Electronic band gap engineering of pyrene-based α-graphyne through chemical functionalization and mechanical strain

Two-dimensional (2D) carbon allotropes beyond graphene, particularly graphynes, offer versatile platforms for tuning structure-property relationships in mixed sp-sp² hybridized lattices. Here, we introduce pyrene-based α-graphyne, a novel derivative constructed via selective linker removal and hydrogen passivation, embedding extended aromatic domains while preserving the α-topology. Density functional theory calculations (PBE-GGA) confirm dynamic and thermal stability up to 2000 K, supported by phonon dispersion and ab initio molecular dynamics simulations. Mechanical analysis reveals high stiffness (Young's modulus ∼174 N m^-1; shear modulus ∼71 N m^-1) and a nearly isotropic elastic response. The pristine lattice exhibits Dirac-like semimetallicity. The hexagonal lattice was transformed into an equivalent orthorhombic supercell, allowing uniaxial compressive and tensile strains along armchair and zigzag directions. Under ±3% strain, a finite band gap emerges symmetrically in the meV regime. Along the zigzag direction, the gap reaches 18.6 meV (-3%) and 11.2 meV (+3%), while along the armchair direction it increases to 20.0 and 14.3 meV, respectively. For equal strain magnitudes, the larger response under armchair deformation reflects stronger modulation of p_z-p_z orbital overlap and strain-induced lifting of Dirac-point degeneracy. Chemical functionalization provides an additional degree of control: selective hydrogenation and fluorination at sp² sites stabilize wide band gaps of 3.93 eV and 3.21 eV, respectively, while complete chlorination destabilizes the lattice due to steric crowding and out-of-plane distortions. Gas adsorption analysis further reveals strong, site-dependent binding for small molecules (Cl₂, F₂, NO, O₂, and CO₂), highlighting chemically active acetylenic regions. Together, these results establish pyrene-based α-graphyne as a mechanically robust, strain-tunable, and chemically responsive 2D carbon framework.