Combining Magnetic Circular Dichroism Spectra with TD-DFT results to understand the effects of massive expansion Of the aromatic ring in Zn-porphyrins

Porphyrins are a diverse group of bioinorganic molecules with a complex cyclic structure composed of four pyrrole rings. They have many unique applications in medicine and energy conversion such as photodynamic therapies and in solar cells. Inclusion of specific functional groups in porphyrins can add new properties. The effects of peripheral substituents on the electronic structure of Zn-anthraquinonoporphyrins were investigated using UV-visible absorption spectroscopy, magnetic circular dichroism (MCD) spectroscopy, and computational modeling methods. Results showed that introduction of the anthraquinone functional groups distorted the symmetry of the porphyrins but more importantly caused a distortion of the excited states as well. This resulted in red-shifting of the porphyrin absorption bands and an intensifying of the Q-band. These properties, particularly shifting the Q band into the near IR, are essential in developing and extending photodynamic therapies since the closer to the IR region a porphyrin absorbs, the farther into the skin it can penetrate and so it becomes a more efficient photosensitizer for singlet O₂ production.