Magnetic field effects on photoinduced electron transfer and the succeeding processes in phenothiazine-viologen linked compounds incorporated into cyclodextrins or reversed micelles

Laser-induced electron transfer in phenothiazine-viologen linked compounds afforded highly active radical pairs, when the linked compounds were incorporated into the cavity of either α- or β-cyclodextrin. Remarkable magnetic field effects on the radical decay rate were observed, and it was ascribed to Zeeman splitting of triplet sublevels of the radical pair. Similar magnetic field effects were also observed with the phenothiazine-viologen linked compounds trapped at walls of microscopic water pools in reversed micelles. Spectroscopic evidences were provided to indicate that the spacer between phenothiazine and viologen units is in extended conformations, and the magnetic field effect was explained in terms of the relaxation mechanism. In zero magnetic field, the radical decay rate was appreciably reduced with decrease of the spacer chain length. Increased singlet-triplet energy separation in the linked compounds with shorter spacer was suggested to be responsible for the reduced decay rate.