Propylenidene: A Novel Metallic Carbon Monolayer with Unconventional Ring Topology

Two-dimensional (2D) carbon allotropes have drawn significant interest owing to their impressive physical and chemical characteristics. Following graphene's isolation, a wide range of 2D carbon materials has been suggested, each with distinct electronic, mechanical, and optical traits. Rational design and synthesis of new 2D carbon structures hinge on experimentally reported precursors. Here, we present a 2D carbon allotrope, propylenidene (PPD), originating from bicyclopropylidene. PPD forms a rectangular lattice with 3, 8, and 10-membered carbon rings. Density functional theory (DFT) simulations investigate its structural, electronic, mechanical, and optical properties. Our study shows PPD to be metallic. PPD exhibits absorption in the infrared and visible range, showing directional dependence in its response. Mechanically, PPD exhibits marked anisotropy; Young's modulus ($Y$) varies between 205.83 N/m and 164.46 N/m. These findings underscore the potential of this novel monolayer in applications such as energy storage, gas sensing, and optoelectronics.