Synthesis and characterization of oligo/polythiophenes bearing stable radicals

Abstract

Two categories of verdazyl radical functionalized oligothiophenes have been prepared: 1,5-diisopropyl-6-oxoverdazyl radical directly linked to terthiophene (2.6), and 1,5- diisopropyl-6-oxoverdazyl radical attached to terthiophene through a π system bridge, e.g., pyridine (2.11). Compound radical 2.6 was prepared by a two step process starting with the condensation of terthiophene carboxaldehyde and 2,4-diisopropylcarbonhydrazide bis-hydrochloride to give the tetrazane 2.5, which was subsequently oxidized chemically to give the corresponding verdazyl radical grafted at the 3’ position of the terthiophene moiety. The latter displays excellent stability toward organic solvents and moisture. The electropolymerization of radical 2.6 resulted in the formation of its polymer (poly(2.6)), which was characterized by cyclic voltammetry and infrared spectroscopy. The electrochemical oxidation of the tetrazane, 2.5, yielded surprisingly a poly(terthiophene) bearing verdazyl radical, with similar electrochemical and infrared properties of those found for the polymer produced in the electro-oxidation of the terthiophene bearing verdazyl radical (poly(2.6)). Moreover, the electrochemical oxidation of 2.5 (beyond its oxidation potential of the tetrazane motif) affords the radical 2.6. A similar strategy has been used for the synthesis and the characterization of tetrazane 2.10 and its corresponding verdazyl 2.11.