Time-Resolved ESR Study on Complex Radical Pairs Formed in the Photolysis of Methylene Blue Included in Water-Soluble Sulfonated Calixarenes
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The photochemical reactions of methylene blue (MB) included in water-soluble sulfonated calix[n]arenes (n = 4, 6, 8) are studied using a time-resolved electron spin resonance method. The chemically induced dynamic electron polarization (CIDEP) spectra show the formation of the complex radical pair composed of the MB monocation radical and calixarene (phenoxyl-type) radical. The lifetime and broadened spectral shape are dependent on the size of the calixarene and are due to the longitudinal and transverse relaxation mainly induced by the tumbling motion of the radical pair with the spin dipole–dipole interaction. The pair dissociates in a few hundreds of nanoseconds in cases of n = 6 and 8.
KeywordsMethylene Blue Spectral Shape Rotational Correlation Time Chemically Induce Dynamic Electron Polarization Radical Pair Mechanism
We would like to thank Prof. Hayashita at Tohoku University for his valuable suggestion and discussion about inclusion compounds. We are also grateful to Instrumental Analysis Center for Chemistry of Tohoku University for the observation of NMR spectra of the present system. A.I. is grateful to the Japan Society for the Promotion of Science for the grant.
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