Photochemistry of 9‐fluorenone oxime phenylglyoxylate: a combined TRIR, TREPR and ab initio study

The photochemistry of 9‐fluorenone oxime phenylglyoxylate ( 1 ) in tetrachloromethane was investigated by a variety of time‐resolved methods [STEP‐SCAN TRIR and time‐resolved EPR (TREPR)]. Photolysis of 1 yields the benzoyl radical, carbon dioxide and the fluorene‐9‐iminyl radical on pulsed irradiation (λ = 355 nm). All radicals have a lifetime in the range of microseconds and can be detected within the rise time of our time‐resolved equipment before undergoing recombination or reactions with the solvent. The benzoyl radical shows a strong absorption ( ( ν C=O = 1824 cm − ) in the IR spectrum. Upon purging the solution with oxygen, the benzoyl radical is quenched to yield the benzoylperoxy radical ( ( ν C=O = 1814 cm − ), which has a lifetime that is several microseconds longer than that of the benzoyl radical. Owing to the lack of a good IR chromophore, the fluorene‐9‐iminyl radical is not detected by IR spectroscopy. It can, however, be detected by TREPR spectroscopy, which allows the detection of a 1 : 1 : 1 triplet of the fluorene‐9‐iminyl radical at 3456 G and a 1 : 2 : 1 triplet of the benzoyl radical at 3460 G.