Research On The Self-assembly And Supramolecular Chiralty Of Dumbbell And V-shaped Rigid-flexible Molecules

Supramolecular assemblies are able to respond to external stimuli by reversibly transfering their strcutures to exhibit special functions resulting from the non-colvant interactions between building blocks, which earned great interest of chemists. Here, we studyed self-assembly and supramolecular chirality of amphiphiles consisting of hexa-p-phenylene conjugated carbazole moieties on both ends and V-shaped aromatic segment connected by a m-pyridine unit respectively.Unlike conventional linear liquid crystal molecules, herein we introduce flexible blocks perpendicularly into both ends of linear aromatic rod to synthesize a new end-capped aromatic amphiphiles. By changing the branched oligoether chains which is tetrabranch 6 or linearbranch 7, we tuned the cross sectional area of the interface between rigid and flexible parts to prepare chiral columnar liquid crystal and nonchiral columnar crystal. The assembled structures were investigated using differential scanning calorimetry(DSC), X-rayscatterings, polarized optical microscopy(POM), circular dichroism(CD). For the strong tendency of anisotropic crystalline ordering, the rod of 7 aggregated in one dimension with an ABAB forming 2D hexagonal columnar crystals. With the same volume fraction of coil segments but increasing of the branch, the larger repulsive force between adjacent molecules and decreasing anisotropy interaction leads to a assembly of chiral hexagonal columnar liquid crystal.In addition, in order to discuss the hydrogen bond effect within the assembly of the rod blocks. We folded linear block into 120 o, and introduced a proton acceptor N atom into the rigid body center. The hydrogen bonds of N-H-O in molecule 22 were tested by Raman spectroscopy in the assembly of molecule 22 in aqueous solution, with –OH bonded to the ends of the rigid blocks. Transmission electron microscopy(TEM) and atomic force microscopy(AFM) showed molecules 22 assembled into ?at sheets consisting of a zigzag conformation based on hydrogen bonding within the rod forming a film in micron scale. When –OH was protected by-CH3, Vapor pressure osmometry(VPO) test indicated molecule 23 assembled into hexameric macrocycles drived by weak J-stacking and hydrophlic-hydrophobic effect, and then stacked into hollow nanotubes by π-π stacking of the macrocycles. Due to steric selectivity of the flexible blocks, molecular chirality successfully transferred to the tubular supramolecular structure.