New Liquid Crystalline [2]Rotaxanes

This thesis presents design, synthesis and characterization of a range of new liquid crystalline interlocked molecules and to study structure-property relationships between rotaxane design and mesomorphism. Chapter 1 introduces concepts of supramolecular chemistry and liquid crystals and cooperative effect between [2]rotaxane and liquid crystals towards functional molecular machines. In Chapter 2, a systematic approach to introduce liquid crystallinity into the 1,2-bis(pyridinium)ethane/DB24C8 motif is described. The chapter begins with synthesis and purification of dumbbells (without macrocycle) and [2]rotaxanes (with macrocycle) substituted with purely aliphatic extended 3,5-disubstituted stoppers with increasing alkyl chain length. Chapter continues with phase characterization and structure-property relationships between dumbbells and rotaxanes. The dodecane chain was sufficiently fluid to induce smectic mesomorphism in both the dumbbell and [2]rotaxane, with [2]rotaxane forming SmA phase by POM and XRD analysis. Chapter 3 presents an extension to Chapter 2 with the addition of longer straight chain and branching aliphatic chains to our 1,2-bis(pyridinium)ethane/DB24C8 rotaxane motif to study structure-property relationships and phase characteristics. The ability of the side-chain to self-organized showed large differences in phase behaviour. The pentadecane straight chain extended [2]rotaxane exhibited a unidentified mesophase, the hexadecane straight chain [2]rotaxane showed SmA mesomorphism, the branched hexadecane and the hyperbranched [2]rotaxanes both showed lamellar soft crystal phases. Chapter 4 describes the effect of applying groups typical for low molecular weight LCs (siloxanes) to our 1,2-bis(pyridinium)ethane/DB24C8 motif and a modified rotaxane design based on a bis(oxymethylbenzylpyridinium)ethane/DB24C8 motif. The structure-property relations between both systems, and in comparison with the dodecane chain substituted systems, are presented. The new design revealed SmC mesophases for both the dodecane and siloxane substituted [2]rotaxanes. Chapter 5 focuses on the introduction of chirality into the siloxane substituted [2]rotaxane with SmC mesomorphism presented in Chapter 4. Chirality was introduced via a chiral anion as well as incorporation of a chiral crown. Observations to changes in the superstructure from the incorporation of chirality is addressed. The chiral anion exchanged [2]rotaxane showed SmC* mesomorphism and the chiral crown [2]rotaxane showed SmX* mesomorphism. Chapter 6 presents the design and synthesis of a molecular shuttle based upon the structure-property relations determined from the previous chapters