Multifunctional cyanoaryl porphyrazine pigments with push-pull structure of macrocycle framing: Photophysics and possible applications

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2025-01, Vol.458, p.115964, Article 115964
• Main Authors: Belashov, A.V., Zhikhoreva, A.A., Lermontova, S.A., Lyubova, T.S., Klapshina, L.G., Semenova, I.V., Vasyutinskii, O.S.
• Format: Article
• Language: English
• Subjects: Albumin; Anti-Kasha rule; Fluorescence lifetime imaging microscopy; Photosensitizer; Porphyrazine derivatives; Viscosity
• ISSN: 1010-6030
• DOI: 10.1016/j.jphotochem.2024.115964

[Display omitted] •Porphyrazine pigments (PP) do not obey the Kasha rule.•Parameters of PP fluorescence from the lowest excited state depend on viscosity.•Porphyrazine pigments bind with albumins and some other biomolecules.•Binding of PP with biomolecules causes rise in fluorescence intensity and lifetime. We report the experimental study of fluorescence properties of three porphyrazine derivatives, distinct in the number of fused aromatic rings in aryl groups contained in the macrocycle frame and/or presence of Pd in the macrocycle, in solutions with biological molecules and in methanol-glycerol mixtures. Spectral and lifetime fluorescence analysis has revealed that all three pigments demonstrated two fluorescence transition bands from the first S1 and the second S2 electronic excited states to the ground state S0, and thus followed the anti-Kasha’s rule. Strong dependence of the quantum yield and lifetimes in the S1 → S0 fluorescence band on solution viscosity was observed. A significant increase of the fluorescence decay times and fluorescence intensity with albumin concentration and with presence of other biological molecules in solution was observed as well. A model of the low-laying energy states of porphyrazine derivatives has been developed for elucidation of the fluorescence properties observed, that took into account several radiative and non-radiative relaxation channels in molecular excited states. In particular, the model suggests that the first electronic excited state consists of planar and bent conformations separated by a potential energy barrier and shows a typical molecular-rotor behavior as a function of solution viscosity. Potential applications of the porphyrazine pigments as viscosity sensors and fluorescence probes were considered.