| Like [6]Helicenebisquinones bearing four side chains, those with three side chains are easily prepared from a cheap dye-intermediate, in this case sodium 4-hydroxynaphthalene-2,7-disulfonate.; The silicon-based (TIPS) side chains allow are easily removed and replaced by ether or ester moieties. Those newly introduced side groups affect the properties of the materials, especially the tendency to self assemble. With dodecyl side chains, the compounds forms long fibers of stacked molecules. With some other ether-based residues, the compounds still aggregate in a similar fashion but fibers are not formed. Instead, columnar liquid crystalline phases are observed. With ester-based chains, no aggregation was observed.; When one of the quinone rings is reduced and acylated with benzyloxyacetyl chloride, the compound (when dissolved in dodecane) aggregates into columns that in turn form a nematic liquid-crystalline phase. This phase can be oriented with an electric field so that the direction of the columns is parallel to it. The sample then shows circular-difference effect in second-harmonic generation. Moreover, the sign of the effect is reversed, when the polarity of the electric field reverses, even though the handedness of the sample remains the same.; When reduced and methylated, [6]- and [7]helicenebisquinones can be selectively functionalized in the 2,15- and 2,17-positions respectively by electrophilic bromination, acetylation, and formylation. The functional groups introduced in this way can then be transformed into others (e.g. acetylenes). The remarkable selectivity is presumably due to the electron donating effects of the methoxy groups in positions 6,11 (for [6]helicene) and 6,13 (for [7]helicene). Also, the methoxy groups on the inner rim of the helicenes can be removed affording salicyl aldehydes and ketones. |
