Studies of the Transient Intermediates in the Photoreduction of Methylene Blue

Abstract

The intermediate species which are produced in the course of the photoreduction of methylene blue have been investigated by flash photolysis in plain aqueous, borate and phosphate buffer solutions with and without reducing agents. In an acidic solution, an absorption band with the lifetime of 30μsec. appears at 375 mμ, while in neutral and basic solutions, two bands appear, at 415 and 520 mμ, with lifetimes of 70∼90 μsec. The bands at 375 and 415 mμ are considered to be due, respectively, to the acidic and basic forms of the triplet state, since the transient spectra change with pH, making an isosbestic point. The band at 415 mμ is overlapped by another one with a lifetime longer by several hundred microseconds; this is presumed to be semiquinone. The intensity of the band at 520 mμ decreases upon the addition of reducing agents and increases upon the introduction of oxygen. Hence, this band may be due to the halfoxidized form of the dye. These results support the reaction scheme that the excited state of the dye reacts with the ground state, which has been proposed in the investigation of steady light photobleaching.

Phosphorescence, optically detected magnetic resonance, and electron paramagnetic resonance studies of the lowest excited triplet state of the anti isomer of a 1,5-diazabicyclo[3.3.0]octadienedione [9,10-dioxa-anti-(methyl, hydrogen)bimane]

“…2 The results of the present ODMR and EPR studies on the compound in a durene host indicate that the molecule is likely to be planar in the Tl state in durene. The energies of the 3nr* and 'nr* states of the bimane in the neat crystal and in a durene host crystal probably represent those of planar excited states.…”

Chromatographic, Mass Spectral, and Visible Light Absorption Characteristics of Toluidine Blue O and Related Dyes

“…Demethylation is known to occur for methylene blue and toluidine blue 0 by photoreduction (17,18). It has also been reported that demethylation of methylene blue occurs under basic conditions (19,20); however, the dye was stable below pH 9.5.…”

Methylene blue based protein solder for vascular anastomoses: An in vitro burst pressure study

“…This leuco form can be oxidised back to MB by atmospheric oxygen, although this reaction is not quantitative and is accompanied by a slight permanent degradation of the dye. A number of different reaction mechanisms have been proposed for the photoreduction of methylene blue [16][17][18]. Kato et al [16] proposed that the semi-reduced species was generated by the reaction with the excited monomer triplet with the ground state monomer.…”

“…A number of different reaction mechanisms have been proposed for the photoreduction of methylene blue [16][17][18]. Kato et al [16] proposed that the semi-reduced species was generated by the reaction with the excited monomer triplet with the ground state monomer. Danziger et al [17] presented a scheme based on the irradiation of MB monomer or dimer, resulting in the formation of a dimeric charge transfer species, leading to the formation of leuco MB (MBH) or regeneration of the ground state.…”