Search

A novel optically active quinquethiophene monomer bearing at the C-β position of thiophene ring a linear C6 alkyl chain and an enantiomerically pure chiral alkyl group, namely 3,3⁗-di n-hexyl-4′,3‴-di[(S)-(+)-2-methylbutyl]-2,2′:5′,2″:5″,2‴:5‴,2⁗-quinquethiophene, has been synthesized and characterized. The regioregular optically active polymer deriving from oxidative polymerization of the monomer has also been characterized. The spectroscopic and chiroptical properties of the polymeric derivative, in particular, indicate enhanced conjugation extension with respect to similar poly(3-alkylthiophene)s reported in the literature and the presence of supramolecular chiral conformations in the microaggregate state.

Ester-functionalized poly(3-alkylthienylene)s were obtained by chemical oxidation with FeCl3. Substituents with both different total length and different distance of the ester group from the thiophene ring were examined. The main reaction solvent studied was chloroform which gave polymers with high molecular weight and incomplete conversion of the monomer. Some polymers were synthesized with a new procedure involving the precipitation of FeCl3 from a saturated nitromethane solution by a tetrachloride solution of the monomer. In this way, lower molecular weights and complete monomer conversion were obtained. The effect of different substituent groups on the polymer microstructure was examined using 1H NMR spectroscopy. With both polymerization procedures, the regioregularity and absorption maximum in the visible spectrum increase with increasing length of the oligomethylenic spacer between thiophene ring and ester group.