Electrogenerated Chemiluminescence of Aromatic Hydrocarbon Nanoparticles in an Aqueous Solution

We report the preparation, characterization, and electrogenerated chemiluminescence (ECL) of rubrene nanoparticles (NPs) and 9,10-diphenylanthracene (DPA) nanorods. The organic NPs were prepared in an aqueous phase using a simple reprecipitation method, i.e., injecting a solution of the hydrocarbon in an organic solvent into water. The resulting NPs can be collected and redispersed to form stable colloidal solutions in water. Rubrene forms spherical nanoparticles (NPs) (diameter similar to 50 nm), while DPA initially forms nanorods with an average size of similar to 500 nm in length and similar to 50 nm in diameter. DPA nanorods grew gradually with time into wires with diameters of similar to 1 mu m and lengths of similar to 10 mu m. ECL emission from these NPs was observed upon electrochemical oxidation in aqueous solutions containing different co-reactants, such as tri-n-propylamine for rubrene and an oxalate ion for DPA NPs. The ECL intensity from rubrene NPs was significantly higher than that from DPA NPs because of the smaller size, and thus there is a higher diffusion coefficient for rubrene as compared to that of DPA NPs.