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The effect of molecular structural changes on the mesomorphic nature of a new class of macrocyclic columnar liquid crystal is reported. Twenty-six new compounds with general molecular structure I were prepared, characterized and compared.Only dodecasubstituted ester derivatives 2d-h exhibit thermotropic mesophases. The design of mesogens based on these new, unusual macrocyclic cores requires the presence of the following structural elements: twelve aliphatic side chains, esters as bridging units and small R groups on the core.

The effect of structural variations on the mesomorphic nature of columnar liquid crystals of general structure I is studied. X-ray crystal structure analyses of compounds l a and 2a reveal the columnar organization of the macrocyclic cores in the solid state. The up and down asymmetry ofthe cores is resolved in an alternating sequence of u p u p and down-down intermolecular contacts. Specific interactions between the R substituents are present, which influence the stacking distance between the cores in the down-down intermolecular contacts. Statistical incorporation of different side chains on the same macrocyclic core produces, when the difference in length between the alkyl chains is appropriate, random mixtures having wide mesomorphic ranges. The increase of disorder associated with the statistical side chain distribution on the core and with the structural heterogeneity of each component of the mixture have the effect of depressing mainly the crystalmesophase transition temperature.

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A series of multi-armed macrocycles with molecular weights up to 4400 Da was studied by desorption chemical ionization. Both negative-and positive-ion spectra exhibited excellent signal-to-noise ratio, despite the limited amount of material sampled (0.1-1 pmol). The molecular ions generally represent the base peaks of the spectra, but the extent of fragmentation increases as the source temperature is raised.