Non-Conjugated Bridge Organic Molecules for TADF OLEDs
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Solution Overview
Problem
Current luminescent molecules for optoelectronic applications have a large energy difference between the singlet and triplet states, which hinders the achievement of short decay times and high photoluminescence quantum efficiency, limiting their effectiveness in devices like OLEDs.
Innovation Solution
The development of organic molecules with a donor and acceptor unit linked by non-conjugated bridges, reducing the wave function overlap and thus the energy difference between the singlet and triplet states, enabling thermally-activated delayed fluorescence (TADF) with improved emission efficiency and color purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional luminescent molecules are used, then the structure is simple, but the energy difference between singlet and triplet states is large, resulting in long decay times and low photoluminescence quantum efficiency
Solution Approach 1:
The molecule is divided into three distinct segments: a donor unit (D), an acceptor unit (A), and non-conjugated bridges (B) connecting them. This segmentation allows independent optimization of each component's properties, enabling precise control over the energy gap between singlet and triplet states while maintaining synthetic feasibility through modular assembly
Solution Approach 2:
Different regions of the molecule are assigned specific functional qualities: the donor unit provides electron-rich character, the acceptor unit provides electron-deficient character, and the bridges provide electrical insulation. This local differentiation of properties enables the molecule to achieve short decay times through small energy gaps without requiring overall structural complexity
2Loss of energy
If conventional luminescent molecules are used, then the molecular structure is simple, but the photoluminescence quantum efficiency is low
Solution Approach 1:
The invention systematically varies key molecular parameters including the choice of donor and acceptor units, the length and type of non-conjugated bridges, and the spatial arrangement of components. These parameter changes enable precise tuning of the energy gap between singlet and triplet states, directly improving photoluminescence quantum efficiency by reducing non-radiative decay pathways
3Use of energy by stationary object
If donor and acceptor units are closely connected, then the wave function overlap is large, but the energy difference between singlet and triplet states becomes too large for effective TADF
Solution Approach 1:
Non-conjugated bridge units are introduced as intermediary components between the donor and acceptor units. These bridges act as electrical insulators that prevent excessive wave function overlap while maintaining the spatial proximity needed for charge transfer. This intermediary structure enables the energy difference between singlet and triplet states to be reduced to the optimal range for TADF without compromising the reliability of the emission process
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
This approach results in a significant reduction of the energy difference between the singlet and triplet states, leading to enhanced TADF performance, including shorter decay times and increased emission quantum efficiency, thereby improving the performance of optoelectronic devices such as OLEDs.
Implementation Method 1
Thermally-activated delayed fluorescence (TADF) can be generated at room temperature by setting a sufficiently small energy difference ΔE (S1−T1) between the T1 state and the singlet state S1 above it
Implementation Method 2
This process is known to those skilled in the art (refer to, for example, A. Parker, C. G. Hatchard; Trans. Faraday, Royal Society of Chem. 1961, 57, 1894), also called frequency boosting based on E type
Data Source
AI summary
The invention relates to purely organic emitter molecules of a new type according to formula I and to the use thereof in optoelectronic devices, in particular in organic light-emitting diodes (OLEDs), comprising donor D: an aromatic or heteraromatic chemical group on which the HOMO is located and which optionally has at least one substitution; acceptor A: an aromatic or heteromatic chemical group on which the LUMO is located and which optionally has at least one substitution; bridge B1, bridge B2: organic groups that link the donor D and the acceptor A in a non-conjugated manner; wherein in particular the energy difference ΔE(S1−T1) between the lowest excited singlet (S1) state of the organic emitter molecule and the triplet (T1) state of the organic emitter molecule lying thereunder is less than 2000 cm−1.