Electronic transport of benzothiophene-based chiral molecular solenoids studied by theoretical simulations

Abstract

By the density-functional-derived tight-binding method, the electronic transport properties of two types of benzothiophene-based molecular wires, i.e., the linear and helical molecular wires have been investigated. In the molecular bridge system where these molecules are connected to the gold electrodes by S–Au bonds, the transmission peaks are found to lie at the energies somewhat lower than 0.5 eV below the Fermi level for both cases. Thus the conductances of both types of wires for the bias voltage less than 1.0 V are not so large without doping. Upon iodine doping, however, the new transmission peaks are found to appear around the Fermi level, particularly in the case of helical wires. It means that the conductances of the helical wires are expected to be improved dramatically by the chemical doping. Therefore, the doped helical molecular wires are predicted to work as molecular solenoids even under lower bias voltages. Next, the applicability of the current-induced magnetic field generated in such a molecular solenoid is considered. As an example, we propose a novel helical molecule where the hydrogen atoms connected to the inner C–C bonds of the helix are substituted by some kind of radicals. In this case the current-induced field can control the alignment of the radical spin orientations.

Soft materials with graphitic nanostructures

“…The branched side chains of 3 likely prevent the formation of a bilayer tape, essential for the nanotube formation. Conductive polymers with helical architectures have attracted attention in view of the concept of molecular solenoids (Akagi et al 1999;Tagami et al 2003). However, this concept has not yet been realized because there are no molecular objects that fulfil certain requisites for conductivity and helicity.…”

Self-assembled graphitic nanotubes with one-handed helical arrays of a chiral amphiphilic molecular graphene

“…Recently, a hot issue of chirality has emerged in relation to the helicity of the hexagonal carbon lattice in carbon nanotubes, because it determines the conductive properties of carbon nanotubes (22-24). Conductive polymers with helical architectures (25) also have attracted attention in view of the concept of molecular solenoids (26,27), although this concept has yet been a dream of scientists, because there are no molecular objects that fulfill certain requisites for conductivity and helicity. Here, we report an example of conductive tubular objects consisting of one-handed helical arrays of a -stacked chiral molecular graphene.…”

Theory of Quantum Conductance of Atomic and Molecular Bridges

“…When the electron incident energy is close to a degenerate molecular level, a strong loop current is often generated inside the molecule. 20,22) For larger molecules, the internal current distribution is similar to that induced by the magnetic field, for example the persistent current. Usually the orbital diamagnetism of a molecule is contributed by an incomplete cancellation of the magnetic moment contributed from internal currents of opposite chiralities.…”

“…As a case study, we show the transmission spectra of the phenalenyl-like molecules, 24) and the alkane molecule. 25) In both cases, the electronic states of the whole systems are described by the density-functional derived self-consistent tight-binding model, [17][18][19][20][21][22][23][24][25] in which the basis is assumed to be the localized atomic orbitals. Figure 5 shows the molecular bridge structures where the phenalenyl-like molecule are attached to the two semiinfinite gold electrodes through the mercapto-vinyl groups.…”

“…[17][18][19][20][21][22][23] We will discuss how the quantum transport through molecular bridges is strongly influenced by the connecting part to the electrodes and how the transport is influenced by the internal structure of the molecule. The first issue is investigated by the case study of the phenalenyl molecule, 24) and we will find that the nodal shape of the corresponding molecular orbital is crucial for the resonant tunneling case.…”