Designing Supramolecular Liquid-Crystalline Hybrids from Pyrenyl-Containing Dendrimers and Arene Ruthenium Metallacycles

The association of the arene ruthenium metallacycle [Ru₄(<i>p</i>- cymene)₄(bpe)₂(donq)₂][DOS]₄ (bpe = 1,2- bis(4-pyridyl)ethylene, donq = 5,8-dioxydo-1,4-naphtoquinonato, DOS = dodecyl sulfate) with pyrenyl-functionalized poly(arylester) dendrimers bearing cyanobiphenyl end- groups is reported. The supramolecular dendritic systems display mesomorphic properties as revealed by polarized optical microscopy, differential scanning calorimetry and small- angle X-ray scattering measurements. The multicomponent nature of the dendrimers and of the corresponding host–guest supramolecules (i.e., end-group mesogens, dendritic core, pyrene unit, aliphatic spacers, and metallacycle) leads to the formation of highly segregated mesophases with a complex multilayered structure due to the tendency of the various constitutive building-blocks to separate in different organized zones. The pyrenyl dendrimers exhibit a multilayered smectic A-like phase, thereafter referred to as LamSmA phase to emphasize this unaccustomed morphology. As for the corresponding Ru₄–metallacycle adducts, they self-organize into a multicontinuous thermotropic cubic phase with the <i>Im</>3¯<i>m</i> space group symmetry. This represents a unique example of liquid- crystalline behavior observed for such large and complex supramolecular host–guest assemblies. Models of their supramolecular organizations within both mesophases are proposed.