10,10-Dimethylanthrone (DMA) (ET = 72 kcal/mol) and dibenzosuberone (DBS) (ET = 66 kcal/mol) show similar photochemical behavior. Laser flash photolysis leads to readily detectable triplets showing λmax = 320 and 530 nm, τT = 2.1 ns for DMA and λmax = 320 and 520 nm, τT = 1.5 µs for DBS, in acetonitrile. Quenching of 10,10-dimethylanthrone triplet, in acetonitrile, by phenol and its derivatives containing polar substituents shows rate constant close to diffusion control (kq ~ 1010 Lmol-1s-1) for all phenols employed. On the other hand, for dibenzosuberone, quenching rate constants ranging from 5.8x107 Lmol-1s-1 (for 3-fluorophenol) to 4.7x109 Lmol-1s-1 (for hydroquinone) were obtained. A Hammett plot for the phenolic hydrogen abstraction rate constants of triplet 2 against σ+ leads to a reaction constant (ρ) showing a value of –0.98, which is fully in accord with those obtained previously for the reaction of nπ* carbonyl compounds with substituted phenols. The energy difference between the triplet excited states of DMA and DBS could be the main factor responsible for their distinct behavior towards the phenolic hydrogen abstraction reaction.
Buy this Article