Terminal Redox‐Site Effect on the Long‐Range Electron Conduction of Fe(tpy)2 Oligomer Wires on a Gold Electrode

This article completes our comprehensive understanding of the electron transport properties of our original π‐conjugated redox‐active molecular wires comprising Fe bridged by p‐phenylene linkers (tpy=2,2′:6′,2′′‐terpyridine). The Fe(tpy)₂ oligomer wires comprise three types of tpy ligands: the anchor tpy ligand ( A series) makes a junction between the wire and electrode, the bridging bis‐tpy ligand ( L series) connects the Fe(tpy)₂ units, and the terminal tpy ligand ( T series) possesses a redox site as a probe for the long‐range electron transport ability. Taking advantage of the precise tunability of the composition of the Fe(tpy)₂ oligomer wires, thus far we investigated how A and L impacted on the electron‐transport ability. The excellent long‐range electron transport ability with ultrasmall attenuation constants (β^d, 0.002 Å^?1 as the minimum) depends on L significantly Chem. Asian J. 2009 , 4, 1361], whereas A is unrelated to the β^d value, but influences the zero‐distance electron‐transfer rate constant, k_et⁰ J. Am. Chem. Soc. 2010 , 132, 4524]. Herein we study the influence of terminal ligand T ^x (x=1–3). β^d is independent of T , however, T³ , with a cyclometallated Ru complex as the redox site, gives rise to a k_et⁰ value greater than T¹ and T² with ferrocene. This series of simple but definitive conclusions indicates that we have reached the stage of being able to precisely design molecular wires to attain desirable single‐molecule electron conduction.