Ruthenium complex charge-transfer process

The ruthenium oligothienylacetylide complexes 93 (Chart 5.30) [106] and the oligothienylferrocene complexes 94a and b were electrochemically polymerized [107]. The voltammetry of poly-94a and poly-94b films contains redox waves due to both the ferrocene and backbone redox couples. Low-energy absorption bands appear upon oxidation of both the Fe centers and the conjugated backbone in the UV-Vis-near-IR spectrum of the films, and these have been attributed to charge-transfer processes. The poor solubility of 94b prevents electropolymerization at room temperature however, polymer films can be prepared at elevated temperatures. Electropolymerization of 95, in which hexyl chains have been added to increase the monomer solubility, has also been reported [108]. 

One such example involves a ruthenium tris(bipyridine) complex, illustrated in Fig. 4.24, in which the metal can accept energy from photons and transfer it to the bipyridine ligands. The process of metal to ligand charge transfer is a well known phenomenon in coordination chemistry and the experimental conditions needed to form the complexes are fairly well understood. Added complexity is encountered when the bipyridine units have been modified as in the work of Hammarstrom [47],... 

Polynuclear metal complexes are more suited for water oxidation catalyst because of their nature to act as multielectron transfer reagents in addition to the fact that charge delocalization can lead to stabilization of the catalyst rather than decomposition during the process. The trinuclear ruthenium complexes Ru-red and Ru-brown, [(NH3)sRu-0-Ru(NH3)4-0-Ru(NH3)j] - (Ru "-Ru" -Ru" ) and [(NH3)sRu-0-Ru(NH3)4-0-Ru(NH3)5] + (Ru -Ru" -Ru ), respectively, have been shown to be efficient water oxidation catalysts for oxygen evolution with high turnover numbers When Ru-red was dissolved in an acidic aqueous solution, it underwent one-electron oxidation with the formation of Ru-brown. When Ru-brown was dissolved in a basic solution, the complex underwent reduction to produce Ru-red. The one-electron oxidation and reduction of the Ru-red and Ru-brown has already been well established (Eq. 11) 6 65-6 )... 

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