Database of Nuclear Independent Chemical Shifts (NICS) versus NICSZZ of Polycyclic Aromatic Hydrocarbons (PAHs)

In the present contribution, we have developed a database, called the FAR-database, where the acronym FAR stands for Fused Aromatic Rings, which presents the results of nuclear independent chemical shifts calculations, NICS(0), NICS(1), NICS(0)ZZ, and NICS(1)ZZ, of 660 neutral benzenoid-PAHs and cyclopenta-fused PAHs. The FAR-database provides NICS data of aromaticity of PAHs that could be used in data science and machine learning. To the best of our knowledge, no such database is available in the literature. The importance of this database lies in its potential to transform data into insight and knowledge. Additionally, a new visual representation of the NICS aromaticity pattern, based on the magnitude of the NICS value, is presented. Nowadays calculations of NICS(0)ZZ or NICS(1)ZZ have become popular methods to evaluate aromaticity of systems. By looking at all the 660 systems in the FAR-database, it becomes evident that NICS(0), NICS(1), and NICS(1)ZZ present similar NICS aromaticity patterns for most of the systems. But the NICS aromaticity patterns found with NICS(0)ZZ in many cases do not agree with the NICS aromaticity patterns found with NICS(0), NICS(1), and NICS(1)ZZ. There are cases where the NICS(0)ZZ aromaticity pattern does not show an aromatic character at all. From XY NICS scan at planes from Z = 0 to Z = 1, it is found that as the Z-height is increased, the π-electron ring current effects are dominant, and the σ-bonding contributions are diminished. Therefore, it is recommended here to compute NICS(1)ZZ instead of NICS(0)ZZ when analyzing NICS of PAHs.