Molecular Assembly and Ferroelectric Response of Benzenecarboxamides Bearing Multiple-CONHC_(14)H_(29) Chains

摘要

Five simple benzenecarboxamide (BC) derivatives bearing multiple —CONHC_(14)H_(29) chains—N,N'-bis-(tetradecyl)-l,4-benzenedicarboxamide (2BC), N,N',N"-tri-(tetradecyl)-1,3,5-benzenetricarboxamide (3BC), N,N',N",N"-tetra(tetradecyl)-l,2,4,5-benzenetetracarboxamide (4BC), N,N',N",N'",N""-penta(tetradecyl)benzene-pentacarboxamide (5BC), and N,N',N",N'",N"",N'""-hexa~ (tetradecyl)benzenehexacarboxamide (6BC)—were examined in terms of their molecular assemblies in solution, organogels, liquid crystals, and solids as well as their phase transition behavior and dielectric responses. The molecular assemblies of compounds 3BC—6BC were dominated by the intermolecular N—H O= hydrogen-bonding interactions along the π-stacking directions and formed one-dimensional π-stacking nanofibers. The excellent organogelation characteristics of compound 3BC were observed in common organic solvents such as ethanol, acetonitrile, acetone, and N,N-dimethylformamide, whereas compounds 4BC and 6BC formed organogels in hexane and/or toluene. Mechanical fraying of the three-dimensional entangled nanofibers in the organogel state resulted in a two-dimensional cobweb-like nanofiber network, where the typical height and width of each nanofiber on the substrate surface were ca. 3.5 and 200 nm, respectively. A single nanofiber was constructed by a π-stacking column through intermolecular N—H 0= hydrogen-bonding interactions, of which the hexagonal arrangement resulted in ordered hexagonal columnar (Col_(ho)) discotic liquid crystalline phases for compounds 3BC—6BC. Both of the intercolumnar and mtracolumnar distances in the Col_(ho) phase were linearly increased according to the number of —CONHC_(14)H_(29) chains. The temperature-and frequency-dependent dielectric constants of compounds 2BC—6BC in cast-films revealed dielectric anomalies around the solid to Col_(ho) phase transition temperatures due to thermally activated molecular motion. Polarization—electric field (P—E) curves of compounds 2BC, 3BC, and 5BC in the mesophases showed hysteretic behavior with ferroelectric ground states, whereas paraelectric behavior with linear P—E dependence was observed for compounds 4BC and 6BC.