Surface films obtained by electrochemical oxidation of 1,11-bis(3-indolizinin-2-ylquinoxalin-2-on-1-yl)-3,6,9-trioxyundecane

Abstract

Electrochemical oxidation of 1,11-bis(3-indolizinin-2-ylquinoxalin-2-on-1-yl)-3,6,9-trioxyundecane in 0.1 M Et4NClO4 in MeCN on a glassy-carbon electrode leads to surface films of two types depending on the film formation mode. Oxidation at controlled first-peak potentials (E p 1 = 0.30 V relative to Fc/Fc+) or in the range of potentials −0.60 → +0.40 → −0.60 V, −0.60 → +0.40 → −1.60 → −0.60 V in the polycycling mode forms a redox-active film that covers the entire surface of the electrode. The quinoxaline fragments of the film are reduced irreversibly in the supporting solution, while the indolizine fragments are reduced reversibly, forming stable radical cation states; the latter are recorded by ESR in the form of a singlet with a variable width (g = 2.0025, ΔH = 0.15−0.5 mT). The oxidized (radical cation) form of the film is conductive, while the neutral film is not. An insulating film is obtained when oxidation is performed under rigid conditions (−0.60 → +1.70 → −1.70 → −0.60 V). Both types of film are colored and have nanosized pores (channels), which can play a discriminant role. It is demonstrated (using the discriminant role of pores) that small molecules may be selectively reduced on film-coated electrodes in the presence of bulkier and more reactive substrates.