Reaction of RuII Diazafluorenone Compound with Nanocrystalline TiO2 Thin Film

Coordination chemistry and applications of versatile 4,5-diazafluorene derivatives

This review article highlights the versatile nature of 4,5-diazafluorene derivatives as ligands, and details some recent advances made using this ligand family.

High extinction coefficient Ru-sensitizers that promote hole transfer on nanocrystalline TiO₂

Two series of Ru(II) polypyridyl compounds with formulas [(bpy)2RuL](PF6)2 and [(deeb)2RuL](PF6)2, where bpy is 2,2'-bipyridine, deeb is 4,4'-diethylester-2,2'-bpy, and L is one of several substituted 9'-(1,3-dithiole-2-ylidene)-4',5'-diazafluorene ligands, were studied as potential photosensitizers for TiO2. These compounds possess notably high extinction coefficients (≥40,000 M(-1) cm(-1) @470 nm) which are shown by time-dependent density functional theory (TD-DFT) calculations to result from overlapping metal-to-ligand charge transfer (MLCT) and ligand-localized transitions. Low-temperature absorption and photoluminescence measurements were suggestive of a short-lived MLCT excited state. When adsorbed onto TiO2 thin films, both the free ligands (L) and their corresponding [(deeb)2RuL](2+) complexes exhibited rapid excited-state electron injection into TiO2; in the case of the complexes, this was followed by rapid (k>10(8) s(-1)) hole transfer from Ru(III) to the 1,3-dithiole ring of the L ligand. Observation of diffusion-limited reductive quenching of the [Ru(bpz)3](2+)* (bpz is 2,2'-bipyrazine) excited state by the L ligands in solution supported the occurrence of intramolecular hole transfer following electron injection by the TiO2-anchored complexes.

Characterization of nanostructured hybrid and organic solar cells by impedance spectroscopy

We review the application of impedance spectroscopy in dye-sensitized solar cells, quantum dot-sensitized solar cells and organic bulk heterojunction solar cells. We emphasize the interpretation of the impedance parameters for determining the internal features of the device, concerning the carrier distribution, materials properties such as the density of states and/or doping of the semiconductors, and the match of energy levels for photoinduced charge generation and separation. Another central task is the determination of recombination mechanisms from the measured resistances, and the factors governing the device performance by combined analysis of resistances as a function of voltage and current-voltage curves.