Organic EL Compound Design for Low Roll-Off Emission
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Solution Overview
Problem
Existing delayed fluorescence materials suffer from reduced light emission efficiency due to exciton accumulation and rapid degradation under high current density, leading to roll-off and short element lifespan, especially in non-doped organic EL light emitting layers, and concentration quenching is a significant issue.
Innovation Solution
An organic compound characterized by a heteraborin skeleton with a selenium or tellurium atom and bulky aryl group, along with a bulky donor type substituent, is used to enhance reverse intersystem crossing rates and suppress concentration quenching, ensuring improved roll-off characteristics and extended lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a non-doped organic EL light emitting layer is formed using only a light emitting material, then the manufacturing process is simplified, but concentration quenching occurs when the concentration of the light emitting material is high
Solution Approach 1:
The patent changes the molecular structure parameters of the light emitting material by introducing a heavy atom (bromine) at the nitrogen atom position of the triphenamine derivative core structure. This structural parameter change increases the reverse intersystem crossing rate constant, which suppresses concentration quenching and enables the material to function effectively at high concentrations in non-doped layers.
Solution Approach 2:
The patent creates a composite molecular structure by combining a triphenamine derivative core with a bulky donor substituent and a heavy atom (bromine). This composite structure integrates multiple functions: the triphenamine core provides the basic delayed fluorescence properties, the bulky donor substituent prevents aggregation, and the bromine atom enhances the reverse intersystem crossing rate, collectively solving the concentration quenching problem.
2Speed
If a heavy atom is introduced to increase the reverse intersystem crossing rate, then the reverse intersystem crossing rate increases, but light emission efficiency decreases due to use of bromine
Solution Approach 1:
The patent applies local quality by placing the heavy atom (bromine) specifically at the nitrogen atom position of the triphenamine derivative core, rather than throughout the entire molecule. This localized placement minimizes the negative impact on light emission efficiency while still achieving the desired increase in reverse intersystem crossing rate. Additionally, the bulky donor substituent is placed at a specific position to provide steric protection without interfering with the heavy atom's function.
Solution Approach 2:
The patent optimizes the parameter of the heavy atom by selecting bromine specifically and positioning it at the nitrogen atom. This parameter optimization, combined with the bulky donor substituent parameter, achieves a balance where the reverse intersystem crossing rate is sufficiently increased while maintaining acceptable light emission efficiency.
3Loss of energy
If delayed fluorescence materials are used to achieve higher light emission efficiency, then light emission efficiency improves, but roll-off occurs due to exciton accumulation in high current density regions
Solution Approach 1:
The patent changes the kinetic parameters of the delayed fluorescence material by introducing the heavy atom, which increases the reverse intersystem crossing rate constant. This parameter change allows the material to more rapidly convert triplet excitons back to singlet excitons, reducing exciton accumulation in high current density regions and suppressing roll-off while maintaining high light emission efficiency.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The organic compound achieves a high reverse intersystem crossing rate, suppressing roll-off and concentration quenching, resulting in a non-doped element with enhanced light emission efficiency and prolonged lifespan.
Implementation Method 1
A donor acceptor type delayed fluorescence material in an excited state causes reverse intersystem crossing from an excited triplet state to an excited singlet state, and then radiates fluorescence when returning from the excited singlet state to the ground state.
Implementation Method 2
it is known to increase the reverse intersystem crossing rate by introducing a heavy atom into a donor acceptor type delayed fluorescence material
Implementation Method 3
By injecting electrons and holes from the pair of electrodes, excitons of a light emitting organic compound in the organic compound layer are produced, and the organic EL element emits light when the excitons return to the ground state.
Implementation Method 4
it is known that the intensity of light emitted from a light emitting material becomes low when the concentration of the light emitting material is high (hereinafter referred to as 'concentration quenching')
Data Source
Figure 1A~1D
Figure 2A~2B
Figure 3
AI summary
An organic compound is represented by formula (1-1) or (1-2) below, in formulas (1-1) and (1-2), Ra1 to Ra4 are each independently selected from a hydrogen atom, an alkyl group, and the like, provided that Ra1 is not a hydrogen atom, X is a selenium atom or a tellurium atom, Y is selected from an oxygen, and the like, D1 is a group represented by any one of formulas (2-1) to (2-5), D2 is a hydrogen atom or a group represented by any one of formulas (2-1) to (2-5), in formulas (2-1) to (2-5) * represents a binding site, Rb1 to Rb9 are each independently selected from a deuterium atom, an alkyl group, and the like, Z is selected from an oxygen atom, and the like, E is a carbon atom, a silicon atom, or a germanium atom, l, m, n, r, or s is an integer of 0 or more and 4 or less, o is an integer of 1 or more and 4 or less, p or q is 0 or 1, and each of t and u is an integer of 0 or more and 5 or less.