The Photoreduction of Methylene Blue by Amines—i. A Flash Photolysis Study of the Reaction Between Triplet Methylene Blue and Amines

Abstract

Abstract— Flash photolysis was used to study the reduction of the triplet state of methylene blue by both alkyl‐ and aryl‐amines. The extent of the formation of the semireduced form of the dye yielded rate constants of interaction between the triplet state and the amine (k5). A correlation between log k5 and ionization potentials for alkylamines (slope = ‐1.75 eV‐1) was interpreted as evidence for the formation of a partial charge‐transfer intermediate. The rate constants (k5) calculated for aryl‐amines approached the rate of diffusion in many cases. A Hammett plot for a series of N, N‐dimethyl‐anilines yielded a moderately large p value (– 3.28) consistent with the formation of a charge‐transfer intermediate. It was concluded that reaction of amines with triplet methylene blue leads to the formation of a partial charge‐transfer intermediate which may undergo complete electron transfer to yield radicals, or undergo spin inversion and return to the ground state.

Methylene Blue as a Photosensitizer and Redox Agent: Synthesis of 5‐Hydroxy‐1H‐pyrrol‐2(5H)‐ones from Furans

“…[2] However,t he ground state of methylene blue also has ar edox potential, [3] which has been reported to facilitate the oxidation of suitable substrates, [4] including carbohydrates [5] and ascorbic acid, [6] but until now only under difficult conditions that have limited wider application. [2] However,t he ground state of methylene blue also has ar edox potential, [3] which has been reported to facilitate the oxidation of suitable substrates, [4] including carbohydrates [5] and ascorbic acid, [6] but until now only under difficult conditions that have limited wider application.…”

“…[1] Intriguingly, upon the addition of benzylamine (1.1 equiv,91mm), instant decolorization of the solution was observed, which suggested Scheme 1. [2] When the same reaction was performed on alarger scale (4 mmol of 1a, with final concentrations of 160 and 3.2 mm for the furan and MB,r espectively), lactam 3aa was produced in 70 %y ield (see the Supporting Information). that MB + had been reduced to leucomethylene blue (LMB).…”

Mechanistic Insights and Kinetic Analysis for the Oxidative Hydroxylation of Arylboronic Acids by Visible Light Photoredox Catalysis: A Metal-Free Alternative

“…This species can also act as a reducing agent. 8,9 Received: June 28, 2013 Published: August 16, 2013 Scheme 1. Photocatalytic Conversion of Arylboronic Acids to Phenols a a As proposed by Xiao and co-workers.…”

Kinetic and redox characteristics of semireduced species derived from phenosafranine in homogeneous aqueous and sodium dodecyl sulfate micellar media

“…Formation of semireduced species of phenazinium dyes has been demonstrated in flash photolysis experiments 4–7. Also, in the case of thiazine dyes the formation of the semireduced species was observed 8–12 in both flash photolysis and pulse radiolysis experiments. Generally in the photoreduction of dyes an intermediate semireduced radical is formed through the excited states of the dye in the presence of a suitable reducing agent 6.…”