Electron spin resonance and electron spin-echo modulation studies of 5-doxylstearic acid and N, N, N′, N′-tetramethylbenzidine photoionization in sodium dodecylsulphate micelles. Effects of 15-crown-5 and 18-crown-6 ether addition

Abstract

Electron spin-echo modulation (e.s.e.m.) and electron spin resonance (e.s.r.) spectra of the photogenerated N, N, N′, N′-tetramethylbenzidine (TMB) cation radical and 5-doxylstearic acid (5-DSA) in frozen micellar solutions of sodium dodecylsulphate containing 15-crown-5 and 18-crown-6 ethers in D₂O and H₂O have been studied as a function of the crown ether concentrations. Modulation effects due to 5-DSA interactions with water deuteriums give direct evidence that both crown ethers are mainly located at the micellar interface and that their interaction causes a decrease of hydration of the micellar interface. Modulation effects from TMB⁺ interaction with water deuteriums indicate that the TMB molecule moves toward the interfacial region when the sodium cation is complexed by the crown ether to decrease the local ionic strength in the interfacial region. The efficiency of charge separation upon TMB photoionization increases ca. 10% with crown ether addition, and correlates with the increased TMB⁺–water interactions. The sodium cation complexation by the crown ether to change the charge distribution and ionic strength at the micellar interface seems to cause the interfacial hydration changes that promote the photoionization efficiency.