Benzonitrile Derivative Host Material Suppresses Roll-Off
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Solution Overview
Problem
Current organic electroluminescent devices face challenges in achieving high luminance and efficiency due to the roll-off phenomenon, which is exacerbated by high current density, and existing materials fail to effectively suppress triplet-triplet annihilation and singlet-triplet annihilation, leading to reduced quantum yield and stability issues.
Innovation Solution
Development of benzonitrile derivatives with a heterocyclic ring structure, specifically carbazole and acridane rings, which emit delayed fluorescence, are designed to have a high triplet energy level, wide bandgap, and deep HOMO level, serving as dopant or host materials in the light-emitting layer to enhance electron injection/transport and stability, thereby improving luminous efficiency and suppressing roll-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent materials are used to generate phosphorescence from triplet excitation state, then luminous efficiency is improved (up to 4 times fluorescence), but the excited triplet state has long lifetime causing energy deactivation through saturation and interactions, resulting in reduced quantum yield
Solution Approach 1:
The patent modifies molecular parameters by introducing specific substituents (carbazole, acridane, dibenzofuran groups) to control the energy levels and lifetimes of excited states, achieving optimal balance between luminous efficiency and quantum yield through parameter optimization
Solution Approach 2:
The patent creates composite fluorescent materials by combining multiple heterocyclic ring structures (carbazole, acridane, dibenzofuran) with benzonitrile core, achieving synergistic effects that simultaneously improve triplet energy levels, reduce annihilation losses, and enhance overall device performance
2Illumination intensity
If high current density is applied to achieve high luminance, then brightness is improved, but the roll-off phenomenon occurs causing efficiency to decrease
Solution Approach 1:
The patent optimizes molecular energy level parameters (triplet energy level, HOMO-LUMO gap) to prevent triplet-triplet and singlet-triplet annihilation at high current densities, thereby suppressing the roll-off phenomenon and maintaining high efficiency across different luminance levels
3Use of energy by moving object
If ordinary TADF light-emitting materials are used, then delayed fluorescence is achieved through thermal energy absorption, but the materials cannot effectively suppress triplet-triplet annihilation and singlet-triplet annihilation
Solution Approach 1:
The patent precisely controls the energy gap between singlet and triplet states (ΔEST) and the triplet energy level (ET) through molecular design, enabling efficient reverse intersystem crossing while preventing annihilation losses by maintaining appropriate energy level separations
Solution Approach 2:
The patent designs composite molecules incorporating carbazole, acridane, and dibenzofuran groups that work synergistically to enhance thermal energy absorption for reverse intersystem crossing while simultaneously raising triplet energy levels to suppress annihilation processes
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 benzonitrile derivatives exhibit high luminous efficiency, stability in thin-film form, and effective suppression of the roll-off phenomenon, resulting in enhanced luminance and prolonged durability of organic electroluminescent devices with improved electron transport and hole blocking capabilities.
Implementation Method 1
A certain kind of fluorescent substance emits fluorescence via intersystem crossing or the like leading to energy transition to an excited triplet state and the subsequent reverse intersystem crossing to an excited singlet state through triplet-triplet annihilation or thermal energy absorption
Implementation Method 2
excitons in an excited triplet state absorb heat produced from a device and undergo intersystem crossing to an excited singlet to emit fluorescence
Implementation Method 3
through triplet-triplet annihilation or thermal energy absorption
Implementation Method 4
carriers are injected from each of both electrodes, i.e., positive and negative electrodes to a light-emitting substance to generate a light-emitting substance in an excited state so as to emit light
Data Source
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AI summary
To provide a light-emitting material of a light emitting layer, particularly a dopant material or a host material of a light emitting layer emitting delayed fluorescence, or a material suitable for a hole blocking layer, as a material for an organic electroluminescent device having a high efficiency, and also to provide an organic photoluminescent device or an organic electroluminescent device having a high efficiency and a high luminance, particularly an organic EL device suppressed in the roll-off phenomenon, by using the material. A material for an organic electroluminescent device, containing a benzonitrile derivative of the following general formula (1), and an organic electroluminescent device containing a pair of electrodes and one layer or plural layers including at least a light emitting layer intervening between the electrodes, the organic electroluminescent device using the material.