X-RAY-DIFFRACTION AND ULTVAVIOLET-VISIBLE ABSORPTION STUDIES ON ELECTROCHEMICALLY SYNTHESIZED POLY(THIOPHENE-3-METHANOL) FILMS

To investigate the effect of the CH2OH substituent on the energy gap o f polythiophene, and to study the possible long-range order in this po lymer, ex situ optical absorption and X-ray diffraction measurements w ere performed on electrosynthesized polythiophene-3-methanol (PTOH) fi lms. In addition, the evolution of the optical absorption of PTOH as a function of applied potential was followed in situ. The diffraction p attern of PTOH is similar to that of liquid thiophene and bithiophene with only one broad peak at Q=1.4 Angstrom(-1), indicating that despit e the two-dimensional deposition process of PTOH, its structure is exc eptionally disordered. The optical absorption spectrum of PTOH shows m aximum absorption at 3.05 eV, which corresponds to a conjugation lengt h of only 5-6 monomer units. Nevertheless, the evolution of the optica l spectrum upon oxidation is characterized by similar features as obse rved for polythiophenes of higher degree of conjugation, namely by a d ecrease in the intensity of the absorption due to valence to conductio n band transition and a simultaneous appearance of a new broad absorpt ion band at 1.65 eV. However, only low doping levels are obtained for PTOH. These results are discussed on the basis of the C-O-C coupling i n PTOH.