Chirogenesis in Zinc Porphyrins: Theoretical Evaluation of Electronic Transitions, Controlling Structural Factors and Axial Ligation.

In the present work, sixteen different zinc porphyrins (possessing different meso substituents) with and without a chiral guest were modelled using DFT and TD-DFT approaches in order to understand the influence of various controlling factors on electronic circular dichroism (ECD) spectra. Two major aspects are influenced by these factors: excitation energy of the electronic transitions and their intensity. In the case of excitation energy, the influence increases in the following order: orientation of the peripheral substituents<substituent's nature<axial ligation. However, the deformation of the porphyrin plane does not affect the excitation energies. In the case of intensity, the influence increases as follows: substituent's nature<conrotatory orientation of the peripheral substituents<deformation of the porphyrin plane<disrotatory orientation of the peripheral substituents<axial ligation.