Electronic and structural characteristics of five poly membered heterocycles (polythiophene, polypyrrole): An ultraviolet and x‐ray photoelectron spectroscopy study

The electronic and structural properties of electrochemically synthetized five poly membered heterocycles [polypyrrole (PP), poly‐N‐methylpyrrole (PNMeP), polythiophene (PT), polybithiophene (PBT), and poly‐3‐methylthiophene (PMeT)] in their doped conducting and undoped semiconducting states have been determined by x‐ray photoelectron spectroscopy (XPS) and UV photoelectron spectroscopy (UPS). A systematic evolution of the π bonding orbitals is observed by going successively from thiophene to bithiophene and to terthiophene which leads finally to the formation of an intrinsic π bonding band for the undoped polythiophene, located at 1.05 eV below the Fermi level Ef. This π bonding band is also detected with PP, PBT, and PMeT in good agreement with theoretical band structure calculations and implies a long range order along the polymeric chains. In contrast, PNMeP valence spectra exhibit broad features connected with the existence of structural defects and/or torsion angle between the monomeric units. Shake...