Aniline Derivatives Situ UV - Visible Spectrum Electrochemical Research

Polyaniline (PAN) has been widely applied to rechargeable batteries,electrocatalysis, chemical biosensor, electrochromic due to its high conductivity, goodredox reversibility, environmental stability etc, so it has caused many peoplesattention. At the same time, there are a lot of reports about functions of PAN. While italso has some disadvantages, for example, the structure of PAN, physical andchemical properties are significantly influenced by pH. Aniline derivatives withspecial functional groups can overcome the weakness to a certain extent.Copolymerization of aniline and its derivatives can not only overcome the shortage,but also further improve properties of aniline.In the copolymerization process, conductive mechanism and various propertiesattract significant interest. The conventional electrochemical methods are difficulty toaccurately reflect the electrode/solution interface changes, but in situultraviolet-visible (UV-vis) spectroscopy can effectively recognize and detect theshort-lived intermediates formed during electrooxidation of aniline and its derivatives.The paper includes three sections as followed:1. In situ UV-vis spectroelectrochemical and cyclic voltammetry (CV)techniques have been used to investigate the homopolymerization andcopolymerization of diphenylamine (DPA) and o-aminophenol (OAP) in4.0mol/LH2SO4solutions. The research results indicate that, DPA and OAP are firstly oxidizedto form their cation radicals during the electrochemical copolymerization, a mixeddimer intermediate is formed through the cross-reaction between the cation radicals ofDPA and OAP and the monomers of DPA and OAP. The new absorption peak at508nm in the UV-vis spectra is assigned to this intermediate. Moreover, it demonstratesthat the copolymerization process is related to the concentration ratio of DPA andOAP. When concentration of DPA becomes dominated, it will inhabit electrooxidationof OAP, further inhabiting the copolymerization of DPA with OAP.2. Electrochemical copolymerization of o-phenylenediamine (OPD) witho-methoxy aniline (OMA) in1.0mol/L HCl solution has been studied using cyclic voltammetry (CV) and in situ UV-vis spectroelectrochemical techniques employingindium tin oxide (ITO)-coated glass electrodes as working electrode. From results ofCVs, it can be seen that the different voltammetric characteristics between thehomopolymerization and copolymerization processes exhibit the occurrence of thecopolymerization, and the different electrochemical behaviors for thecopolymerization of OMA and OPD with different concentration ratios show thedependence of copolymerization on the concentration ratios of OMA and OPD in thefeed. At a constant potential of0.9V, the in situ UV-vis spectroelectrochemical resultsreveal the formation of a mixed oligomer intermediate in the initial stage ofcopolymerization through the cross-reaction of the cation radical of OMA and OPD.The absorption peaks located at403-422nm and482-492nm in the UV-vis spectraare assigned to different structure intermediates. The results can also be confirmed byderivative cyclic voltabsorptogram (DCVA). The transformation between oxidizedintermediate and reduced intermediate can be detected in the UV-vis spectra atsweeping potential. The copolymer has also been characterized by using Fouriertransform infrared spectroscopy (FT-IR).3. The in situ UV-vis spectroelectrochemical study on the homopolymerizationand copolymerization of m-phenylenediamine (MPD) and o-methoxy aniline (OMA)has been performed using indium tin oxide (ITO)-coated glass electrodes as workingelectrode in1.0mol/L H2SO4. The results indicate that at0.9V potential, MPD andOMA are respectly oxidized to form the m-phenylenediamine cation radical (MPDCR)and o-methoxy aniline cation radical (OMACR) during the electrochemicalcopolymerization of MPD and OMA, and then a mixed dimer/oligomer intermediateis formed by the cross-reaction between MPDCR and OMACR. Thecopolymerization of MPD and OMA will be restricted with increase of MPDconcentration in solution. To further study on copolymerization of MPD and OMA,cyclic voltammetry (CV) technique has been used to investigate thehomopolymerization and copolymerization of MPD and OMA with differentconcentration ratios, it reveals that MPD shows low conductivity; copolymerizationprocess is related to the concentration ratio of MPD and OMA. With DCVA, electron transfer situation of fixed wavelength can be detected at different potential.