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

Abstract

A family of novel Thermally Activated Delayed Fluorescence (TADF) emitters have been synthetized by a straightforward and metal-free synthesis, and structurally characterized. In this work we keep fixed the acceptor moiety, 4-(1H-imidazol-1-yl)benzonitrile, and systemically tested different donors to correlate their photophysical and electrochemical properties with their performance in electrochemiluminescence using both benzoyl peroxide as coreactant and coreactant free (annihilation) conditions. Some compounds exceed the efficiency of the standard [Ru(bpy)3]Cl2 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 redox processes rather than by the photophysical properties in terms of photoluminescence quantum yield or excited state lifetime. In addition, the annihilation electrochemiluminescence efficiency strongly depend on the pulse sequence. The imidazole moiety can be conveniently alkylated allowing the insertion of functional groups, such a carboxylic acid, enabling practical applications.