Abnormal anti-Stokes Raman scattering and surface-enhanced infrared absorption spectroscopy studies of carbon nanotubes electrochemically functionalized with poly(2,2′-bithiophene-co-pyrene)

Abstract A new composite material was synthesized via the electrochemical oxidation of 2,2′-bithiophene (BTh) and pyrene (Py) monomers dissolved in a solution of LiClO 4 in CH 3 CN onto a working electrode of Au coated with a film of single-walled carbon nanotubes (SWNTs). The interaction of the poly(2,2′-bithiophene-co-pyrene) (PBTh–Py) with the SWNTs and the orientation of the copolymer on the working electrode were studied by anti-Stokes and Stokes Raman scattering and FTIR spectroscopy in the grazing-incidence angle reflection geometry. The Raman lines at 1464 and 1435 cm −1 , attributed to the symmetric stretching modes of the C C bond in the quinoid and aromatic rings of the PBTh–Py copolymer, were observed when the working electrode is either a blank Au film or a Au support coated with a SWNT film. In the latter case, charge transfer occurs at the interface of the two constituents. This charge transfer leads to functionalization of the carbon nanotubes with the copolymer molecules. The presence of enhanced anti-Stokes Raman lines at −1461, −1435 and −1187 cm −1 indicates a resonant optical excitation process of the PBTh–Py/SWNT composite. The FTIR spectra acquired under polarized light for the PBTh–Py copolymer electrosynthesized on a bare Au support reveal significant changes in the absorption bands situated in the spectral ranges of 1000–1150 and 1550–1650 cm −1 that originate in the surface-enhanced IR absorption (SEIRA) processes. The functionalization of the SWNTs with the PBTh–Py copolymer is evidenced by the enhancement of the absorption of the FTIR bands at 793 and 846 cm −1 , which are assigned to the C S C deformation vibrational mode and the substituted benzene ring, respectively, due to the effects of steric hindrance that are induced for the copolymer molecules by the binding of carbon nanotubes.