At this time, we find no clear structural pattern of the top insulators; a broad variation of motifs is represented and the top insulators consist of at least two heteroatoms. Still, it is notable that between each of Comp260-7, Comp216-4, and Comp214-8-ranked 1, 2, and 5 in Table -only a single germanium atom has been changed to a silicon atom. We hypothesize that there is a balance in the electronic structure that regulates the transmission. Altering the molecular structure allows a finetuning of the s-interference effect. Understanding this interplay between the different atoms in sconjugated molecules using simple electronic structure models will be an important goal for future work. Let us briefly compare the transmissions of the two top candidates, Comp260-7 and Comp683-6, with Si222 as plotted in Figure . The transmission of Comp260-7 has an antiresonance at around -1 eV that is much sharper than that of Si222. Despite the sharp antiresonance, Comp260-7 actually has the highest transmission of the three at the Fermi energy. The transmission of Comp683-6 is suppressed over a much broader energy range without a clear antiresonance. Though all three are very good insulators, they may be suitable for different applications. A narrow antiresonance in the transmission may be suitable for conductance suppression in a small bias range, which may facilitate conductance switching. Furthermore, a sharp antiresonance is also a criterion for high thermopower, which we reported for a derivative of Si222. Conversely, when the transmission is suppressed over a broad energy range, the molecule will be insulating over a larger bias-range and is likely to be less sensitive to changes in the chemical environment. A special property of Si222 is that the insulating bicyclic unit is, in theory, more insulating than a gap the same dimensions. If we cut away the three silicon-bridges of the bicyclic structure, pacify the two remaining silicon atoms with hydrogen atoms and calculate the transmission for the frozen structure, the transmission is around an order of magnitude higher than that of the molecule. This procedure gives a measure of how strong the transmission-suppression is in the bicyclic moiety. Shown in Figure , we perform this procedure on Comp260-7 and Comp638-6. In both cases the transmission at the Fermi energy is over an order of magnitude lower for the full molecule than for the cut junctions.