Isoprene photodimerization

Photodimerization of isoprene has also been observed using ferrocene as sensitizerproduct distribution in this case was similar to that observed using high-energy photosensitizers. To account for this behavior, the following mechanism was proposed, where 7 indicates a triplet level of isoprene higher than the lowest triplet ( ) ... 

The photodimerization of thymine derivatives was then studied in the presence of isoprene as the triplet quencher. The data obtained were plotted using the Stern-Volmer equation (3) derived from Scheme 10, in which only the excited triplet state is... 

From the intercepts of the lines, values of <1>DF(/<1>DF at l/[isoprene] = 0 were obtained. Thus, the portion of the quantum efficiency for the photodimerization, which resulted only from the singlet state, was estimated (Table 14). The photodimerization from the singlet state was found to be a minor reaction in DMSO solution. In DMSO-EG, however, about half of the efficiency for the photodimerization was derived from the singlet state. 

Photodimerization of isoprene to 1,5-dimethylcyclo-octa-l,5-diene and 1,6-dimethylcyclo-octa-1,5-diene is discussed. Evidence has been presented for a multistep process in the oligomerization of butadienes with nickel... 

Thymine derivatives " are very resistant to UV irradiation in dilute solution because the triplet state is the precursor of the photodimer and intersystem crossing of thymine is very low. The yield of the photodimer in solution is low, but a high yield of photodimer can be obtained with acetone as the sensitizer. In DNA polymers and solid state, however, the photodimerization reaction is fast and proceeds through the singlet state. The photodimerizations of thymine oHgomers and polymers were studied in the presence of isoprene as a triplet quencher. The photodimerization of the thymine, monomeric and dimeric model, were quenched by isoprene, but the photodimerization of a polymer with thymine units was not quenched. This result appears to indicate that the photodimerization of aggregated thymine compounds occurs almost completely from the singlet state. ... 

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