Photodecaging from 9-substituted 2,7-dihydroxy and dimethoxyfluorenes: competition between heterolytic and homolytic pathways.

2,7-Dihydroxy-9-fluorenol (9), 2,7-dimethoxy-9-fluorenol (10), and 2,7-dimethoxy-9-acetoxyfluorene (11) were prepared and their photochemistry was studied in methanol and aqueous methanol solution in the hopes of observing efficient expulsion of the substituents positioned at the 9-position. For all three compounds, the primary photoproducts were 2,7-disubstituted-9-fluorenes and 2,7-disubstituted-9-methoxyfluorenes. A mechanism of reaction is proposed for production of these products, and involves competing homolytic and heterolytic pathways that produce radical and carbocation intermediates. Reaction quantum yields (for substrate disappearance) ranged between 0.21 and 0.31.