Electron spin resonance and electron spin echo modulation studies of N,N,N′,N′-tetramethylbenzidine photoionization in sodium dodecylsulfate micelles: structural effects of alcohol and crown ether addition

Abstract

Electron spin echo modulation (ESEM) and electron spin resonance (ESR) spectra of the photogenerated N,N,N′,N′-tetramethylbenzidine cation radical (TMB⁺) in frozen micellar solutions of sodium dodecylsulfate containing 2-propanol, 1-propanol, 1-pentanol, 1-octanol, 2-propanol-d₇, 1-octanol-d₁₇ in D₂O and H₂O or 15-crown-5, 18-crown-6 ethers in D₂O have been studied as a function of the alcohol or crown ether concentration from 0 to 200 mM. Modulation effects due to the TMB⁺ interactions with deuteriums in D₂O and in H₂O in TMB/SDS/alcohol systems give direct evidence that 2-propanol is mainly located at the micellar interface, whereas the alkyl chain of 1-octanol is located deeper in the micelle. Alcohol addition leads to an increase of water penetration into the micellar interface in the order 1-propanol<2-propanol ≤ 1-pentanol<1-octanol. Modulation effects due to TMB⁺ in TMB/SDS/crown systems indicate that the TMB molecule moves toward the interfacial region when sodium cation is complexed by the crown ether. The efficiency of charge separation upon TMB photoionization increases with alcohols or crown ethers addition and correlates with the increased TMB⁺-water interactions.