Spiro[4,4]nonatetraene and spiro[4,4]nona-1,3,7-triene

Symmetric Spirenes: Promising Building Blocks for New Generation Opto-Electronic Materials

The spiroconjugated hydrocarbons, and in particular spirenes, show unique properties among the numerous π-conjugated materials; they are quite rigid systems, with a subsequently small excitation reorganisation energy, and hence are...

Pentadiamond: A Hard Carbon Allotrope of a Pentagonal Network of sp^{2} and sp^{3} C Atoms

A pentagonal covalent network consisting of sp^{2} and sp^{3} C atoms has been investigated based on the density functional theory. Our theoretical investigations clarified that the pentagonal covalent network is a metastable three-dimensional carbon allotrope with the Fm3[over ¯]m space group possessing remarkable mechanical properties: relatively high bulk modulus of 381 GPa together with a negative Poisson's ratio of -0.241. Accordingly, the pentagonal covalent network possesses extremely high Young's and shear moduli of 1691 and 1113 GPa, respectively, surpassing those of the diamond. The electronic structure of the pentagonal network is a semiconductor with an indirect band gap of 2.52 eV between L and X points for valence and conduction band edges, respectively, with the relatively small carrier masses.