Temperature dependent iodide oxidation by MLCT excited states.
نویسندگان
چکیده
The metal-to-ligand charge transfer (MLCT) excited states of two related heteroleptic Ru(ii) compounds [Ru(bpy)2(deeb)](2+) and [Ru(bpy)2(deebq)](2+), where bpy is 2,2'-bipyridine, deeb is 4,4'-(CO2CH2CH3)2-2,2'-bipyridine and deebq is 4,4'-(CO2CH2CH3)2-2,2'-biquinoline, were characterized in fluid acetonitrile by temperature dependent photoluminescence spectroscopies as well as quenching by iodide ions. Photoluminescence emanates from a manifold of thermally equilibrated excited states referred to as the thexi states. Evidence for activated internal conversion to a 4(th) MLCT excited state was garnered from an Arrhenius analysis of temperature dependent lifetime data. The activation energy was found to be 550 cm(-1) for [Ru(bpy)2(deeb)](2+)* and 1200 cm(-1) for [Ru(bpy)2(deebq)](2+)*. The pre-exponential factor abstracted from the Arrhenius analysis of the [Ru(bpy)2(deebq)](2+)* data suggested that ligand field excited states might be populated, however there was no evidence for ligand loss photochemistry under the conditions studied. The excited states were found to quench iodide by a dynamic process in good agreement with the Stern-Volmer model. Transient absorption data showed that the quenching mechanism was electron transfer to generate an iodine atom and a reduced ruthenium compound as products. The quenching rate constants abstracted from temperature dependent Stern-Volmer quenching data were corrected for diffusion and activated complex formation to yield electron transfer rate constants that were found to increase markedly with temperature. An Arrhenius analysis of the electron transfer data revealed that electron transfer from iodide to the d-orbitals of the excited state was an activated process with an Ea of 2400 cm(-1) for [Ru(bpy)2(deeb)](2+) and 3300 cm(-1) for [Ru(bpy)2(deebq)](2+).
منابع مشابه
Visible light generation of I-I bonds by Ru-tris(diimine) excited states.
Seven Ru-tris(diimine) compounds were prepared to study the photooxidation of iodide. Iodide oxidation results in the formation of I-I bonds, and it is therefore relevant to the conversion and storage of solar energy. Iodide oxidation is also a key step for electrical power generation in dye-sensitized solar cells. The mechanistic details of iodide oxidation and I-I bond formation were elucidat...
متن کاملOrigin of electronic absorption spectra of MLCT-excited and one-electron reduced 2,2â€2-bipyridine and 1,10-phenanthroline complexes
UV–Vis absorption spectra of one-electron reduction products and MLCT excited states of [ReCl(CO)3(N,N)] (N,N = 2,20-bipyridine, bpy; 1,10-phenanthroline, phen) have been measured by low-temperature spectroelectrochemistry and UV–Vis transient absorption spectroscopy, respectively, and assigned by open-shell TD-DFT calculations. The characters of the electronic transitions are visualized and an...
متن کاملTuning the excited-state energy of the organic chromophore in bichromophoric systems based on the Ru(II) complexes of tridentate ligands.
A series of new heteroleptic and homoleptic Ru(II) complexes containing variously substituted bis(pyridyl)triazine ligands has been prepared and their absorption spectra, redox behaviour and luminescence properties (both in fluid solution at room temperature and in a rigid matrix at 77 K) have been investigated. For some compounds, X-ray structures have also been determined. The new bis(pyridyl...
متن کاملManipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution.
Developing light-harvesting and photocatalytic molecules made with iron could provide a cost effective, scalable, and environmentally benign path for solar energy conversion. To date these developments have been limited by the sub-picosecond metal-to-ligand charge transfer (MLCT) electronic excited state lifetime of iron based complexes due to spin crossover - the extremely fast intersystem cro...
متن کاملProbing the excited state dynamics of a new family of Cu(I)-complexes with an enhanced light absorption capacity: excitation-wavelength dependent population of states through branching.
The ultrafast dynamics of six homoleptic Cu(I)-complexes and their respective ligands was examined through time-resolved electronic absorption spectroscopy in the subpicosecond time domain, in a variety of solvents, and at different excitation wavelengths. Results indicate that after excitation of the complexes in the blue part of the spectrum, the initially formed intraligand (IL) singlet exci...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
- Dalton transactions
دوره 43 47 شماره
صفحات -
تاریخ انتشار 2014