Sandwiches “EGaIn|Ga2O3|LB monolayer of 2|Au” and “EGaIn|Ga2O3|LB monolayer of 3|Au” rectify. They are formed from a Langmuir–Blodgett (LB) monolayer of 2 or 3 transferred onto thermally evaporated gold. Molecules 2 and 3 are of the donor-sigma-acceptor (D-σ-A) type and have the same perylenebisimide (PBI) acceptor as previously studied molecule 1. Molecule 1 has the weak donor pyrene, 2 has the good donor ferrocene, and 3 has the very strong donor N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD). All three molecules have a long swallowtail ending in a thioacetyl group, which ensures slow chemisorption onto the Au electrode. These molecules were contacted directly by a gallium indium eutectic (EGaIn) drop, covered by a defective oxide Ga2O3 layer. As before for 1, the direction of rectification for 2 is bias-dependent. In the ±1.0 V range, the rectification is at positive V, with a rectification ratio (RR) that is initially greater than 5 and then decreases on successive scans to 2, while the currents decrease by as much as 2 orders of magnitude. In the ±2.5 V range, the rectification direction for 2 reverses, while upon repeated scanning the rectification ratio (in the negative direction) increases and the currents decrease. For molecule 3, both directions have a charge-trapped state (Coulomb blockade) leading to Voffset in both biases, but at high potentials rectification set is, with large RR (up to 2,800) at ±2.5 V.

Examples of coordination compounds that act as molecular rectifiers are rare. Recently a pentacoordinate [N2O2] Fe(III) surfactant, namely [FeIII(LN2O2)Cl] (1), was studied as a Langmuir–Blodgett (LB) monolayer between two Au electrodes, “Au | LB1 | Au”. Rectification was observed, but only at low currents. In order to verify the current rectification of this species, a new setup is used, where an LB monolayer of 1 is placed between Au and a soft contact of gallium indium eutectic (EGaIn), as the “sandwich” “EGaIn/Ga2O3 | LB1 | Au”. When scanned from 0 to −1.5 V, 90% of the sandwiches remained stable, while scanning from 0 to + 1.5 V only 10% remained stable. For the scan range of ± 0.7 V, 90% of the sandwiches were stable on the first scan; about half of them could withstand repeated scans; the rectification ratios (RR) at 0.7 V ranged between 3 and 12. Pushing the bias range to ±1.0 V, the RR increased to between 50 and 150, but the sandwiches lasted for at most three full scans.

A molecule containing an electron donor (pyrene, Py), an insulating tetramethylene bridge, an electron acceptor (perylenebisimide, PBI) and a bis-decyl swallowtail with two terminal thioesters was studied for its electrical rectification as a Langmuir–Blodgett (LB) monolayer between two Au electrodes at room temperature (over a 8 month period, the thioester terminations chemisorbed partially (about 15%) onto the bottom Au electrode). At lower bias (<±1.5 Volts), the direct current was greater at positive than negative bias; at higher bias (±2.0 and ±2.5 Volts), the conduction was larger at negative bias: this “Janus” switching was repeatable when the bias ranges were changed. At constant bias range, repeated scans showed a gradual decrease in conductivity. Ancillary characterization data are reported.

A single molecule composed of three linked moieties can function as an amplifier of electrical current, when certain conditions are met by the molecular orbitals of the three component parts. This device should exhibit power gain at appropriate voltages. In this work, we will explain a plausible mechanism by which this device should work, and present its operating characteristics. In particular, we find that a fundamental requirement for current amplification is to have the LUMO of the central moiety more strongly coupled to a control electrode than it is to the other orbitals in the molecule, while the HOMO of this moiety should be more strongly coupled to the orbitals in the other moieties than it is to the control electrode.

Unimolecular or molecular-scale electronics has made huge progress towards unimolecular resistors, switches, rectifiers, negative differential resistance devices, and gain-less single-electron transistors. Twelve unimolecular rectifiers have been found in Tuscaloosa, and many others elsewhere. The challenges are to understand the “metal|molecule” interface and to make reliable unimolecular electronic devices.

A molecule containing an electron donor (pyrene, Py), an insulating tetramethylene bridge, an electron acceptor (perylenebisimide, PBI) and a bis-decyl swallowtail with two terminal thioesters was studied for its electrical rectification as a Langmuir–Blodgett (LB) monolayer between two Au electrodes at room temperature (over a 8 month period, the thioester terminations chemisorbed partially (about 15%) onto the bottom Au electrode). At lower bias (<±1.5 Volts), the direct current was greater at positive than negative bias; at higher bias (±2.0 and ±2.5 Volts), the conduction was larger at negative bias: this “Janus” switching was repeatable when the bias ranges were changed. At constant bias range, repeated scans showed a gradual decrease in conductivity. Ancillary characterization data are reported.