Singlet oxygen sensitized delayed fluorescence as tool for estimation of photooxidation properties and oxygen sensing

The singlet oxygen sensitized delayed fluorescence (SODF) is relatively rare phenomenon observed for some fluorescent photosensitizers. SODF is generated from repopulated S1 excited states of the photosensitizer from its... [ view full abstract ]

The singlet oxygen sensitized delayed fluorescence (SODF) is relatively rare phenomenon observed for some fluorescent photosensitizers. SODF is generated from repopulated S₁ excited states of the photosensitizer from its long-lived triplet states by singlet oxygen (O₂(¹Δ_g)) nearby formed via photosensitized reaction. The prerequisites of SODF include high concentration of fluorescent photosensitizer with longer lived triplet states, proper energy of the triplet states and high concentration of O₂(¹Δ_g) generated in close proximity of the triplets. SODF can be finding on polymer nanomaterials enriched with porphyrin photosensitizers. These materials have potential broad applications in medicine due antibacterial and antiviral properties of photogenerated O₂(¹Δ_g).^1,2

Herein we report the study of sulfonated polystyrene nanoparticles (NPs) with encapsulated hydrophobic 5,10,15,20-tetraphenylporphyrin or ionically entangled tetracationic 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin. A simple nanoprecipitation method was used for preparation of stable NPs from sulfonated electrospun nanofiber membranes. The materials were studied by microscopic methods, dynamic light scattering, steady state and time-resolved absorption and fluorescence spectroscopy. Photooxidation ability was measured as kinetic of photodegradation of uric acid or formation of I₃^- in iodide test.

These photoactive nanoparticles exhibit an effective photogeneration of O₂(¹Δ_g) under irradiation by visible light leading to strong signal of SODF. Photophysical evaluation reveal that SODF of nanoparticles depends on the mode of photosensitizer bounding, concentration of photosensitizer and dissolved oxygen O₂(³Σ_g^-) and the temperature in aqueous solutions. Applications of SODF toward dissolved oxygen sensing and monitoring of photooxidation ability in aqueous media are demonstrated and discussed.

Acknowledgment:

This work was supported by the Czech Science Foundation (16-15020S) and by Operational programme Research, Development and Education, Charles University Centre of Advanced Materials, CZ.02.1.01/0.0/0.0/15_003/0000417.

References:

[1] Henke P., Kozak H., Artemenko A., Kubát P., Forstová J., Mosinger J., ACS Appl. Mater. Interfaces, 6, 15 (2014).

[2] Henke P., Kirakci K., Kubát P., Fraiberk M., Forstová J., Mosinger J., ACS Appl. Mater. Interfaces, 8, 38 (2016).