Control over Molecular Orbital Gating and Marcus Inverted Charge Transport in Molecular Junctions with Conjugated Molecular Wires

Abstract

Recently it is discovered that molecular junctions can be pushed into theMarcus Inverted region of charge transport, but it is unclear which factors are important. This paper shows that the mechanism of charge transport across molecular wires can be switched between the normal and Marcus Inverted regions by fine-tuning the molecule-electrode coupling strength and the tunneling distance across oligophenylene ethynylene (OPE) wire terminated with ferrocene (Fc) abbreviated as S-OPE n Fc (n = 1-3). Coherent tunneling dominates the mechanism of charge transport in junctions with short molecules (n = 1), but for n = 2 or 3 redox reactions become important. By weakening the molecule-electrode interaction by interrupted conjugation, S-CH 2 -OPE n Fc, intramolecular orbital gating can occur pushing the junctions completely into the Marcus Inverted region. These results indicated that weak molecule-electrode coupling is important to push junctions into the Marcus Inverted Region.

Resolving charge transfer mechanisms in molecular tunnel junctions using dynamic charge transfer and static current–voltage measurements

“…We draw the following conclusions from the results: (1) in the CHC study, CT from the LUMO+2 level, which is strongly delocalized over the molecule results in shorter CT times and smaller β values than CT from the more Fc-localized LUMO+1 orbital. (2) In the J ( V ) measurements, β values consistently exhibit higher values at +1 V than those at −1 V. We attribute this difference to the distinct tunneling mechanisms: coherent tunneling at +1 V (lacking molecular orbital involvement) and incoherent tunneling at −1 V (where charge injection in the LUMO is mediated by the HOMO dominated charge transport 27 ). (3) The β values associated with CT time derived from LUMO+1 closely mirror the β values corresponding to J at −1 V. We believe this correspondence arises from the similarity in the spatial distribution revealed by DFT calculations of the LUMO+1 (regulating CHC CT) and HOMO and LUMO (regulating J ( V ) at −1 V).…”

“…The self-assembled monolayers (SAMs) of these molecules were formed on template-stripped Au, Ag and Pt surfaces following earlier reported methods. 27 In the CHC scheme as illustrated in Fig. 1a, CT from molecular orbitals to the metal can in principle be explored via the promotion of excited electrons into low-lying unoccupied molecular orbitals (LUMOs) above the E F of the metal electrodes, in this case specifically the LUMO+1 level with strong Fc contribution and the more delocalized LUMO+2.…”

“…2), which allows it to participate in the mechanism of charge transport. 27 The shared elements of the charge transfer/transport mechanism in the CHC experiment and at negative bias in the J ( V ) measurements both involving the LUMO(s) are illustrated in Fig. 1.…”

Deciphering I–V characteristics in molecular electronics with the benefit of an analytical model

“…The development of reliable approaches to electrically contact single molecules and molecular assemblies over the last 20-25 years has resulted in a broad spectrum of intriguing discoveries. [1][2][3][4][5][6][7][8][9][10][11] Researchers now build metal-molecule-metal junctions that exhibit a range of behaviors, including current rectification, [12][13][14][15] switching, [16][17][18] photoconductivity, [19][20][21] magnetoresistance, [22][23][24] and negative differential resistance [25][26][27] that may hold promise for future nanotechnologies. These milestones reflect both technical advances in molecular junction formation and increased understanding of fundamental structure-property relationships in the field of molecular electronics.…”

A convenient synthesis of ferrocene-(ethynylphenyl)thioacetates

“…2 These electronic properties have made ferrocene an ideal candidate for studies in the field of molecular electronics. 3…”