Graphynes

Graphynes are a class of two-dimensional carbon allotropes that are structurally distinct from graphene. While graphene consists solely of hexagonal carbon rings, graphynes incorporate both hexagonal and specific types of alkynyl linkages between these rings. This incorporation of sp-hybridized carbon atoms alongside the sp2-hybridized carbon atoms of the hexagonal rings gives graphynes unique electronic and structural properties. The precise arrangement of these alkynyl linkages leads to a variety of different graphyne structures, often denoted by Greek letters or numbers, such as $\alpha$-graphyne, $\beta$-graphyne, and graphdiyne.

These structural variations result in diverse electronic band structures. Many graphynes exhibit Dirac cones, similar to graphene, which are responsible for their high charge carrier mobility. However, unlike graphene, some graphynes are predicted to be semiconductors, possessing a tunable band gap. This semiconducting nature, along with their inherent two-dimensional structure, makes graphynes promising candidates for applications in electronics, such as field-effect transistors and optoelectronic devices. Their unique electronic properties are a direct consequence of the extended $\pi$-conjugation system that arises from the alternating sp2 and sp hybridized carbon atoms. Research into graphynes is ongoing, focusing on their synthesis, characterization, and the exploration of their potential technological applications.