Abstract
Four unconventional triazine-based dendrimers have been prepared and characterized by (1) H and (13) C NMR spectroscopies, mass spectrometry, and elemental analysis. Based on DSC studies, polarizing microscopy, and powder XRD, two of these dendrimers, containing linkers with an odd number of carbon atoms, were observed to display columnar liquid-crystalline phases during thermal treatment. However, the other two dendritic analogues, containing linkers with an even number of carbon atoms, were not observed to behave correspondingly. Based on computer simulation, we reasonably assume that the dendrimers with an odd number of carbon atoms in their linkers distort their molecular shape and adopt two isomeric structures due to asymmetrical congestion. This reduces the molecular π-π face-to-face interaction, which in turn causes the dendrimers to form columnar LC phases during thermal treatment. However, the dendrimers with an even number of carbon atoms in their linkers have more symmetrical skeletons and do not display any liquid-crystalline phase upon thermal treatment. This new strategy should be applicable for eliciting the columnar liquid-crystalline properties of other types of unconventional dendrimers with rigid frameworks.
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