Mechanistic aspects of the quenching of triplet methylene blue by complexes of cobalt(II)

Journal Article · Thu Nov 13 04:00:00 EST 1980 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100460a009· OSTI ID:6869123

Ohno, T; Lichtin, N N

A Q-switched ruby laser emitting 1.0-J flashes at 693.4 nm was used in a flash-photolytic, kinetic-spectrometric investigation of the mechanism of quenching of 10 ..mu..M triplet methylene blue by Co/sup II/(edta)/sup 2 -/, Co/sup II/(TIM)(H/sub 2/O)/sub 2//sup 2 +/, Co/sup II/(phen)/sub 3//sup 2 +/, and Co/sup II/(tpy)/sub 2//sup 2 +/ (edta = ethylenediamine-N,N-N',N'-tetraacetic acid; TIM = 1,4,8,11-tetraaza-2,3-dimethylcyclotetradeca-1,3,8,10-tetraene; phen = 1,10-phenanthroline; and tpy = 2,2',2''-terpyridine) in water and aqueous EtOH at pH approx. 2 and approx. 6, where the species quenched and the product of its reductive quenching are, respectively, /sup 3/MBH/sup 2 +/ and MBH/sup +/. Specific rates of quenching, k/sub q/, of net electron transfer during quenching, k/sub et/, and the kinetics of decay of the products of quenching were determined. Specific rates, k/sub ret/, of reverse electron transfer from MBH/sup +/. to complexes of Co(III), Co/sup III/L/sub x//sup m+1/, were evaluated by generating MBH/sup +/. by quenching /sup 3/MBH/sup 2 +/ with diphenylamine in the presence of Co/sup III/L/sub x//sup m+1/. Values of F/sub 1/ = k/sub et//k/sub q/, of F/sub 2/ = k/sub ret//k/sub D/, where k/sub D/ is the diffusion-controlled specific rate of encounter, and of F/sub 1/ + F/sub 2/ are compared with analogous data for quenching of /sup 3/MBH/sup 2 +/ by complexes of Fe(II) and with the detailed reversible electron-transfer model which was developed for the latter processes. It is concluded that reversible electron transfer is not the only significant mechanism of quenching of /sup 3/MBH/sup 2 +/ by the four complexes of Co(II) employed in this research. At least one other mechanism, e.g., energy transfer or physical quenching, is followed to a significant degree.

• Research Organization: Boston Univ., MA
• OSTI ID: 6869123
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 84:23; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
400500* -- Photochemistry
AMINES
AMINO ACIDS
ANTI-INFECTIVE AGENTS
ANTIMICROBIAL AGENTS
AZINES
CARBOXYLIC ACIDS
CHELATING AGENTS
CHEMICAL REACTIONS
CHLORIDES
CHLORINE COMPOUNDS
COBALT COMPLEXES
COMPLEXES
DATA
DECOMPOSITION
DRUGS
EDTA
ELECTROMAGNETIC RADIATION
EXPERIMENTAL DATA
HALIDES
HALOGEN COMPOUNDS
HETEROCYCLIC COMPOUNDS
INFORMATION
KINETICS
LASER RADIATION
METHYLENE BLUE
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PHENANTHROLINES
PHENOTHIAZINES
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PYRIDINES
RADIATIONS
REACTION KINETICS
SCINTILLATION QUENCHING
TRANSITION ELEMENT COMPLEXES