Effect of geometrical torsion on the rectification properties of diblock conjugated molecular diodes

We model several Au/conjugated molecule/Au junctions in the presence of molecular geometrical torsions. A rectification ratio of around 10 in the twisty diphenyldipyrimidinyl system is obtained, which is in good agreement with experiment. Deeper insight into the rectification mechanism of the conjugated molecular diodes is presented on the basis of simulations in a set of simpler but similar junctions. The rectification effect ( the ratio) is significantly improved with increasing the molecular twist, while the conductance is reduced accordingly. Our results suggest that the rectification can be enhanced by the geometrical-torsion-induced reduction in the conjugation length of organic molecules. (C) 2014 AIP Publishing LLC.