Nj. Turro et al., PHOTOIONIZATION OF PHENOTHIAZINE - EPR DETECTION OF REACTIONS OF THE POLARIZED SOLVATED ELECTRON, Journal of the American Chemical Society, 117(49), 1995, pp. 12273-12280
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.