Two-Dimensional Electrochemiluminescence: Light Emission Confined at the Oil–Water Interface in Emulsions Stabilized by Luminophore-Grafted Microgels

We describe a method to confine electrochemiluminescence (ECL) at the oil–water interface of emulsion droplets that are stabilized by luminophore-grafted microgels. These hydrogel nanoparticles incorporating covalently bound Ru­(bpy)₃²⁺ as the luminophore are irreversibly adsorbed at the interface of micrometric oil droplets dispersed in a continuous aqueous phase. We study the electrochemical and ECL properties of this multiscale system, composed of a collection of droplets in close contact in the presence of two types of model coreactants. ECL emission is observed upon oxidation of the coreactant and of the luminophore. ECL imaging confirms that light is emitted at the surface of oil droplets. Interestingly, light emission is observed more than 100 μm far from the electrode. It is possibly due to the interconnection between redox-active microgels, making an entangled two-dimensional network at the dodecane–water interface and/or to some optical effects related to the light propagation and refraction at different interfaces in this multiphasic system. Confining ECL in such an inhomogeneous medium should find promising applications in the study of compartmentalized systems, interfacial phenomena, sensors, and analysis of single oil droplets.