Water-compatible electrogenerated chemiluminescence effect derived from readily accessible tripyridinium salts

Considering that numerous studies have shown pyridinium salts can be reduced electrochemically to form cationic radicals, we wonder whether these cationic radicals can further react with co-reactants to create excited-state species that display electrogenerated chemiluminescence (ECL). Herein, four tripyridinium salts were synthesized using a simple method, achieving relatively high yields of over 87%. Optical and electrochemical analyses revealed that these tripyridinium salts, which feature a large conjugated system, demonstrated notable electrochemical and photoluminescent properties. Most importantly, when paired with potassium persulfate as a co-reactant, distinct ECL behavior was observed even in water, with emissions detected at around 478 nm. The maximum ECL efficiency (Φ_ECL) of the synthesized salts, using Ru(bpy)₃²⁺ as a reference, was found to be 10.2%. Furthermore, we conducted a detailed investigation into the luminous mechanism behind ECL generation from the tripyridinium salts.