Ligand effects on charge transport in platinum(II) acetylides

To investigate the electrical characteristics of organometallic complexes as molecular conductors, organometallic pi-conjugated molecules of the type trans-[PtL2(CCC6H4SAc-4)2], where L = PCy3, PBu3, PPh3, P(OEt)3, P(OPh)3, were synthesized and characterized by NMR, IR, UV, and X-ray spectroscopies. For the three complexes (L = PCy3, PPh3, and P(OEt)3) that could be measured using a cross-wire junction technique, the current-voltage (I-V) characteristics of a molecular monolayer of these complexes showed no ligand effect, despite spectroscopic evidence that electronic interaction between the phosphine ligands and the pi-system does occur. It was concluded that the tunneling efficiency across the molecule is the determining factor for conduction in this metal-molecule-metal system. It was also shown that the incorporation of a transition metal in pi-conjugated molecular wires does not adversely affect charge transport compared to all-carbon pi-conjugated molecular wires.