PHOTOIONIZATION OF PHENOTHIAZINE - EPR DETECTION OF REACTIONS OF THE POLARIZED SOLVATED ELECTRON

Photoionization of phenothiazine (PTH) and reactions of the solvated e lectron with some electron accepters were studied with steady state an d time-resolved EPR and transient optical absorption techniques. Time- resolved EPR spectra from the phenothiazine cation radical (PTH .(+)) and hydrated electron (e(aq)(-)) formed in sodium 1-dodecylsulfate (SD S) micellar solution were observed in emission. By contrast, PTH .(+) formed by photoionization of PTH in alcohols gives absorptive EPR sign als. The spin polarization carried by the hydrated electron in SDS sol utions can be transferred effectively to a stable nitroxyl free radica l 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl (N .(-)) present in the bulk aqueous phase. EPR and flash photolysis measurements show th at this electron spin polarization transfer process proceeds with a ra te which is approximately five times faster than the chemical reaction between e(aq)(-) and N .(-). The marked difference in rates is attrib uted to differences in spin-statistical factors and difference in reac tion radii for spin exchange compared to reaction. In alcohol solution s of PTH and a nitroxyl stable radical (2,2,6,6-tetramethylpyperidin-1 -oxyl, TEMPO), excitation of PTH also results in emissive polarization of the EPR spectrum of the stable radical. In this case the polarizat ion is produced by the interaction between PTH triplets and TEMPO (dou blet-triplet radical pair CIDEP). Trapping of e(aq)(-) produced by pho toionization of PTH in SDS solution by electron accepters such as acry lamide and chlorophenols yields free radicals whose formation was moni tored with time-resolved EPR and flash photolysis.