20π Antiaromatic Isophlorins without Metallation or Core Modification**

Isophlorins (two-electron-reduced porphyrins) with 20π antiaromaticity have been synthesized by metallation or core modification (replacing the inner NHs less bulky atoms) thus far. The core-modification number (CMN) is an important factor for stability of isophlorins against their oxidation to porphyrins. However, small CMN (≤ 2), i.e., without significant modification, are difficult synthesize and understanding structure–antiaromaticity relationships. Herein, we report synthesis free-base (metal-free) antiaromatic no (CMN=0) first time in literature. β-Tetracyanoporphyrins were successfully reduced hydrazine corresponding under aerobic conditions. These porphyrin/isophlorin transformations reversible. Their structure studied via 1 H NMR UV-vis/near-infrared absorption spectroscopy, X-ray diffraction theoretical calculations.