Remarkably little is known about the metal-to-ligand charge transfer (MLCT) excited state relaxation pathways for coordination compounds used in dye sensitized solar cells (DSSCs) of the type cis-Ru(LL)2(X)2, where LL is a bipyridyl ligand and X is CN- or NCS-. Variable temperature photoluminescence studies of cis-Ru(LL)2(X)2 compounds were compared to Ru(bpy)32+ and Os(bpy)32+, where bpy is 2,2'-bipyridine, in order to identify relaxation pathways in fluid solution and when anchored to mesoporous TiO2 or ZrO2 thin films. An Arrhenius analysis revealed internal conversion to two different states, assigned to an upper MLCT excited state and a ligand field (LF) excited state. Non-radiative decay through LF states was sensitive to the ligand identity, but in a manner not fully consistent with the spectrochemical series. An important finding is that population of LF excited states associated with unwanted photochemistry is unlikely to occur in DSSCs based on cis-Ru(LL)2(NCS)2 type compounds at room temperature.

Excited state relaxation of ruthenium polypyridyl compounds relevant to dye-sensitized solar cells

245th National Meeting (2013)

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