Charge transport: through space keeps up with the pace

Charge transport is a fundamental and crucial process in organic electronics. Modern understanding of the transport has shown that, on single molecule level, this process can be described by through bond (TB) and through space (TS) models. The quantitative deciphering of the TB process has been established in recent years by the aid of scanning tunneling microscope (STM) technique and by making use of a variety of well-defined conjugated rod-like molecules as conducting channels. Although it has been a common sense that the TS – interaction plays a key role in several processes of organic electronics, the TS process still needs to be investigated in more detailed ways. One of the challenges is the unavailability of right model conjugated molecules to support the rigid estimation of the TS process on single molecular level. Paracyclophanes seem to be ideal model molecules. But in fact, the linkage between the conjugated moieties in paracyclophanes is alkyl and the saturated spacers only allow for evaluating a TS charge transfer/transport event but cannot provide channels to examine the TS and TB processes both in situ and in sync. Column phase formed by discotic conjugated molecules offers a unique channel to measure the TS charge transport, but it is helpless to understand the TB transport process in the same column. Consequently, the detailed understanding of the TS charge transport lagged behind the TB case. Reporting on Angew. Chem. Int. Ed., Zhou, Zhao, Tang and their colleagues [1] contribute elegant model molecules to the help of understanding. The electronic structure of the model compound is shown in Figure 1(a). (Z)-o-BPTPE is a folded molecule containing a pair of well -stacked biphenyls tethered by a vinyl group. The -stacked region in (Z)-o-BPTPE is about two-fold larger than that in paracyclophane. Meanwhile, the vinyl linkage that holds two biphenyls together is superior to the alkyl chain in paracyclophane in two aspects. On one hand, conjugated linkage offers the spacer with electronic conductivity thereby the TB and TS processes can be estimated in situ and in sync; and on the other hand, it bestows the whole molecule with enhanced structure rigidity and stability, thus produce more reliable and reproducible single-molecule junctions for the