We have utilized electrochemical, UV-vis absorption/emission spectroscopy, and UV-vis spectroelectrochemistry to investigate the electronic structure of 5,5 "-diphenyl-2,2’:5’2 "-terthiophene (Ph(2)Tth) and the complexes [Cp/Cp*Ru(eta(6)-Ph(2)Tth)]PF6 and [(Cp/Cp*Ru)(2)(eta(6),eta(6)-Ph(2)Tth)](PF6)(2) (Cp=cyclopentadienyl; Cp*=pentamethylcyclopentadienyl). Uncomplexed Ph(2)Tth behaves as if the 2,2’:5’2 "-terthiophene (Tth) core has two weakly conjugated, sterically blocking phenyl group substituents. The nature of the phenyl substituents are altered by complexation with "Cp/Cp*Ru+" to create [Cp/Cp*Ru(phenyl)](+) substituents. Electrochemical studies show that Ph(2)Tth exhibits two reversible oxidation processes that produce the radical cation and dication forms of the Tth core. The complexes of Ph(2)Tth also exhibit localized Tth core oxidations that have E degrees s shifted to more positive potentials by about 150 mV per metal center. This shift is attributed to the positive charge of a [Cp/Cp*Ru-(phenyl)](+) substituent. The electronic absorption and emission spectra of the complexes are also indicative of the Tth chromophore. The lambda(max) of the pi-pi* transition for the Tth core is sensitive to the nature of the substituent and is red shifted by metal complexation. The complexes exhibit room temperature emission that is quenched by intramolecular processes involving the metal center and additionally by acetonitrile. For the Cp complexes in acetonitrile, quenching leads to decomplexation of Ph(2)Tth; fur the Cp* complexes, no decomplexation is observed. Spectroelectrochemical studies show that the radical cations of Ph(2)Tth and the monoruthenated complexes exhibit a small degree of pi-dimerization at room temperature; the diruthenated complexes show no evidence of pi-dimerization. Studies of the complexes with [Cp/Cp*Ru(phenyl)](+) substituents indicate that the properties of the Tth core can be modulated by the transition metal substituent(s).