Photodynamic therapy (PDT) is a well-established treatment option in the treatment of certain cancerous and pre-cancerous lesions. Though best-known for its application in tumor therapy, historically the photodynamic effect was first demonstrated against bacteria at the beginning of the 20^th century. Today, in light of spreading antibiotic resistance and the rise of new infections, this photodynamic inactivation (PDI) of microbes, such as bacteria, fungi, and viruses, is gaining considerable attention. This review focuses on the PDI of viruses as an alternative treatment in antiviral therapy, but also as a means of viral decontamination, covering mainly the literature of the last decade. The PDI of viruses shares the general action mechanism of photodynamic applications: the irradiation of a dye with light and the subsequent generation of reactive oxygen species (ROS) which are the effective phototoxic agents damaging virus targets by reacting with viral nucleic acids, lipids and proteins. Interestingly, a light-independent antiviral activity has also been found for some of these dyes. This review covers the compound classes employed in the PDI of viruses and their various areas of use. In the medical area, currently two fields stand out in which the PDI of viruses has found broader application: the purification of blood products and the treatment of human papilloma virus manifestations. However, the PDI of viruses has also found interest in such diverse areas as water and surface decontamination, and biosafety.

A crucial factor in choosing a porphyrin or analogous photosensitizer for photodynamic therapy (PDT) is its ability to incorporate into the cells. For hydrophobic compounds that partition passively into the cytoplasmic membrane, a partition coefficient between an organic solvent and water, P, is one factor that could be used to predict the molecule's ability to diffuse into biomembranes. We synthesized several porphyrins, modified with two, three or four meso‐substituents and studied their spectroscopic and photophysical properties. The octanolwater partitioning coefficients, log P, were calculated as a parameter for hydrophobicity. We found these porphyrins to be very hydrophobic, with log P values in the range of 8.9–11.8. These were correlated with the binding constants of these porphyrins into liposomes, K_b, as well as to their uptake by cells. The correlation between the estimated log P and K_b is nearly linear but negative, indicating, apparently, that there is lesser binding to liposomes with increased hydrophobicity. On the other hand, all of the studied porphyrins are taken up by cells, but there is no clear correlation between cellular uptake and the log P or K_b. Lipinski's pharmacological “rule of 5” predicts poor permeation of drugs into cells when log P is greater than five. This may be relevant for diffusional binding to liposomes, where aqueous aggregation can interfere strongly with cellular uptake. In such extreme conditions, neither liposome binding nor other rules seem to predict porphyrin behavior in vitro.

This review follows the research, development and clinical applications of the photosensitizer 5,10,15,20‐tetra(m‐hydroxyphenyl)chlorin (mTHPC, temoporfin) in photodynamic (cancer) therapy (PDT) and other medical applications. Temoporfin is the active substance in the medicinal product Foscan® authorized in the EU for the palliative treatment of head and neck cancer. Chemistry, biochemistry and pharmacology, as well as clinical and other applications of temoporfin are addressed, including the extensive work that has been done on formulation development including liposomal formulations. The literature has been covered from 2009 to early 2022, thereby connecting it to the previous extensive review on this photosensitizer published in this journal [Senge, M. O. and J. C. Brandt (2011)Photochem. Photobiol.87, 1240–1296] which followed its way from initial development to approval and clinical application.

The generation of bio‐targetable photosensitizers is of utmost importance to the emerging field of photodynamic therapy and antimicrobial (photo‐)therapy. A synthetic strategy is presented in which chelating dipyrrin moieties are used to enhance the known photoactivity of iridium(III) metal complexes. Formed complexes can thus be functionalized in a facile manner with a range of targeting groups at their chemically active reaction sites. Dipyrrins with N‐ and O‐substituents afforded (dipy)iridium(III) complexes via complexation with the respective Cp*‐iridium(III) and ppy‐iridium(III) precursors (dipy=dipyrrinato, Cp*=pentamethyl‐η⁵‐cyclopentadienyl, ppy=2‐phenylpyridyl). Similarly, electron‐deficient [Ir^III(dipy)(ppy)₂] complexes could be used for post‐functionalization, forming alkenyl, alkynyl and glyco‐appended iridium(III) complexes. The phototoxic activity of these complexes has been assessed in cellular and bacterial assays with and without light; the [Ir^III(Cl)(Cp*)(dipy)] complexes and the glyco‐substituted iridium(III) complexes showing particular promise as photomedicine candidates. Representative crystal structures of the complexes are also presented.