Abstract
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, Keq1 > 106 M-1, and the second ion-pair equilibrium was estimated to be Keq2 = (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.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.