To assess the effects of molecular symmetry on the phase transitions of columnar liquid crystals, we prepared a family of 19 discotic mesogens. This series of dibenzophenazine derivatives allowed us to compare the differences in phase transitions between sixteen pairs of isomers that differed in terms of their overall symmetry. It was found that the more symmetrical isomer had a significantly higher melting temperature in all but one case, whereas symmetry appeared to have a lesser impact on clearing temperature. A similar relationship between symmetry and melting point is also observed for triphenylene-based discotic mesogens; in these systems, the clearing points show a stronger dependence on molecular symmetry.

Salts of bis [[1,1′-biphenyl]-2,2′-diolato-O,O′] borate (4) were prepared by the reaction of boric acid with 2,2′-dihydroxybiphenyl in the presence of various cations. Ten salts were crystallized, and their structures were solved by X-ray diffraction. In all cases examined, spiroborate 4 favors enantiomeric (R,R) and (S,S) structures with a flattened D 2 geometry. Moreover, the crystals analyzed all incorporate the two enantiomers in a 1:1 ratio, even when the cations themselves are chiral and enantiomerically pure. In crystals of certain salts (NH 4 + , NH 2 Me 2 + , NMe 4 + , PPh 4 + , and MBA + ), the packing of spiroborate 4 can be considered to define homochiral layers; in other salts, however, the organization of the anions is helical (NMe 4 + ), columnar (NPr 4 + ), or can be described as either layered or columnar (NBu 4+ and NPent 4 + ). These variations presumably arise because neighboring anions are not positioned reliably by strong directional interactions between them. Derivatives of spiroborate 4 that can engage in such interactions are expected to have well-defined molecular geometries and to serve as effective subunits for engineering crystals and other ordered materials with predetermined structures and properties.

Several recent reports have claimed that catechol and its derivatives undergo electropolymerization when oxidized to form poly(o-phenylene)s. We demonstrate that the products of these electrochemical reactions are likely triphenylene derivatives rather than polymeric materials.

Three series of dibenzo[a,c]phenazines were prepared in an order to assess the impact of side chain position on the phase stability of columnar liquid crystals. Each series was composed of four isomeric compounds differing only in the disposition of hexyloxy and decyloxy chains around the central aromatic core, giving rise to electronically similar compounds with varying shapes and symmetries. The substitution pattern was found to have a moderate effect on the clearing transition of the liquid crystal but a larger impact on the melting temperatures. These observations suggest a viable strategy for controlling the phase range of liquid crystals via judicious choice of peripheral chain structure and location.

The photochromism of two 2,3-diarylbenzo[g]quinoxaline derivatives was explored. Irradiating 2,3-diphenylbenzo[g]quinoxaline with 350 nm light led to the formation of its photodimer, which could be reverted to its monomers either thermally or photochemically.The resulting photodimer absorbs at a longer wavelength than analogous dianthracene derivatives. 2,3-Dipyridylbenzo[g]quinoxaline was also observed to undergo photodimerization. The ability of these readily prepared benzoquinoxaline derivatives to undergo [4 + 4]-photocycloaddition reactions makes them attractive alternatives to anthracene derivatives.