Application of TD-DFT Theory to Studying Porphyrinoid-Based Photosensitizers for Photodynamic Therapy: A Review

An important focus for innovation in photodynamic therapy (PDT) is theoretical investigations. They employ mostly methods based on Time-Dependent Density Functional Theory (TD-DFT) to study the photochemical properties of photosensitizers. In the current article we review the existing state-of-the-art TD-DFT methods (and beyond) which are employed to study the properties of porphyrinoid-based systems. The review is organized in such a way that each paragraph is devoted to a separate aspect of the PDT mechanism, e.g., correct prediction of the absorption spectra, determination of the singlet–triplet intersystem crossing, and interaction with molecular oxygen. Aspects of the calculation schemes are discussed, such as the choice of the most suitable functional and inclusion of a solvent. Finally, quantitative structure–activity relationship (QSAR) methods used to explore the photochemistry of porphyrinoid-based systems are discussed

How Many Ligands Can Be Bound by Magnesium–Porphyrin? A Symmetry-Adapted Perturbation Theory Study

The stability of complexes of magnesium–porphyrin with one or two identical ligands from the set water, pyridine, imidazole, acetate, acetonitrile, dimethyl sulfoxide (DMSO), ethyl acetate, or acetylacetone was examined using symmetry-adapted perturbation theory (SAPT) for minimum geometries obtained by density-functional theory (DFT). The nonadditive contributions to the interaction energy of the porphyrin ring with two ligands were also included and found to be very small in almost all cases. The stability of the complexes under standard conditions is predicted on the basis of the free Gibbs energy. The analysis of individual components of the SAPT interaction energy allows us to explain why the complexation of the second ligand is not energetically preferred in some cases

Have photosynthetic pigments been formulated for chemical stability? A cursory insight into the reactivity of magnesium porphyrinoids

<p>Magnesium complexes with reduced tetrapyrrolic ligands are active compounds of plant and bacteria photosystems. However, also the porphyrin complex appears as an intermediate on the biosynthetic pathway of the photosynthetic pigments. Its transformations, in particular the reduction of pyrrole rings, lead to the acquisition of the properties that are primary for activity in antenna systems and reaction centers. On the other hand, modifications of the porphyrin system must affect the resistance to destructive processes, such as loss of metal ion and its substitution. In order to compare the stability of three natural Mg complexes, namely Mg protoporphyrin IX, chlorophyll a, and bacteriochlorophyll a, spectroscopic studies in solution were performed. The difference in the electronic structure of the macrocyclic ligand was the basic variable in testing the action against d-electron metal salts and acetic acid. The spectroscopic studies were supplemented with calculations using the Density Functional Theory which provided insight into the stability of M(II)-N bonds depending on the dimension of the delocalized electron system. The results indicate the decreasing stability of Mg(II) complexes on the biosynthetic pathway, thereby providing an additional justification for incorporation of the metal ion into porphyrin prior to the electronic modifications of the tetrapyrrolic system.</p