Sensitization energy level, triplet excited

A study has been made of the relative efficiencies with which various transition metal chelates quench triplet benzophenone.194 The chelates vary widely in efficiency, and no generalizations can be drawn except that in some cases triplet energy transfer to a coupled metal-ligand triplet energy level probably accounts for at least part of the quenching. Rare earth ions can quench excited triplets by energy transfer, since, as discussed earlier, sensitized fluorescence of the metal ion results. 

The efficiency in the transfer of energy from the triplet states of various compounds to ground singlet states of isoprene, 1,3-pentadiene, and 2,3-dimethylbutadiene have been studied. The diene molecules become excited to their lowest triplet states and undergo chemical reactions which may be dimerization or stereoisomerization. As in the case of butadiene, the energy level of the sensitizer in its lowest triplet state determines the magnitude of the energy that is transferred to the diene and the course of its subsequent reactions. Typically, in the case of... 

It is reported that the oxidation of several excited xanthene dyes at n-ZnO electrodes occured via the triplet state. This was concluded from the result that the quantum efficiency of the sensitization current decreased upon addition of a typical triplet quencher [27]. Another interesting example is Ru(bipy)3, which shows in solution an intersystem crossing yield of unity [11]. Nearly all electron transfer reactions between the Ru complex and an electron acceptor in solution occur via the triplet state. In the case of adsorbed Ru(bipy)3, electron transfer from the excited singlet and from the triplet to the semiconductor electrode is possible depending on the coupling of the dye to the semiconductor (see Section 10.2.6). It should be mentioned here that the energy levels of the excited Ru complex given in Fig. 10.4, were calculated for a triplet state. 

Many photo-dimerizations of functional groups, like the ones shown above, require the presence of photosensitizers. These compounds may be selectively excited to their triplet state by sensitizers with the right type of energy levels. For efficient energy transfer to occur, the triplet energy of the donor... 

The stilbene photoisomerization through the triplet potential surface can be sensitized by a donor molecule excited to its triplet state, which is energetically dose to the stilbene exdted triplet level Ti ([52, 53]. The sensitizers (donors) with triplet energies of at least 255kJ/mol (in a case of unsubstituted stilbene) transfer their energies to both trans and cis isomers of the stilbene molecule in the ground state in a diffusion-controlled process. The reaction proceeds from an initial... 

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