The effect of aza substitution at different sites of a benzimidazole derivative of a perylenetetracarboxylic-3,4,9,10 acid is investigated theoretically. These, as yet nonexistent aza derivatives have been subjected to theoretical analysis at PM3 (RHF) type semiempirical calculations. The results indicate that all the structures are stable but endothermic. Substitution of nitrogen on the bay region of the perylene core is more favored. The electronic and vibrational spectra have also been computed.