Unimolecular rectification of monolayers of CH3C(O)S–C14H28Q+–3CNQ− and CH3C(O)S–C16H32Q+–3CNQ− organized by self-assembly, Langmuir–Blodgett, and Langmuir–Schaefer techniques

Abstract

The advantage of “self-assembly” (strong covalent binding to substrates) was combined with the advantage of Langmuir–Blodgett (LB) or Langmuir–Schaefer (LS) transfer to a solid substrate (quantitative transfer of monolayers to the substrate). The electrical rectification (asymmetric conduction) by a monolayer of thioacetylalkylquinolinium tricyanoquinodimethanide was critically compared when these molecules had been transferred, by such competing techniques, onto gold electrodes, and then covered by a “cold gold” pad electrode. Unimolecular rectification was observed in the expected directions in the LB and LS monolayers. The Self-Assembled Monolayers (SAMs) were disordered; macroscopic measurements of rectification were unsuccessful for the SAMs, but successful for the down-stroke LB and LS monolayers, whose orientation and potential bonding to the Au surface should be identical to that of an ideal SAM.