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Photophysical and photochemical characteristics of free‐base and Zn(II) complexes of N‐methylated tetra‐ and tripyridylporphyrins

Photodynamic therapy (PDT) is a fairly new, non‐invasive method used for the destruction of cancer tissue, which can be applied alone or in combination with other therapies such as surgery, chemotherapy or radiotherapy [1]. It is based on a combination of individually nontoxic components, photosensitizer (PS), light and oxygen, which, acting together, can lead to cytotoxic effect. The most used PSs have tetrapyrrole‐based structures, such as porphyrins, chlorins and bacteriochlorins as main representatives. Some of their characteristic photophysical and photochemical properties that are important for PDT encompass stability, strong absorption and fluorescence spectra, and efficient production of singlet oxygen [2]. Another advantage of PS with tetrapyrrole structure is a relatively easy chelation with the pyrrole nitrogen atoms that can lead to modification of photophysical properties and differences in photodynamic activity. It was shown that chelation with Zn(II) can improve photophysical properties of potential tetrapyrrole‐based PSs toward longer lifetime of the PSs triplet excited state, increasing the possibility for 3PS* to interact with molecular oxygen and/or cellular targets [3, 4]. In our previous work, synthesis and photophysical properties of a series of amphiphilic pyridylporphyrins was described and their PDT activity demonstrated [5]. Our further study that we wish to present here includes a new approach to methylation and chelation of tetraand tripyridylporphyrins with Zn(II). The photophysical and photochemical properties, notably absorption and fluorescence spectra, singlet oxygen production using 1, 3‐ diphenylisobenzofuran (DPBF) photodegradation method, as well as lipophilicity of the obtained complexes will be presented and described in comparison to their free‐base counterparts.

Porphyrin ; Photodynamic therapy ; Lipophilicity ; Singlet oxygen

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