Thermally Activated Delayed Fluorescent Materials Combining Intra- and Intermolecular Charge Transfers

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Thermally activated delayed fluorescence (TADF) materials are crucial for efficient organic light-emitting diodes (OLEDs).
• Controlling charge transfer (CT) states is key to optimizing TADF properties.
• Existing TADF materials often face challenges with efficiency roll-off.

Purpose of the Study:

• To develop a novel TADF compound with a donor-σ-acceptor (D-σ-A) motif.
• To investigate the effect of dual intramolecular (intra-CT) and intermolecular (inter-CT) charge transfer on TADF emission.
• To evaluate the compound as both an emitter and a sensitizing host.

Main Methods:

• Synthesis of a novel TADF compound, 9-(3-((4,6-diphenyl-1,3,5-triazin-2-yl)oxy)phenyl)-3,6-diphenyl-9H-carbazole (PhCz-o-Trz).
• Utilizing a flexible small space σ-junction to modulate intra-CT and enhance inter-CT.
• Characterization of the compound's photophysical properties in amorphous aggregates.
• Testing PhCz-o-Trz as an emitter and a sensitizing host for fluorescent and phosphorescent dopants.

Main Results:

• The developed PhCz-o-Trz compound exhibits a D-σ-A structure with a unique σ-junction.
• Coexistence of intra-CT and inter-CT in amorphous aggregates was achieved, enhancing singlet-triplet mixing.
• This dual CT mechanism significantly boosts the triplet-to-singlet spin-flip transition, leading to enhanced TADF emission.
• PhCz-o-Trz demonstrated high efficiencies as both an emitter and a sensitizing host, with reduced efficiency roll-off.

Conclusions:

• The novel PhCz-o-Trz compound effectively utilizes dual charge transfer states for efficient TADF emission.
• The findings provide a new strategy for designing advanced TADF materials.
• This work deepens the understanding of TADF mechanisms, particularly the role of dual CTs.