TADF Compounds with Aromatic Spacer Rings for OLEDs
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Solution Overview
Problem
Current OLED technologies face limitations due to the rarity, high cost, and toxicity of heavy metals used in second-generation phosphorescent emitters, and there is a need for improved compounds that can efficiently harness both singlet and triplet excitons for enhanced performance in display and lighting applications.
Innovation Solution
Development of Thermally Activated Delayed Fluorescence (TADF) compounds with specific aromatic spacer rings and heterocyclic moieties that segregate HOMO and LUMO, allowing efficient reverse intersystem crossing and radiative fluorescence, thereby overcoming the limitations of previous OLED generations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If phosphorescent emitters with heavy metals are used, then both singlet and triplet excitons are harvested for emission, but the rarity, high cost and toxicity of these metals are important detracting features
Solution Approach 1:
The patent removes heavy metal elements from the emitter structure entirely, extracting the harmful component while preserving the desired functionality. The TADF mechanism achieves triplet exciton harvesting without requiring phosphorescent heavy metals, thus eliminating their rarity, cost and toxicity issues.
Solution Approach 2:
The invention replaces expensive, rare heavy metals with organic compounds based on common elements. The TADF emitters use readily available organic materials that are cheaper and less toxic, sacrificing the long-lived phosphorescent emission for shorter-lived but equally efficient TADF emission.
2Device complexity
If fluorescent emitters are used, then the device structure is simpler, but the efficiency is intrinsically capped at 25% due to only being able to recruit singlet excitons
Solution Approach 1:
The patent changes the emission mechanism parameter from simple fluorescence to thermally activated delayed fluorescence. By introducing thermal energy activation and delayed emission components, the system can access both singlet and triplet excitons while maintaining organic material simplicity, achieving over 25% efficiency without complex phosphorescent structures.
3Use of energy by moving object
If donor and acceptor moieties are placed nearly orthogonal to each other in TICT design, then a small energy gap between singlet and triplet excited states is achieved, but the emission wavelength may be limited
Solution Approach 1:
The patent applies local quality by positioning donor and acceptor moieties at specific orientations (including orthogonal arrangements) to create localized electronic structures with desired properties. This spatial arrangement enables small singlet-triplet energy gaps for efficient TADF while the specific molecular design allows tuning of emission wavelengths across different regions of the spectrum.
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 TADF compounds exhibit improved efficiency, blue-shifted emission, and shorter emission lifetimes, leading to more robust and efficient light-emitting devices with reduced metal usage, addressing the drawbacks of previous OLED technologies while maintaining high performance.
Implementation Method 1
the electrons in the triplet state can return to the singlet state by reverse intersystem crossing (RISC) using thermal energy, followed by radiative fluorescence
Implementation Method 2
small organic molecules, emitting via a thermally activated delayed fluorescence (TADF) mechanism
Implementation Method 3
The small ΔE ST is realized by spatial separation between HOMO and LUMO to minimize the electronic repulsion between these orbitals
Implementation Method 4
harvest both singlet and triplet excitons for emission due to the enhanced intersystem crossing (ISC) mediated by the large spin-orbit coupling of heavy metals
Implementation Method 5
enhanced intersystem crossing (ISC) mediated by the large spin-orbit coupling of heavy metals such as iridium(III) and platinum(II)
Data Source
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AI summary
Thermally Activated Delayed Fluorescence (TADF) compounds wherein two aromatic heterocyclic moieties are provided as acceptor groups, spaced apart from two donor moieties by an aromatic spacer ring, are described. Charged organic TADF species having a similar structure are also described. The TADF compounds and charged organic TADF species may be employed as emitter material in light emitting devices such as OLEDs and LEECs. Also described TADF compounds wherein at least one donor moiety is substituted by at least one substituent that is a phosphine oxide or a phosphine sulphide.