In situ resonance Raman spectroscopy of polyazulene on aluminum

Polyazulene (PAz) has been electrochemically deposited on different electrode substrates. The films were characterized with Raman and UV-vis spectroscopy. The spectroelectrochemical studies were performed in situ during p- and n-doping (electrochemical oxidation and reduction, respectively). The focus of this work was mainly on the charging and discharging reactions of PAz on Al substrates. The results were compared to the corresponding results obtained from PAz on Pt substrates. Three different excitation wavelengths (514, 633, and 780 nm) were used in the Raman experiments and the resonance enhancement effect was observed when changing the wavelength of the excitation line. The vibrational behavior of PAz deposited on Al was very similar to that of PAz deposited on Pt during p-doping. Furthermore, it was found that the vibrational responses during p- and n-doping are different indicating that the electronic structure of PAz is not the same during positive and negative charging. It was concluded that PAz is not reversibly n-doped on Al. The n-doping on Pt was shown to be more reversible. In this paper, the important correlation between UV-vis and Raman spectroscopy is discussed as well as the correlation between doping-induced infrared active bands and Raman bands of neutral PAz.