An electron magnetic resonance study of the photoionization of a series of N-alkylphenothiazines in AOT reverse micelles

N-Alkylphenothiazines (PC{sub n}, n=1,3,6,9,12,16) were photoirradiated in sodium bis(2-ethyl-1-hexyl) sulfosuccinate (aerosol octyl or AOT) reverse micelles to study the photoionization efficiency as a function of the interior water pool size and the location of the phenothiazine chromophore with respect to the AOT/D{sub 2}O interface. To optimize the photoyield, the dimensions of the occluded water pool were varied by changing the ratio of the number of water molecules to surfactant monomers. The photoyield shows a dependence on the length of the pendant alkyl chain. The highest photoyield, measured by electron spin resonance, is obtained for w{sub 0}=5 (w{sub 0} = [D{sub 2}O]/[AOT]); it decreases as the interior water pool size is increased. This observation is interpreted as showing that hydration of the sodium countercation with increasing interior water pool results in an increase of the anionic charge of the interface which increases the barrier for electron transmission. Electron spin echo modulation studies in D{sub 2}O show that the deuteron modulation depth increases as the size of the interior water pool increases but shows only a weak dependence on the alkyl chain length. Electron nuclear double resonance (ENDOR) studies show that the proton density in the vicinity of the paramagnetic cationic radicalmore » decreases as the size of the interior water pool increases. The ENDOR data do not show any significant dependence on the length of the pendant alkyl chain. Consequently, optimization of the charge separation of the photoproducts is best achieved by minimizing the size of the interior water pool. 38 refs., 7 figs.« less