Optical properties of oriented thin films of oligothiophenes

Optical absorption and photoluminescence of both unsubstituted and alkyl-substituted 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 linear optical properties, are observed upon molecular deposition onto properly cleaved potassium acid phtalate substrates. X-ray diffraction data and optical 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 unsubstituted and laterally substituted oligothiophenes provides novel information on the electronic structure of these compounds