The Synthesis of Functionalised Diaryltetraynes and Their Transport Properties in Single-Molecule Junctions

The synthesis and characterisation is described of six diaryltetrayne derivatives [Ar-(CC)(4)-Ar] with Ar=4-NO2-C6H4- (NO(2)4), 4-NH(Me)C6H4- (NHMe4), 4-NMe2C6H4- (NMe(2)4), 4-NH2-(2,6-dimethyl)C6H4- (DMeNH(2)4), 5-indolyl (IN4) and 5-benzothienyl (BTh4). X-ray molecular structures are reported for NO(2)4, NHMe4, DMeNH(2)4, IN4 and BTh4. The stability of the tetraynes has been assessed under ambient laboratory conditions (20 degrees C, daylight and in air): NO(2)4 and BTh4 are stable for at least six months without observable decomposition, whereas NHMe4, NMe(2)4, DMeNH(2)4 and IN4 decompose within a few hours or days. The derivative DMeNH(2)4, with ortho-methyl groups partially shielding the tetrayne backbone, is considerably more stable than the parent compound with Ar=4-NH2C6H4 (NH(2)4). The ability of the stable tetraynes to anchor in Au|molecule|Au junctions is reported. Scanning-tunnelling-microscopy break junction (STM-BJ) and mechanically controllable break junction (MCBJ) techniques are employed to investigate single-molecule conductance characteristics.