg (0.30 mmol) of bisdibenzylideneacetone palladium and 1.08 g (0.011 mol) of tert-butoxy sodium were added, and the system was purged with nitrogen, and then 20 ml of dehydrated toluene and tri-tert-butylphosphine 10 A 0.6%% hexane solution was added, and the mixture was stirred at 80 ° C. for 6 hours. After completion of the reaction, the reaction solution was cooled to room temperature, water was added, and the precipitated solid was collected by suction filtration and washed with dichloromethane. The obtained white solid was purified by alumina column chromatography (chloroform) and recrystallized from dichloromethane to obtain 2.66 g of a white powdery solid in a yield of 93%.

When the obtained white powdery solid was analyzed by nuclear magnetic resonance ( ¹ H-NMR), the following results were obtained, confirming that it was a benzidine derivative represented by the structural formula (2). . A ¹ H-NMR chart is shown in FIG.
¹ H-NMR (300 MHz, DMSO-d ₆ ) δ ppm: 7.93-7.89 (m, 8H), 7.39-7.33 (m, 10H), 7.19-7.14 (m, 8H), 7.09-6.96 (m, 6H), 6.89-6.84 (m, 8H), 6.69 (d, 4H, J = 7.5 Hz), 6.54 (d, 2H, J = 7.8 Hz), 6.25 (d, 2H, J = 2.4 Hz)

  A synthesis scheme (b-2) of the synthesis method described above is shown below. Thus, the compound of the present invention can be synthesized by a coupling reaction of N, N'-diphenylbenzidine and 2-bromo-spiro-9,9'-bifluorene.

  Further, the glass transition temperature, crystallization temperature, and melting point of the obtained compound were examined using a differential scanning calorimeter (DSC: Differential Scanning Calorimetry, manufactured by PerkinElmer, model number: Pyris1 DSC). Here, the measurement by DSC was performed according to the following procedure. First, after heating the sample (the obtained compound) to 450 ° C. at a temperature increase rate of 40 ° C./min, the sample was cooled to a glass state at a temperature increase rate of 40 ° C./min. And the sample which became a glass state was heated with the temperature increase rate of 10 degree-C / min, and the measurement result as shown in FIG. 9 was obtained. In FIG. 9, the horizontal axis represents temperature (° C.), and the vertical axis represents heat flow (upward is endothermic) (mW). From the measurement results, it was found that the obtained compound had a glass transition temperature of 172 ° C. and a crystallization temperature of 268 ° C. Moreover, it turned out that melting | fusing point is 323 to 324 degreeC from the intersection of the tangent line at 312 degreeC and the tangent line at 327 to 328 degreeC. Thus, the obtained compound has a high glass transition temperature of 172 ° C. and has good heat resistance. Moreover, in FIG. 9, the peak showing crystallization of the obtained compound is broad, and it was found that the obtained compound is a substance that is difficult to crystallize.

  Moreover, when the obtained compound was formed into a film by a vapor deposition method and the ionization potential of the compound in a thin film state was measured using a photoelectron spectrometer (AC-2, manufactured by Riken Keiki Co., Ltd.), it was -5.3 eV. It was. Moreover, the absorption spectrum of the compound in a thin film state is measured using a UV / visible light spectrophotometer (manufactured by JASCO Corporation, V-550), and the wavelength of the absorption edge on the long wavelength side of the absorption spectrum is defined as the energy gap. When the LUMO level was determined, the LUMO level was -2.5 eV. Here, in FIG. 10, the absorption spectrum in the thin film state of the obtained compound is shown. In FIG. 10, the vertical axis represents absorbance (no unit), and the horizontal axis represents wavelength (nm). FIG. 11 shows an emission spectrum of the obtained compound in a thin film state. In FIG. 11, the vertical axis represents emission intensity (arbitrary unit), and the horizontal axis represents wavelength (nm).

  In addition, when 4.74 g of the obtained compound was purified by sublimation under conditions of 14 Pa and 350 ° C. for 24 hours, 3.49 g could be recovered, and the recovery rate was 74%.

  A compound having a glass transition temperature of 172 ° C. obtained by the synthesis described in Step 2 of Synthesis Example 1 (hereinafter referred to as BSPB. Note that the compound represented by the structural formula (2) is determined by the nuclear magnetic resonance method. A light-emitting element manufactured using the above-described method will be described with reference to FIGS.

  A first electrode 702 was formed over an indium tin oxide containing silicon by a sputtering method over a glass substrate 701. The film thickness was set to 110 nm.

  Next, DNTPD was formed over the first electrode 702 by a vacuum evaporation method, so that a first layer 703 made of DNTPD was formed. The film thickness was set to 50 nm.

  Next, a BSPB film was formed on the first layer 703 made of DNTPD by a vacuum evaporation method to form a second layer 704 made of BSPB. The film thickness was 10 nm.

Next, Alq ₃ and coumarin 6 were formed over the second layer 704 made of BSPB by a co-evaporation method, so that a third layer 705 containing Alq ₃ and coumarin 6 was formed. Incidentally, coumarin 6 was to include 0.5 wt% with respect to Alq _3. As a result, the coumarin 6 is dispersed in Alq ₃ . The film thickness was 37.5 nm. Note that the co-evaporation method is an evaporation method in which evaporation is performed simultaneously from a plurality of evaporation sources.

Then, on the third layer 705 containing Alq ₃ and coumarin 6, a Alq _3, was deposited by vacuum evaporation to form a fourth layer 706 made of Alq _3. The film thickness was 37.5 nm.

Next, a calcium fluoride film was formed on the fourth layer 706 made of Alq ₃ by a vacuum evaporation method to form a fifth layer 707 made of calcium fluoride. The film thickness was 1 nm.

  Next, aluminum was deposited over the fifth layer 707 made of calcium fluoride by a vacuum evaporation method, whereby a second electrode 708 was formed.

In the light-emitting element manufactured as described above, when a voltage is applied to the first electrode 702 and the second electrode 708 to pass a current, the coumarin 6 emits light. At this time, the first electrode 702 functions as an anode and the second electrode 708 functions as a cathode. The layer 703 made of DNTPD is a hole injection layer, the layer 704 made of BSPB is a hole transport layer, the layer 705 containing Alq ₃ and coumarin 6 is a light emitting layer, and the layer 706 made of Alq ₃ is an electron transport layer. As a layer, the layer 707 made of calcium fluoride functions as an electron injection layer.

  FIG. 12 shows current density-luminance characteristics, FIG. 13 shows voltage-luminance characteristics, and FIG. 14 shows luminance-current efficiency characteristics of the light-emitting element of this example. In FIG. 12, the horizontal axis represents current density and the vertical axis represents luminance. In FIG. 13, the horizontal axis represents voltage and the vertical axis represents luminance. In FIG. 14, the horizontal axis represents luminance and the vertical axis represents current efficiency.

  The light emission spectrum of the light emitting element of this example had a peak at 510 nm, and the CIE chromaticity coordinates were (x, y) = (0.25, 0.66).

  As can be seen from the above results, the light-emitting element of this example can obtain light emission derived from coumarin 6 well. This is because no excitation energy was transferred from the layer 705 functioning as the light emitting layer to the layer composed of the benzidine derivative of the present invention, and the layer composed of the benzidine derivative of the present invention functioned well as a hole transport layer. It is believed that there is. Thus, the benzidine derivative of the present invention is suitable for use as a hole transport material.

4A and 4B illustrate one embodiment of a light-emitting element of the present invention. 4A and 4B illustrate a light-emitting element of the present invention. 4A and 4B illustrate a light-emitting device to which the present invention is applied. 6A and 6B illustrate a circuit included in a light-emitting device to which the present invention is applied. The top view of the light-emitting device to which this invention is applied. 4A and 4B illustrate a frame operation of a light-emitting device to which the present invention is applied. Sectional drawing of the light-emitting device to which this invention is applied. The figure of the electronic device to which this invention is applied. The figure of the measurement result which carried out differential scanning calorimetry analysis of the benzidine derivative of the present invention. The figure of the absorption spectrum of the benzidine derivative of the present invention. The figure of the emission spectrum of the benzidine derivative of the present invention. FIG. 11 is a graph showing current density-luminance characteristics of a light-emitting element using a benzidine derivative of the present invention. FIG. 6 is a graph of voltage-luminance characteristics of a light-emitting element using a benzidine derivative of the present invention. FIG. 11 is a graph showing luminance-current efficiency characteristics of a light-emitting element using the benzidine derivative of the present invention. The figure which shows the result of having analyzed the white powdery solid synthesize | combined in step 2 of the synthesis example 1 by the nuclear magnetic resonance method.

Explanation of symbols

101 1st electrode 102 2nd electrode 113 Light emitting layer 112 Hole transport layer 114 Electron transport layer 111 Hole injection layer 115 Electron injection layer 114 Electron transport layer 6500 Substrate 6503 FPC
6504 Printed Wiring Board (PWB)
6511 Pixel portion 6512 Source signal line driving circuit 6513 Writing gate signal line driving circuit 6514 Erasing gate signal line driving circuit 901 First transistor 902 Second transistor 903 Light emitting element 911 Gate signal line 912 Source signal line 913 Writing Gate signal line driving circuit 914 erasing gate signal line driving circuit 915 source signal line driving circuit 916 power supply 917 current supply line 918 switch 919 switch 920 switch 1001 first transistor 1002 second transistor 1003 gate signal line 1004 source signal line 1005 Current supply line 1006 Electrode 501 Subframe 502 Subframe 503 Subframe 504 Subframe 501a Writing period 501b Holding period 502a Writing period 502b Holding period 503a Writing Only period 503b holding period 504a writing period 504b holding period 504c erasing period 504d non-light emitting period 10 substrate 11 transistor 12 light emitting element 13 first electrode 14 second electrode 15 light emitting layer 16 first interlayer insulating film 16a first interlayer insulating film 16b 1st interlayer insulation film 16c 1st interlayer insulation film 17 Wiring 18 Partition layer 19 2nd interlayer insulation film 19a 2nd interlayer insulation film 19b 2nd interlayer insulation film 5521 Main body 5522 Case 5523 Display part 5524 Keyboard 5551 Display part 5552 Main body 5553 Antenna 5554 Audio output unit 5555 Audio input unit 5556 Operation switch 5531 Display unit 5532 Case 5533 Speaker 701 Substrate 702 First electrode 703 First layer 704 Second layer 705 Third layer 706 Fourth layer 707 5 layers 708 second electrode

Claims (11)

A benzidine derivative represented by the general formula (1).

(In the formula, R ¹ represents either hydrogen or an alkyl group having 1 to 4 carbon atoms.) A benzidine derivative represented by the structural formula (2).

  The light emitting element which has a layer containing the benzidine derivative of Claim 1 or Claim 2 between a pair of electrodes.   A compound obtained by a coupling reaction of N, N′-diphenylbenzidine and 2-bromo-spiro-9,9′-bifluorene and having a melting point of 323 ° C. to 324 ° C.   The light emitting element which has a layer containing the compound of Claim 4 between a pair of electrodes. A hole transport material comprising a benzidine derivative represented by the general formula (1).

(In the formula, R ¹ represents either hydrogen or an alkyl group having 1 to 4 carbon atoms.) A hole transporting material containing a benzidine derivative represented by the structural formula (2).

  A hole transport material comprising a compound obtained by a coupling reaction of N, N′-diphenylbenzidine and 2-bromo-spiro-9,9′-bifluorene and having a melting point of 323 ° C. to 324 ° C.   A light emitting device comprising a layer made of the hole transport material according to claim 6.   A light-emitting device using the light-emitting element according to any one of claims 3, 5, and 9 in a pixel portion. An electronic apparatus using the light-emitting device according to claim 10 for a display portion.

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