Directional dispersion in quaterthiophene single crystals and oriented thin films

Optical spectra of both single crystals and thin films of quaterthiophene are reported. The measured absorbance spectra of single crystals show a strong dependence on the angle of incidence as a consequence of the direction and high oscillator strength of the corresponding bu exciton transition. A similar behaviour can be observed for polycrystalline films deposited on potassium acid phtalate crystals, thus indicating that a preferential orientation of the domains both azimuthally and texturally can be induced on the whole area of the sample by the interaction between the molecule and the substrate. However, in the case of films two possible domain orientations are found, whose relative probability have been estimated and found to depend on the deposition conditions.