Part I: Self-assembling dendrimers using the DDA-AAD hydrogen bonding motif. Part II: Supramolecular discotic liquid crystals through hydrogen bond mediated self-assembly.

摘要

In part I, a heterocyclic unit which contains complementary donor-donor-acceptor (DDA) and acceptor-acceptor-donor (AAD) (G·C-like) hydrogen bonding arrays at an angle of about 60° was used to self-assemble dendrimers into a hexamer. To investigate its ability to self-assemble higher generation dendrimers, second and third generation Fréchet-type dendron were attached to the 8-amino group the 2,8-diamino-2-N-ethylpyrimido-(4,5- b)[1,8] naphthyridine-3H-4-one subunit. Studies using 1H NMR, size exclusion chromatography (SEC) and dynamic light scattering (DLS) support the cooperative formation of cyclic hexamers in apolar solvents. The stability of the self-assembled dendrimers is dependent on the size of the attached dendron. Pair-wise mixing studies with different generation dendritic monomers indicate their usefulness in constructing dynamic combinatorial libraries.; In part II, the ability of this heterocyclic unit to generate a self-assembled structure in bulk was tested by attachment of a 3,4,5-tris-dodecyloxybenzyl group to the 8-amino group and evaluating the mesomorphic properties of the resulting derivative. Cumulative solution studies by 1H NMR, SEC and DLS indicate the formation of a hydrogen bonded cyclic hexamer in apolar solvents. The studies by differential scanning calorimetry (DSC), polarized light microscopy (PLM) and X-ray diffraction (XRD) indicate that the hexameric disks can stack in bulk to form thermotropic columnar mesophases. The mesophases exist across a large temperature range (>248°C).