Edge modification of PAHs: the effect of embedded heterocycles on the aromaticity pattern

International audienceAromaticity studies carried out on the condensed model system 2 with different heteroatoms showed that the NICS(1) aromaticity in the five-membered ring correlates with that in the parent five-membered ring having the same heteroelement. Although the local aromaticity pattern is clearly determined by the Clar structure, as evidenced by the local aromaticity values in the reference molecules R1-3, the modifying effect of the heteroatom is significant. The correlation between the NICS(1)5 and NICS(1)6 aromaticities of the neighbouring rings is excellent, by modification of the heterocycle, we can engineer the aromaticity of the connecting six-membered ring as well. Geometry based aromaticity indices do not correlate well with NICS values probably due to annellation effects between rings with different aromatic character. Calculations with the different tested basis sets don’t show significant differences, therefore the use of the computationally cheaper methods is envisaged during further investigations of corresponding systems with extended π-framework