An insight into the local aromaticities of polycyclic aromatic hydrocarbons and fullerenes

In this work we quantify the local aromaticity of six-membered rings in a series of planar and bowl-shaped polycyclic aromatic. hydrocarbons (PAHs) and fullerenes. The evaluation of local aromaticity has been carried out through the use of structurally (HOMA) and magnetically (NICS) based measures, as well as by the use of a new electronically based indicator of aromaticity, the para delocalization index (PDI), which is defined as the average of all the Bader delocalization indices between para-related carbon atoms in six-membered rings. The series of PAHs selected includes C10H8, C12H8, C14H8, C20H10, C26H12, and C30H12, with benzene and C-60 taken as references. The change in the local aromaticity of the six-membered rings on going from benzene to C-60 is analyzed. Finally, we also compare the aromaticity of C-60 with that of C-70, open [5,6]- and closed [6,6]-C60NH systems, and C60F18.