Chapter 6. Reference Photosensitizers for the Production of Singlet Oxygen
Résumé
Determination of the quantum yield of singlet molecular oxygen production (ΦΔ) by a photosensitizer is often based on relative methods (1O2 reactivity or phosphorescence). The experimental results obtained for a sensitizer of unknown ΦΔ (sample) are compared with those of a well-known standard or reference sensitizer of preferably high and accurately determined ΦΔ under appropriate experimental conditions. This chapter discusses the efficiency of 1O2 production on the basis of intrinsic or photosensitizer-dependent factors (nature and configuration of the excited state, lifetime, quenching ability by O2 and photostability) and extrinsic or medium-dependent factors (oxygen concentration, solvent viscosity and polarity, photosensitizer aggregation state, temperature and pressure). Analysis of these factors determines the general features required for any reference 1O2 photosensitizer. Phenalenone, an aromatic ketone, fulfills all these requirements and consequently can be termed as the universal reference compound for ΦΔ determination. Besides phenalenone, other aromatic ketones, heterocycles, carbon nanoforms or coordination compounds with accurately determined ΦΔ values can also be used as references for 1O2 production, not only in solution but in the solid phase as well (organic/inorganic materials such as dye-doped monoliths, films, or micro-/nanofibers and particles). Values of ΦΔ and other photophysical data for 1O2 generation by reference systems are collected in this chapter.