Gold(III) TADF-TSDP Emitters for Stable Blue OLEDs
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Solution Overview
Problem
Current OLED technologies face challenges with the stability and efficiency of blue-emitting materials, particularly in the gold(III) system, where blue emitters have short operational lifetimes and contribute to the degradation of display colors, and existing TADF emitters suffer from inefficient spin-forbidden processes leading to long-lived triplet states and reduced quantum efficiency.
Innovation Solution
Development of luminescent small-molecular and dendritic gold(III) compounds with close-lying singlet and triplet excited states exhibiting both thermally activated delayed fluorescence (TADF) and thermally stimulated delayed phosphorescence (TSDP) properties, utilizing specific donor and acceptor units and pincer ligands to achieve efficient spin-allowed reverse internal conversion, thereby providing multiple pathways for radiative decay and enhancing photoluminescence quantum yields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If blue-emitting gold(III) compounds are used in OLEDs, then the device can achieve high brightness and color purity, but the operational lifetime is short and display colors degrade
Solution Approach 1:
The patent changes the photophysical parameters of the gold(III) compounds by introducing specific ligand designs (C^N^C pincer ligands with electron-donating groups) that modify the energy levels and lifetimes of excited states, thereby extending operational lifetime while maintaining brightness
Solution Approach 2:
The patent creates composite luminescent systems by combining gold(III) centers with organic ligand frameworks, achieving a synergistic effect where the metal center provides phosphorescence and the ligand structure enables TADF-TSDP mechanisms for enhanced stability
2Duration of action of moving object
If conventional TADF emitters are used, then the device can achieve long-lived triplet states, but the spin-forbidden processes reduce quantum efficiency
Solution Approach 1:
The patent introduces thermally stimulated delayed phosphorescence (TSDP) as an intermediary mechanism that facilitates spin-allowed transitions through triplet-triplet energy transfer, acting as a bridge between the triplet excited state and the ground state to improve quantum efficiency
Solution Approach 2:
The patent utilizes thermal energy to induce phase transitions in the excited state population, enabling upconversion from triplet to singlet states through reverse intersystem crossing (RISC) and facilitating efficient radiative decay through multiple pathways
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 compounds achieve shorter excited state lifetimes, higher photoluminescence quantum yields, and improved external quantum efficiency, addressing the stability issues of blue emitters and enhancing the performance of OLEDs through the TADF-TSDP mechanism, which is unique and unprecedented in the literature.
Implementation Method 1
close-lying singlet and triplet excited states exhibiting thermally activated delayed fluorescence (TADF)
Implementation Method 2
close-lying singlet and triplet excited states exhibiting thermally stimulated delayed phosphorescence (TSDP)
Implementation Method 3
The introduction of a heavy metal center into the organic frameworks can effectively lead to a strong spin-orbit coupling and thus promotes an efficient intersystem crossing from the singlet excited state to the lower-energy triplet excited state
Implementation Method 4
efficient spin-allowed reverse internal conversion
Data Source
AI summary
Described herein is a novel concept of the realization of thermally activated delayed fluorescence (TADF) and thermally stimulated delayed phosphorescence (TSDP) to harvest light emission from the higher-energy singlet and triplet excited states via the up-conversion from the lowest-energy triplet excited state by efficient reverse internal conversion together with reverse intersystem crossing as well as the development of emitters with TADF and TSDP properties, as exemplified by a new class of gold (III) compounds with TADF and TSDP properties. The gold (III) compounds include N-heterocycle-containing cyclometalating tridentate ligand and one auxiliary ligand, both coordinated to a gold (III) metal centre and having the chemical structure shown in generic formula (I).