Redox-active catechol-functionalized molecular rods: Suitable protection groups and single-molecule transport investigations

The synthesis of molecular rod 1 comprising a central redox-active unit and two terminal acetyl-protected sulfur groups is reported. Various protecting groups for the catechol moiety were investigated and protected precursors 14-18 were synthesized. In particular, ethyl orthoformate 17 can be easily and selectively deprotected in mild acidic conditions ruling out the need for a strong Lewis acid like boron tribromide. The redox activity of 1 was confirmed by cyclic voltammetric investigations. Gold-molecule-gold junctions were formed with the dimethyl-protected rod 18. Single-molecule transport investigations using this molecular rod revealed a set of three single-junction conductance values varying over two orders of magnitude.