Methyl viologen fluorescence

Methyl viologen (l,T-dimethyl-4,4 -bipyridylium dichloride, MV " ) promotes photoanodic dissolution in aerated CdS solution Figure 8 shows how the rate of dissolution depends on the concentration. The colloid has a weak fluorescence at 620 nm which is quenched by. The curves for fluorescence and dissolution in Fig. 8 are symmetric, which indicates that the two processes have a common intermediate that reacts with M. These effects are explained by the following mechanism ... 

Fig. 8. Intensity of fluorescence and rate of photoanodic dissolution of colloidal CdS as function of the concentration of added methyl viologen...

Serpone et al. studied the fluorescence emitted from a CdS sol containing half-reduced methyl viologen, MV, and residual the MV being produced by... 

With respect to using methyl viologen as electron relay, it might be of interest to note tlmt MV " can be oxidized by positive holes produced in illuminated colloidal semiconductors such as Ti02 Two oxidation products of MV are 1, 2 -di-hydro-l,r-dimethyl-2 -oxo-4,4 -bipyridylium chloride and 3,4-dihydro-l,r-dime-thyl-3-oxo-4,4 -bipyridylium chloride, which can readily be detected by their strong fluorescences at 516 nm and 528 nm, respectively. These products are also produced in the direct photolysis of MV " solutions and in the reaction of MV "" with OH radicals in homogeneous solution... 

There is no evidence for ground state charge-transfer complex formation between stilbenes and neutral amines. Amine cations and dications are powerful electron acceptors and can form ground state complexes in which t-1 serves as the electron donor. Complex formation between t-1 and the organic dication methyl viologen is responsible for quenching of the fluorescence of surfactant stilbenes in organized assemblies (112). 

Figure 1 Stem Volmer plot of fluorescence intensity of the polymer MPS-PPV (inset) in the presence of methyl viologen (MV2+). slope of line gives Ksv = 1.8 x 107 M-1.

Similar to other d -d systems, the drnuclear iridium(I) complex [Ir(/x-pz)(COD)]2 (23) showed spin-allowed and spin-forbidden (da — pa) absorption bands at 498 and 585 nm, respectively. Under ambient conditions, the complex displayed fluorescence at 564 nm and phosphorescence at 687 nm, which were assigned to singlet and triplet excited states of (da — pa) character. The triplet excited state of the complex was a powerful reductant with an excited-state reduction potential E° (Ir2+ ) of-1.81 V vs. SSCE. Facile electron transfer reactions occurred between the excited complex and methyl viologen and other pyridinium acceptors. The absence of an inverted effect for the forward electron transfer reactions, and the presence of such inverted behavior for the back-electron-transfer reactions were observed and explained. ... 

It was further shown that perfusion chromatography apparently yields complexes of both high purity and stmctural and functional integrity. For instance, the core complex (fraction V) was reported to have an activity of 1535 pmoles O mg Chl /r, almost 70% higher than the native PS-1 complex, when assayed by methyl viologen reduction using the (DClP-i-Ascorbate) couple as the electron donor. The integrity of the reaction-center core complex was further corroborated by the notably low fluorescence quantum yield of 0.4% for the fractionated CCl fraction. 

Rhodamine 6G in an ionically conducting polymer were formed as a result of the local decomposition of the quencher, methyl viologen. The latter was incorporated inside the film with the dye and quenched the fluorescence of the Rhodamine 6G. However, when a tungsten tip biased at -4 V versus the platinum substrate was scanned at 1 /xm- s the quencher was decomposed, probably due to its reaction with hydroxyl ions that were generated at the tip, and the fluorescence of the dye was recovered. The authors concluded that the factors governing the resolution of the patterns were the... 

PIGIIRE 2. a) Dark relaxation kinetics of variable fluorescence after switching off the actinic light of leaf disk treated by 170 a methyl viologen. b) kinetics of variable fluorescence of leaf disk treated by 200 yuM Cl-CCP -.- measuring light only at the presence of Cl-CCP. 

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