A spectroscopic study of the growth and redox processes of electrodeposited polybithiophene films

Electrochemically prepared polybithiophene films were characterized during polymerization and as a function of the redox potential via in situ measurements of absorption and fluorescence spectra. Ex situ measurements of the fluorescence of undoped films were performed as a function of temperature and film thickness. The absorption spectra were observed to depend significantly on the film thickness, showing that the morphology of the films changes during the polymerization, while the fluorescence spectra are independent of the film thickness and attributed to the longest-conjugation-length segments in the film. The absorption spectra of the p-doped polymer films were obtained from reflectance and transmission spectra recorded during the polymerization and reduction process. The shape of the spectra and, in particular, the position of the extinction maximum, that we observe at 692 nm, differs significantly from previously reported results. On the other hand, the energy of the extinction maximum is close to the calculated singlet excitation energies of oligothiophene bications.