Charge separation in photoredox reactions. Technical progress report, June 15, 1993--June 15, 1996

The structural aspects controlling charge separation in molecular photoionization reactions in organized molecular assemblies involving micelles, reverse micelles and vesicles and in microporous silica gel materials are being studied by optical and electron magnetic resonance techniques including the time domain technique of deuterium electron spin echo modulation (ESEM) and matrix proton electron nuclear double resonance (ENDOR) to measure weak electron-nuclear dipolar interactions. ESEM and matrix ENDOR are particularly well adapted to the study of disordered systems as exemplified by micelles and vesicles. In addition to conventional studies by optical absorption and electron spin resonance, ESEM and matrix ENDOR complement each other and enable independent detection and analysis of extremely weak electron-nuclear dipolar interactions which give structural information often not available by other experimental techniques. The complementarity of using both these techniques greatly strengthens the conclusions reached. Since dipolar interactions are averaged out by molecular tumbling in liquid - solutions, their exploitation requires studies in rapidly frozen solutions. A variety of experiments has shown that micellar and vesicular structure is retained in these rapidly frozen solutions. Also, the conformation of x-doxylstearic acid spin probes has been studied as a function of x in cationic and anionic vesicles in liquid solution by detailed simulation of the electron spin resonance lineshapes. The conformation changes with x and with vesicle charge type are the same as independently measured in frozen solutions by variations of the deuterium electron spin echo modulation depth. This shows that embedded photoionizable molecules in frozen vesicle solutions have similar locations and conformations as in liquid vesicle solutions