OPTICAL AND STRUCTURAL-PROPERTIES OF ELECTRODEPOSITED POLYBITHIOPHENEFILMS DURING THE FILM GROWTH AS A FUNCTION OF THE REDOX POTENTIAL

The optical properties of p-doped polybithiophene films were investiga ted during the polymerization and discharging process using in situ sp ectroscopy, while the fluorescence and absorption spectra of the undop ed films were ex situ monitored as functions of the film thickness and temperature. The in situ absorption spectra of polybithiophene were o bserved to depend significantly on the film thickness showing that bot h the mean effective conjugation length of the polymer chains and the morphology of the films changes during the polymerization. The absorpt ion maximum at 692 nm is assigned to bicationic segments. The similarl y structureless absorption spectrum of undoped polybithiophene exhibit s a maximum at 480 nm which corresponds to a conjugation length of 7 t hiophene units, whereas the red-shifted fluorescence spectrum shows a well-resolved vibrational structure and is attributed to the longest-c onjugation length segments (ca. 11 thiophene units) in the film.