Electrochemiluminescence of surface bound microparticles of ruthenium complexes

The ability to study electrochemiluminescence (ECL) and related phenomena in solids is Crucial to practical applications such as novel analytical and light-emitting devices. In this study we have used electrochemical, spectroscopic and Surface techniques to explore the solid-state electrochemistry and electrochemiluminescence properties of two ruthenium complexes: [Ru(dpp)(3)](PF6)(2) and [Ru(tmp)(3)](PF6)(2) (where dpp is 4,7-diphenyl-1,10-phenanthroline and tmp is 3,4,7,8-tetramethyl-1,10-phenanthroline). We employed a novel method for the characterization of solid-state ECL properties by using surface bound microparticles of these compounds. For light-emitting devices and other solid-state applications it is essential to determine the mobility of charged species, electrons and ions. and thus emphasis has been given to the measurements of transport properties. In the solid-state, stable voltammetric responses have been observed for both materials, characterized by semi-infinite linear diffusional charge transport at relatively fast scan rates. The deposits call be also exhaustively oxidized at longer experimental timescales, exhibiting finite diffusional type voltammetric behaviour. We show that the oxidation and reduction rate depend not only on the Structure of the phenanthroline ligand but also On the identity and concentration of the anion of the Supporting electrolyte. This Suggests that ion insertion/desertion into the solid is rate limiting rather than electron self-exchange. In situ electrochemical AFM reveals that initial redox cycling, necessary to "break-in" the system, is accompanied by Subtle morphological changes, implying that the cycling promotes an electrochemical change in the solid phase. Electrochemiluminescence was observed from the microparticle films when oxidized in the presence of a Suitable coreactant. The intensity of ECL is lower compared to the Solution phase system because the reaction with the coreactant occurs only ill the surface of each particle. Annihilation between the sequentially oxidized and reduced forms of the material, which likely Occurs in the bulk of the solid rather than at the surface, produces ECL which is notably more intense.