Orbital Control of Long-Range Transport in Conjugated and Metal-Centered Molecular Electronic Junctions

Large area molecular junctions consisting of covalently bonded molecular layers between conducting carbon electrodes were compared for Co and Ru complexes as well as nitroazobenzene and anthraquinone to investigate the effect of molecular structures and orbital energies on electronic behavior. A wide range of molecular layer thickness (d) from 1.5–28 nm was examined and three distinct transport regimes in attenuation plots of current density (J) vs thickness were revealed. For d 12 nm, transport depends on the electric field rather than bias, with the slope of ln J vs d near-zero when plotted at a constant electric field. At low temperature (T < 150 K), transport is nearly activationless and likely occurs by sequential tunneling and/or field-induced i...