Aromaticity and antiaromaticity are fundamental concepts in organic chemistry that significantly influence the properties of cyclic π-conjugated systems. While aromatic compounds following Hückel's (4n+2)π-electron rule are well-studied due to their stability, antiaromatic compounds with 4nπ-electrons remain rare due to their inherent instability. However, understanding antiaromaticity is crucial not only for fundamental chemistry, but also because antiaromatic compounds exhibit unique electronic properties that make them promising candidates for organic electronic materials and optoelectronic devices. Recent advances in synthesis have enabled the preparation of increasingly stable antiaromatic systems, renewing interest in their properties and applications. Among these, porphyrinoid-based antiaromatic molecules, particularly isophlorins (two-electron-reduced porphyrins), have emerged as valuable platforms for investigating antiaromaticity. Core-modified isophlorins, where heteroatoms, such as oxygen and sulfur replace pyrrole nitrogen atoms, offer opportunities to modulate their electronic structure and stability. The properties of antiaromatic compounds can be tuned through various structural modifications. Recent studies have revealed that substituents influence their electronic structure, stability, and assembly behavior. Among antiaromatic porphyrinoids, norcorrole derivatives are extensively studied with various aryl and alkyl substituents at meso-positions. However, the relationship between substituent effects and antiaromaticity has not yet been systematically discussed in these compounds.