Several studies have provided important insights into substituent effects on antiaromatic systems. Takase et al. demonstrated that the electronic properties of π-extended antiaromatic systems can be systematically controlled by altering the structural relationship between substituents and the macrocycle. Salikov et al. showed that the antiaromaticity of cycloheptatrienyl anions is primarily determined by the geometry of the anion, which in turn is controlled by the substituent properties. More recently, Shimizu and coworkers reported that meso-substituents of 5,15-dioxaporphyrins affect their crystal packing and oxidation behavior, although the antiaromaticity itself was relatively unchanged in their system. Our previous work demonstrated that introducing electron-withdrawing cyano groups at the β-positions of isophlorins significantly enhanced their stability while reducing antiaromaticity due to π-conjugation effects. These studies suggest that the relationship between substituents and antiaromaticity vary significantly depending on the molecular framework and position of substitution.