Journal of the American Chemical Society
Journal of the American Chemical Society
5 years ago

Bromide Photo-oxidation Sensitized to Visible Light in Consecutive Ion Pairs

Bromide Photo-oxidation Sensitized to Visible Light in Consecutive Ion Pairs
Wesley B. Swords, Guocan Li, Gerald J. Meyer
The titration of bromide into a [Ru(deeb)(bpz)2]2+ (Ru2+, deeb = 4,4′-diethylester-2,2′-bipyridine; bpz = 2,2′-bipyrazine) dichloromethane solution led to the formation of two consecutive ion-paired species, [Ru2+, Br–]+ and [Ru2+, 2Br–], each with distinct photophysical and electron-transfer properties. Formation of the first ion pair was stoichiometric, Keq 1 > 106 M–1, and the second ion-pair equilibrium was estimated to be Keq 2 = (2.4 ± 0.4) × 105 M–1. The 1H NMR spectra recorded in deuterated dichloromethane indicated the presence of contact ion pairs and provided insights into their structures and were complimented by density functional theory calculations. Static quenching of the [Ru(deeb)(bpz)2]2+* photoluminescence intensity (PLI) by bromide was observed, and [Ru2+, Br–]+* was found to be nonluminescent, τ < 10 ns. Further addition of bromide resulted in partial recovery of the PLI, and [Ru2+, 2Br–]* was found to be luminescent with an excited-state lifetime of τ = 65 ± 5 ns. Electron-transfer products were identified as the reduced complex, [Ru(deeb)(bpz)2]+, and dibromide, Br2•–. The bromine atom, Br•, was determined to be the primary excited-state electron-transfer product and was an intermediate in Br2•– formation, Br• + Br– → Br2•–, with a second-order rate constant, k = (5.4 ± 1) × 108 M–1 s–1. The unusual enhancement in PLI for [Ru2+, 2Br–]* relative to [Ru2+, Br–]+* was due to a less favorable Gibbs free energy change for electron transfer that resulted in a smaller rate constant, ket = (1.5 ± 0.2) × 107 s–1, in the second ion pair. Natural atomic charge analysis provided estimates of the Coulombic work terms associated with ion pairing, ΔGw, that were directly correlated with the measured change in rate constants.

Publisher URL: http://dx.doi.org/10.1021/jacs.7b06735

DOI: 10.1021/jacs.7b06735

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.