Singlet sensitizer

Sensitizer singlet formed Intersystem crossing of sensitizer Energy transfer to reactant molecule... 

Schmittel cyclization, 4f 30, see also Cycloaromatization reactions Schreiner cyclization, f 30, see also Cycloaromatization reactions Sensitizers, singlet oxygen, 233-234, 235-236... 

In the triplet counting technique the substance whose intersystem crossing yield is to be determined is used as a sensitizer for the photoisomerization of piperylene (1,3-pentadiene). Under conditions where essentially all of the sensitizer triplets are intercepted by diene, the quantum yield of isomerization is directly proportional to the intersystem crossing yield of the sensitizer. If the diene interferes with sensitizer singlets however, the yield of triplets will fall, resulting in an anomalously low value for 0,. 

Steel and coworkers194 have also noted that 2,3-diazabicyclo[2.2.1]-heptene-2 (39) quenches the fluorescence of naphthalene. A more extensive study of this compound was carried out by Engel195 who reported that there was a sharp drop in the efficiency of sensitized decomposition and in the rate of sensitizer fluorescence quenching as the sensitizer singlet energy fell below that of 39. This points out a key difference between azo compounds and the cases discussed previously namely, there is a spectroscopic azo singlet state lying below that of the sensitizer. 

Berliner, L.J., Ogata, T. 1997. Riboflavin-sensitized singlet oxygen formation in milk. In Food and Free Radicals (M. Hiramatsu, T. Yoshikawa, M. Inoue, eds.), pp. 119-122, Plenum Press, New York. 

The newest results obtained by Rabek and Rfinby (67) show that during dye sensitized singlet oxygen photo-oxidation of cis- and trans-polybutadiene rapid degradation ocour what has been indicated by viscosity (Fig.4) and Gel Permeation Chromatography (GPC)(Pig.5). 

The sensitized oxidation is initiated by the absorption of a light quantum by a sensitizer S under formation of a singlet-excited sensitizer which is transformed to a triplet-excited sensitizer. Singlet oxygen 02 is formed in the system by the energy transfer to the ground state triplet oxygen157-159 ... 

Non-fluorescing excited states of alkanes. Several relatively long-lived non-fluorescing ("dark") excited states of hydrocarbons capable of sensitizing singlet solute luminescence have been proposed in recent years. 

Electrochemical oxidation of tropanes" in acetonitrile involves the formation of methylene-NN-bis-nortropanyl, of N/V-bis-nortropanyl, of N-formyl-nortropine, and of N-cyanomethyl-nortropane. Dye-sensitized singlet oxygen, produced by laser excitation," converts tropinone into iV-formyl-nortropanone in moderate yields. Photochemical demethylation of cocaine to norcocaine has been carried out," but the yields are less satisfactory than in the chemical ... 

---