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

A family of novel thermally activated delayed fluorescence (TADF) emitters has been synthesized by a straightforward and metal-free synthesis, and structurally characterized. In this work we kept the acceptor moiety, 4-(1H-imidazol-1-yl)benzonitrile, fixed and systemically tested different donors to correlate their photophysical and electrochemical properties with their performance in electrochemiluminescence using both benzoyl peroxide as co-reactant and co-reactant free (annihilation) conditions. Some compounds exceeded the efficiency of the standard [Ru(bpy)(3)]Cl-2 by up to 28 times with benzoyl peroxide and 38 times in annihilation. Interestingly, we found that the efficiency is mainly dictated by the electrochemical reversibility of the redox processes rather than by the photophysical properties in terms of photoluminescence quantum yields or excited-state lifetime. In addition, the annihilation electrochemiluminescence efficiency strongly depends on the pulse sequence. The imidazole moiety can be conveniently alkylated, thus allowing the insertion of functional groups, such a carboxylic acid, and enabling practical applications.

Automated summary

A family of novel thermally activated delayed fluorescence (TADF) emitters was synthesized by a simple and metal-free method, and their structures were characterized. The photophysical and electrochemical properties of different donors were systematically tested and correlated with their performance in electrochemiluminescence using benzoyl peroxide as a co-reactant or in annihilation conditions. Efficiency in electrochemiluminescence was mainly determined by the electrochemical reversibility of the redox processes rather than the photophysical properties, and the annihilation efficiency strongly depended on the pulse sequence. The alkylated imidazole moiety allowed for the insertion of functional groups, enabling practical applications.