Singlet oxygen definition

The phenomenon of fluorescence has been synonymous with ultraviolet (UV) and visible spectroscopy rather than near-infrared (near-IR) spectroscopy from the beginning of the subject. This fact is evidenced in definitive texts which also provide useful background information for this volume (see, e.g., Refs. 1-6). Consequently, our understanding of the many molecular phenomena which can be studied with fluorescence techniques, e.g., excimer formation, energy transfer, diffusion, and rotation, is based on measurements made in the UV/visible. Historically, this emphasis was undoubtedly due to the spectral response of the eye and the availability of suitable sources and detectors for the UV/visible in contrast to the lack of equivalent instrumentation for the IR. Nevertheless, there are a few notable exceptions to the prevalence of UV/visible techniques in fluorescence such as the near-IR study of chlorophyll(7) and singlet oxygen,<8) which have been ongoing for some years. 

The application of photodynamic therapy (PDT) in treatment of bacterial infections will definitely continue to attract the attention of scientists. It is considered unlikely that bacteria develop resistance against singlet oxygen therefore, PDT may become a useful weapon to battle infections. For treatment of infections in the oral cavity, a smart toothpaste containing a photosensitizer that is selectively absorbed by bacteria is under development. This can be used in combination with a laser toothbrush designed recently (Moore, 1998). Sensitizers can further be incorporated into bandages for disinfection of wounds or in cellophane films used to wrap food (Moore, 1998). 

A photosensitized process of Type II is by definition an energy transfer process [5]. The most common Type II process is oxidation via singlet oxygen ( O2) formation ... 

Production of Active Oxidants The major oxidants generated in the atmosphere are ozone, O3, the hydroxyl radical OH, and the nitrate radical -ONOi, while in the aquatic environment singlet oxygen, 2, would appear to be the more significant. The importance of these components in environmental transformations is based on an understanding of the conditions needed for their generation, definition of environmental concentrations, and appropriate kinetics. 

Oxazole cycloadditions have been reported with alkyne dienophiles (tandem Diels-Alder addition and retro Diels-Alder loss of a nitrile leads on to furans), benzyne (the primary adduct can be isolated), and with typical alkene dienophiles. The primary adducts from addition of singlet oxygen rearrange, by a mechanism which is not definitely established, to form triamides, themselves useful synthetic intermediates. The only example of this sort of process with an imidazole is an intramolecular example, the product in this case being a pyr-role. ... 

The nonequivalence of the rates of photosensitized reactions in heterogeneous nanophases of glassy polymers is proved in experiments with naphthalene phosphorescence decay. For example, it is shown [13] that in aerated PMMA films fluorescence of singlet-excited naphthalene molecules N can be decayed by tinuvin P, but this does not affect the rate of naphthalene dissociation. The latter is consumed in the process, the rate of which is not defined by the concentration of particles responsible for fluorescence. Under such conditions, according to definition by the authors [13], primary chemical acts are inevitable. However, in the absence of oxygen tinuvin P slows the photochemical process down in accordance with a decrease of singlet-excited naphthalene molecule concentration. 

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