Synthesis and characterization of a new soluble, structurally well-defined conjugated polymer alternating regioregularly alkylated thiophene oligomer and 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) tetramers alternated with either 2,2'-bipyridine or its Ru(II) complex (Ru(bipy)(3)(2+)). A preliminary optimization of the cross-coupling conditions enabled 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 spectroscopies as well as by electrochemical techniques. Interestingly, H-1 NMR spectra not only confirmed the structure of the synthesized polymers but also contributed to estimating the length of polymer chains together with gel permeation chromatography and light-scattering experiments. UV-visible experiments indicated that the delocalization of pi-orbitals occurs efficiently in our conjugated structures and involves both oligothiophene and metal-free or ruthenium chelating bipyridine units, while electrochemical experiments revealed electronic interactions between the conjugated backbone and the ruthenium complexes in the metal-containing polymer.