According to the calculations, the pentagonal rings (ring D) of the neutral and anionic forms of 2a show NICS(1) values of +0.18 and -6.03, respectively, implying that the pentagon was converted from non-aromatic to aromatic under basic conditions. The NICS(1) values indicated that the aromaticity of ring F decreased under basic conditions. These results suggest that the anionic form of 2a makes a large contribution to the fluorenyl-anion-type resonance, as shown in Figure . In contrast, the NICS(1) values show that the aromatic characters of the A, B, and F rings of the anionic form of 3a is weaker than that of the neutral form, and the local antiaromatic character of ring D increases under basic conditions, suggesting that the contribution of quinoid resonance increases under basic conditions. These calculations suggest that the characteristic chromic properties of 2 and 3 are caused by the different resonance hybrids.