Stereostructural Effects in the Electrochemical Properties of Self-Assembled Monolayers

Abstract

Large-area metal/molecule/metal junctions based on self-assembled monolayers (SAMs) of organothiolates are of interest for the investigation of charge transport across ultrathin organic films and the fabrication of molecular electronic devices such as diodes and switches. Several reports demonstrate an odd-even dependency in the rate of charge transport across SAMs of the redox-active ferrocenylalkanethiolates Fc(CH2) n S1, 2 and insulating n-alkanethiolates CH3(CH2) n S3-6. This parity effect is attributed to small changes in the orientation of the terminal functional group (ferrocene or methyl) and in the alkyl chain packing in SAMs consisting of an odd versus even number of methylene repeat units (n odd or n even). These odd-even differences ultimately impact device performance. For instance, junctions comprising gold-supported Fc(CH2) n S SAMs (Figure 1) of n even present lower leakage currents and rectify current, while those of n odd do not.1, 2 We have sought experimental evidence for odd-even distinctions in the molecular organization of these SAMs using electrochemistry,7 infrared reflection-absorption spectroscopy (IRRAS), contact angle goniometry, and surface stress measurements8. The findings of these investigations will be presented in this talk.