Photo sensitizer

Delahoy, A., Doele, B., Ellis, F., Ramaprasad, K., Tonon, T., and Van Dine, J., Amorphous Silicon Films and Solar Cells Prepared by Mercury-Sensitized Photo-CVD of Silane and Disilane, Materials Issues in Applications of Amorphous Silicon Technology, (D. Adler, et al., eds), MRS Proc., (49) 33-39 (1985)... 

As with 2-cyclopentenone, the ratio (70) (71) varies with the molar concentration of the enone, the head-to-head dimer (71) becoming increasingly important at higher concentrations/133 This reaction is efficiently sensitized by acetophenone, benzophenone, thioxanthone, and naphthalene. The same enone concentration effect was observed in the sensitized photo-dimerization as in the direct photolysis. Similarly, quenching of the dimerization by piperylene was not accompanied by a change in dimer ratio. Systematic... 

It is clear from this that the sensitized reaction has a higher quantum efficiency than the the reaction following direct photo-activation. A comparison of quantum efficiencies for direct and sensitized photo-ring opening is given in Table 7, showing that the sensitized process has an efficiency of unity. 

C3 Aryl ttioxanes (75a, 75b) 5 steps (R) Dye-sensitized photo- oxygenation 30 nM (NF54) 10 mgkg i Toxicity studies reved that 11b has a similar tiierapeutic index to artelinic acid 109, no... 

Sensitized photo-oxidation of substituted cyclohexanone silyl enol ethers yields substituted cyclohex-2-enones." For example, menthone may yield (8 X=H) or (15) depending upon the direction of enolization " the corresponding hydroxy-... 

Full details of Barton s selenofenchone (212 X = Se) and fenchylidenefeachane (212 X = 2-fenchylidene) synthesis (Vol. 6, p. 40) have been published" and Wynberg has discussed the antipodal interaction effect in the reductive dimerization of (+)- and ( )-camphor to bornylidenebornanes (Vol. 7, p. 41)," sensitized photo-oxidation of which has also been reported." The CuCl2-promoted dimerization of camphor-lithium enolate yields the expected mixture of dia-... 

Of particular importance in the geriatric patient Due to systemic absorption bradycardia, arrhythmias, hypotension, dizziness, fatigue, somnolence, confusion, hallucinations, psychosis, headaches, bronchospasm, alopecia, arthralgia, impotence due to topical administration stinging, tearing, blurred vision, light sensitivity/photo-phobia, dryness, decreased visual acuity... 

The sensitized photo-Fries rearrangement of 55 in benzene, toluene, and in concentrated polystyrene solution in dioxane is effectively quenched with biacetyl.4 This phenomenon must again be attributed to quenching of the aromatic energy donor, because in pure dioxane the photorearrangement of 55 is not influenced by biacetyl (vide supra). 

Dye-sensitized photo excitation (eg with TTP, below) Photosensitizer + hv — - Photosensitizer ... 

Faust, B. C., and J. Hoigne, Sensitized photo-oxidation of alkylphenols by fulvic acid and natural water , Environ. Sci. Technol., 21,957-964(1987). 

A violet-grey crystalline variety is obtained by melting vitreous selenium at 200° C. and cooling rapidly under pressure. The slender crystals are very sensitive photo-electrieally, but are very unstable.2... 

The efficiency of energy conversion in the polymers, i.e. how much the change in shape of the chain is induced by a photon, is, however, rather low. They need many photons and a high content of pendant photochromic chromophores to induce a large conformation change. To make a sensitive photo-responsive polymer, i.e. one which responds more efficiently to fewer photons, it is necessary to introduce an amplification mechanism to the system. One possible way of achieving this is to utilize the phase transition of polymers [7,8]. 

Sensitized photo-oxidation reactions are an example of such photoactivated catalysis (Section 4.5) in which C would be a dye which absorbs light and forms excited oxygen molecules (P) through energy transfer these excited oxygen molecules then lead to various oxidation reactions. There are other important examples of photoactivated catalysis in photoelectrochemistry (section 4.5.1). 

Cancer cells differ from normal cells in several ways, and these differences must be exploited in chemical treatments. In particular, it is found that certain chemicals concentrate in cancer cells in preference to normal cells, and phototherapy is based on a sensitized photo-oxidation process which destroys the essential components of the cell. 

Figure 7. An idealized model for CdS sensitized photo reduction of water by PhSH in aqueous DODAC or DODAB vesicles. The exact position of the colloid represented here as generated on the outside surface of the vesicles, is based on fluorescence quenching experiments performed in anionic DHP vesicles, assuming similar inters actions of the CdS particles with both types of vesicles.

Decarroz C, Wagner JR, van Lier JE, Krishna CM, Riesz P, Cadet J (1986) Sensitized photo-oxidation of thymidine by 2-methyl-1,4-naphthoquinone. Characterization of the stable photoproducts. Int J Radiat Biol 50 491-505... 

V-Formylkynurenine is one of the 16 autoxidation products of tryptophan (51) (Fig. 8). The dye-sensitized photo-oxygenation of tryptophan in sodium carbonate - acetic acid buffer (pH 7) gave TV-for my Iky n urenine as the major product (52). This is also the oxidation product of tryptophan with hydrogen peroxide (53) and with ozone (54). This is an interesting case the same degradation impurity can be obtained in different ways, probably... 

Nakagawa M, Yokoyama Y, Kato S, Hino T. Dye-sensitized photo-oxygenation of tryptophan. Tetrahedron 1985 41 2125-2132. 

Singlet-Oxygen Ene-Sensitized Photo-Oxygenations Stereochemistry and Mechanisms... 

In 1939, Kautsky [5,6] reported experimental evidence for a metastable reactive oxygen molecule and the intermediate in dye-sensitized photo-oxygenation reactions. Kautsky s results were extensive and his conclusions basically correct based on what is known today. However, his proposal was rejected by many reputable scientists (e.g., see Ref. 6) and it was never accepted during his lifetime. 

Scheme 4 Proposed mechanism of the sensitized photo-oxygenation of alkene 1.

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