Applications of electron spin echo spectroscopy to location control of alkylphenothiazine derivatives in photoinduced charge separation across vesicles, micelles and reverse micelle interfaces

Abstract

The efficiency of photoinduced charge separation across surfactant interfaces of micelles and vesicles depends in part on the location of electron donors and acceptors relative to the interface. Achievement and assessment of control of such location by the addition of pendant alkyl chains to donors and acceptors is shown to be achievable. The net photoionization efficiency can be measured by electron spin resonance of radical ions in frozen surfactant solutions. Assessment of relative locations of radical ions with respect to a surfactant interface has been achieved by analysis of electron spin-echo modulation from deuterium in deuterated water at the interface. Results for a series of positive, neutral and negatively charged alkylphenothiazine derivatives in vesicle, micelle and reverse micelle surfactant assemblies of different interface charge are discussed. Controlling factors involve the alkyl chain length of the electron donors, the relative charge of the surfactant assembly interface versus that of the electron donor derivative, and the degree of molecular order in the interface. Secondary factors include alkyl chain bending, photoinduced radical conversion and back electron transfer.