Influence of ion pairing on the oxidation of iodide by MLCT excited states
2011 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 40, no 15, 3830-3838 p.Article in journal (Refereed) Published
The oxidation of iodide to diiodide, I2[radical dot]-, by the metal-to-ligand charge-transfer (MLCT) excited state of [Ru(deeb)3]2+, where deeb is 4,4[prime or minute]-(CO2CH2CH3)2-2,2[prime or minute]-bipyridine, was quantified in acetonitrile and dichloromethane solution at room temperature. The redox and excited state properties of [Ru(deeb)3]2+ were similar in the two solvents; however, the mechanisms for excited state quenching by iodide were found to differ significantly. In acetonitrile, reaction of [Ru(deeb)3]2+* and iodide was dynamic (lifetime quenching) with kinetics that followed the Stern-Volmer model (KD = 1.0 +/- 0.01 [times] 105 M-1, kq = 4.8 [times] 1010 M-1 s-1). Excited state reactivity was observed to be the result of reductive quenching that yielded the reduced ruthenium compound, [Ru(deeb-)(deeb)2]+, and the iodine atom, I[radical dot]. In dichloromethane, excited state quenching was primarily static (photoluminescence amplitude quenching) and [Ru(deeb-)(deeb)2]+ formed within 10 ns, consistent with the formation of ion pairs in the ground state that react rapidly upon visible light absorption. In both solvents the appearance of I2[radical dot]- could be time resolved. In acetonitrile, the rate constant for I2[radical dot]- growth, 2.2 +/- 0.2 [times] 1010 M-1 s-1, was found to be about a factor of two slower than the formation of [Ru(deeb-)(deeb)2]+, indicating it was a secondary photoproduct. The delayed appearance of I2[radical dot]- was attributed to the reaction of iodine atoms with iodide. In dichloromethane, the growth of I2[radical dot]-, 1.3 +/- 0.4 [times] 1010 M-1 s-1, was similar to that in acetonitrile, yet resulted from iodine atoms formed within the laser pulse. These results are discussed within the context of solar energy conversion by dye-sensitized solar cells and storage via chemical bond formation.
Place, publisher, year, edition, pages
Royal Society of Chemistry, 2011. Vol. 40, no 15, 3830-3838 p.
I-I BONDS; ELECTRON-TRANSFER; DYE; SALTS; COMPLEXES; ATOMS; FILMS
IdentifiersURN: urn:nbn:se:kth:diva-51576DOI: 10.1039/c0dt01447hISI: 000288961100011OAI: oai:DiVA.org:kth-51576DiVA: diva2:464759
QC 201112212011-12-212011-12-132011-12-21Bibliographically approved