Raman Studies On Several Conducting Polymers

Conducting polymers are novel materials with wide potential applications. Mucheffort has been devoted to understand and utilize them both theoretically andexperimentally. Although Raman spectroscopy has been found to be an effective toolfor study conducting polymers, up to date, researches in this field are far fromsufficient. Thus, in present dissertation, we study three conducting polymers,polyfuran (Pfu), polynaphthalene (Pnap) and polyaniline (Pani) by using Ramanspectroscopy. Polyfuran consists of simple heteroaromatic rings in its chain back bone.Although its structure is relatively simple, the assignments of its Raman spectra arestill controversial. We obtained the Raman spectra of Pfu with different excitationlasers, and the results indicated that the oxidized species are "the second component"of "the second component of the bimodal distribution of conjugation lengths" shownin the Raman spectra reported by other research groups. The charge carrier of dopedPfu was determined by absorption spectra. Combined with the results of quantumcalculation, the Raman assignments of doped Pfu were provided. Polynaphthalene is formed by direct inter connection of polynuclear rings.Raman spectra assignments of Pnap are not reported because of its relative complexstructure. We characterized the structure of Pnap. Together with the results ofquantum calculation, the Raman bands of pristine Pnap have been assigned. Moreover,bands of chain stretching in Raman spectra of Pnap move to higher wavenumberswith the increasing of the polymerization degree, which shows a contrary trend toconducting polymer containing simply aromatic rings, such as polythiophene,polypyrrole, etc. It is mainly because that the dihedral angles of inter-rings enhancedwith the increase of polymerization degree, which leads that longer polymer chain hasa worse conjugation expansion. Polyaniline differs from the common conjugated polymers since it is constitutedby non-direct interconnection of simple aromatic rings. It was uncertain whether the - II -Abstractrules concluded from other simple conducting polymers were applicable to Pani. Wefound that the doping level of electrochemically deposited Pani films increase withthe increase of film thickness. It is coincide with other conducting polymers, and thisphenomenon is resulted from the easier diffusion of counter ion in the more porous ofthicker Pani films. Furthermore, we studied the Raman spectra of the three groundstates of Pani during the heating and cooling processes, and their conformationchanges were discussed.