Abstract: The molecular geometries of porphin and those modified with —CH=CH2, —COCH3, —CHOHCH₃, —CHNH₂CH₃, or —CHSHCH₃ groups were optimized at the B3LYP/6-31G (d, p) level of density functional theory (DFT). At the same time, their absorption spectra and ¹H NMR were also calculated. The results illustrated that these substitution groups had differential spatial positions and did not disturb the structure of porphin extremely. Meanwhile, they have re-adjusted the contribution of atomic charges of porphin and then have changed the LUMO-HOMO energy gaps of porphin. As a result, the absorption spectra and 1H NMR were changed accordingly.

Key words: Porphrin, Substitution, Density functional theory, Absorption spectrum, ¹H NMR