Synthesis and characterization of a new soluble, structurally well-definedconjugated polymer alternating regioregularly alkylated thiophene oligomerand 2,2 '-bipyridine units: Metal-free form and Ru(II) complex

The Pd-catalyzed Stille cross-coupling reaction has been used to synthesize novel pi-conjugated polymers based on regioregular 3-(octylthiophene) tetr amers alternated with either 2,2'-bipyridine or its Ru(II) complex (Ru(bipy )(3)(2+)). A preliminary optimization of the cross-coupling conditions enab led the synthesis of high molecular, structurally defined, and defect-free copolymers. Both are well-soluble in common organic solvents, which allowed their easy characterization by standard H-1 NMR and UV-visible spectroscop ies as well as by electrochemical techniques. Interestingly, H-1 NMR spectr a not only confirmed the structure of the synthesized polymers but also con tributed to estimating the length of polymer chains together with gel perme ation chromatography and light-scattering experiments. UV-visible experimen ts indicated that the delocalization of pi-orbitals occurs efficiently in o ur conjugated structures and involves both oligothiophene and metal-free or ruthenium chelating bipyridine units, while electrochemical experiments re vealed electronic interactions between the conjugated backbone and the ruth enium complexes in the metal-containing polymer.