Enhancing the Operational Lifetime of OLEDs Through the Modulation of Rigidity and Excited-State Properties

Area of Science:

• Materials Science
• Organic Electronics
• Photochemistry

Background:

• Development of efficient and stable blue emitters is critical for organic light-emitting diodes (OLEDs).
• Multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters offer potential for high photoluminescence quantum yield (PLQY) and fast decay times.
• Molecular design plays a key role in tuning the excited-state dynamics and performance of TADF emitters.

Purpose of the Study:

• To design and synthesize novel blue-emitting MR-TADF molecules with enhanced planarity and rigidity.
• To investigate the impact of molecular structure on excited-state dynamics, photophysical properties, and OLED performance.
• To establish structure-property relationships for developing robust blue MR-TADF emitters.

Main Methods:

• Synthesis of a series of MR-TADF molecules (BNO, BNDO, BNTO) featuring fused boron/nitrogen and C=O/N frameworks via stepwise intramolecular electrophilic acylation.
• Characterization of molecular structure using computational studies and single-crystal X-ray diffraction.
• Evaluation of photophysical properties (PLQY, emission lifetime) and fabrication of OLED devices.

Main Results:

• Enhanced planarity was observed in BNDO and BNTO molecules.
• Synthesized compounds exhibited efficient blue emission with PLQYs approaching unity and short delayed lifetimes (<2 µs).
• BNTO-based OLEDs demonstrated sky-blue emission (489 nm) and achieved a device operational lifetime (LT70) of over 500 hours at 1000 cd m⁻².

Conclusions:

• Molecular rigidity and planarity significantly influence the excited-state dynamics and performance of MR-TADF emitters.
• The designed MR-TADF molecules are promising candidates for efficient and stable blue OLED applications.
• Strategic manipulation of molecular structure is essential for optimizing blue emission and device stability in OLEDs.