Understanding the transport of charge across non-covalently bonded molecules is key to our understanding of many diverse systems, from oxidative damage and repair of DNA to the efficiency of organic electronic materials. Single-molecule break junctions are an important stage on which to test and develop this understanding and they have now been used by Delft researchers Ferdinand C. Grozema, Herre S. J. van der Zant and colleagues to show that electronic transport through a π-stacked dimer can be precisely controlled by mechanically manipulating its conformation and thus turning destructive interference effects ON or OFF. The cover shows the electrodes of a break junction connected by a π-stacked dimer, the molecular orbitals of which are also shown.

Abstract
Recent observations of destructive quantum interference in single-molecule junctions confirm the role of quantum effects in the electronic conductance properties of molecular systems. These effects are central to a broad range of chemical and biological processes and may be beneficial for the design of single-molecule electronic components to exploit the intrinsic quantum effects that occur at the molecular scale. Here we show that destructive interference can be turned on or off within the same molecular system by mechanically controlling its conformation. Using a combination of ab initio calculations and single-molecule conductance measurements, we demonstrate the existence of a quasiperiodic destructive quantum-interference pattern along the breaking traces of π-stacked molecular dimers. The results demonstrate that it is possible to control the molecular conductance over more than one order of magnitude and with a sub-ångström resolution by exploiting the subtle structure–property relationship of π-stacked dimers.

Full article: Riccardo Frisenda, Vera A. E. C. Janssen, Ferdinand C. Grozema, Herre S. J. van der Zant & Nicolas Renaud (2016): 'Mechanically controlled quantum interference in individual π-stacked dimers'. Nature Chemistry 8,1099–1104 doi:10.1038/nchem.2588