Chain-length dependent para-phenylene film- and needle-growth on dielectrics

Surface unit cells of vacuum grown ultrathin films of blue-light emitting para-phenylene oligomers on alkali halides and on muscovite mica have been determined using low energy electron diffraction. Both, films from upright and from laying molecules are grown on alkali halide (1 0 0) and mica (0 0 1) single crystal faces. On alkali halide (1 0 0) faces the ordered growth of upright phenylene molecules with several rotational domains is observed, whereas on mica (0 0 1) single crystalline aggregates (“nanofibers”) of laying molecules are formed. Their mutual parallel orientation is strictly determined by the orientation of mica surface dipoles. Structural information from diffraction experiments is complemented by morphological information using fluorescence- and atomic force microscopy as well as UV/vis absorption spectroscopy.