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_nPhA, where n is the number of carbon atoms in the alkyl chains, n = 12), was newly designed synthesized in order to investigate the supramolecular ordered structures induced by phase separation, hydrogen (H)-bonding, and π-π stacking interaction. This symmetrically tapered d-C₁₂PhA biphenylamide consists of three different parts: H-bondable 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 ₁₂PhA biphenylamide were characterized by differential calorimetry (DSC), one-dimensional (ID) wide-angle X-ray diffraction (WAXD), ID and 2D Fourier-transform infrared spectroscopy (FT-IR), and solid-state ¹³C nuclear magnetic resonance (NMR). The symmetrically tapered d-C₁₂PhA biphenylamide formed a columnar (φ_H) liquid crystalline (LC) mesophase at a cooling process and a highly ordered columnar (φ_HK) crystalline phase at a subsequent heating process. Selected area electron diffractions (SAED) from single crystals combined with the results WAXD and POM suggest that discotic building blocks are constructed by three d-C₁₂PhA biphenylamides rotating 60° with respect to neighboring ones and the ABC stacked discotic building blocks further self-assemble into columns and then these columns laterally close-packed to give nanorods. Furthermore, it was identified that the long axis of column is parallel to the long axis of rods.