<p>The nitro (-NO₂) groups attached to the conjugated rings of 5,10,15,20-tetrakis (4-nitrophenyl) porphyrin (TNPP, chemical formula H₂C₄₄H₂₄N₈O₈) induce significant dipole polarization due to their electronegativity. Replacing nitrogen atoms within the macrocycle with carbon has a profound impact on both the synthetic feasibility and structural stability of the macrocyclic framework. In this study, the structures, stability, and electronic properties of TMC₄₄H₂₄N₈O₈ and its derivatives have been systematically investigated using density functional theory (DFT). The results indicate that substituting two adjacent nitrogen atoms in the macrocycle with carbon greatly enhances the structural stability of TMC₄₄H₂₄N₈O₈. Additionally, transition metal (TM) atoms have a distinct preference for embedding into derivatives where two nitrogen atoms positioned diagonally in the macrocycle are replaced by carbon. Among the studied complexes, FeC₄₅H₂₄N₇O₈ exhibits the highest chemical activity. CrC₄₄H₂₄N₈O₈ displays the maximum spin value, while manganese-embedded derivatives also achieve the highest spin magnitudes. These findings offer valuable theoretical insights to guide the rational design of TNPP-based metalloporphyrins, enabling precise tuning of macrocyclic architectures and deliberate engineering of TM centers for targeted applications.</p>