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

Spectroelectrochemical behavior of polyaniline in nonaqueous electroly tes has been studied by Raman spectroscopy using two excitation Lines: blue (457 nm) and infrared (1064 nm). It has been demonstrated that i n the electrolytic solution consisting of tetrabutylammonium tetrafluo roborate/diphenyl phosphate/acetonitrile both oxidation processes (oxi dation of leucoemeraldine to emeraldine and emeraldine to pernigranili ne) can be investigated by Raman spectroscopy. The blue excitation lin e is very insensitive to the oxidation and protonation changes occurri ng during the first oxidation process and reveals only the reduced seg ments of polyaniline chains. However in the second oxidation process s ignificant changes in the Raman spectra occur, consistent with the for mation of pernigraniline units accompanied by deprotonation of the pol ymer. No Raman spectrum can be recorded for the most reduced form of p olyaniline using the infrared excitation line. However gradual oxidati on of the polymer results in the appearance of the Raman bands charact eristic of the oxidized units which are strongly resonantly enhanced. The infrared Line is extremely sensitive toward the existence of proto nated segments and allows for direct monitoring of the deprotonation p rocesses occurring during the second oxidation process (i.e. the oxida tion of emeraldine to pernigraniline).