Efficient annihilation electrochemiluminescence of [Ru(bpy)3]2+ within a deep eutectic solvent as green electrolyte

The generation of annihilation electrochemiluminescence (ECL) is typically limited to highly purified organic solvent-supporting electrolyte solutions or ionic liquids. Herein, we have prepared a deep eutectic solvent (DES) based on choline chloride (ChCl) and lactic acid (LA), which was directly used to investigate the annihilation ECL of [Ru(bpy)3]2+ for the first time. [Ru(bpy)3]2+ could be oxidized to stable [Ru(bpy)3]3+ radicals, while reduced to unstable [Ru(bpy)3]+ radicals in ChCl-LA DES. Moreover, [Ru(bpy)3]3+ was sufficiently stable on the time scale to react with [Ru(bpy)3]+ in ChCl-LA DES, resulting in the generation of intense annihilation ECL by a potential scanning or pulsing. This annihilation ECL system was further integrated into chitosan (CS) for the formation of homogenous and microporous ChCl-LA DES/CS/[Ru(bpy)3]2+ ionic gel, which was used as the emitting layer in ECL devices (ECLDs). The display performances for the ECLDs were demonstrated based on the efficient annihilation ECL in the ionic gel, giving bright light-emission visible to naked eye. Hence, this work confirmed the possibilities for studying annihilation ECL and its application in ECLDs using green DESs and CS materials.