UPS studies of conducting polymers: dopant effect on conjugated polymer systems sensitive to conductivity

The valence bands of polypyrrole doped with various types of dopant have been investigated in order to clarify the polymer configurations associated with lattice distortion due to the dopants. Ultraviolet photoemission spectroscopy (UPS) spectra of doped and reduced polypyrrole exhibits two characteristic shoulders theoretically assigned to 2b1 and 1a2 π-orbitals. Increase of the density of states (DOS) at the 2b1 level and decrease of the DOS at 1a2 observed in the doped state indicate that doping affects the 2b1 valence band related with π-orbitals of the N atom, which suggests the lattice distorted structure of the conjugated polymer system. Valence bands of samples doped with cyclic and polycyclic compounds give different spectrum profiles due to the π-electron systems.