Secondary Donor Engineering for High-Efficiency Orange-Red Thermally Activated Delayed Fluorescence Emitters

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Achieving efficient orange-red emission in thermally activated delayed fluorescence (TADF) materials is hindered by the difficulty in balancing small singlet-triplet energy gaps and high radiative decay rates.
• Molecular design strategies are crucial for optimizing excited-state properties in TADF emitters.

Purpose of the Study:

• To propose and investigate a modification site engineering strategy for secondary donors to enhance orange-red emission in TADF materials.
• To synthesize and characterize two isomeric emitters, ND28DBT and ND37DBT, based on a naphthalimide-dimethylacridine core with dibenzothiophene units.

Main Methods:

• Synthesis of isomeric TADF emitters ND28DBT and ND37DBT.
• Theoretical analysis of excited-state properties.
• Photophysical characterization including photoluminescence quantum yield (PLQY) and external quantum efficiency (EQE) measurements.

Main Results:

• ND37DBT exhibited a more favorable excited-state configuration, promoting efficient reverse intersystem crossing (RISC) and accelerated radiative decay.
• ND37DBT achieved a high PLQY of 70%, a fast RISC rate of 6.25 × 10^5 s^-1, and an excellent EQE of 22.1%.
• Minimal efficiency roll-off was observed for ND37DBT at 100 cd m^-2.

Conclusions:

• Precise control over secondary donor modification sites is a powerful strategy for designing high-efficiency orange-red TADF materials.
• The proposed strategy successfully led to the development of ND37DBT, a promising candidate for advanced optoelectronic applications.