Metallic and semiconducting 1D conjugated polymers based on –S–C$\equiv$C– repeating units in poly(sulfur acetylide)

Abstract

The existence and the properties of a new 1D conjugated polymer, poly(sulfur acetylide), with –S–C$\equiv$C– repeating unit are predicted on the basis of density functional theory calculations. Depending on the conformation of the polymer, specifically on the C–S–C angles, the corresponding material is either a metallic conductor (C–S–C near linear) or a semiconductor (C–S–C not linear). It is a semiconductor with 1.6 eV band gap in the minimum energy conformation bent geometry. The polymer can be stretched out at a relatively large and impractical energy cost of 2.6 eV per –S–C$\equiv$C– unit upon which it becomes a metallic conductor. However, this semiconductor–metal transition appears to be unique in as much as it happens along a bending mode of the polymeric backbone. This new material appears to be easy to synthesize and is expected to be stable under normal conditions. Despite its simplicity and close relation to other well-known 1D conjugated polymers, such as poly(sulfur nitride) $\hbox {(SN)}_{x}$, polyacetylene $\hbox {(CH)}_{x}$ or polyyne (–C$\equiv$C–)$_{x}$, poly(sulfur acetylide) still remains to be explored.