Photochemical Magnetic Field Effects of 4-Methyl-2-quinolinecarbonitrile

Article abstract of DOI:10.1246/bcsj.58.3423

The irradiation of 4-methyl-2-quinolinecarbonitrile 1 in ethanol or cyclohexane resulted in the formation of 2-(1-hydroxyethyl)-4-methylquinoline 2 or 2-cyclohexyl-4-methylquinoline 3 in the yield of ca. 48 or 65percent.The effects of an external magnetic field upon the photosubstitution reaction were investigated in either the absence or presence of 1,3-pentadiene (triplet quencher).In the case of the photosubstitution reaction (1->2) in ethanol, the chemical yield of 2 increased quadratically with an increase in the field strength (magnetic field effect due to HFI-J mechanism).The addition of 1,3-pentadiene caused a complete disappearance of the Δg magnetic field effect.Thus, the formation of 2 at a zero field was concluded to occur from the S₁-state via the singlet hydrogen-bonded radical pair.In the case of the photosubstitution reaction (1->3) in cyclohexane, the chemical yield of 3 decreased steeply upon the application of a magnetic field of 40mT (magnetic field effect due to HFI mechanism) and a further increase in the field strength resulted in a quadratic increase in the yield (magnetic field effect due to Δg mechanism).Neither an HFI nor a Δg magnetic field effect was observed in the presence of 1,3-pentadiene.The reaction was thus concluded to proceed from the S₁ and T₁ states via the singlet and triplet radical pairs.Reaction mechanisms deduced from the external magnetic field effects were consistent with the results of Stern-Volmer analyses.