Electron transfer reactions of excited dyes with metal complexes. Progress report, March 1, 1978-February 28, 1979. [Iron-methylene blue]

Technical Report · Thu Mar 15 00:00:00 EST 1979

DOI:https://doi.org/10.2172/5508964· OSTI ID:5508964

Lichtin, N N

An intense absorption band of /sup 3/MBH/sup 2 +/ at 700nm was characterized in several media and its pK/sub A/ was measured to be 7.17 +- .1 in water. Flash photolysis show that semiethylene blue, MBH/sup +/, formed by quenching /sup 3/MBH/sup 2 +/ with Fe/sub II/(H/sub 2/O)/sub 6//sup 2 +/, decays by disproportionation at a diffusion-controlled rate. Rates of decay of the photostationary state of solutions of MB/sup +/ and Fe/sup II/(H/sub 2/O)/sub 6//sup 2 +/ in acidic media were measured using crossed beams to yield specific rates of oxidation of leucomethylene blue (MBH/sub 3//sup 2 +/) by MB/sup +/ (synproportionation) and by Fe(III). Laser flash-photolysis shows that quenching of MB/sup +/(S/sub 1/) by Fe(H/sub 2/O)/sub 6//sup 2 +/ can result in electron transfer to give MBH/sup +/. Profound differences between processes initiated by quenching triplet methylene blue with Fe(H/sub 2/O)/sub 6//sup 2 +/ and with stable coordination complexes of Fe(II) were found. Quenchers included (Fe/sup II/(CN)/sub 6/)/sup 4 -/, (Fe/sup II/(CN)/sub 4/(bpy)/sub 2/)/sup 2 -/, (Fe/sup II/(CN)/sub 2/(bpy))/sup 0/, and (Fe/sup II/(bpy)/sub 3/)/sup 2 +/. Measurements were made in aqueous and aqueous-alcoholic solutions at pH 2, 4.4, and 8.2. Quenching of /sup 3/MBH/sup 2 +/ or /sup 3/MB/sup +/ by a stable complex of Fe(II) is diffusion-controlled and 10/sup 2/ to 10/sup 3/ times the rate at which Fe(H/sub 2/O)/sub 6//sup 2 +/ quenches /sup 3/MBH/sup 2 +/. Net electron transfer accounts for less than 1/3 of total quenching by complexed Fe(II). In contrast, quenching by Fe(H/sub 2/O)/sub 6//sup 2 +/ goes essentially entirely with net electron transfer. It is concluded that quenching of triplet methylene blue by complexes proceeds via electron transfer which is reversible in the encounter complex. The MBH/sup +/ which results from net electron transfer from complexes of Fe(II) decays essentially entirely to MB/sup +/ via oxidation by complexed Fe(III); no disproportionation has been observed.

• Research Organization: Boston Univ., MA (USA)
• DOE Contract Number: EY-76-S-02-2889
• OSTI ID: 5508964
• Report Number(s): COO-2889-7
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
IRON COMPLEXES
CHEMICAL REACTION KINETICS
METHYLENE BLUE
COMPLEXES
CYANIDES
FERRICYANIDES
PHOTOLYSIS
SCINTILLATION QUENCHING
TRIPLETS
AMINES
AZINES
CHEMICAL REACTIONS
CHLORIDES
CHLORINE COMPOUNDS
DECOMPOSITION
DRUGS
HALIDES
HALOGEN COMPOUNDS
HETEROCYCLIC COMPOUNDS
KINETICS
MULTIPLETS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PHENOTHIAZINES
PHOTOCHEMICAL REACTIONS
REACTION KINETICS
TRANSITION ELEMENT COMPLEXES
400000* - Chemistry