Oligoaryl cruciform structures as model compounds for coordination-induced single-molecule switches

The synthesis of two new cruciform structures 3 and 4 comprising an oligo(phenylene-vinylene) (OPV) and a perpendicular oligoaryl bar - namely an oligophenylene (OP) (3) and a naphthyl-phenyl-naphthyl system (4) - is reported. The OPV rod consists of two terminal pyridine units, whereas the oligoaryl rod bears two terminal acetylsulfanyl groups as protected anchor groups. The OPV bar was assembled via a Horner-Wadsworth-Emmons reaction, which directly led to the desired E,E isomers. The perpendicular oligoaryl bars were assembled with a Suzuki reaction using the corresponding boronic acids, which were already fitted with an ethyl-trimethylsilane (ethyl-TMS) sulfanyl group. In a last step, the ethyl-TMS-protected sulfur atoms were transprotected to the thioacetyl units. The cruciform structures 3 and 4 are model compounds to investigate a coordination-induced single-molecule switch exploiting the potential-dependant different bonding strengths of the anchor groups to gold. Metal-molecule-metal junctions were formed using a mechanically controllable break junction (MCBJ) setup. Current traces of molecular junctions were statistically analyzed. Further investigations of model compounds consisting only of the single bar confirm that individual molecules carrying the required function for the switching experiments were trapped between two electrodes and were mainly immobilized via thiol-gold anchor bonds.