Spiro Azafluorene Compounds for Delayed Fluorescence OLEDs
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Solution Overview
Problem
Current organic electroluminescent devices face limitations in luminous efficiency due to the low utilization of excited singlet states and the long lifetime of triplet excitons, which leads to inefficient energy use and reduced quantum yield.
Innovation Solution
Development of spiro compounds with an azafluorene ring structure that emit delayed fluorescence, utilizing a small difference between excited triplet and singlet energies and high oscillator strength, allowing for improved exciton transfer and enhanced luminous efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent materials are used to generate phosphorescence from excited triplet state, then luminous efficiency is expected to improve up to four times that of fluorescence, but the long lifetime of excited triplet state causes energy deactivation through saturation and interactions, resulting in low quantum yield
Solution Approach 1:
The patent changes the energy parameters of the system by designing spiro compounds with specific HOMO-LUMO energy levels and small singlet-triplet energy gaps. This allows the material to utilize both singlet and triplet excitons effectively, converting the previously harmful long-lived triplet state into a useful resource for delayed fluorescence emission, thereby achieving high quantum yield and luminous efficiency simultaneously
Solution Approach 2:
The patent converts the harmful long lifetime of triplet excitons (which causes energy deactivation and low quantum yield) into a beneficial feature for delayed fluorescence. By designing materials with small singlet-triplet energy gaps, the triplet excitons can be thermally activated to singlet state and emit delayed fluorescence, turning the previously problematic long-lived triplet state into an additional light emission pathway that improves overall luminous efficiency
2Productivity
If only 25% of generated excitons are excited to excited singlet state, then normal fluorescence can be achieved, but the remaining 75% in excited triplet state are underutilized, limiting overall energy efficiency
Solution Approach 1:
The patent makes the light-emitting material universal by enabling it to utilize both singlet and triplet excitons for light emission. The spiro compound design allows normal fluorescence from singlet excitons and delayed fluorescence from triplet excitons, effectively making the material capable of converting all types of excitons (both the usual 25% singlet and the previously wasted 75% triplet) into useful light output, thereby achieving near-100% internal quantum efficiency
Solution Approach 2:
The patent achieves continuous useful action by creating a dual emission pathway where both singlet and triplet excitons continuously contribute to light emission. The delayed fluorescence mechanism ensures that triplet excitons are continuously converted to singlet state and emitted as light, maintaining a continuous flow of energy conversion from both exciton types into useful luminous output without energy loss
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 spiro compounds with an azafluorene ring structure enable high luminous efficiency, low driving voltage, and improved durability in organic electroluminescent devices by effectively utilizing both singlet and triplet excitons, leading to increased external quantum efficiency and emission luminance.
Implementation Method 1
Devices that use light emission caused by thermally activated delayed fluorescence (TADF) have also been developed
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
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
Implementation Method 4
excitons in an excited singlet state emit fluorescence as per normal
Data Source
AI summary
A compound that emits fluorescence and delayed fluorescence is provided as a material for an organic electroluminescent device of high efficiency, and an organic photoluminescent device and an organic electroluminescent device of high efficiency and high luminance are provided using this compound. The spiro compound of a general formula (1) having an azafluorene ring structure is used as a constituent material of at least one organic layer in an organic electroluminescent device that includes a pair of electrodes, and one or more organic layers sandwiched between the pair of electrodes.