Electrochemistry of functionalized azo azulenes

The electrochemical study of certain azulene bis azo derivatives meta or para substituted is connected to the potential applications (enhanced NLO coefficients [1] and electrochromic behaviour) of this type of compounds. New compounds were studied by cyclic (CV) and differential pulse voltammetry (DPV), in TBABF₄ 0.1 M, CH₃CN or CH₃CHCl₂ in order to find some rules regarding the influence of substituents position versus azo groups on the redox behaviour of azulene and azo groups. These electrochemical methods allowed establishing the oxidation and reduction processes characteristic for this type of compounds. Comparisons with common azo derivatives lead to conclusions regarding the enhanced azulene electro-reactivity in respect with aromatic structures [2]. The presence of two azo groups, especially when are para orientated, increases the polarization of the molecule, fact that facilitates the electrochemical generation of radical-ions. The presence of the alkyl substituents modifies both the electron density and the planarity of the azulene moiety toward the rest of the molecule. The modification of the glassy carbon electrodes with the polyazulene films was tested in view of obtaining new electrode materials [3]. The modulation of the structure parameters lead to important changes in the polymerization process being connected to the redox potentials and concentration in the synthesis solution. The formation of substituted poly-azo-azulene films was accomplished through electrochemical oxidation by scanning or controlled potential electrolysis. Conductive or isolating films have been obtained on glassy carbon, using CH₃CN or CH₃CHCl₂ as solvents and 0.1 M TBAP or TBABF₄ as supporting electrolytes [2], starting from differently substituted bis azo azulenes.