A planar nongraphitic zero-bandgap sp2 carbon phase made by the reaction of γ-graphyne

What is it about?

We discovered that a novel planar sheet carbon phase unexpectedly transforms highly exothermally when heated up to 310°C. This starting carbon phase is called graphyne, since it contains the aromatic rings in graphene that are each separated by a triple bond, which is called an yne group. While previous work had postulated that these acetylene groups would react inter-sheet by formation of the polyene chains found in polyacetylene, we found by spectroscopic and diffraction measurements that this thermal reaction occurs intra-plane by the conversion of the triple bonds into sp2 carbon ring segments within a planar carbon sheet structure by a process that we call ringization. This new carbon phase contains only the sp2 carbons found in graphene but contains 5,6 and larger carbon rings, along with possibly smaller carbon rings. Our theoretical work predicts that the sheets can minimize their energy by forming periodic planar sheet structures. The most energetically favorable structure is called 5,6,9 ringene, because of its content of sp2 carbon rings.

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Photo by Roberto Sorin on Unsplash

Photo by Roberto Sorin on Unsplash

Why is it important?

While the well-known graphene, and its bulk version called graphite, has enormous commercial importance for practical applications like in mechanical structures, supercapacitors, batteries, and state-of-art electronic devices, graphene is the only previously known planar all-sp2 carbon phase. We discovered in our work that graphyne decreases its bandgap from about 0.5 eV to zero during this reaction and that our ringized graphyne is dopable, so a host of new structures are available for application evaluations.

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