Chemically Induced Dynamic Electron Polarization. IV. The Photolysis of 1,4-Naphthoquinone

Electron spin resonance emission was studied from the photochemically produced 1,4-naphthosemi-quinone radical in liquid methanol, ethanol, isopropanol, ethylene glycol, and in acetic acid in the presence of 2,6-di-tert-butylphenol. This chemically induced dynamic electron polarization is due to the optically spin polarized triplets of the parent quinone and their subsequent hydrogen abstraction reaction with retention of the polarization in the resultant semiquinone radicals. In the acetic acid–2,6-di-tert-butylphenol system, emission was observed also from the phenoxy counter radical. The magnitude of the polarization at constant microwave power was found to be temperature dependent. The comparison of the photochemical theory and the radical-pair theory is examined in the light of some of the results obtained.