Energy‐Level Alignment for Single‐Molecule Conductance of Extended Metal‐Atom Chains

Abstract

The use of single-molecule junctions for various functions constitutes a central goal of molecular electronics. The functional features and the efficiency of electron transport are dictated by the degree of energy-level alignment (ELA), that is, the offset potential between the electrode Fermi level and the frontier molecular orbitals. Examples manifesting ELA are rare owing to experimental challenges and the large energy barriers of typical model compounds. In this work, single-molecule junctions of organometallic compounds with five metal centers joined in a collinear fashion were analyzed. The single-molecule i-V scans could be conducted in a reliable manner, and the EFMO levels were electrochemically accessible. When the electrode Fermi level (EF ) is close to the frontier orbitals (EFMO ) of the bridging molecule, larger conductance was observed. The smaller |EF -EFMO | gap was also derived quantitatively, unambiguously confirming the ELA. The mechanism is described in terms of a two-level model involving co-tunneling and sequential tunneling processes.

Revisit of trinickel metal string complexes [Ni3L4X2] (L = dipyridylamido, diazaphenoxazine; X = NCS, CN) for quantum transport

“…In general, a molecule with a higher bond order is associated with a smaller HOMO‐LUMO gap which implies a better alignment for the EFMO to the EFermi. Hence, an analogy of metal‐metal bond orders to the HOMO‒–LUMO gap is suggested as a simplified interpretation to the relative conductance of metal strings and is consistent with the good correlation between the measured conductance and their metal‐metal bond orders found in our previous studies . Herein, we present our first attempt at the modeling of junctions of metal string complexes, conceivably still with a great simplification.…”

“…Hence, those with better conjugation or smaller highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) gaps exhibit a superior conductance for molecules with similar lengths and the same anchoring group. Similar correlation of molecular conductance with structures and FMO is less explored for those containing metal atoms despite their rich characteristics like electrochemical redox reactions, magnetoresistance, spintronics, and mechanochemistry . Their properties and structures can be profoundly tuned with a variety of metal centers and ligands.…”

Inorganic and Organometallic Molecular Wires for Single‐Molecule Devices

“…As mentioned in Introduction, control of the energy difference between E F and E MO leads to variable conductance. Gating is one of the possible methods to control E MO , and Jin, Peng, and Chen reported gating experiments of Ni, Co and Cr homo‐pentanuclear EMACs 11 (Figures a and ) . The E MO of molecular wires was controlled by applying the potential of the working electrode ( E wk ) against the reference electrode in the MMM junction.…”

Side‐Group‐Mediated Mechanical Conductance Switching in Molecular Junctions

“…So far, a variety of stimuli has been demonstrated to trigger a reversible change in the conductance state, the most studied being light and electrochemical potential. In these cases, the stimulus acts on the molecular backbone through which charge is transported, for instance by photoexcitation, photoinduced E–Z isomerization or cyclization and electrochemical reduction or oxidation . A conductance switch can be induced in a molecular device also through mechanical stimuli such as junction compression or elongation.…”