Photosensitized Generation of Singlet Oxygen

Abstract

This work gives an overview of what is currently known about the mechanisms of the photosensitized production of singlet oxygen. Quenching of ππ* excited triplet states by O2 proceeds via internal conversion of excited encounter complexes and exciplexes of sensitizer and O2. Both deactivation channels lead with different efficiencies to singlet oxygen generation. The balance between the deactivation channels depends on the triplet‐state energy and oxidation potential of the sensitizer, and on the solvent polarity. A model has been developed that reproduces rate constants and efficiencies of the competing processes quantitatively. Sensitization by excited singlet states is much more complex and hence only qualitative rules could be elaborated, despite serious efforts of many groups. However, the most important deactivation paths of fluorescence quenching by O2 are again directed by excess energies and charge‐transfer interactions similar to triplet‐state quenching by O2. Finally, two recent developments in photo‐sensitization of singlet oxygen are reviewed: Two‐photon sensitizers with particular application potential for photodynamic therapy and fluorescence imaging of biological samples and singlet oxygen sensitization by nanocrystalline porous silicon, a material with very different photophysics compared to molecular sensitizers.

Triplet Excited States and Singlet Oxygen Production by Analogs of Red Wine Pyranoanthocyanins

“…However, for compounds 3 and 6-8, (1 À Φ f )/Φ D (max) increases almost linearly with increasing k q , indicating that k d is bimodal, with one component that is relatively structure insensitive and another that is responsible for an increase in k q . In general, k q is found to correlate with the oxidation potential of the sensitizer, as expected for charge-transfer quenching or electron transfer from the sensitizer to molecular oxygen (24,27,28). In the present case, however, the sensitizer is cationic and electron-withdrawing substituents (26) such as nitro or cyano, which should increase the oxidation potential, actually increase k q much more than electron-donating substituents (26) such as methyl or methoxy.…”

Evaluation of 405‐nm monochromatic light for inactivation of Tulane virus on blueberry surfaces

“…Production of singlet oxygen can also be enhanced by the interaction of multiring structured compounds that are chemically similar to porphyrin (Costa et al 2012). These chemical compounds are commonly used to inactivate certain pathogens within blood and blood products (Corbin 2002;Schmidt 2006). Two food-grade chemicals that are singlet oxygen enhancers are rose bengal, also known as red food dye 105, and riboflavin, which is also known as vitamin B2 (Lenard et al 1993;Huang et al 2004;Costa et al 2012).…”

The Influence of Oxygen Depletion and Photosensitizer Triplet‐state Dynamics During Photodynamic Therapy on Accurate Singlet Oxygen Luminescence Monitoring and Analysis of Treatment Dose Response

“…In PDT, the dose is related to the amount of photosensitizer (PS) and light delivered, together with the available molecular oxygen ( 3 O 2 ) concentration (5). These three components interact to generate reactive oxygen species, including singlet oxygen ( 1 O 2 ) (6). The reactions involved in photosensitized generation of 1 O 2 are depicted in the Jablonski diagram in Fig.…”