Orbital Views on Electron-Transport Properties of Cyclophanes: Insight into Intermolecular Transport

Abstract

Electron-transport properties of cyclophanes are investigated with qualitative Hückel molecular orbital analysis for better understanding of the intermolecular interaction in molecular devices. Charge and electron transfers often take place via through-space interactions, which are observed both in large biological molecules and in organic molecular crystals. Since the intermolecular electronic coupling in ³-stacked structures plays an important role in total device performance, in this work [2,2]paracyclophane is studied to investigate the effect of the intermolecular interactions in aromatic hydrocarbons on its electron-transport properties. According to the orbital symmetry rule, the symmetry-allowed and symmetry-forbidden connections for electron transport between the benzene rings are predicted just from the phase and amplitude of the frontier orbitals. The meta connection is symmetry allowed for electron transport while the para and ortho connections are symmetry forbidden. The qualitative predictions made with the Hückel approximation are found consistent with the calculation results obtained with density functional theory. The qualitative but essential understanding in the orbital views would extend the application of the rule from a single molecule to a crystal structure for the development of high-performance molecular devices.

Large Conductance Variations in a Mechanosensitive Single-Molecule Junction

“…Along these lines, the [2.2]paracyclophane (PC) compound is highly appealing. 20 First described by Farthing et al in 1949, it consists of two stacked benzene rings that are mechanically stabilized by two nonconjugated linkers. 21 Integrated as central unit of an oligo-phenylene-ethynylene (OPE) rod with terminal binding groups to gold electrodes ( Figure 1 ), we show here that using a mechanically controlled break junction (MCBJ) the π-stacking (and, therefore, the conductance) can be modulated by exerting a mechanical shear force to it.…”

π-Stacked Polymer Consisting of a Pseudo–meta–[2.2]Paracyclophane Skeleton

“…No essential differences in optical properties among the π-stacked molecules comprising pseudo– o –, – m –, and – p –linked [2.2]paracyclophanes were observed. It was reported that pseudo-m-linked [2.2]paracyclophane is symmetry-allowed for electron transport [28]. The present polymer can be a promising candidate to function as a single molecular wire that transfers electron effectively.…”

Electron transfer pathways in mixed‐valence paracyclophane‐bridged bis‐triarylamine radical cations

“…The quantum interference picture has emerged as a powerful tool in molecular conductance for relating the observed transmission through molecules bound between two gold electrodes to electronic structure, namely to molecular‐orbital considerations . The computational modeling by Solomon et al of benzene π‐stacks connected to gold electrodes would suggest higher transmission near the Fermi level for a pseudo ‐ meta than for a pseudo ‐ para arrangement, due to pronounced destructive interference effects for the latter.…”

“…The dependence of electronic coupling and conductance on the relative arrangements and spatial dislocations of the π‐systems and on the location of the points of connection to the locations of charge injection (redox centers or the leads in actual conduction experiments) is of central interest in this context. Such questions have recently been addressed by quantum‐chemical methods for unlinked π‐stacked benzene rings connected to electrode models, using either concepts based on quantum interference or on orbital‐symmetry‐based pictures . Nodes in the frontier orbitals lead to a strong influence of the connection points on the computed transmission near the Fermi level, but the latter also depends crucially on the charge‐injection energy …”