Molecule‐Electrode Interfaces Controlled by Bulky Long‐Legged Ligands in Organometallic Molecular Wires

Abstract Precise control of molecule‐electrode interface is essential for molecular devices. Herein, new ruthenium acetylide molecular wires with long‐legged phosphine ligands to form a sterically controlled molecule‐electrode interface are designed. The sharpened Raman signals ascribed to acetylene stretching are observed for the self‐assembled monolayers (SAMs) of the molecular wires with the biphenyl‐ (2^Au) and tert‐butylbiphenyl‐substituted long‐legged dppe‐type ligands (3^Au), suggesting that steric hindrance causes formation of uniform SAMs. Scanning tunneling microscope break‐junction (STM‐BJ) study of 3^Au reveals narrow conductance features compared with those of 1^Au bearing the parent dppe ligands, indicating formation of a uniform molecular junction. Furthermore, the effective electronic interactions between the molecule and electrodes are unique to the long‐legged derivatives, as revealed by the surface‐enhanced Raman scattering study. Thus, the bulky long‐legged strategy turns out to provide a design concept for a well‐defined molecule‐electrode interface.