Photochemical generation of 9H-fluorenyl radicals.

A series of 9-substituted fluorenols and 9,9′-disubstituted-9,9′-bifluorenyls were irradiated to give products derived from fluorenyl radicals. Product distribution was solvent dependent. A TEMPO adduct was isolated from the photoexcitation of 9-fluorenol. An unusual unsymmetrical 3,9′-bifluorenyl was observed from the photolysis of 9-trifluoromethylfluorenol and 9,9′-di(trifluoromethyl)-9,9′-bifluorenyl in more polar or hydrogen-bonding solvents. The electronic nature of 9-substituted fluorenyl radicals was probed using theoretical calculations showing the dipolar character of species with electron-deficient groups. These constitute the first examples of “doubly destabilized” radicals.