Two-Dimensional Carbon Graphenylene

In addition to graphite and diamond, which have been known for centuries, the family of carbon allotropes has undergone significant expansion in recent decades. This expansion can be attributed to the discovery of fullerenes, carbon nanotubes, and graphene. Carbon, with its exceptional chemical properties, can combine with itself or other elements to create not only countless organic molecules but also innovative carbon allotropes. By combining sp-, sp2-, and sp3-hybridized carbon atoms, a diverse range of carbon allotropes with varying dimensions can be formed. Among these, the sp2-carbon allotropes, such as fullerenes, nanotubes, and graphene, have garnered significant interest due to their remarkable properties and potential applications in emerging technologies. Researchers are currently investigating novel two-dimensional carbon materials based on graphenylene, utilizing density functional and tight-binding techniques. Similar to graphene-based nanotubes, a two-dimensional graphenylene sheet can be seamlessly rolled into an armchair, zigzag, or chiral-oriented cylinder. The resulting nanotube exhibits 4-, 6-, and 12-membered rings with three different bond lengths, resulting in a nonuniform electron density distribution. This nanotube can be characterized using the well-known (n,m) nomenclature. In graphenylene, the presence of dodecagonal rings creates 3.3 Å diameter holes. As the nanotube diameter decreases, these pores transform into saddle-shaped paraboloids. In this chapter, we discuss the characteristics of a novel, nondelocalized, two-dimensional sp2-carbon network using the DFT method, considering functionalization and structure. The network is composed of cyclohexatriene units with two different C-C bonds inside a C6 ring. Theoretical studies reveal that graphenylene possesses periodic pores with an average diameter of 3.2 Å and exhibits semiconductor behavior with a small direct band gap. These properties make graphenylene a promising material for various applications, including electronic devices, gas separation, storage, energy, and catalysis.