Rational Design of the First Nonspherical Dendrimer Which Displays Calamitic Nematic and Smectic Thermotropic Liquid Crystalline Phases

The synthesis of the racemic AB₂ rodlike mesogenic monomer based on conformational isomerism, 13-hydroxy-1-(4-hydroxyphenyl)-2-(4-hydroxy-4″-p-terphenylyl)tridecane (5), and the preparation via the convergent approach of its first four generations of monodendrons and dendrimers are described. All monodendrons and dendrimers exhibit thermotropic cybotactic nematic, smectic, and crystalline phases which are generated from the anti conformation of the structural repeat unit derived from 5, and therefore, they do not exhibit a spherical shape. The dependence of various transition temperatures on the generation number or on the molecular weight of these monodendrons and dendrimers follows trends similar to those of linear main chain liquid crystalline polymers containing rodlike mesogenic units. However, at similar molecular weights the viscosity of the nematic phase of these dendrimers is lower than that of the corresponding hyperbranched and linear polymers. This novel class of liquid crystalline dendrimers opens many new synthetic, theoretic, and practical opportunities in the fields of dendrimers and molecular, macromolecular, and supramolecular liquid crystals.