Organic materials with diverse molecular designs show multifunctional properties such as coupled ferroelectric, optical, ferromagnetic, and transport properties. We report the design of an alkylamide-substituted pyrene derivative displaying fluorescent ferroelectric properties coupled with electron transport properties. In solution phase, this compound displayed concentration-dependent fluorescence, whereas in xerogels, a fluorescent green organogel (>0.1 mM) and entangled nanofibers were observed. A discotic hexagonal columnar liquid crystalline phase was observed above 295 K due to intermolecular hydrogen bonding and π-stacking interactions. The direction of the hydrogen-bonded chains could be inverted by the application of an external electric field along the π-stacked column, resulting in ferroelectric polarization-electric field (P-E) hysteresis. The local electric field arising from the ferroelectric macrodipole moment arrangement along the π-stacking direction affected the electron transport properties on the π-stack of pyrenes, thus confirming the current-switching phenomena according to P-E hysteresis. We report that multifunctional properties such as ferroelectricity, fluorescence, and electron transport switching were successfully achieved in hydrogen-bonded dynamic π-molecular assemblies.
Five simple benzenecarboxamide (BC) derivatives bearing multiple −CONHC14H29 chainsN,N′-bis(tetradecyl)-1,4-benzenedicarboxamide (2BC), N,N′,N″-tri(tetradecyl)-1,3,5-benzenetricarboxamide (3BC), N,N′,N″,N″-tetra(tetradecyl)-1,2,4,5-benzenetetracarboxamide (4BC), N,N′,N″,N‴,N⁗-penta(tetradecyl)benzenepentacarboxamide (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∼O= hydrogen-bonding interactions, of which the hexagonal arrangement resulted in ordered hexagonal columnar (Colho) discotic liquid crystalline phases for compounds 3BC–6BC. Both of the intercolumnar and intracolumnar distances in the Colho phase were linearly increased according to the number of −CONHC14H29 chains. The temperature- and frequency-dependent dielectric constants of compounds 2BC–6BC in cast-films revealed dielectric anomalies around the solid to Colho 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.
Alkylamide (−CONHC n H2n+1)-substituted benzene and its pyrene derivatives have shown a discotic hexagonal columnar liquid-crystalline phase through a one-dimensional (1D) intermolecular N–H···O hydrogen-bonding interaction, the direction of which is inverted through the application of an alternate current voltage. The polar hydrogen-bonding chains and dipole inversion reveal a ferroelectric polarization–electric field (P–E) hysteresis curve. Non-π-planar helicene derivatives bearing two −CONHC14H29 chains also indicate a ferroelectric response. The racemic helicene derivative shows a bilayer lamellar liquid-crystal phase within a temperature range of 330–420 K, whereas there is no liquid crystallinity for the optically active derivative because of the different molecular assembly structure. The racemic phase is constructed through a two-dimensional (2D) N–H···O hydrogen-bonding network, which shows ferroelectric P–E hysteresis curves at above 340 K. The collective dipole inversion in the 2D layer contributes to the ferroelectricity in the lamellar phase. The remanent polarization (P r) of 11.1 μC cm–2 is about 6 times higher than those of the π-planar benzene- and pyrene-based 1D ferroelectrics. Both the density of the hydrogen-bonding site and the domain orientation in the 2D system are higher than those of the 1D columnar system.
The synthesis and assembly behavior of hexathioalkyl sumanenes, having a different feature of surface electrostatic potential from non-substituted sumanene, are described.
The absorption and fluorescence spectra of chiral alkylamide-substituted pyrene derivatives (R-1 and S-1) in the solution phase were consistent with the formation of N−H•••O hydrogenbonded helical π-stacked one-dimensional (1D) supramolecules (R-1) n and (S-1) n in methylcyclohexane (MCH), toluene, chloroform (CHCl 3 ), and tetrahydrofuran (THF); the π-stacked structures and aggregation number (n) were governed by the concentration (c) and solvent polarity. The aggregation of (R-1) n and (S-1) n in MCH and toluene was much greater than that in THF and CHCl 3 , and excimer emission of excited-state (R-1) n * and (S-1) n * supramolecules with n ≥ 2 was observed in all solvents. Interestingly, the circular polarized luminescence (CPL) spectra of (R-1) n * and (S-1) n * revealed a g lum value of 0.03 in MCH at c > 1 × 10 −6 M. Circular dichroism and CPL spectra revealed the formation of hydrogen-bonded helical 1D supramolecular assemblies in the ground and excited states. The helicities of the 1D supramolecular assemblies of (R-1) n and (S-1) n in CHCl 3 were inverted as compared to those in MCH and THF. The solvent polarity and concentration were sensitive to the π-stacked structure and helical configuration of the N−H•••O hydrogen-bonded 1D supramolecular assemblies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.