Thiophene oligomers have been studied so far mainly for their semiconductor and charge-transport properties. However, these compounds are also highly fluorescent and soluble. Solubility and fluorescence frequencies and efficiencies can be tailored by means of appropriate functionalization of the aromatic backbone. Functionalization with the isothiocyanate group (-N=C=S) allows these molecules to form covalent bonds with NH2-containing biomolecules and give rise to optically and chemically very stable fluorescent bioconjugates. Examples of photostable conjugates formed with monoclonal antibodies are reported.