Sensitizers, triplet energy

Attempts to sensitize the rearrangement with benzophenone, propiophenone, and chlorobenzene failed, as indicated in Table 8.1. Although the reaction could not be sensitized, triplet energy transfer was taking place inasmuch as compound (1) quenched the photoreduction of benzophenone without the formation of any new products (Table 8.2). 

Significantly, there is no variation in the relative product distribution in this case as a function of the sensitizer triplet energy. 9-Anthraldehyde (Et = 42 kcal/mole) was ineffective as sensitizer for this reaction, presumably because its lowest triplet is lower in energy than that of cyclo-pentadiene.<23>... 

As with cyclopentadiene, the relative yields of products (19)—(21) were relatively insensitive to the sensitizer triplet energy(37) although an effect of temperature on dimer distribution has been noted.0,28 The direct photolysis of cyclohexadiene with wavelengths greater than 330 nm yielded products (19)—(21), although the product distribution in this case was more nearly statistical [(19) (20) (21) = 44% 2470 33%] 28 . 

The product distribution in this reaction was found to be dependent upon the triplet energy of the sensitizer. Variation of the relative amounts of cyclobutanes (32) and (33) to cyclohexene (34) with sensitizer triplet energy... 

In the initial work135,136 on the sensitized isomerization of stilbene, it was found that quinone sensitizers gave photostationary states which were trans-rich relative to those predicted by energy transfer (Fig. 3). The original plot of sensitizer triplet energy versus isomer ratio of the photostationary state therefore showed several maxima and minima. Later work on the rates of energy transfer from various sensitizers to stilbene proved that the plot was in fact a smooth curve and that the photostationary states observed with quinones were not the true ones.137 Irradiation of benzene solutions of... 

Azides. In a study of the photosensitized decomposition of alkyl azides,202 an apparently linear relationship between sensitizer triplet energy and the log of the rate constant for energy transfer was obtained. Phenan-threne, however, gave a somewhat larger value than expected for this rate constant, which was determined from the variation in quantum yield of... 

Sensitizer Triplet energy, kcal/mole [TWICI. 

Triplet Energies of Common Sensitizers Sensitizer Triplet energy (kcal/mol)... 

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