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Insights into Photoinduced Electron Transfer Between [Ru(mptpy)2]4+ (mptpy = 4'-(4-methylpyridinio)-2,2':6',2"-terpyridine) and [S2O8]2– : Computational and Experimental Studies

Kaledin, A. L. and Huang, Z. and Yin, Q. and Dunphy, E. L. and Constable, E. C. and Housecroft, C. E. and Lian, T. and Hill, C. L. and Musaev, D. G.. (2010) Insights into Photoinduced Electron Transfer Between [Ru(mptpy)2]4+ (mptpy = 4'-(4-methylpyridinio)-2,2':6',2"-terpyridine) and [S2O8]2– : Computational and Experimental Studies. Journal of Physical Chemistry A, 114 (21). pp. 6284-6297.

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Official URL: http://edoc.unibas.ch/dok/A5841498

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Abstract

The mechanism and electron transfer dynamics of the reaction [RuII(mptpy)2]4+ + hν + [S2O8]2− → [RuIII(mptpy)2]5+ + SO42− + SO4−• were studied using various computational (density functional and exciton interaction theories) and experimental (transient absorption, static and time-resolved fluorescence spectroscopy, and other) techniques. The results were compared with those recently reported for [Ru(bpy)3]2+ dye [ref 18]. It was found that the excitation energy of [Ru(mptpy)2]4+ is about 0.4−0.5 eV smaller than that of [Ru(bpy)3]2+, which is consistent with the measured absorption maxima of 445 and 507 nm, for [Ru(bpy)3]2+ and [Ru(mptpy)2]4+, respectively. The smaller excitation energy in [Ru(mptpy)2]4+ correlates with much slower electron transfer rates to persulfate compared to [Ru(bpy)3]2+. The quenching of the photoexcited [Ru(mptpy)2]4+ by [S2O8]2− occurs via a unimolecular mechanism with formation of a weak ion-pair complex {[Ru(mptpy)2]4+···([S2O8]2−)n}, where n = 1 and 2. The initial photon is absorbed by the [Ru(mptpy)2]4+ fragment forming an MLCT state, e.g., the bright singlet state S1. This S1 state undergoes a fast spin−orbit coupling induced intersystem crossing to a lower-lying triplet and rapid subsequent relaxation down to the lowest triplet T1 via internal conversion and collisions with solvent molecules. At this stage, the electron transfer from [Ru(mptpy)2]4+ to a loosely attached [S2O8]2− occurs in a dark reaction via elongation of the O−O peroxo bond of the oxidant [S2O8]2−. The electron transfer lifetimes in water are calculated to be 1/κ1 = 199.4 ns and 1/κ2 = 108.4 ns, for the 1:1 and 1:2 complexes, respectively. The computed electron transfer lifetimes (1/κ1) are in reasonable agreement with their experimental values of 298 and 149 ns for the 1:1 and 1:2 complexes, respectively. The effect of solvent polarity on electron transfer rates is found to be significant: the less polar acetonitrile slows the rate by an order of magnitude compared to water.
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Anorganische Chemie (Housecroft)
UniBasel Contributors:Housecroft, Catherine Elizabeth and Constable, Edwin Charles and Dunphy, Emma
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:American Chemical Society
ISSN:1089-5639
e-ISSN:1520-5215
Note:Publication type according to Uni Basel Research Database: Journal article
Identification Number:
Last Modified:08 May 2017 07:29
Deposited On:14 Sep 2012 06:53

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