Electrochemical investigation of 2-[8-hydroxyquinoline-5-yl)azo]benzo[$c$]cinnoline on a platinum electrode in dimethysulfoxide

Abstract

2-[8-hydroxyquinoline-5-yl)azo]benzo[c]cinnoline was synthesized for the first time and shown to possess electrochromic characteristic, i.e. changing color during the forward and back electrolysis at --1.35 V and 0.00 V, respectively, in DMSO medium. Therefore, the electrochemical investigation of this compound appears to be worthwhile. The electrochemical reduction of 2-[8-hydroxyquinoline-5-yl)azo]benzo[c]cinnoline was investigated by cyclic voltammetry, controlled potential electrolysis, and chronoamperometry techniques in the presence of 0.10 mol L$^{-1}$ tetrabutylammonium tetrafluoroborate in dimethyl sulfoxide at platinum electrode. 2-[8-Hydroxyquinoline-5-yl)azo]benzo[c] cinnoline displays three sharp cathodic peaks and three anodic peaks in the cyclic voltammogram. The diffusion coefficients and the number of electrons transferred were calculated by using an ultramicroelectrode and platinum electrode. The number of transferred electrons was found to be one for each peak. The standard heterogeneous rate constant for reduction was calculated by the Klingler--Kochi technique. The electrochemical reduction mechanism of 2-[8-hydroxyquinoline-5-yl)azo]benzo[c]cinnoline was also investigated by using various electrochemical techniques, such as bulk electrolysis, and spectroscopic methods, like electron spin resonance spectroscopy. Bulk electrolysis results also provided evidence for each peak belonging to reduction of one electron, two of which were confirmed by electron spin resonance spectroscopy. This new chemical is found to be an electrochromic substance.