Phase behaviors and supra-molecular structures of a series of symmetrically tapered bisamides

Abstract

A series of symmetrically tapered 1,4-bis[3,4,5-tris(alkan-1-yloxy)benzamido] benzene bisamides (CnPhBA, where n is the number of carbon atoms in the alkyl chains, n = 10, 12 and 16), was synthesized in order to investigate the effect of alkyl chain length on supra-molecular ordered structures induced by hydrogen (H)-bonding and micro-phase separation. These bisamides consist of a rigid aromatic bisamide core with three flexible alkyl chains at each end of the core. Major phase transitions and their origins in CnPhBA bisamides were studied with differential scanning calorimetry, one-dimensional (1D) wide angle X-ray diffraction (WAXD), infrared spectroscopy, and solid-state carbon-13 nuclear magnetic resonance experiments. The structures of these compounds in different phases were identified using 2D WAXD from oriented samples and were also confirmed by selected area electron diffractions in transmission electron microscopy from stacked single crystals and by computer simulations. All of the CnPhBA bisamides in this series formed a highly ordered oblique columnar (W OK ) phase and a low-ordered oblique columnar (W OB ) phase, similar to a recent report on C14PhBA.1 The two main driving forces in the formation of these two supra-molecular columnar structures were identified: One was the H-bond formation between N-H and CLO groups, and the other was the micro-phase separation between the bisamide cores and the alkyl chains. With increasing the length of alkyl tails, the isotropization temperature decreased, while the disordering temperature of the alkyl tails increased. The 2D lattice structures perpendicular to the columnar axis also increasingly deviated from the pseudohexagonal packing with increasing the alkyl tail length. However, the alkyl tail length did not have a significant influence on the packing along the columnar axis direction. Utilizing polarized optical microscopy, the phase identifications were also supported by the observation of texture changes and molecular arrangements inside of the micro-sized domains.

Alkyl Tail Length Dependence of Structures in a Series of Symmetrically Tapered Bisamides Exhibiting Self‐Assembled Supramolecular Columnar Phases

“…10, even). [1,2] However, the alkyl tail length did not have a significant influence on the packing along the column (c ¼ 0.96 nm). No liquid crystalline (LC) columnar phase was observed.…”

“…10, even). [1,2] Dramatic structure and phase behavior differences between C8PhBA and other CnPhBA bisamides were observed. This finding indicated that the C8PhBA having eight carbons in its alkyl tails represents a transition…”

“…It was found that all of these CnPhBA bisamides formed a highly ordered oblique columnar (F OK ) phase and a low-ordered oblique columnar (F OB ) phase. [1,2] To study the dependence of structure on alkyl chain length in this series of symmetrically tapered bisamides, we focus on the structural and phase transitions of CnPhBA (n¼6 and 8) via differential scanning calorimetry, one-dimensional (1D) and 2D wide angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy. Structural evolutions and phase identifications were also supported by texture changes observed by polarized optical microscopy.…”

“…[1,2] The final compounds were purified through repeated chromatography with a silica gel using an acetone-benzene (5 : 95) mixture as the eluting solvent, followed by recrystallization from an ethanol-benzene mixture and vacuum drying. The purity of the materials was verified by thin layer chromatography (TLC) and nuclear magnetic resonance (NMR).…”

“…[1,2] It was found that a disc-building block was generated through the intermolecular H-bonding of four CnPhBA, and these supramolecular discs further self-assembled into two oblique columnar phases. The highly ordered oblique columnar (F OK ) phase at low temperatures transformed into the low-ordered oblique columnar (F OB ) phase at high temperatures before the isotropic melt (I).…”