Electrical Rectification in a Monolayer of Zwitterions Assembled by Either Physisorption or Chemisorption

Rectification by a monolayer of (acetylthioundecyl)quinolinium tricyanoquinodimethanide, 6, sandwiched or physisorbed or chemisorbed on gold electrodes, was studied by scanning tunneling microscopy and scanning tunneling spectroscopy, and also by macroscopic “gold | monolayer | gold” pads, using either physisorption (Langmuir−Blodgett deposition, followed by partial chemisorption) onto a Au substrate or chemisorption (“self-assembly” onto Au surface). Rectification ratios of 5 to 7 were seen by scanning tunneling spectroscopy of individual molecules, as expected, but the macroscopic films are too disordered to show dramatic rectification ratios.