Phase behaviors and structures of a symmetrically tapered biphenylamide.

A symmetrically tapered N,N'-bis[tris[(2-dodecylaminocarbonyl)ethyl]methyl]]-4,4'-biphenylamide (d-C(n)PhA, where n is the number of carbon atoms in the alkyl chains, n = 12), was newly designed and synthesized in order to investigate the supramolecular ordered structures induced by phase separation, hydrogen (H)-bonding, and pi-pi stacking interaction. This symmetrically tapered d-C(12)PhA biphenylamide consists of three different parts: H-bondable hydrophilic amide moieties, a rigid hydrophobic biphenyl aromatic core, and three flexible hydrophobic alkyl chains at each end of the core. Major phase transitions and supramolecular structures in d-C(12)PhA biphenylamide were characterized by differential scanning calorimetry (DSC), one-dimensional (1D) wide-angle X-ray diffraction (WAXD), 1D and 2D Fourier-transform infrared spectroscopy (FT-IR), and solid-state (13)C nuclear magnetic resonance (NMR). The symmetrically tapered d-C(12)PhA biphenylamide formed a hexagonal columnar (Phi(H)) liquid crystalline (LC) mesophase at a cooling process and a highly ordered columnar (Phi(HK)) crystalline phase at a subsequent heating process. Selected area electron diffractions (SAED) from single crystals combined with the results of WAXD and POM suggest that discotic building blocks are constructed by three d-C(12)PhA biphenylamides rotating 60 degrees with respect to neighboring ones and the ABC stacked discotic building blocks further self-assemble into columns and then these columns are laterally close-packed to give nanorods. Furthermore, it was identified that the long axis of column is parallel to the long axis of rods.