Redox behavior, chromatographic and spectroscopic characterization of some reactive pconjugated π-conjugated 4′-tricyanovinylhydrazone dyes

A series of pi-conjugated nonlinear 4'-tricyanovinylhydrazone (TCH) dyes was synthesized and characterized. The redox behaviors of the TCH dyes were studied by direct current (DC), and derivative polarography (DP), cyclic voltammetry (CV) and controlled potential coulometry (CPC). Excluding the nitro derivatives, the DC and DP polarograms of the compounds at pH < 5 showed two irreversible waves (peaks) corresponding to reduction of the C=C- and the hydrazone ( C=N-) groups. The DC and DP polarography of the nitro derivatives at pH < 5 showed three waves (peaks). Plots of cathodic peak current (i(p),(c)) vs. square root of scan rate (v(1/2)) and log i(p,c) vs. log v at -0.59 and -0.93 V at pH 4.46 were linear. The kinetic parameters (log k(f,h,)(o) Delta G* and D) of the compounds were determined. Poor correlations for substituents on the E-1/2 of the dyes with the Hammett substituent constants were noticed. Based on the chromatographic separation, spectroscopic characterization and molecular weight determination of the end products of the electrolyzed species of 4'-nitrotricyanovinylhydrazone, an electrochemical reduction mechanism is proposed.