Macrocyclic Covalent Encapsulation of a Multi-Resonant Emitter: Understanding and Controlling Interactions in Highly...

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Multi-resonant thermally activated delayed fluorescence (MR-TADF) emitters are key for blue organic light-emitting diodes (OLEDs) due to their high efficiency and narrowband emission.
• However, planar structures of MR-TADF materials cause intermolecular interactions in solid-state films, leading to reduced color purity and efficiency.
• Existing MR-TADF emitters often struggle to meet the strict color standards required for next-generation displays.

Purpose of the Study:

• To address the limitations of planar MR-TADF emitters by developing a strategy to enhance their performance in solid-state devices.
• To investigate the impact of macrocyclic encapsulation on the photophysical properties and device performance of blue-shifted MR-TADF emitters.
• To establish macrocyclic encapsulation as a viable method for improving MR-TADF materials for high-performance OLEDs.

Main Methods:

• Synthetically encapsulating a blue-shifted MR-TADF emitter within a protective macrocyclic ring.
• Utilizing spectrally resolved transient photoluminescence measurements to analyze emission characteristics and identify aggregate/excimer formation.
• Fabricating and testing OLED devices using the encapsulated emitter with a hyperfluorescent strategy.

Main Results:

• Macrocyclic encapsulation was found to shield the MR-TADF core, enhancing radiative rate, photoluminescence quantum yield (PLQY), and reverse intersystem crossing (RISC) efficiency.
• The macrocycle effectively suppressed the formation of emissive aggregates and excimers in the solid-state, preserving narrowband deep-blue emission and reducing nonradiative losses.
• The encapsulated emitter achieved a maximum external quantum efficiency (EQE) of 33% with CIE coordinates (0.146, 0.046) at 451 nm, meeting BT.2020 blue color requirements.

Conclusions:

• Macrocyclic encapsulation is a novel and effective strategy for enhancing the performance of MR-TADF emitters.
• This approach overcomes the limitations posed by intermolecular interactions in planar MR-TADF materials, leading to improved color purity and efficiency.
• The developed material represents a significant advancement in deep-blue OLED technology, demonstrating the potential of macrocyclic encapsulation for future display applications.