Phosphorescence emission from spatial stacks of phenanthrene units in oligo(9,10-phenanthrene)s.

The covalent linkage of phenanthrene units at 9 and 10 positions resulted in a broadening of the absorption band and a red-shift of the fluorescence band in ethanol compared with its monomer. Spatial stacking of phenanthrene units also altered the spectral shape of phosphorescence emission, and the oligomer film emitted phosphorescence at room temperature.

Stacking Control by Molecular Symmetry of Sterically Protected Phthalocyanines.

The synthesis and characterization of two phthalocyanine (Pc) structural isomers, 1 and 2, in which four 2,6-di(hexyloxy)phenyl units were attached directly to the 1,8,15,22- or 1,4,15,18-positions of the Pc rings, are described. Both Pcs 1 and 2 exhibited low melting points, i.e., 120 and 130 °C respectively, due to the reduction in intermolecular π-π interaction among the Pc rings caused by the steric hindrance of 2,6-dihexyloxybenzene units. The thermal behaviors were investigated with temperature-controlled polarizing optical microscopy, differential scanning calorimetry, powder X-ray diffraction, and absorption spectral analyses. Pc 1, having C4h molecular symmetry, organized into a lamellar structure containing lateral assemblies of Pc rings. In contrast, the other Pc 2 revealed the formation of metastable crystalline phases, including disordered stacks of Pcs due to rapid cooling from a melted liquid.