Unimolecular rectifiers: Present status

Many experimental issues presented here must be resolved before we can really understand unimolecular rectification. Nevertheless, at the University of Alabama six unimolecular rectifiers have been studied (Fig. 1, 1-6). Langmuir-Blodgett (LB) or Langmuir-Schaefer (LS) monolayer films of these molecules show asymmetric electrical conductivity between Au and Al electrodes. When the films are very compact (LS of 4, LB of 5), and if there is finite intramolecular charge transfer (ICT, or intervalence transfer, IVT), then the electrical behavior persists for many cycles of measurement.