Excited-State Relaxation of Ruthenium Polypyridyl Compounds Relevant to Dye-Sensitized Solar Cells
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- 作者：Ryan M. O鈥橠onnell ; Patrik G. Johansson ; Maria Abrahamsson ; Gerald J. Meyer
- 刊名：Inorganic Chemistry
- 出版年：2013
- 出版时间：June 17, 2013
- 年：2013
- 卷：52
- 期：12
- 页码：6839-6848
- 全文大小：481K
- 年卷期：v.52,no.12(June 17, 2013)
- ISSN：1520-510X
文摘
Remarkably little is known about metal-to-ligand charge transfer (MLCT) excited-state relaxation pathways for the ruthenium polypyridyl compounds commonly utilized in dye-sensitized solar cells. Herein, we report variable-temperature photoluminescence studies of compounds of the general type cis-Ru(LL)2(X)2, where LL is a bipyridyl ligand and X is CN鈥?/sup> or NCS鈥?/sup>, and contrast them with the well-known Ru(bpy)32+ and Os(bpy)32+, where bpy is 2,2鈥?bipyridine, to identify relaxation pathways. In fluid acetonitrile and propylene carbonate solutions, excited-state relaxation was found to obey a first-order kinetic model. An Arrhenius analysis revealed internal conversion to two different states, assigned to an upper MLCT excited state and a ligand field excited state. Relaxation through the upper MLCT excited state typically displayed pre-exponential factors of 107鈥?08 s鈥? with activation energies of 400鈥?00 cm鈥?, while relaxation rates through ligand field states occurred with 1014鈥?015 s鈥? and activation energies of 4000鈥?000 cm鈥?. Nonradiative decay through LF states was sensitive to the ligand identity, but in a manner that was not fully consistent with the spectrochemical series. Excited-state relaxation of cis-Ru(dcbH2)2(NCS)2, where dcbH2 is 4,4鈥?(CO2H)2-2,2鈥?bipyridine, sometimes termed N3, anchored to mesoporous TiO2 or ZrO2 thin films immersed in CH3CN occurred through the upper MLCT excited state with activational parameters in surprisingly good agreement with those abstracted from data measured in fluid solution. An important finding from these studies is that the population of dissociative ligand field excited states is unlikely to lead to unwanted photochemistry of dye-sensitized solar cells based on cis-Ru(LL)2(NCS)2-type compounds at room temperature.