Molecular rectification: Confirmation of its molecular origin by chemical suppression of the electrical asymmetry

Bis[N-(ω-decyl)-5-(4-dimethylaminonaphthalen-1-yl-methylene)]-5,6,7,8-tetrahydroisoquin-olinium]-disulfide diiodide forms self-assembled monolayers (SAMs) on gold substrates in which the acceptor–(π-bridge)–donor moieties are aligned: Au|Au–S–C10H20–A+–π–D (I−). These diode-like molecules exhibit rectification ratios of 30–80 at ±1 V but display symmetrical current–voltage (I–V) characteristics when exposed to HCl and rectify again when exposed to NH3. This reversible switching is explained by protonation/deprotonation of the amino group which disrupts/restores the donor–acceptor combination and provides evidence of the molecular origin of the electrical asymmetry.