Functional singlet oxygen generators based on porphyrazines with peripheral 2,5-dimethylpyrrol-1-yl and dimethylamino groups

• Investigated compounds were observed to be singlet oxygen generators.
• Ability of aggregation was detected in several solvents.
• Photobleaching, singlet oxygen generation, fluorescence quantum yields were measured.
• Life times of fluorescence of compounds were determined.
• Deaerated samples had lower efficacy of photobleaching and singlet oxygen generation.

Photochemical, photophysical and spectral properties of three synthesized porphyrazines, with 2,5-dimethylpyrrol-1-yl and dimethylamino substituents were studied to test their potential usefulness in photodynamic therapy. The porphyrazines are metallated at the core with Mg(II) – MgPz and Zn(II) – ZnPz ions; the third one was in demetallated form (2HPz). The compounds were irradiated with a xenon lamp. The photodegradation, steady-state and time-resolved absorption and emission studies of porphyrazines were performed in different solvents. Quantitative evaluation was made on the basis of photodegradation kinetic parameters. The photodegradation process appeared to follow in two (MgPz and ZnPz) or one (2HPz) stages first-order kinetics. The demetallated porphyrazine was found to be more stable then MgPz and ZnPz. Solvatochromic effects were evaluated by monitoring the changes in UV–vis spectra. The correlation between the Q-band shift towards longer wavelengths and the refractive index of the solvent was tested. The fluorescence spectra were evaluated and the quantum yield of emission was determined. Singlet oxygen generation and quantum yield (ΦΔ) were investigated, in aerobic condition and in the environment with limited access of oxygen with 1,3-diphenylbenzisofuran as a chemical quencher. The mechanism of photochemical reaction for all Pzs studied was proved to be of type II.

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