Magnetic field and magnetic isotope effects on the recombination kinetics of covalently-linked ketyl-phenoxyl triplet radical pairs

The recombination kinetics of three photogenerated covalently-linked ketyl-phenoxyl triplet radical pairs,³PhC^.(OD)C₆H₄O(CH₂) _n OC₆H₄C₆H₄O^.] (n=3, 6, and 10), and of the corresponding deuterated derivatives were examined by the laser flash technique under an external magnetic field (up to 0.2 T) in a CDCl₃/CD₃OD (21) mixture. In zero magnetic field, radical pairs (RPs) with small exchange interactions (n=6 and 10) are characterized by high values of the magnetic isotope effect (MIE), which reach 3 for pairs withn=10. Under strong magnetic fields (up to 0.2 T), the values of MIE decrease to 1.2 to 1.1. The photochemical behavior of covalently-linked RPs is compared with that of similar unlinked RPs in micelles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 442–446, March, 1995.The authors are grateful to V. F. Tarasov, A. I. Shushin (N. N. Semenov Institute of Chemical Physics, RAS) and V. A. Nadtochenko (Institute of Chemical Physics in Chernogolovka, RAS) for helpful discussions.