Tuning Conductance in Aromatic Molecules: Constructive and Counteractive Substituent Effects

Abstract

Destructive quantum interference in aromatic hydrocarbons can be tuned using chemical substituents; however, classical chemical intuition is not enough to explain the effects on electron transport. Using Hückel theory and density functional theory calculations, in combination with the Landauer–Büttiker approach for charge transport, novel substituent effects are demonstrated. For a 1,3-linked benzene, an electron acceptor in position 2 is shown to have the same effect on the antiresonance energy as an electron donor in position 4 and vice versa. Substituents in position 5 have no effect on the antiresonance energy. The effects appear to be additive, such that a donor in position 2 will counteract a donor in position 4, leading to cancellation of the substituent effect. Counter- and nonactive substituent positions exist for all aromatic hydrocarbons and can be predicted using a diagrammatic approach. This insight should be useful when substituents are to be used for tuning destructive quantum interference features in the transmission relative to the Fermi energy of the electrodes.

Tuning the thermal conductance of molecular junctions with interference effects

“…Following the analogy with electronic systems, we analyze now, how the inclusion of additional substituents modifies the interference patterns 36 . For this purpose we investigate the phonon transport through benzenediamine junctions, if two H atoms are replaced by two Br atoms.…”

“…Theoretically this topic has been explored extensively in the last two decades [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] . In particular, special attention has been devoted to the role of Fano resonances [28][29][30][31][32] and to the determination of general rules governing the appearance of quantum interference effects in molecules with extended π-electron systems [33][34][35][36] . Also different experimental reports in recent years have convincingly shown the influence of the quantum interference on electronic transport of molecular junctions, as illustrated by measurements of linear conductances and current-voltage characteristics [37][38][39][40][41][42][43][44][45][46][47][48] .…”

Destructive quantum interference in electron transport: A reconciliation of the molecular orbital and the atomic orbital perspective

“…In order to allow for a simple analytical treatment, the derivation of the scheme also originally assumed sites with identical onsite energies and couplings to each other 30,31 . This assumption was later lifted in an attempt to generalize the method now also allowing for hetero atoms in the molecular structure but this came at the price of increased mathematical complexity 32,49 . Another assumption was that the only energy E, where T (E) is of interest is the Fermi energy because it defines the zerobias conductance and therefore the rules only apply at E = E F .…”

“…In principle, it would also be possible to account for the presence of hetero atoms within the scheme as it has been done elsewhere 32,49 for a treatment of DTE containing its sulfur sites but this would come at the price of diminishing the scheme's simplicity and would not provide any important arguments for the present discussion. This AO scheme considers all orbitals in an AO representation and relies on the structure of the entire Hamiltonian thereby strongly reflecting the respective molecular topology.…”

On the resilience of magic number theory for conductance ratios of aromatic molecules

“…In the literature, several papers discuss the conditions for destructive QI, for which ≈ 0 [6,[9][10][11][12][13][14][15][16][17][18][24][25][26][27][28][29]. On the other hand, magic ratio theory aims to describe constructive QI, for which may take a variety of non-zero values.…”