The development of experimentally feasible two-dimensional (2D) carbon allotropes possessing distinctive properties unattainable by graphene is imperative for the advancement of next-generation carbon-based electronics. Utilizing synthesized polyacetylene and alkane precursors, here we identify a novel 2D tetragonal carbon network, designated as apographene, through a bottom-up strategy. Characterized by an ${\mathrm{sp}}^2/{\mathrm{sp}}^3$ hybridization ratio of 2:1, apographene demonstrates remarkable thermodynamic stability, surpassing that of the experimentally confirmed $\gamma$-graphyne, $\gamma$-graphdiyne, and $\beta$-graphdiyne, and exhibits superior in-plane strength compared to the mechanical robustness of graphene. Our first-principles calculations indicate that apographene functions as an intrinsic Dirac semimetal, encompassing four highly anisotropic Dirac cones with a Fermi velocity ratio of 14.5:1; notably the maximum velocity exceeds that observed in graphene. Interestingly, unconventional Dirac nodal lines, characterized by the coexistence of open and closed configurations, appear within deeper frontier bands, thereby offering electrolyte-gate tunability for topological electronic states. The pronounced anisotropic Dirac dispersion near the Fermi level yields substantial conductivity anisotropy (with a ${\sigma }_{xx}/{\sigma }_{yy}$ ratio reaching up to 31.3), enabling quasi-one-dimensional directional polarization, which serves as a foundation for anisotropic Dirac transport sensors. These findings propose a novel carbon allotrope that integrates structural robustness with exotic quantum states, alongside highlighting a precursor-directed bottom-up approach for the design of unexplored 2D materials.

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• Elastic modulus
• Electronic structure
• Topological materials
• 2-dimensional systems
• Graphene
• Density functional calculations