An achiral disk-shaped molecule (2) having one imidazole unit was found to be assembled into long and twisted nanoscopic fibers having 10 - 100 nm width as shown by transmission electron microscopy (TEM) and atomic force microscope (AFM). Compound 2 leads to spontaneous chiral symmetry breaking through the steric effect of imidazole units during the formation of one-dimensional stacks. The imidazole in 2 acts as a molecular adaptor to form hydrogen bonds and accumulate metal ions. The supramolecular connection of 2 with benzene-1,3,5-tricarboxylic acid through the hydrogen bonds exhibited a thermotropic liquid crystalline properties. Silver nanoparticles were deposited onto the self-assembled nanofibers by the photoreduction of silver ions.
Tetrathiafulvalenes (TTF) S-TTF and R-TTF having four chiral amide end groups self-organize into helical nanofibers in the presence of 2,3,5,6-tetrafluoro-7,7',8,8'-tetracyano-p-quinodimethane (F(4)TCNQ). The intermolecular hydrogen bonding among chiral amide end groups and the formation of charge-transfer complexes results in a long one-dimensional supramolecular stacking, and the chirality of the end groups affects the molecular orientation of TTF cores within the stacks. Electronic conductivity of a single helical nanoscopic fiber made of S-TTF and F(4)TCNQ is determined to be (7.0+/-3.0)x10(-4) S cm(-1) by point-contact current-imaging (PCI) AFM measurement. Nonwoven fabric composed of helical nanofibers shows a semiconducting temperature dependence with an activation energy of 0.18 eV.
The synthesis of
artificial ion channels is one of the core areas
of biomimetics and is aimed at achieving control over channel functionality
by careful design and selection of the constituent components. However,
the optimization of ionic conductivity in the channel in the crystalline
state is challenging because of crystal strain, polymorphism, and
potentially limited stability. In this study, the pore size of cylindrical
channels was controlled with the aim of optimizing ionic conductivity.
We prepared two isomorphic salts, Li2([18]crown-6)3[Ni(dmit)2]2(H2O)4 (1) and Li2([15]crown-5)3[Ni(dmit)2]2(H2O)2 (2),
both of which possess ion channels formed by a one-dimensional array
of crown ethers, Li+ ions, and crystalline water molecules.
Meanwhile, [Ni(dmit)2]− (S = 1/2) molecules formed a ladder configuration with J
rung/k
B = −631(5) K, J
leg/k
B = −185(5)
K for 1, and J
rung/k
B = −517(4) K, J
leg/k
B = −109(5) K for 2. For 1, the Li+ ionic conductivity
at 293 K in the crystalline state was enhanced from 1.89(18) ×
10–8 S·cm–1 to 2.46(6) ×
10–7 S·cm–1 via dehydration.
Furthermore, analysis of Li+ ionic conductivities of 2, which incorporated a crown ether with a smaller cavity
(the cavity diameters of [18]crown-6 and [15]crown-5 are 2.60–3.20
Å and 1.70–2.20 Å, respectively) at the same temperature both before and after dehydration
revealed conductivities of 1.93(31) × 10–8 S·cm–1 and 7.01(21) × 10–7 S·cm–1, respectively. This molecular design approach can
contribute to increasing the ionic conductivity as well as the development
of all-solid-state lithium ion batteries and other electronic device
fabrications.
Herein we report the synthesis of α-Dawson type POM, Li6[α-P2W18O62]·28H2O, directly from the use of Li2WO4 as the tungstate source. The salt obtained was soluble not only in water but also in a range of polar and non-polar organic solvents, such as benzene.
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