Conducting Polymers Based on Alkylthiopyrroles

Abstract

Three 3,4-bis(alkylthio)pyrroles ( 5a − c ) were synthesized by a nonclassical pyrrole ring formation reaction followed by alkylation of the dithiol-2-one functional group. UV−vis absorption studies together with time dependent density-functional theory (TD-DFT) computations suggest that the monomers ( 5a − c ) display low-energy π−σ* transitions ( 5a, 254 nm; 5b, 232 nm; 5c, 240 nm) compared to pyrrole (208 nm). Cyclic voltammetry investigations show that the monomers 5a − c possess significantly lower oxidation potentials (0.60 V for 5a, 0.58 V for 5b, and 0.71 V for 5c ) than unsubstituted pyrrole (1.0 V). The corresponding polymers were successfully prepared by anodic electropolymerization and/or chemical oxidation (FeCl 3 as oxidant) and investigated by cyclic voltammetry, spectroelectrochemistry and in situ conductivity studies. Our investigations of monomeric 3,4-disubstituted pyrroles and corresponding polymers suggest that the electron donating alkylthio substituents at the 3- and 4-positions of the pyrrole ring play an important role for the electrochemical properties of polymers; e.g., the maximal conductivity of poly(ethylenedithiopyrrole) is ca. 10 times higher than that of poly[bis(propylthio)pyrrole].