JP3269345B2 - Organic light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting device.

[0002]

2. Description of the Related Art Since a low-voltage driven high-efficiency light emitting device using an organic compound was announced in 1987, organic electroluminescent devices (hereinafter referred to as organic EL devices) have been actively studied. Was. Thereafter, the light emitting element was made to have a two-layer structure of a hole transporting layer and an electron transporting light emitting layer, thereby realizing highly efficient light emission. It has also been suggested that by doping the light emitting layer with a laser dye, it is possible to achieve multicolor emission and higher efficiency.

As an application of these organic EL elements, a large-screen display device is considered, and a display device using a conventional cathode ray tube (hereinafter referred to as Cathode).
(Ray Tube Display: CRT) has a problem in that, due to its structure, the size of the screen is increased, the depth of the device is increased, the device itself is enlarged, and the power consumption is increased. However, if an organic EL material is used, the organic EL material emits light by enjoying electrons between the excited state and the ground state of atoms in the first place, so that power consumption does not increase and the organic material is Since it is very light, there is no problem at all with respect to upsizing of the apparatus.

Plasma display devices have been widely studied as display devices for large screens which overcome the above-mentioned problems of CRTs. However, since organic EL elements can be manufactured by simply depositing a thin film, they are manufactured. The process is simplified, and there is a possibility that the manufacturing cost can be significantly reduced, and practical use of the organic EL element is expected.

[0005] Among these organic EL devices, Tris (8-quinolinol) in which three molecules of 8-quinolinol are coordinated around aluminum has recently been attracting attention.
ate) aluminum (III) (hereinafter referred to as aluminum quinoline or Alq3). This aluminum quinoline is considered to be a promising material from the viewpoint of a manufacturing process such as vapor deposition together with its high luminous efficiency.

[0006]

However, these devices have a luminous efficiency of 1.6 lm / a in the case of aluminum quinoline.
In the case of w and beryllium quinoline, it is 3.5 lm / w, which is not enough for 20 lm / w required for practical use.
Therefore, an object of the present invention is to provide an organic EL light emitting device having a higher luminous efficiency than a conventional organic EL material.

[0007]

In order to achieve the above object, the present invention provides a molecule having a structure in which oxygen and nitrogen are directly or indirectly connected to a pi-conjugated carbon main chain. An organic light-emitting device containing an organic light-emitting device, in which an electron-donating functional group is connected to a molecule by substitution. Further, the present invention is characterized in that a halogen, oxygen, nitrogen, sulfur, a benzene ring or a methyl group is used as the functional group.

[0008]

Therefore, in a light emitting device comprising a molecule or a molecular aggregate having a structure in which oxygen and nitrogen are composed of at least one or more carbon atoms and are directly or indirectly connected to a pi-conjugated main chain, The luminous efficiency and the electron transition probability are proportional to each other in the Born-Oppenheimer approximation. Therefore, increasing the electron transition probability leads to increasing the luminous efficiency of the material. According to the molecular orbital method, which is usually used as a method to theoretically consider the physical properties of materials, the electronic transition probability is calculated based on the molecular orbital coefficient of the transition source and the molecular orbital coefficient of the transition destination when the electron makes a transition. It is proportional to the size of the overlap between the two orbits. In addition, by multiplying this orbital coefficient by the electron density of the orbit, it is proportional to the electron density, and by increasing the electron density, the luminous efficiency is increased by increasing the probability of electron transition involving the orbital. Becomes possible.

[0009]

FIG. 1 shows the structure of one aluminum quinoline molecule whose structure has been optimized by the molecular orbital method, and FIG. 2 shows its orbital correlation diagram. As shown in FIG. 1, aluminum quinoline 1 is composed of quinolinol oxygen and nitrogen 6
It is arranged to take a coordination structure. However, the bond order of the aluminum with oxygen and nitrogen is 0.7
It is considered that the covalent bond is small and the ionic bond due to electrostatic force is large. In addition,
The bond order is 1.0 for a single bond, 2.0 for a double bond,
It becomes 3.0 etc. by a triple bond. In addition, the molecular orbitals of the aluminum quinoline near the highest occupied orbital (HOMO) and the lowest unoccupied orbital (LUMO) have a large coefficient to the atomic orbital of quinolinol. Therefore, it was found that aluminum itself does not directly contribute significantly in the luminescence absorption process (which affects luminous efficiency), and that the electron transition process in the quinolinol molecule is considered to be important.

Next, the electronic state of quinolinol, which is considered to be important in the luminescence absorption process as described above, will be described. Depending on the pH of the solution of quinolinol (hereinafter referred to as Q-OH), a proton desorbing species (hereinafter referred to as QO-) and a protonated species (hereinafter referred to as Q-OH) as shown in FIG.
-OH2 +), but it is experimentally known that there is a difference between the respective absorption intensity and excitation energy. Therefore, the mechanism was studied by performing one-electron excitation configuration calculation (SE-CI).

FIG. 3 shows the result of electron density analysis on the ground state of each molecular species, and FIG. 4 shows the result of excitation energy by one-electron excitation configuration calculation of each molecular species.

Next, FIG. 5 shows a conceptual diagram of the electron transition energy in the light emitting process and the light absorbing process. In FIG. 5, (a) shows a case where there is a difference between the absorption energy and the emission energy.
(B) shows a case where there is no difference between the two.
When there is a difference in light emission energy, the energy difference E1 is mainly consumed as vibration energy or the like.
Strictly speaking, as shown in FIG. 5, there is a difference in the transition energy between the light emission process and the light absorption process, that is, the wavelength of light emitted or absorbed, which is represented by E1. In the range of the Heimer approximation, E1 is smaller than E2, and it can be considered that the energies of the light absorption process and the light emission process are almost the same.

As described above, aluminum itself does not directly contribute greatly in the luminescence absorption process (affects the luminous efficiency), and it is considered that the electronic transition process in the quinolinol molecule is important. According to the above, the electronic transition of aluminum quinoline occurs between oxygen and nitrogen in the molecule of quinolinol, and the intensity is proportional to the electron density on the oxygen atom (FIG. 6). Then, assuming that the electron transition probability is P (x), according to the molecular orbital method,

[0014]

(Equation 1)

The electron density MA on an atom is

[0016]

(Equation 2)

Can be written as Where Ψ0 is the wavefunction of the ground state of the molecule, Ψab is the wavefunction of the one-electron excitation configuration, ψa is the original molecular orbital of the excited electron, ψb is the molecular orbital occupied when the electron is excited, χr is the atomic orbit, C is the molecular orbital coefficient, X is the coordinate axis, and x is the coordinate axis of each electron. In addition, each integral value <χr | eΣxk | χs> or <
χr | χt> is a constant value in this case unless the positions of oxygen and nitrogen of quinolinol change. Therefore, from the above description and the above two formulas, a large electron density on oxygen means that its molecular orbital coefficient is large, which means that the electron transition probability between oxygen and nitrogen is large. That is. This relationship is shown in the table below.

[0018]

[Table 1]

At this time, if there is no change in the molecular structure,
χr | eΣxk | χs> and <χr | χt> take constant values.

Considering that the emission intensity and the absorption intensity are proportional to the electron transition probability, it can be understood that an increase in the electron density on oxygen contributes to an increase in the emission intensity and the absorption intensity.
That is, it leads to an increase in luminous efficiency.

As described above, one of the guidelines for increasing the light absorption / emission efficiency of an organic EL device having a quinolinol molecular structure as a basic skeleton is to increase the electron density of oxygen.

Therefore, in the present invention, light emission is achieved by using a molecular structure in which 8-quinolinol, which is a ligand of aluminum quinoline used in an organic EL light emitting device, is substituted with an electron donating functional group as shown in the following representative examples. Improved efficiency.

[0023]

[0024]

Embedded image

[0025]

[0026]

Embedded image

[0027]

[0028]

In the above formula (3) , X is OH, NH
₂ , SH, or C ₆ H ₅ . Ma
In the chemical formula 4, X is OH, NH ₂ , SH, C ₆ H
Either ₅ or CH ₃ .

And (Chemical Formula 3) is a compound obtained by substituting an electron-donating substituent at the para position with respect to the oxygen of 8-quinolinol.
( Formula 4) is an example of 8-quinolinol substituted at the para position as viewed from the nitrogen.

In the above (Chemical Formula 3) and (Chemical Formula 4) , examples of the electron donating functional group include fluorine (F) and hydroxyl group (O
H), an amino group (NH ₂ ), a thiol group (SH), and a methyl group (CH ₃ ), which are respectively a halogen, a functional group to which oxygen is directly bonded, a functional group to which nitrogen is directly bonded, And a functional group to which sulfur is directly bonded.

[0032]

Embedded image

The above (Chemical Formula 5) is the same as the above (Chemical Formula 3),
This shows the structure of 8-quinolinol as a basic skeleton when designing the molecular structure shown in (Chem. 4) .

Next, light emission and light absorption when the molecule represented by the above formula (3) is formed into a polymer will be described.

[0035]

Embedded image

In the above (Chemical formula 6), the molecule represented by the (Chemical formula 3) is formed into a polymer, and the polymer is formed by using fluorine as a functional group of the electron donating group. And (
FIG. 7 shows the relationship between the electron density and the absorption intensity of the molecules shown in 3) and (Chem. 6) .

As is clear from FIG. 7, as with quinolinol and its proton-desorbed and added species, there is a proportional relationship between the electron density on oxygen and the absorption intensity. The increase in intensity is proportional to the increase in luminous efficiency.

In summary, the electron transition of aluminum quinoline is mainly performed between oxygen and nitrogen in the quinolinol molecule, and the absorption intensity is proportional to the electron density of aluminum quinoline molecule on oxygen. Therefore, several molecules with the basic structure of the molecular structure of quinolinol were created, and as a result of calculating the electron density and absorption intensity on oxygen,
Also, by substituting or adding an electron-donating group which increases the electron density on oxygen, the absorption intensity can be increased.

In addition to the above-mentioned electron-donating functional groups, oxygen, alkoxy, carbonyl, amide, alkyl, thiol, sulfide, thioaldehyde, thioketone, thioacetal, thiocarbonyl Groups and the like.

Similarly, a functional group having a molecular structure to which selenium is directly bonded, a functional group having a molecular structure to which a benzene ring is directly bonded, and the like are also conceivable as electron-donating functional groups.

[0041]

As described above, according to the present invention, a molecule having a structure in which oxygen and nitrogen are directly or indirectly connected to the main chain of carbon having pi conjugation is contained. An organic light-emitting device, which has a configuration in which an electron-donating functional group is connected to a molecule by substitution,
The luminous efficiency can be increased by increasing the valence electron density on oxygen atoms and increasing the electron transition probability.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the structure of an aluminum quinoline molecule in an example of the present invention.

FIG. 2 is an aluminum quinoline molecular orbital correlation diagram in an example of the present invention.

FIG. 3 is a structural diagram of quinolinol in an embodiment of the present invention.

FIG. 4 is a diagram showing excitation energy of quinolinol in an example of the present invention.

FIG. 5 is a conceptual diagram of an electron transition energy in a light emission / absorption process.

FIG. 6 is a graph showing the relationship between the electron density and the absorption intensity of aluminum quinoline molecules in an example of the present invention.

FIG. 7 is a diagram showing the relationship between the electron density and the absorption intensity of aluminum quinoline molecules in an example of the present invention.

[Explanation of symbols]

 1 aluminum quinoline

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-372688 (JP, A) JP-A-5-331460 (JP, A) JP-A-5-105872 (JP, A) 145146 (JP, A) JP-A-6-313168 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 33/14 C09K 11/06 CA (STN) REGISTRY (STN)

Claims (2)

(57) [Claims] An 8-quinolinol derivative represented by the formula (1)
To have an Al complex having as a ligand (hereinafter 5 mol%
The organic light emitting device characterized excluding). Embedded image (X1 is a hydroxyl group, an amino group, a mercapto group, a phenyl
Group or a methyl group. ) 2. Having an Al complex having an 8-quinolinol derivative represented by the formula (2) as a ligand (5 mol% or less)
The organic light emitting device characterized excluding). Embedded image ( X2 represents a hydroxyl group, an amino group, a mercapto group, or
It is any of phenyl groups . )