Stability and Electronic Properties of Biphenylene Based Functionalized Nanoribbons and Sheets

By means of first principle calculations, we have performed a theoretical characterization of the stability and electronic properties of sheets and nanoribbons that were recently synthesized employing octafunctionalized biphenylenes as building blocks. We found that the biphenylene sheet has a strong metallic character that is difficult to inhibit employing low levels of functionalization. Hydrogenation at full coverage induces a metal to insulator transition, but the band gap opened is very large, i.e., 6.6 eV. When other functional groups such as fluorine or chlorine are attached, the band gap can be regulated. The most effective chemical modification, in terms of gap opening, is the combination of hydrogen/chlorine or fluorine/chlorine. For the latter functional groups, band gaps similar to those of rutile were calculated at the HSEH1PBE/6-31G* level of theory. The biphenylene sheet functionalized on one side with fluorine and with chlorine on the other presented a CC bond length equal to 1.76 Å, one of the longest reported up to date. In contrast with recent claims, we found that, for armchair biphenylene nanoribbons, the twist induced by the functionalization of the edges does not increase the band gaps of the nanoribbons. Moreover, in some cases the gaps were reduced as we observed when the edges where saturated with hydrogen atoms. Finally, the high reactivity of the sheet indicated that it is may have promising applications in catalysis.

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