Organic/metal interfaces in self-assembled monolayers of conjugated thiols: A first-principles benchmark study

We present an extensive theoretical study of a self-assembled monolayer of a prototype π-conjugated thiol on Au(1 1 1). A series of experimentally accessible quantities are calculated and compared to available experimental data. After assessing the methodology and re-evaluating experimental data in the light of our theoretical results, we focus on the interfacial phenomena determining the modification of the effective workfunction of the substrate and link our findings to the energetic alignment of the frontier molecular orbitals with the metal Fermi level. Since we find no evidence of charge transfer between metal and molecule, the observed interfacial phenomena are rationalized in terms of charge fluctuations and electrostatics at the atomic length scale. The microscopic picture established in this work provides a deeper understanding of the interfacial processes that govern the working principle of single-molecule electronics and organic electronic devices.