Optical properties of oriented thin films of oligothiophenes

Optical absorption and photoluminescence of both unsubstituted and alkyl-su bstituted oligohiophenes thin films, grown on various inorganic and organic substrates with the Molecular Beam Deposition technique, have been studied . Dramatic orientation effects, associated with large dichroism in the line ar optical properties, are observed upon molecular deposition onto properly cleaved potassium acid phtalate substrates. X-ray diffraction data and opt ical anisotropy are consistent with a card pack supramolecular organization , In which the separation between the molecules and their orientation with respect to the substrate are strongly affected by the lateral substitutions . The polarization behavior of the optical excitations in films of both uns ubstituted and laterally substituted oligothiophenes provides novel informa tion on the electronic structure of these compounds.