ULTRAVIOLET PHOTOELECTRON-SPECTRA OF ELECTROPOLYMERIZED POLYMERS - POLYAZULENE, POLYPYRENE AND POLYCARBAZOLE

Ultraviolet photoelectron spectra (UPS) of electrochemically synthesized conducting polymers, polyazulene, polypyrene and polycarbazole, are measured. When the polymers are doped with either ClO4- or BF4-, the spectral onsets move toward the Fermi level (E(F)), which is related to an improvement of the electric conductivity upon doping. As the bandgaps of both doped polycarbazole and polypyrene estimated from UPS are more than 1 eV, their expected conductivities are poor. On the other hand, doped polyazulene gives virtually 0 eV bandgap, which agrees well with its reported high conductivity. UPS of polycarbazole and polypyrene correspond with those of gaseous carbazole and pyrene, respectively, which suggests a small interaction between the monomer molecules in these polymers. UPS of polyazulene and azulene show poor correspondence, which indicates a strong interaction between the azulene units in the polymer. The difference between these two groups is discussed from the point of view of molecular conformation derived from steric hindrance.