Engineering the Macrocyclic Donor Structures towards Deep-Blue Thermally Activated Delayed Fluorescence Emitters.

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Deep-blue thermally activated delayed fluorescence (TADF) emitters are crucial for high-performance organic light-emitting diodes (OLEDs), particularly for display applications.
• Developing efficient deep-blue TADF molecules requires precise molecular engineering of donor-acceptor systems.

Purpose of the Study:

• To report an efficient molecular engineering approach for developing deep-blue TADF molecules by modifying donor/acceptor features in D-π-A configured systems.
• To synthesize and characterize novel TADF emitters by introducing oxygen and sulfone bridge units onto macrocyclic donors.
• To establish a clear structure-property-performance relationship for guiding the design of efficient deep-blue TADF emitters.

Main Methods:

• Synthesis and characterization of novel TADF molecules (c-ON-MeTRZ, c-NS-MeTRZ, c-NN-MePym) with modified macrocyclic donors.
• Photophysical characterization including photoluminescence quantum yields (PLQYs) and analysis of TADF properties.
• Fabrication and testing of deep-blue TADF OLED devices using synthesized emitters with different hosts (mCPCN, DPEPO) to evaluate external quantum efficiency (EQE) and Commission Internationale de I'Eclairage (CIE) coordinates.

Main Results:

• Two new deep-blue TADF emitters, c-ON-MeTRZ and c-NS-MeTRZ, were synthesized, showing blue-shifted emission and high PLQYs compared to a model molecule.
• OLED devices incorporating c-ON-MeTRZ achieved a maximum EQE of 30.2% (CIE: 0.14, 0.13), which improved to 34.4% with a polar host (DPEPO).
• Devices with c-NS-MeTRZ achieved a maximum EQE of 15.4% (CIE: 0.14, 0.09), improving to 29.3% with DPEPO, attributed to stabilized charge transfer states and reduced energy gaps.

Conclusions:

• The molecular design strategy effectively modulates macrocyclic donor characteristics for efficient deep-blue TADF emitters.
• High horizontal dipole ratios (85-89%) contribute to improved light out-coupling efficiency in the fabricated OLEDs.
• The study establishes a comprehensive structure-property-performance relationship, validating the molecular design approach for advanced OLED applications.