The Transport Properties of Cross-Conjugated Molecules

As mentioned in the introduction, the reduced transport through the short path is, in fact, an effect of quantum interference. It is common for molecules with cross-conjugated paths spanning the two electrodes. In fact, many molecules exhibit interference effects, but they are not always in an energy range that would make the effect observable experimentally. 

The critical component for our purpose here is the central double bond. When we have both binding groups attached to the same carbon atom of the double bond, we have our cross-conjugated path between the electrodes. The transmission for these three molecules is shown separated into symmetry (a and it) components. That is, we can isolate the contributions to the total transmission that are carried by the a and ic systems within the molecule. In all cases, the black line is the symmetry component and the black line is the total transmission, which is simply a sum of the two components. 

In the cross-conjugated system, the situation changes. The 3t-transmission has a sharp dip very close to the Fermi energy this is a signature of destructive interference. As the ji-transport is suppressed, the total transmission is actually dominated by the underlying o-transport near the Fermi energy. This is why the 

This is perhaps a somewhat surprising result. We normally consider that fully conjugated molecules will be dominated by the % system. Of course, if the Jt-transport approaches zero, this cannot be the case. As soon as we move away from the interference feature (in energy), the it-system again dominates the transport and a cross-conjugated molecule simply resembles any other conjugated molecule. 

Molecules 1-3 and our short path are cross-conjugated in the sense of the Phelan and Orchin definition. However, one can see exactly the same effect if the 

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In this chapter, we focus on electron transport through molecules bound between gold electrodes, and even more specifically, we will focus on the theoretical description of the transport properties of cross-conjugated molecules. 

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