In situ Resonance Raman Spectroscopy of Polyazulene on Aluminum

Abstract

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.

Structural Electrochemistry from Freestanding Polypyrrole Films: Full Hydrogen Inhibition from Aqueous Solutions

“…This conclusion is in good agreement with the high spin [ 17,55,56 ] and charged state [ 57 ] content detected in reduced fi lms of conducting polymers by electron paramagnetic resonance (EPR) or Raman spectroscopy. Beyond the closing potential, both electronic and ionic fi lm conductivities must be high enough to allow the electrochemical reduction to go beyond -2.50 V. Most of the available analytical methodologies allow the detection of such high ionic concentrations in the fi lm.…”

Electrochemical polymerization and characterization of a poly(azulene)-TiO2 nanoparticle composite film

“…The reason is that the vibrations originating from quinoid and neutral units will be differently resonance enhanced by the applied excitation lines. Excitation with k exc = 514 nm enhances the resonance effect of the Raman lines originating from the neutral segments of the film, while excitation with k exc = 633 nm enhances more the vibrations associated with the quinoid units in the film [31]. It has also been shown that the D band shifts towards lower active frequencies with decreasing energy of the exciting laser line [29].…”

Electrochemical preparation of oligo(azulene) on nanoporous TiO2 and characterization of the composite layer

“…4a shows the CVs of OAz-TiO 2 composite layer when potential cycling was performed to 0.6, 0.9, and 1.0 V starting from -0.4 V. In each CV the third cycle in the respective potential region is shown. p-doping of OAz in the nanoporous TiO 2 layer starting at approximately 0 V in the positive potential scan demonstrates the electron donor property of OAz [21,[28][29][30][31][32]. The current response in the capacitive charging region of OAz-TiO 2 composite layer between -0.4 and 0.35 V depends strongly on the degree of the remaining charge in OAz after oxidation.…”

“…The absorbance of PAz in the UV and visible spectral regions is also rather broad [20][21][22][23][24][25][26] making PAz an attractive material for applications in solar cells. PAz has also been shown to have electron-donating properties [21,[28][29][30][31][32]. The oxidized form of the fused-ring monomer Az, resonancestabilized azulenylium carbocation, used in this study is very stable [33].…”