Singlet Oxygen Kinetics in Polymeric Photosensitizers

Abstract

Nanoparticles built up from polythiophenes act as photosensitizers without embedding any additional chromophores. The self-organized water-soluble nanoparticles in this work are made from polythiophene precursors with alkyl side chains which were combined with diphosphatidylcholine-polyethylene glycol in different mass ratios. The fluorescence and singlet oxygen quantum yields of such nanoparticles can be tuned by varying the mass ratio of the two components. Two unique properties of these polymeric photosensitizers result in special singlet oxygen kinetics. First, the backbone orientation of the polythiophene influences the probability of triplet excitons, which have a high mobility across all the nanoparticle and, second, oxygen can diffuse in and out of the polymeric photosensitizer. Therefore, most of the singlet oxygen is generated inside the nanoparticle, close to the surface, soon after oxygen diffuses in. After generation, the majority of the singlet oxygen diffuses out of the nanoparticle. Using highly sensitive time- and spectrally resolved singlet oxygen phosphorescence detection, the oxygen diffusion can be confirmed, and the observed kinetics and quantum yield variations can be explained based on the polymer–semiconductor model. Whenever singlet oxygen kinetics in polymeric nanostructures are investigated, such oxygen diffusion effects have to be taken into account.

Analysis of the Isotopic Purity of D2O with the Characteristic NIR-II Phosphorescence of Singlet Oxygen from a Photostable Polythiophene Photosensitizer

“…On the basis of the criteria, we think polythiophene (PT) may be appropriate, partially because its large π-conjugated backbone and delocalized electronic structure may endow it with broad absorption (Figures A and S3). Besides, Wohlgenannt et al stated that PTs exhibited interesting chromic features, i.e., the conformational change of the conjugated backbone results in a great change of the absorption and the ratio between singlet and triplet excited states (Figure B). , Generally, a twisted structure is advantageous for the population of the excited triplet states. − Therefore, polythiophene with a twisted structure due to the steric hindrance of phenyl groups (PT10, with 10 carbon atoms on the side chain) was prepared for investigations (for details, see Section 3 in the SI).…”

“…It should be noted that the typical 1 O 2 formation rate is difficult to be derived from such profiles, probably due to the influence of the relatively long laser pulse here (10–20 μs, Figures E and S6). ,− …”

“…It should be noted that the 1275 nm phosphorescence from RB is almost featureless in H 2 O (Figures A and S10) but a small peak is observed from PT10 (Figures D and S10). It is suggested that under light excitation, excited-state excitons can interact with the dissolved oxygen inside the polymer, and singlet oxygen is generated inside but near the polymer surface …”

“…It is suggested that under light excitation, excited-state excitons can interact with the dissolved oxygen inside the polymer, and singlet oxygen is generated inside but near the polymer surface. 32 The singlet oxygen generation (Φ Δ ) of PT10 was evaluated using 1,3-diphenylisobenzofuran (DPBF)-based chemical trapping with RB as the standard photosensitizer (see Section 4 in the SI for details). 44 As shown in Figure S11, when the mixed solution of PT10 and DPBF was irradiated with 532 nm light, the characteristic absorption of DPBF at 410 nm decreased gradually.…”

Superhydrophobic Surfaces as a Source of Airborne Singlet Oxygen through Free Space for Photodynamic Therapy

“…Future work in the area would benefit from increased loading of the plastron with triplet sensitizer sites that may be used to increase the output of airborne 1 O 2 . Also, an assessment of singlet oxygen sensitizers (e.g., phthalocyanine, chlorin, and metal–organic ones) , and particle types (e.g., porous, nonporous, and plasmonic nanoparticles), − and contributions from convection would also help in the optimization of SH surfaces for 1 O 2 output. Such future studies are important for gaining an understanding of the delivery of airborne 1 O 2 to infected biological sites.…”