Spiro Units Embedded in the B/N Center for Constructing Highly Efficient Multiple Resonance TADF Emitters

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Conventional molecular designs for organic light-emitting diodes (OLEDs) often use spiro units peripherally.
• Developing efficient and stable emitters with narrow emission spectra is crucial for advanced display technologies.

Purpose of the Study:

• To design and synthesize novel multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters.
• To investigate the impact of incorporating the 9,9'-spirobi[fluorene] (SF) unit into the core of boron/nitrogen multiple resonance (B/N-MR) emitters.
• To evaluate the performance of these emitters in OLED devices.

Main Methods:

• Synthesis of four novel MR-TADF emitters (SF-BN1 to SF-BN4) featuring integrated SF units.
• Characterization of photophysical properties, including photoluminescence quantum yields (PLQYs) and full-width at half-maximum (FWHM).
• Fabrication and testing of OLED devices using the synthesized emitters, analyzing external quantum efficiency (EQE) and electroluminescent (EL) properties.

Main Results:

• Novel emitters exhibit narrow FWHM (15-21 nm) in solution and high PLQYs (up to 90%) in films.
• OLEDs based on SF-BN1 achieved high EQE (29.0%) with blue emission close to the BT.2020 standard.
• OLEDs based on SF-BN3 demonstrated high EQE (29.8%) and hyperfluorescent OLEDs reached 35.5% EQE.
• Subtle changes in emitter structure and device parameters significantly influence optical and EL properties.

Conclusions:

• Full or partial incorporation of the SF unit into the B/N-MR core is a viable strategy for developing high-performance MR-TADF emitters.
• The developed emitters show great potential for achieving efficient and spectrally pure emission in OLED applications.
• Understanding structure-property relationships is key to optimizing emitter and device performance.