Hybridized Charge-Transfer Window within a Fully Conjugated Multi-Resonance Thermally Activated Delayed Fluorescence...

Area of Science:

• Organic electronics
• Materials science
• Photophysics

Background:

• Multi-Resonance (MR) thermally activated delayed fluorescence (TADF) materials offer narrow emission and high efficiency for blue organic light-emitting diodes (OLEDs).
• Conventional MR-TADF emitters face challenges with large singlet-triplet energy gaps and slow reverse intersystem crossing (RISC) rates.
• Overcoming these limitations is crucial for advancing blue OLED technology.

Purpose of the Study:

• To design and synthesize novel deep blue MR-TADF molecules.
• To minimize the singlet-triplet energy gap and accelerate the RISC rate.
• To achieve efficient and stable blue emission in OLED devices.

Main Methods:

• Integration of intramolecular short-range and long-range charge transfer mechanisms.
• Design of molecules with hybridized excited states for narrow emission bandwidth.
• Synthesis and characterization of the bfDOB-BN2 MR-TADF emitter.

Main Results:

• The bfDOB-BN2 emitter shows narrow blue emission at 447 nm with a 20 nm FWHM.
• A small singlet-triplet energy gap of 0.04 eV and an ultrafast RISC rate of 2.1 × 10^6 s^-1 were achieved.
• The TADF OLED device demonstrated a high external quantum efficiency of 37.5%.

Conclusions:

• The designed MR-TADF molecules effectively minimize energy gaps and accelerate RISC rates.
• Intramolecular long-range charge transfer contributes significantly to the emission process.
• These findings pave the way for high-performance deep blue OLEDs.