Chapter 7: The Sensitized Production of Singlet Oxygen Using Two-Photon Excitation

The one-photon photosensitized production of singlet oxygen has been studied and exploited extensively for the past ∼50 years. The photosensitized production of singlet oxygen under conditions in which the sensitizer simultaneously absorbs two photons is a relatively new field that allows us to study issues and exploit phenomena not possible with the one-photon counterpart. Much of the information gleaned from experiments that examine the two-photon sensitized production of singlet oxygen contribute to a better understanding of fundamental principles of photophysics (e.g., the interaction between the radiation field and a molecule, effect of molecular structure on light-induced transitions between electronic states, etc.). However, from the perspective of someone interested in processes that depend on singlet oxygen, the two-photon process probably has its greatest effect as a mechanistic tool that allows for unique spatial and spectral control of singlet-oxygen production in complicated heterogeneous systems (e.g., a mammalian cell). Selected aspects of the two-photon sensitized production of singlet oxygen, including its production in experiments involving single mammalian cells, are discussed in this chapter.