ELECTROCHEMICAL OXIDATION OF POLYANILINE IN NONAQUEOUS ELECTROLYTES - IN-SITU RAMAN-SPECTROSCOPIC STUDIES

Spectroelectrochemical behavior of polyaniline in nonaqueous electrolytes has been studied by Raman spectroscopy using two excitation Lines: blue (457 nm) and infrared (1064 nm). It has been demonstrated that in the electrolytic solution consisting of tetrabutylammonium tetrafluoroborate/diphenyl phosphate/acetonitrile both oxidation processes (oxidation of leucoemeraldine to emeraldine and emeraldine to pernigraniline) can be investigated by Raman spectroscopy. The blue excitation line is very insensitive to the oxidation and protonation changes occurring during the first oxidation process and reveals only the reduced segments of polyaniline chains. However in the second oxidation process significant changes in the Raman spectra occur, consistent with the formation of pernigraniline units accompanied by deprotonation of the polymer. No Raman spectrum can be recorded for the most reduced form of polyaniline using the infrared excitation line. However gradual oxidation of the polymer results in the appearance of the Raman bands characteristic of the oxidized units which are strongly resonantly enhanced. The infrared Line is extremely sensitive toward the existence of protonated segments and allows for direct monitoring of the deprotonation processes occurring during the second oxidation process (i.e. the oxidation of emeraldine to pernigraniline).