Photochemistry of 2,7-disubstituted-9-fluorenyl alcohols and esters
LE3 .A278 2009
Master of Science
The disubstituted fluorenyl alcohols 51- 52 and ester 53 were synthesized from fluorene and the photochemistry of 50- 53 was investigated. Compounds 50- 53 had moderate reaction quantum yields. 1H NMR and GC- MS product studies identified the photoproducts of 50- 53 generated by photolysis in water, methanol and acetonitrile. There was an apparent competition between heterolytic and homolytic pathways. Data was compiled to construct mechanistic schemes that illustrated the pathways involved in the photolysis of 50- 53. 50 and 51 likely formed excited state phenolates from excited state proton transfers which generated a respective quinone methide due to heterolysis, a 9- radical from homolysis and possibly a radical by electron transfer. UV- Vis identified the presence of highly coloured byproducts generated by 50 and 51 due to the presence of the 2- and 7- hydroxyl groups. The byproducts may be a quinones formed through the aforementioned electron transfer pathway. 52 and 53 likely underwent heterolysis and homolysis to form a 9- carbocation and 9- radical, respectively. Triplet excited state quenching of 50- 53 suggested that photolysis occurred through singlet or short triplet excited states. Photophysical characterizations of 50- 53 showed low fluorescence quantum yields for 50- 53 that were consistant for fluorenyl compounds. Water quenched the fluorescence of 50- 52 while little change was noticed for 53. Singlet excited state lifetimes for 50- 53 were ~ 3- 7ns in water, acetonitrile and cyclohexane. This data suggested that 50- 53 experienced static quenching. Since 50- 53 had only moderate reaction quantum yields and generated many photoproducts by both heterolysis and homolysis, they did not meet the requirements to pose as adequate models for novel photocages.
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