Static and Dynamic Quenching of Ru(II) Polypyridyl Excited States by Iodide

Abstract

The metal-to-ligand charge-transfer (MLCT) excited states of Ru(bpy)(2)(deeb)(PF(6))(2), where bpy is 2,2-bipyridine and deeb is 4,4'-(CO(2)CH(2)CH(3))(2)-2,2'-bipyridine, in dichloromethane were found to be efficiently quenched by iodide at room temperature. The ionic strength dependence of the UV-visible absorption spectra gave evidence for ion pairing. Iodide was found to quench the excited states by static and dynamic mechanisms. Stern-Volmer and Benesi-Hildebrand analysis of the spectral data provided a self-consistent estimate of the iodide-Ru(bpy)(2)(deeb)(2+) adduct in dichloromethane, K = 59 700 M(-1). Transient absorption studies clearly demonstrated an electron-transfer quenching mechanism with transient formation of I(2)(*)(-) in high yield, phi = 0.25 for 355 or 532 nm excitation. For Ru(bpy)(2)(deeb)(PF(6))(2) in acetonitrile, similar behavior could be observed at higher iodide concentrations than that required in dichloromethane. The parent Ru(bpy)(3)(2+) compound also ion pairs with iodide in CH(2)Cl(2), and light excitation gave a higher I(2)(*)(-) yield, phi = 0.50. X-ray crystallographic, IR, and Raman data gave evidence for interactions between iodide and the coordinated deeb ligand in the solid state.

Visible light generation of I–I bonds by Ru-tris(diimine) excited states

“…To our knowledge, ½RuðdmbÞ 2 ðbpzÞðPF 6 Þ 2 and ½RuðbpmÞ 2 ðdeebÞðPF 6 Þ 2 are compounds that have not been previously reported. The photophysical properties for all other compounds have been well characterized in the literature, and they agree with the results presented in this study (12,14,17,18).…”

“…To our knowledge, ½RuðdmbÞ 2 ðbpzÞðPF 6 Þ 2 and ½RuðbpmÞ 2 ðdeebÞðPF 6 Þ 2 are compounds that have not been previously reported. The photophysical properties for all other compounds have been well characterized in the literature, and they agree with the results presented in this study (12,14,17,18).The Ru 2þ compounds ranged in color from bright orange for ½RuðbpzÞ 2 ðdeebÞðPF 6 Þ 2 to a deep red for ½RuðdmbÞ 2 ðbpzÞ ðPF 6 Þ 2 , and they displayed absorption features in the 400-to 500-nm range, which is consistent with MLCT transitions. Extinction coefficient spectra of ½RuðbpyÞ 2 ðdeebÞ 2þ and, its one electron reduced form ½RuðbpyÞ 2 ðdeeb − Þ þ are shown in Fig.…”

“…This bond formation chemistry is also of major importance in dye-sensitized solar cells where I − /I 3 − is the most widely used redox mediator (7-11). We have previously reported the photooxidation of iodide using Ru-tris(diimine) compounds in fluid solution (1,2,(12)(13)(14). These compounds are known for their exceptional absorption properties in the visible region, and their long-lived metal-toligand charge transfer (MLCT) excited states (15, 16).…”

Effect of the Presence of Iodide on the Electron Injection Dynamics of Dye-Sensitized TiO2-Based Solar Cells

“…The practice of omitting the colored I 3 -component from the supporting electrolyte, and replacing it with nonredox active species such as ClO 4 -, for example, when carrying out timeresolved studies of the electron transfer dynamics of these cells is generally done out of convenience, due the high optical density associated with solutions that are ∼ 0.05 M in I 3 -. However, recent work suggesting that I -can quench the excitedstate of certain sensitizers, 24,25 a process that would have a significant impact on the overall injection yield and therefore on the maximum current density, compelled us to consider whether the injection dynamics observed in the absence of the I 3 -/I -redox couple were reflective of processes occurring in the functional device.…”

Excited state behaviour of substituted dipyridophenazine Cr(iii) complexes in the presence of nucleic acids

“…Such behaviour is characteristic of dynamic quenching. 48 It is also evident that for emission quenching by GMP {Fig. 5(a)} the lifetime and steady state Stern-Volmer plots deviate from each other only slightly, indicating that the quenching proceeds predominantly by a dynamic process.…”