Energy transfer from sensitizer singlet

As a consequence of energy transfer from excited singlet state or triplet state of a sensitizer to molecular oxygen may be formeds <, ... 

The production of 02 has been reported to occur by energy transfer from the singlet- and triplet-excited states of the sensitizer, but that from the triplet excited state is highly preferred because singlet-triplet interaction is of very low probability. The lifetime of 02 is highly dependent on the solvent medium and the presence of scavengers or oxidizable acceptors it was determined to be about 3.1 x 1(T6 s in water (Rodgers and Snowden, 1982) and 50 to 100 x 106 s in lipid (Henderson and... 

The primary interaction of singlet oxygen, produced by energy transfer from the excited sensitizer, with the diene can give rise to an exciplet that then collapses to peroxide, to a 1,4-biradical or to a 1,4-zwitterion alternatively, the adduct is the result of a concerted action without the involvement of an intermediate. Detailed kinetic Diels-Alder investigations of singlet oxygen and furans indicate that the reactions proceed concertedly but are asynchronous with the involvement of an exciplex as the primary reaction intermediate [63]. 

Nitroimidazoles (such as metronidazole and misonidazole) can enhance the porphyrin sensitized Type I photooxidations83 that is, electron transfer from the sensitizer to the oxygen molecule is facilitated to give more of the superoxide ion (Scheme 6). The Type II mechanism operates by energy transfer from the sensitizer to afford the singlet oxygen84. 

This phenomenon is possible in molecules like naphthalene, anthracene and Pyrene, each of which happens to have the lowest singlet energy level about twice hat of the respective triplet. For the generation of these triplets in high concentrations (T — T) type energy transfer from a suitable donor is necessary. Delayed fluorescence in naphthalene has been sensitized by phenanthrene. according to the following scheme ... 

Energy transfer from singlet or triplet states of suitable organic molecules can cause excitation of the central metal ion in a coordination compound. Photosensitization of Cr(III) complexes by biacetyl leads to aquation reaction of Cr(NH3)5 (NCS)2 ion. The aquation of (NH3) is hundred times more than that of (NCS) for the sensitized reaction, whereas it is only 66 times on direct excitation of Cr(IlI). This shows that energy... 

The reaction mechanism involves as attack of electrophilic singlet oxygen 102 on the corrinoid re-system. 102 is generated by the energy transfer from either a photoexcited complex or a sensitizer (methylene blue). Vitamin B12 itself is not photosensitive. The yield of the products depends on ring substituents, in all cases, however, the reaction is very selective. 

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