FOURIER-TRANSFORM INFRARED-SPECTROSCOPY STUDY OF DOPANTS OF POLYPYRROLE

Electrochemically synthesized BF4-doped as-grown polypyrrole, PP(BF4), shows no clear sign of dopant in Fourier transform infrared reflection absorption spectroscopy (FTIR RAS) measurements, while measurement on the doped polypyrrole synthesized in electrolyte containing TCNQ and BF4, PP(TCNQ)(BF4), exhibits characteristic peaks due to TCNQ. The observed CH in-plane and out-of-plane modes and the ring modes of pyrrole rings were split in the FTIR RAS spectrum of PP(TCNQ)(BF4). The splitting indicates overlapping of the bands due to the polymer pyrrole ring and the TCNQ benzene ring. A newly appeared peak at 2140 cm-1 can be assigned to a band due to the nitrile group of TCNQ and its large frequency shift implies charge transfer from the polymer backbone to a TCNQ molecule, creating a TCNQ anion, or structural deformation at the hydrogen-deficient nitrogen site of the polymer backbone, creating -N = C = N-.