The synthesis of molecular rods with a transversal push-pull system

The design and synthesis of the molecular cruciforms 1-4 consisting of an oligophenylene-ethynyl backbone with an acetyl-protected sulfur anchor group on one end and a crossing oligophenylene cross-bar with terminal trifluoromethyl and dimethylamino groups as transversal push-pull system are reported. These cruciforms 1-4 are model compounds to investigate electronic potential-dependent switching properties of molecular junctions. While the oligophenylene-ethynyl backbone is responsible for the electronic transport properties, the transversal push-pull system should alter the tilt angle of the rod upon alignment in an electric field. As the tunnel distance at the rods end to the opposite electrode depends on the tilt angle of the rod, a considerable dependence of the transport current on the tilt angle is expected. The investigation of such transport mechanisms with the model compounds 1-4 may unravel the origin of negative differential conductance phenomena in devices consisting of sandwiched self assembled monolayers between two electrodes. The reported cruciform structures display limited stability features in the presence of acids. Their assembly is based on metal catalyzed cross coupling reactions with the chromatographic separation of two, on opposite sides mono-protected. regioisomers as key step. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).