Effects of EDTA Derivatives on the Photoreduction of Methyl Viologen by a Thiacarbocyanine Sensitizer in a Micellar Solution

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Abstract
The photoinduced reduction of Methyl Viologen (MV2+) by ethylenediaminetetraacetate (EDTA), 1,2-propanediamine-N,N,N′,N′-tetraacetate (MeEDTA), and trans-1,2-cyclohexanediamine-N,N,N′,N′-tetraacetate (CyDTA) was investigated by using 3,3′-dioctadecylthiacarbocyanine (C18–18+) as a sensitizer in a micellar solution of a nonionic surfactant, heptaethylene glycol monododecyl ether. The production rate of reduced Methyl Viologen (MV+·) decreased with the light-irradiation time, while the deceleration increased in the order of: CyDTA<MeEDTA<EDTA. The concentration of the EDTA derivatives at the micellar surface was estimated to be in the order of EDTA<MeEDTA<CyDTA, this difference in the concentration being attributed to such hydrophobic groups as methyl group and cyclohexane ring in the EDTA-derivative molecules. The high concentration of the EDTA derivatives at the surface accelerated the reaction of the sensitizer divalent cation radical (C18–182+·) with the EDTA derivatives, prevented the consumption of MV+· through the back reaction of C18–182+· with MV+·, and facilitated the efficient photoproduction of MV+·. It was demonstrated that the hydrophobic interaction between the EDTA-derivative molecules and the micellar surface is an important factor in determining the efficiency of the photoinduced MV+· production.

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