Fine tuning of the electronic properties of linear pi-conjugated oligomers by covalent bridging.

A series of oligothienylenevinylenes, pi-conjugated oligomers rigidified by ethylene bridges attached at different sites of the conjugated backbone, have been constructed by multistep synthetic methodologies. Electronic absorption spectra show that the rigidification of the conjugated system produces a bathochromic shift of the absorption maximum and a narrowing of the HOMO-LUMO energy gap, as compared to the spectra of an open-chain reference compound. The cyclic voltammograms of all oligomers show that these compounds can be reversibly oxidized into their cation radicals and dications and that rigidification produces a large negative shift of the first oxidation potential, which is indicative of a considerable increase of the HOMO level.