Doping of Partially Saturated Nanothreads within Density Functional Theory

A novel one-dimensional carbon nanomaterial, known as nanothreads, has recently been synthesized by slowly compressing crystalline, solid benzene from high pressure. A comprehensive advanced solid-state NMR analysis reveals that approximately a third of carbon atoms reside in the partially saturated structures, the degree-4 nanothreads, with isolated double bonds retained in the recovered sample. Some enumerated degree-4 structures, like IV-12 and IV-18, have much smaller distances between the double bonds than that in normal materials due to the rigid sp³ backbone, which leads to very dispersive bands near the Fermi level and may make these threads feasible to be doped. We investigated such doping computationally, using jellium models, alkali intercalation, and nitrogen substitution on the carbon backbone in both pristine and partially fluorinated IV-12 and IV-18 threads. Under doping, the IV-12 thread collapses to fully saturated structures, probably due to the strongly overlapping of the double bonds. There is no clear evidence for charge transfer in the pristine IV-18 thread, but the partially fluorinated IV-18 thread can be doped; this system may constitute a new type of conductive polymer.