Cascade Effect of a Dimerized Thermally Activated Delayed Fluorescence Dendrimer

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• High horizontal orientation of Thermally Activated Delayed Fluorescence (TADF) emitters is crucial for enhancing external quantum efficiency (EQE) in organic light-emitting diodes (OLEDs).
• Developing effective molecular design strategies for solution-processable TADF emitters with improved horizontal orientation remains a significant challenge.

Purpose of the Study:

• To design and synthesize a novel dimerized TADF dendrimer, D4CzBNPh-SF, utilizing a phenyl bridge to connect two TADF units.
• To investigate the impact of this dimerized structure on molecular orientation, photophysical properties, and device performance.

Main Methods:

• Synthesis of a dimerized TADF dendrimer (D4CzBNPh-SF) featuring a phenyl bridge.
• Characterization of photophysical properties including photoluminescence quantum yield and reversed intersystem crossing rate.
• Fabrication and testing of non-doped and TADF-sensitized fluorescence OLED devices using D4CzBNPh-SF as the emitter or sensitizer.

Main Results:

• The D4CzBNPh-SF molecule achieved a high horizontal dipole ratio of 78% due to extended π-conjugation.
• Demonstrated a fast reversed intersystem crossing rate (6.08×10^6 s^-1) and a high photoluminescence quantum yield (95%) in neat films.
• Achieved a maximum EQE of 32.6% for non-doped solution-processed OLEDs and 30.7% for TADF-sensitized fluorescence devices.

Conclusions:

• The dimerized TADF dendrimer structure effectively enhances horizontal molecular orientation and charge transfer properties.
• Solution-processed OLEDs utilizing D4CzBNPh-SF exhibit record-breaking EQE, demonstrating the potential of this molecular design strategy.
• The developed TADF emitters show promise for high-performance, solution-processable optoelectronic devices.