ELECTROCHEMICAL INVESTIGATION OF RUTHENIUM AND OSMIUM OLIGOTHIOPHENE COMPLEXES - HOW DOES METAL-BINDING AFFECT OLIGOTHIOPHENE PI-SYSTEM

We have studied the electrochemistry of a series of oligothiophene com plexes with one or more ''CpRu+'' ''CpRu(+)'', or ''CpOs(+)'' fragmen ts (Cp=cyclopentadienyl; Cp=pentamethylcyclopentadienyl) attached to the oligothiophene pi-system. This series varies the metal (Ru or Os), ancillary ligand (Cp or Cp), ring substituents (phenyl or methyl gro ups), and length of the oligothiophene (1-4 rings). The peak potential s for the oxidation of the free oligothiophenes and their complexes in dicate that the electron hole produced upon oxidation of tile complexe s is delocalized on the uncomplexed rings of the oligothiophene. Oxida tion of the complexes results in conductive films-on the electrode but the composition of the electrodeposited films is unclear. The electro n added upon reduction of the complexes is localized on the [Cp/CpM(t hiophene)](+) unit formed by complexation of the oligothiophene. We pr opose that complexation of a thiophene ring converts it into a [Cp/Cp M(thiophene)](+) unit and removes it from conjugation with the remaini ng, uncomplexed rings. The unbound rings function as a shortened, meta l-substituted oligothiophene unit. Complexation of oligothiophenes by ''CpRu+'', ''CpRu(+)'', and ''CpOs(+)'' fragments is a rational metho d for controlling the properties of oligothiophenes.