Continuous Photoreduction of Methyl Viologen Using Disubstituted Terthiophenes and EDTA in Aqueous Solution

Abstract

The continuous photoreduction of methyl viologen by 5,5″‐bis(aminomethyl)‐2,2′:5′,2″‐terthiophene (AT) and 2,2′:5′,2″‐terthiophene‐5,5″‐dicarboxylic acid (CT), using EDTA as a sacrificial electron donor, has been investigated in aqueous solution at various pH. Apparent rates and efficiencies of production of the methyl viologen radical cation (MV+) were found to be dependent on the pH, the concentrations of all three components and the intensity of the incident light. The highest conversion efficiency (77%) was shown by the bis(aminoniethyI (‐substituted terthiophene AT at pH 7.7. The quantum yield for the formation of MV+ under these conditions was 0.24, which is comparable with other common systems

Self-Repairing Photosensitized Electron Transfer from Thiones to Methyl Viologen in Aqueous Media

“…After the decay of 3 (2-PyT)*, new absorption bands of MV •+ appeared at 390 and 600 nm. 6,13,18,19 The decay rate of 3 (2-PyT)* at 460 nm seems to be in good agreement with the rise rate of MV •+ at 600 nm (inset in Figure 4), indicating that MV •+ is formed due to electron transfer from 3 (2-PyT)* to MV 2+ at pH 7.00 as in eq 1. 7a,11,14,15 A similar behavior was observed at pH 4.01 and 9.18.…”

“…The new absorption band appearing at 605 nm is attributed to the methyl viologen radical cation (MV •+ ). 6,13,18,19 The absorption intensity of MV •+ increases with the time of the steady-light illumination and reaches a maximum concentration at ca. 1.5 min (inset of Figure 2).…”

“…Since 3 (PT)* and MV •+ were observed in the same time frame, the efficiency of MV •+ formation due to photoreduction of MV 2+ via 3 (PT)* could be calculated from the absorbance (A C refers to maximum absorbance of MV •+ and A T to initial maximum absorbance of 3 (PT)*) and extinction coefficients ( C refers to that of MV •+ and T to that of 3 (PT)*) as in eq 2. 20,21 Upon substitution of the reported values for C and T , [13][14][15]19 [MV •+ ] max /[ 3 (PT)*] max values were evaluated. The plot of [MV •+ ] max /[ 3 (PT)*] max vs [MV 2+ ] reaches a plateau, yielding the electron-transfer quantum yield (Φ et ).…”

“…[8][9][10] In general, addition of an excess of a "sacrificial" electron donor is necessary to repair the photooxidized sensitizers, resulting in the whole process becoming cyclic with respect to both photosensitizer and MV 2+ . [11][12][13] The net reaction is thus the sensitizer-catalyzed photoreduction of MV 2+ by the sacrificial electron donor.…”

A rapid screening of Ru(II) photosensitizers

“…( 13) is more electrostatically favoured than either the forward reaction or the subsequent eqn. (14). If eqn.…”