ORGANOMETALLIC TERTHIOPHENE DERIVATIVES - MODULATION OF THE TERTHIOPHENE CORE OF 5,5''-DIPHENYL-2,2' 5'2''-TERTHIOPHENE VIA [CPRU](+) AND [CP-ASTERISK-RU](+) SUBSTITUENTS/

We have utilized electrochemical, UV-vis absorption/emission spectrosc opy, and UV-vis spectroelectrochemistry to investigate the electronic structure of 5,5 ''-diphenyl-2,2':5'2 ''-terthiophene (Ph(2)Tth) and t he complexes [Cp/CpRu(eta(6)-Ph(2)Tth)]PF6 and [(Cp/Cp*Ru)(2)(eta(6), eta(6)-Ph(2)Tth)](PF6)(2) (Cp=cyclopentadienyl; Cp=pentamethylcyclope ntadienyl). Uncomplexed Ph(2)Tth behaves as if the 2,2':5'2 ''-terthio phene (Tth) core has two weakly conjugated, sterically blocking phenyl group substituents. The nature of the phenyl substituents are altered by complexation with ''Cp/CpRu+'' to create [Cp/Cp*Ru(phenyl)](+) su bstituents. Electrochemical studies show that Ph(2)Tth exhibits two re versible oxidation processes that produce the radical cation and dicat ion forms of the Tth core. The complexes of Ph(2)Tth also exhibit loca lized Tth core oxidations that have E degrees s shifted to more positi ve potentials by about 150 mV per metal center. This shift is attribut ed to the positive charge of a [Cp/CpRu-(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 trans ition for the Tth core is sensitive to the nature of the substituent a nd is red shifted by metal complexation. The complexes exhibit room te mperature emission that is quenched by intramolecular processes involv ing the metal center and additionally by acetonitrile. For the Cp comp lexes in acetonitrile, quenching leads to decomplexation of Ph(2)Tth; fur the Cp complexes, no decomplexation is observed. Spectroelectroch emical studies show that the radical cations of Ph(2)Tth and the monor uthenated complexes exhibit a small degree of pi-dimerization at room temperature; the diruthenated complexes show no evidence of pi-dimeriz ation. Studies of the complexes with [Cp/CpRu(phenyl)](+) substituent s indicate that the properties of the Tth core can be modulated by the transition metal substituent(s).