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Metal Coordination Effects on the Photophysics of Dipyrrinato Photosensitizers.

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Within this work, we review the metal coordination effect on the photophysics of metal dipyrrinato complexes. Dipyrrinato complexes are promising candidates in the search for alternative transition metal photosensitizers for application in photodynamic therapy (PDT). These complexes can be activated by irradiation with light of a specific wavelength, after which, cytotoxic reactive oxygen species (ROS) are generated. The metal coordination allows for the use of the heavy atom effect, which can enhance the triplet generation necessary for generation of ROS. Additionally, the flexibility of these complexes for metal ions, substitutions and ligands allows the possibility to tune their photophysical properties. A general overview of the mechanism of photodynamic therapy and the properties of the triplet photosensitizers is given, followed by further details of dipyrrinato complexes described in the literature that show relevance as photosensitizers for PDT. In particular, the photophysical properties of Re(I), Ru(II), Rh(III), Ir(III), Zn(II), Pd(II), Pt(II), Ni(II), Cu(II), Ga(III), In(III) and Al(III) dipyrrinato complexes are discussed. The potential for future development in the field of (dipyrrinato)metal complexes is addressed, and several new research topics are suggested throughout this work. We propose that significant advances could be made for heteroleptic bis(dipyrrinato)zinc(II) and homoleptic bis(dipyrrinato)palladium(II) complexes and their application as photosensitizers for PDT.



coordination chemistry, dipyrrinato complexes, heavy atom effect, metal atom effect, photochemistry, photodynamic therapy, photophysics, singlet oxygen generation, triplet photosensitizer, triplet-triplet annihilation, Photosensitizing Agents, Coordination Complexes, Reactive Oxygen Species, Palladium, Ligands, Photochemotherapy, Zinc

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This work has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska‐Curie Grant Agreement No. 764837 and was supported by the Higher Education Authority and the Department of Further and Higher Education, Research, Innovation and Science (Ireland) and with the support of the Technical University of Munich—Institute for Advanced Study through a Hans Fischer Senior Fellowship (MOS). Par‐ tial support was provided by Science Foundation Ireland (SFI) (grant 21/FFP‐A/9214).