The induced current strengths and aromatic pathways of heteroporphyrins and their antiaromatic derivatives

Abstract

The characters of heteroporphyrins and their antiaromatic derivatives are systematically investigated, based on the gauge including magnetically induced current method as well as dissected NICS(0)πzz values. In particular, calculations are used to elucidate the influence of the substitution of NH by oxygen and sulfur atoms on the aromatic (antiaromatic) character and how the heteroatoms (N, O, and S) affect the induced current strengths as well as the current pathways in different porphyrinoids. The magnetically induced current strengths as well as nucleus independent chemical shifts of aromatic heteroporphyrins and antiaromatic 22,24-dideazaheteroporphyrins have been studied using the density functional theory method. The induced current strengths and pathways are obtained by numerical integration of the induced current densities following the specific chemical bonds. The total induced current strengths of antiaromatic 22,24-dideazaheteroporphyrins is about 6 nA/T weaker than the one for the heteroporphyrins in absolute value. The substitution of pyrrole NH groups by O and S atoms does not change the total induced current strengths. The induced currents around the molecular macroring split at the heterocycles (pyrrole, furan, and thiophene) into the inner and outer routes. The heteroatoms (N, O, and S) have high resistance and consequently lead to a weaker induced current strength than the one passing the outer route in aromatic heteroporphyrins. For antiaromatic 22,24-dideazaheteroporphyrins, the heteroatoms enhance the current strength and change the main current pathway into the inner route. The induced current strength following the NH moiety is stronger than the one passing the oxygen moiety of furan ring and the sulfur moiety of the thiophene ring in both heteroporphyrins and 22,24-dideazaheteroporphyrins.