It should be noted that the total value (solid lines) of the three isoelectronic species on the NICSzz curve intersects with the component of π electron contribution (dashed lines) near x = 1 Å, meaning that NICSzz at a distance of 1 Å from the ring center is almost exclusively derived from π electrons. The analysis results of ∫NICSzz corroborate the conclusions from the NICS(1)zz calculations above. To verify the conclusions stated from the NICS analyses from electronic structure point of view, we calculated another popular quantitative indicator of molecular aromaticity, the multi-center bond order (MCBO), which is also known as multi-center bond index, and also listed it in Table . The comparison reveals that the aromatic characters as reflected by the MCBO value is in line with those obtained through NICSzz, namely aromaticity of carborazine is modestly less than benzene but significantly higher than borazine.