Cage escape yields from the quenching of Ru(bpy) sub 3 sup 2+ by methylviologen in aqueous solution

Journal Article · Thu Jun 16 04:00:00 EDT 1988 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100323a029· OSTI ID:7003009

Hoffman, M Z ^[1]

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1. Boston Univ., MA (USA)

The primary quantum yield of formation of Ru(bpy){sub 3}{sup 3+} and methylviologen radical cation (MV{sup {center dot}+}), {phi}, resulting from the oxidative quenching of Ru(bpy){sub 3}{sup 2+} by methylviologen (MV{sup 2+}) in aqueous solution, has been determined by the use of pulsed-laser flash photolysis ({lambda}{sub exc} = 532 nm; {lambda}{sub mon} = 450 nm) as a function of (MV{sup 2+}), ionic strength, and pH in the absence and presence of Na{sub 2}SO{sub 4}, C{sub 2}O{sub 4}{sup 2{minus}} (Na{sup +} or K{sup +} salt), and ethylenediaminetetraacetate (EDTA). Inasmuch as {phi} = {eta}{sub q}{eta}{sub ce}, where {eta}{sub q} is the efficiency of the quenching of Ru(bpy){sub 3}{sup 2+} (=k{sub q}MV{sup 2+}/(k{sub 0} + k{sub q}(MV{sup 2+}))) and {eta}{sub ce} is the cage escape efficiency of the germinate redox pair, values of {eta}{sub ce} are easily calculated. The values of {eta}{sub ce} are a complex function of the solution medium parameters, reflecting the self-aggregation of MV{sup 2+}, the presence of ion-pair aggregates of MV{sup 2+} and EDTA, and the effect of the ionic strength of the solution on the rate constant of the cage escape reaction. Values range from {approx} 0.45 in the limit of zero ionic strength at (MV{sup 2+}) {ge} 5 mM to {approx} 0.10 at high ionic strength (3.0 M) in the presence of Na{sub 2}SO{sub 4} and C{sub 2}O{sub 4}{sup 2{minus}}; {eta}{sub ce} followed an empirical relationship as a function of {mu}: {eta}{sub ce} = (2.22 + 3.81 {mu} {sup {1/2}}){sup {minus}1}. For solutions containing 0.010-0.10 M EDTA, {eta}{sub ce} is generally lower than that predicted by the empirical relationship, indicating the existence of a specific effect for that reagent due, perhaps, to the presence of ion-paired aggregated of MV{sup 2+} and EDTA. The results obtained here compare very well with values of {eta}{sub ce} reported by other investigators.

• OSTI ID: 7003009
• Journal Information: Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 92:12; ISSN 0022-3654; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
AQUEOUS SOLUTIONS
AZINES
BIPYRIDINES
CATIONS
CHARGED PARTICLES
CHEMICAL REACTIONS
COMPLEXES
CRYSTAL STRUCTURE
DATA
DECOMPOSITION
DISPERSIONS
EXPERIMENTAL DATA
HETEROCYCLIC COMPOUNDS
INFORMATION
IONS
LASERS
LUMINESCENCE
MIXTURES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOLYSIS
PULSE TECHNIQUES
PYRIDINES
RADICALS
RUTHENIUM COMPLEXES
SOLUTIONS
TRANSITION ELEMENT COMPLEXES