Highly Efficient Electrochemiluminescence from Imidazole-Based Thermally Activated Delayed Fluorescence Emitters

Area of Science:

• Organic Chemistry
• Materials Science
• Photochemistry

Background:

• Thermally activated delayed fluorescence (TADF) emitters are crucial for efficient organic light-emitting diodes (OLEDs).
• Developing metal-free TADF emitters offers advantages in cost and environmental impact.
• Electrochemiluminescence (ECL) is a promising light-generation technique with diverse applications.

Purpose of the Study:

• To synthesize and characterize a new family of metal-free TADF emitters.
• To investigate the structure-property relationships of these emitters in electrochemiluminescence.
• To compare their performance against a standard ruthenium complex.

Main Methods:

• Straightforward, metal-free synthesis of novel TADF emitters.
• Systematic variation of donor moieties while keeping the acceptor fixed.
• Photophysical and electrochemical characterization.
• Evaluation of ECL performance with and without a co-reactant (benzoyl peroxide).

Main Results:

• Synthesized novel TADF emitters with excellent structural characterization.
• Achieved ECL efficiencies significantly exceeding the standard [Ru(bpy)₃ ]Cl₂ (up to 28x with benzoyl peroxide, 38x in annihilation).
• Found electrochemical reversibility to be the primary factor for efficiency, more so than photoluminescence quantum yield or excited-state lifetime.
• Demonstrated that annihilation ECL efficiency is pulse sequence-dependent.
• Showed that the imidazole moiety can be functionalized for practical applications.

Conclusions:

• A new class of highly efficient, metal-free TADF emitters for ECL applications has been developed.
• Electrochemical properties, particularly redox reversibility, are key determinants of ECL performance.
• The modular design allows for tuning and integration into functional devices.