Photoreduction of methylviologen using methylacridine orange in the presence of triethanolamine in ethanol–water mixtures

Abstract

Photoreduction of methylviologen (MV 2+) by 10-methylacridine orange (MAO +) in the presence of triethanolamine (TEOA) has been investigated in ethanol–water mixed solvents by means of steady-state and laser-flash photolysis in visible/near-IR regions. The complete conversion from MV 2+ to MV + was observed under the condition of [MV 2+]>[MAO +] in the presence of an excess TEOA. By laser-flash photolysis measurements, the various rate constants for the electron transfer processes ( k et) have been determined. The k et values for electron transfer from the triplet state of MAO + ( 3( MAO +) ∗ ) to MV 2+, which is the initial step of oxidative route, are in the order of 10 8 M −1 s −1. The rate constant of back electron transfer between the ion radicals (MV + and (MAO +) +) was ca. 3×10 8 M −1 s −1, while the back electron-transfer process was suppressed on addition of TEOA. The k et values from TEOA to 3( MAO +) ∗ , which is the initial step of reductive route, are in the order of 10 5 M −1 s −1. The k et value for electron transfer from (MAO +) − to MV 2+ was estimated to be 4.7×10 8 M −1 s −1. Contributions of the oxidative and reductive routes of 3( MAO +) ∗ to the MV + formation vary with TEOA concentration. High quantum yields for the MV + formation were evaluated. The effects of the ion salt and solvents on the rate constants and quantum yields were found.