Why are some polycyclic aromatic hydrocarbons extremely reactive?

Higher members of the polyacene series are extremely reactive although they are aromatic in nature. This aspect of aromatic chemistry can be explained using conventional indices of kinetic stability, such as a localization energy and a HOMO-LUMO energy separation. Large polyacene molecules have smaller localization energies and smaller HOMO-LUMO energy separations than their respective polyene references defined using matching polynomials. These molecules are presumed to be thermodynamically more stable but kinetically less stable than non-aromatic polyolefins. The same situation is sometimes observed in other groups of polycyclic aromatic hydrocarbons (PAHs). Such highly reactive PAH molecules were found to be substructures of metallic one-dimensional benzenoid polymers.