Spectroelectrochemical properties of the poly[(2,5-bisoctyloxy)-1,4-phenylenevinylene]/single-walled carbon nanotube composite

Abstract

Using surface-enhanced Raman scattering (SERS) and photoluminescence (PL) studies, new data concerning the electrochemical oxidation both of poly[(2,5-bisoctyloxy)-1,4-phenylene-vinylene] (BO-PPV) and the BO-PPV/HIPCO single-walled carbon nanotubes (SWNTs) composite are presented in this paper. The SERS studies performed at the excitation wavelengths of 752nm and 532nm of the BO-PPV/SWNTs composite that ensure the resonant excitation of the semiconductor and metallic nanotubes, respectively, reveal that the mixing of the two constituents results, on the one hand, in an isolation of semiconducting nanotubes from the bundles containing both metallic and semiconducting tubes and, on the other hand, in a functionalization of metallic SWNTs with BO-PPV. The isolation of semiconducting SWNTs is demonstrated by the narrowing of the G band and the change of the ratio between the intensities of the Raman lines situated in the low-frequency range that are assigned to the radial breathing vibrational modes. An additional isolation of the semiconducting nanotubes from the SWNTs bundles is reported when an electro-oxidation of the BO-PPV/SWNTs composite was performed in the potential range of (0; +2)V vs. Ag/AgCl. According to the Fourier transformed infra-red (FTIR) spectra and the SERS studies performed at an excitation wavelength of 1064nm, the chemical interaction of BO-PPV with HIPCO SWNTs reveals a charge transfer between the two constituents that leads to the formation of BO-PPV covalently functionalized SWNTs. The BO-PPV luminescence quenching effect induced by the presence of SWNTs that consists of a change in the relative intensities of the three PL bands of the polymer peaked at 1.73eV, 1.9eV and 2.07eV is due to the metallic tubes. The appearance of a new emission band at 2.32eV was regularly observed when electrochemical oxidation of the BO-PPV/SWNTs composite was performed in the potential range of (0; +2)V. The PL band at 2.32eV corresponds to ClO4− ions, which compensates the positive charges of BO-PPV generated during the electrochemical doping process.