The DFT-study at the B3LYP/6-31G level has been conducted to analyze the interactions of pyrene-based graphene fragments with toxic gases F2, AsH3, PH3, and HF. Three diamond-shaped n-pyrene clusters (n = 3, C30H14; n = 4, C48H18; n = 5, C70H22) were systematically optimized, and their adsorption behavior was investigated through the total and adsorption energies, frontier molecular orbital (HOMO – LUMO) distributions, and energy gaps. The results revealed that gas adsorption induces significant modifications in the electronic structure of the pyrene clusters, with variations depending on both the cluster size and gas nature. The calculated adsorption energies demonstrated a size-dependent trend, indicating that increasing the number of zigzag edges in pyrene enhances surface reactivity toward certain analytes. These findings highlight the potential of pyrene-based graphene nanostructures as selective and efficient sensors for hazardous gases.