Magnetic field effects on radical pairs photochemically derived from 2,3,6,7-dibenzofluorenone

Abstract

2,3,6,7-Dibenzofluorenone triplets react with triethylamine, 2,4,6-trimethylphenol and ascorbyl-palmitate in micellar solutions to yield radical pairs which are sensitive to magnetic field effects whenever separation is inefficient. The three substrates afford three distinctively different scenarios with respect to the confinement of daughter radicals within the micellar phase. Triethylamine and corresponding radicals are soluble in water, which results in rapid entry—exit equilibria with the micellar phase, and negligible magnetic field effects. Conversely, ascorbyl-palmitate and its radicals are virtually insoluble in water, thus being confined to the micellar phase. Application of an external magnetic field attenuates the geminate recombination of radicals, probably through slowing down T +T 0 and T −T 0 interconversions. The case of 2,4,6-trimethylphenol is intermediate, with the proportion of radicals that escape geminate recombination increasing with increasing applied field. The relevance of these reactions in relation to the use of 2,3,6,7-dibenzofluorenone or molecules of comparable solubility as a triplet probe in biological systems is discussed.