Janus Reversal and Coulomb Blockade in Ferrocene-Perylenebisimide and N,N,N',N'-Tetramethyl-para-phenylenediamine-Perylenebisimide D-σ-A Rectifiers.

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.