Spin-orbit coupling and magnetic field effects in photoredox reactions of ruthenium(II) complexes

Journal Article · Thu Jun 29 04:00:00 EDT 1989 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100350a025· OSTI ID:7197238

Steiner, U E; Wolff, H; Ulrich, T ^[1]; Ohno, Takeshi ^[2]

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1. Universitaet Konstanz (West Germany)
2. Osaka Univ. (Japan)

Spin-orbit coupling (SOC) and magnetic field effects (MFEs) on the efficiency {eta}{sub net} of net electron transfer in the reductive and oxidative quenching of excited Ru{sup II} trisbipyridyl complexes have been investigated by nanosecond laser flash spectroscopy and by a special continuous photolysis technique. The reductive process was studied with tris(4,4{prime}-bis(ethoxycarbonyl)-2,2{prime}-bipyridine)ruthenium(2+) quenched by anilines X-An (X = H, 4-Cl, 4-Br, 2-I, 4-I). Increasing SOC of the substituent X leads to a decrease of relative {eta}{sub net} values (1.0, 0.79, 0.45, 0.22, 0.12). With X = 4-I {eta}{sub net} is decreased by 12.5 {plus minus} 2.5% in a magnetic field of 1 T. These effects are interpreted as SOC effects of the X center on the spin-forbidden back electron transfer in triplet radical pairs. The oxidative process was studied with (Ru{sup II}(2,2{prime}-bipyridine){sub 3}){sup 2+} and methylviologen (MV{sup 2+}) as a quencher. Here a MFE of {minus}10% at 1 T was observed on the yield of radicals detected on the nanosecond time scale. A detailed MF dependence between 0 and 1 T of the yield of MV{sup {center dot}+} radicals was measured by continuous photolysis using EDTA as a sacrificial electron donor to reduce Ru{sup III}. The MFE shows a gradual onset followed by a linear increase above 50-100 mT. The onset field decreases and the (negative) slope of the MFE increases as the solvent viscosity is increased in water/ethylene glycol mixtures. On the basis of measurements of lifetime and radical yield at various quencher concentrations, it is shown that the magnetic field mainly affects {eta}{sub net} and not the rate of quenching k{sub q}, as recently asserted by other authors. The MFE is attributed to SOC effects in the Ru{sup III} complex constituent of the primary radical pair.

• OSTI ID: 7197238
• Journal Information: Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 93:13; ISSN JPCHA; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400000* -- Chemistry
400500 -- Photochemistry
CHEMICAL REACTIONS
CHEMISTRY
COMPLEXES
DATA
DATA ANALYSIS
DECOMPOSITION
EXPERIMENTAL DATA
INFORMATION
MAGNETIC FIELDS
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
ORIENTATION
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
PHOTOLYSIS
REDOX REACTIONS
RUTHENIUM COMPLEXES
SPIN ORIENTATION
TRANSITION ELEMENT COMPLEXES