Columnar structures from asymmetrically tapered biphenylamide

An asymmetrically tapered N,N'-tris[[(2-dodecylaminocarbonyl)ethyl]methyl]- 4-biphenylamide (asym-C₁₂PhA, where n is the number of carbon atoms in the alkyl chains, n = 12) was newly designed and synthesized. In this asymmetrically tapered asym-C₁₂PhA biphenylamide, H-bondable hydrophilic amide moieties are located at between a rigid hydrophobic biphenyl rod and three flexible hydrophobic alkyl chains. Computer energy minimization indicated that three-dimensional (3D) geometry of asym-C₁₂PhA biphenylamide looks like a cone with dimensions of 3.01 nm in height and 1.44 nm in bottom radius. Phase transitions and supra- molecular structures were identified utilizing the combined techniques of differential scanning calorimetry, 1D wide-angle X-ray diffraction (1D WAXD), Fourier-transform infrared spectroscopy, and solid-state ¹³C nuclear magnetic resonance analyses. The asym-C₁₂PhA self-assembled into a highly ordered columnar mesophase just below the isotropization temperature and then transformed to 3D columnar crystalline phase (ø_Cr) on further cooling. Selected area electron diffractions in transmission electron microscopy (TEM) along with 1D WAXD and cross-polarized optical microscopy suggested that discotic building blocks were constructed by rotating 120° of three asym-C₁₂PhA with respect to neighboring ones and the tmb (top-middle-bottom) stacked discotic building blocks further self-organized into columns. These columns are laterally intercalated to form the ø_Cr phase. On the basis of the TEM image and polyethylene surface decoration technology, it was identified that the self-assembled asym-C₁₂PhA fibers with ̃1 μm in diameter and several millimeters in length were braids of tiny single crystals.