Electrochemical investigation into the interaction between various pyrrolemoieties and the well-known electron acceptor, tetracyanoethylene

The charge transfer (CT) complexes between tetracyanoethylene (TCNE) and va rious pyrrole moieties (pyrrole, N-methylpyrrole and N-phonylpyrrole) have been characterised by UV-vis spectroscopy with values for their extinction coefficients (epsilon), equilibrium constants (K), lambda (max) values, hea ts of formation (DeltaH), along with thermodynamic and kinetic information regarding their instability in solution being obtained. The tricyanovinylat ed products of the reaction between TCNE and the pyrrole moieties have been isolated and fully characterised. The three tri-cyanovinylated pyrrole spe cies namely, 2-tricyanovinyl-pyrrole (C4H4N-C5N3), 2-tricyanovinyl-N-methyl pyrrole (C5H6N-C5N3) and 2-tricyanovinyl-N-phenylpyrrole (C10H8N-C5N3), hav e been characterised electrochemically by cyclic and normal pulse voltammet ries. Each compound exhibits an irreversible anodic wave at more positive p otentials than the unsubstituted monomer species along with a reversible re duction based one-electron redox couple. The calculated diffusion coefficie nts are similar to solution phase species, C4H4N-C5N3 (3.77 x 10(-5) cm(2) s(-1)), C5H6N-C5N3 (1.099 x 10(-5) cm(2) s(-1)) and C10H8N-C5N3 (2.382 x 10 (-5) cm(2) s(-1)). The reduction based redox processes for all synthesised compounds exhibited facile kinetics with heterogeneous rate constants, k(0) , of 2.65 x 10(-2) cm s(-1) (C4H4N-C5N3), 1.35 x 10(-2) cm s(-1) (C5H6N-C5N 3) and 7.85 x 10(-3) cm s(-1) (C10H8N-C5N3) Conducting polypyrrole and poly (N-methylpyrrole) films were grown electrochemically, by both chronocoulome try and cyclic voltammetry from reaction solutions of TCNE and the various pyrrole moieties. However, it was found that it was possible to form conduc ting polymer films from acetonitrile solutions containing the monomer speci es (0.1 M) in the absence of background electrolyte and TCNE. Upon electroc hemical switching in various electrolyte solutions, between oxidised and re duced states the polypyrrole films exhibited cation movement as the predomi nant process that maintains charge neutrality. The latter films were unstab le towards electrochemical cycling with a loss of global electroactivity af ter ten scans. On the other hand the poly(N-methylpyrrole) films exhibited anion movement as the predominant process upon redox switching with the fil ms exhibiting a high level of stability towards electrochemical cycling. (C ) 2001 Elsevier Science Ltd. All rights reserved.