Synthesis and electrical characterization of oligo(phenylene ethynylene) molecular wires coordinated to transition metal complexes

Abstract

Organometallic wires are interesting alternatives to conventional molecular wires based on a pure organic system because of the presence of d orbitals in the transition metal complex. However, synthetic problems, such as decreased stability of the compounds when labile metal complexes are present, often impede their isolation in a pure state and preclude a rapid development of such hybrid molecular wires. In this work, we show that preassembled self-assembled monolayers (SAM) based on pyridine-terminated 1-((4- acetylthiophenyl)ethynyl)- 4-((4-pyridyl)ethynyl)benzene can act as a template for the architectural build up of a second layer of transition metal complexes to form an array of organometallic molecular wires on gold. RuII(terpy)(bipy) 2+ (terpy =2, 2′: 6′, 2″-terpyridine and bipy = 2, 2′-bipyridine) or cyclometalated PtII(pbipy) (pbipy = 6-phenyl-2, 2′-bipyridine) were axially coordinated onto the organic SAM via its terminal pyridinium moieties. Current-voltage studies show that the electronic coupling between the transition metal and organic wire produces a molecular wire that exhibits higher conductance than the original organic chain. The presence of the transition metal complexes in the hybrid molecular wire introduces distinctive negative differential resistance (NDR) effects. © 2009 American Chemical Society.