Redox behavior and electrochemiluminescence of transition metal complexes in mesoporous films
Description
This body of work outlines the modification of commercially available indium-doped tin oxide (ITO) on glass supports by a 1--10 mum thick film of nanocrystalline, optically transparent, semiconducting TiO 2, resulting in electrodes to which a higher than monolayer coverage of photochemically active dye can be effected. The purpose of this was twofold---to study the intrinsic behavior of transition metal complexes within TiO 2 films by a variety of spectroscopic and electrochemical methods, including electrogenerated chemiluminescence (also called electrochemiluminescence or ECL), and to explore the possibility of using this type of electrode as ECL sensors for small molecules A series of six different ruthenium tris(bipyridyl) chromophores, functionalized with varying numbers of either phosphonic or carboxylic acid moieties capable of adsorbing to metal oxides, were synthesized. Their adsorption to and behavior within mesoporous TiO2 films were studied by a number of techniques, yielding a wealth of information, such as the correlation between functional group number and loading yield of the semiconducting film and the nature of the adsorption process A segment of this work focuses on the electrochemiluminescent performance of the modified electrodes and documents a rather surprising result, the indirect observation of ion migration of Ru3+ within the film and away from the ITO surface in the presence of an applied potential. While this phenomenon prohibits the utilization of electrodes modified in this manner as anything other than qualitative sensors, its ascertainment lays the groundwork for the changes necessary to make a more efficient sensor The last chapter explores the possibility of prohibiting ion migration of the dye by permanently anchoring appropriately modified ruthenium diimine complexes to either the mesoporous TiO2, or ITO surface by covalent attachment. While covalent attachment of the dye to both surfaces was successful, neither method resulted in electrodes capable of observable ECL, and it was determined that another route will be required to bring about a quantitative sensor