ELECTROCHEMISTRY OF NEW HETEROAROMATIC-COMPOUNDS OF PYRROLOPYRROLE

An electrochemical study of new bicyclic heteroaromatic compounds, viz., 1,3,4-and 1,2,4-trimethyl-1,4-dihydropyrrolo[3,2-b]pyrroles(1,3,4- and 1,2,4-TMPP[3,2-b]) was carried out. 1,3,4-TMPP[3,2-b] could be electropolymerized on basalplane pyrolytic graphite (BPG), In-Sn oxide conducting glass (ITO), and Pt and Au electrodes, while 1,2,4-TMPP[3,2-b] could not be electropolymerized. The polymeric film (poly-1,3,4-TMPP[3,2-b]) prepared from 1,3,4-TMPP[3,2-b] was electroactive in both acetonitrile and aqueous solutions. The film displayed an electrochromic property, i.e., the oxidized form is reddish purple and the reduced one is almost transparent. The conductivity of the oxidized form was 7.0 x 10(-10) S/cm at 298 K. The energy gap of this polymer film was estimated to be 3.10 eV. The film thickness (phi) was linearly related to the amount (Q) of charge passed during the electropolymerization, with Q in the range of 0-15 mC/cm2 (slope of the phi-vs. Q plot: 4.7 x 10(-4) cm3/C). Based on the electrochemical behavior of a series of pyrrolo[3,2-b]pyrroles examined in this study and in previous works (1-3), it was found that the anodic peak potentials of these monomers as well as the formal redox potentials (E-degrees') of the polymers shift in the positive direction with an increase in the number of the methyl groups on the pyrrolo[3,2-b]pyrrole ring. The electropolymerization of 1,4-dihydropyrrolo[3,2-b]pyrrole, 1,4-dimethyl-1,4-dihydropyrrolo[3,2-b]pyrrole, and 1,3,4-TMPP[3,2-b]proceeds mainly via alpha - alpha-coupling.