Citrazinic acid is used as a convenient starting material for both tridentate 2,6-di(pyrazol-1-yl)-pyridine and tetradentate 6,6'-di(pyrazol-1-yl)-2,2'-bipyridine ligands containing carboxylic groups useful for further anchoring of sensitizer on TiO(2) for dye-sensitized solar cells (DSCs). Using 2,6-dichloro-4-carboxypyridine, the synthesis of the terdentate ligands was improved compared to previously used 2,6-dibromo-4-carboxypyridine or 2,6-dichloro-4-ethylcarboxylate pyridine. Controlling the reaction conditions, it is possible to efficiently obtain the monosubstituted 2-chloro-6-pyrazol-1-yl-4-carboxypyridine, a key intermediate for the preparation of tetradentate 6,6'-di(pyrazol-1-yl)-4,4'-dicarboxy-2,2'-bipyridine ligand. (C) 2010 Elsevier Ltd. All rights reserved.

Based on the Horner–Emmons–Wadsworth reaction, a convenient synthetic route for the extension of the π-system on 4,4′-disubstituted-2,2′-bipyridines was used to develop a novel series of functionalized ligands for DSC applications.

A novel ligand, 5,5'-(2,2'-bipyridine-4,4'-diyl)-bis(thiophene-2-carboxylic acid) (BTC), and its Ru-II complex (BTC-1) in which the anchoring group is attached to the thiophene units were developed. Using a low-volatility electrolyte and 3.3 mu m mesoporous TiO2 films BTC-1 achieved a solar-to-electricity conversion efficiency of 6.1%, compared to 4.8% for N719 under the same experimental conditions.

We present two sensitizers, Ru(4,4'-dicarboxyvinyl)-2,2'-bipyridine)(4,4'-dinonyl-2,2'-bipyridine)(NCS)(2) (K9) and Ru(4,4'-dicarboxy(phenylethenyl)-2,2'-bipyridine)(4,4'-dinonyl-2,2'-bipyridine)(NCS)(2) (K23), which were synthesized and characterized by analytical, spectroscopic, and electrochemical impedance measurements. The two sensitizers that contain hydrophobic alkyl chains and an extended pi-conjugation bridge between carboxylic acid groups and the ruthenium chromophore center exhibit enhanced red response and higher molar extinction coefficients when compared to the Ru(4,4'-dicarboxy-2,2'-bipyridine)(4,4'-dinonyl-2,2'-bipyridine)(NCS)(2) (Z907) sensitizer. The performances of the K9, K23, and Z907 sensitizers in nanocrystalline TiO2-based thin film solar cells were studied using transparent 2.6-mu m-thick mesoporous layers, which show short-circuit photocurrent densities (J(sc)) of 7.80, 8.31, and 7.16 mA/cm(2), corresponding to overall conversion efficiencies of 4.14, 4.41, and 4.06%, respectively. The increase in the J(sc) of the cells with K9 and K23 with respect to that with Z907 is due to the enhanced molar extinction coefficient of the new sensitizers. The incident monochromatic photon-to-current conversion efficiency for die K23 is plotted as a function of excitation wavelength show in the plateau region 79% and even at 700 nm 69%.

AbstractRed OLED: An orange–red‐emitting iridium complex (N958) was prepared, and its photophysical and device‐based characteristics were investigated. Despite N958 displaying quite poor photophysical properties in solution (acetonitrile), organic light‐emitting diode (OLED) devices based on the complex exhibit an efficiency close to 10 %.magnified image

Patent numbers: US8440843 (B2)AU2005266755 (B2)US2011190501 (A1)US7932404 (B2)CN101023502 (B)EP1774550 (B9)US2009000658 (A1)AT409948 (T)EP1774550 (B1)KR20070085221 (A)CN101023502 (A)EP1774550 (A1)WO2006010290 (A8)AU2005266755 (A1)WO2006010290 (A1)EP1622178 (A1) Reference EPFL-PATENT-211652Search for this record at the European Patent Office Record created on 2015-09-22, modified on 2016-08-09

Recombination between injected electrons and iodine limits the photovoltage in dye-sensitized solar cells (DSSCs). We have recently suggested that many new dye molecules, intended to improve DSSCs, can accelerate this reaction, negating the expected improvement (J. Am. Chem. Soc. 2008, 130, 2907). Here we study two dyes with only a two-atom change in the structure, yet which give different Vocs. Using a range of measurements we show conclusively that the change in Voc is due solely to the increase in the recombination rate. From the structure of the dyes, and literature values for iodine binding of similar compounds, we find that it is very likely that the change in Voc is due solely to the difference in iodine binding at the site of the two-atom change. Using the large amount of literature on iodine complexation, we suggest structures for dyes that might show improved Voc.

A simple mononuclear cyclometallated iridium(iii) complex exhibits white photo- and electro- luminescence in the wavelength range from 440 to 800 nm, which originates from a single emitting excited state of mixed character.

Highly phosphorescent blue-light-emitting anionic iridium complexes (C4H9)4N[Ir(2-phenylpyridine)2(CN)2] (1), (C4H9)4N[Ir(2-phenyl-4-dimethylaminopyridine)2(CN)2] (2), (C4H9)4N[Ir(2-(2,4-difluorophenyl)-pyridine)2(CN)2] (3), (C4H9)4N[Ir(2-(2,4-difluorophenyl)-4-dimethylaminopyridine)2(CN)2] (4), and (C4H9)4N[Ir(2-(3,5-difluorophenyl)-4-dimethylaminopyridine)2(CN)2] (5) were synthesized and characterized using NMR, UV-vis absorption, and emission spectroscopy and electrochemical methods. In these complexes color and quantum yield tuning aspects are demonstrated by modulating the ligands with substituting donor and acceptor groups on both the pyridine and phenyl moieties of 2-phenylpyridine. Complexes 1-5 display intense photoluminescence maxima in the blue region of the visible spectrum and exhibit very high phosphorescence quantum yields, in the range of 50-80%, with excited-state lifetimes of 1-4 micros in acetonitrile solution at 298 K. DFT and time dependent-DFT calculations were performed on the ground and excited states of the investigated complexes to provide insight into the structural, electronic, and optical properties of these systems.

A new ion-coordinating ruthenium polypyridyl sensitizer, NaRu(4-carboxylic acid-4'-carboxylate)(4,4'-bis[(triethyleneglycolmethylether) heptylether]-2,2'-bipyridine)(NCS)(2) (coded as K68), has been synthesized and characterized by H-1 NMR, FTIR, UV-Vis absorption and emission spectroscopy. A power conversion efficiency of 6.6% was obtained for dye-sensitized solar cells (DSCs) based on the K68 dye and a newly developed binary ionic liquid electrolyte containing 1-propyl-3-methyl-imidazolium iodide (PMII) and 1-ethyl-3-methyl- imidazolium tetracyanoborate (EMIB(CN)(4)). For a non-volatile organic solvent based electrolyte, a photovoltaic power conversion efficiency of 7.7% was obtained under simulated full sun light and exhibited a good thermal stability during the accelerated test under 80 degrees C in the dark. Solid-state DSCs incorporating K68 also perform remarkably well, out-performing our previously best ruthenium complexes employed in this type of DSC. (c) 2007 Elsevier B.V. All rights reserved.

We compare a series of molecular sensitizers in dye-sensitized solar cells containing the organic hole transporter 2,2',7,7'-tetrakis(N,N-di-p-methoxypheny-amine)-9,9'-spirobifluorene (spiro-MeOTAD). Charge recombination is reduced by the presence of "ion-coordinating" moieties on the dye, with the longest electron lifetime and highest solar cell efficiency achieved using a novel sensitizer with diblock alkoxy-alkane pendent groups. By further increasing the optical path length in the active layer, we achieve a power conversion efficiency of over 5% under simulated sun light.

In this study, a novel phosphorescent Ir(III) complex [Ir(2-phenylpyridine)2(4,4'-bis(2-(4-N,N-methylhexylaminophenyl)ethyl)-2-2'-bipyridine)Cl] (for convenience, the complex was given the synonym N-948) has been designed and synthesized, to be used as an oxygen probe. It was characterized by spectroscopic and analytical methods when incorporated in a polystyrene and nanostructured metal oxide support. N-948 is the first Ir complex in the literature with a luminescence emission at a wavelength higher than 650 nm (665 nm), with a quantum yield higher than 0.50 (0.58 +/- 0.05) and an extremely long phosphorescence lifetime (102 micros) which has been used for developing oxygen-sensitive films. In addition, the new complex shows a Stern-Volmer constant which is 20 times higher than that of other Ir complexes known from the literature when they are immobilized in polystyrene. The sensing film shows long-term stability (up to 12 months), complete reversibility of the signal quenched by oxygen and a quick response time to various oxygen concentrations (<2 s changing from 10 vol% pO2 to 90 vol% pO2). Thus, it is an interesting and promising complex for developing oxygen-selective sensors for gas analysis and the analysis of dissolved oxygen.

We report a combined experimental and theoretical study on cationic Ir(III) complexes for OLED applications and describe a strategy to tune the phosphorescence wavelength and to enhance the emission quantum yields for this class of compounds. This is achieved by modulating the electronic structure and the excited states of the complexes by selective ligand functionalization. In particular, we report the synthesis, electrochemical characterization, and photophysical properties of a new cationic Ir(III) complex, [Ir(2,4-difluorophenylpyridine)2(4,4'-dimethylamino-2,2'-bipyridine)](PF(6)) (N969), and compare the results with those reported for the analogous [Ir(2-phenylpyridine)2(4,4'-dimethylamino-2,2'-bipyridine)](PF(6)) (N926) and for the prototype [Ir(2-phenylpyridine)2(4,4'-tert-butyl-2,2'-bipyridine)](PF(6)) complex, hereafter labeled N925. The three complexes allow us to explore the (C/\N) and (N/\N) ligand functionalization: considering N925 as a reference, we investigate in N926 the effect of electron-releasing substituents on the bipyridine ligand, while in N969, we investigate the combined effect of electron-releasing substituents on the bipyridine ligand and the effect of electron-withdrawing substituents on the phenylpyridine ligands. For N969 we obtain blue-green emission at 463 nm with unprecedented high quantum yield of 85% in acetonitrile solution at room temperature. To gain insight into the factors responsible for the emission color change and the different quantum yields, we perform DFT and TDDFT calculations on the ground and excited states of the three complexes, characterizing the excited-state geometries and including solvation effects on the calculation of the excited states. This computational procedure allows us to provide a detailed assignment of the excited states involved in the absorption and emission processes and to rationalize the factors determining the efficiency of radiative and nonradiative deactivation pathways in the investigated complexes. This work represents an example of electronic structure-driven tuning of the excited-state properties, thus opening the way to a combined theoretical and experimental strategy for the design of new iridium(III) phosphors with specific target characteristics.

Mesoscopic dye-sensitized solar cells (DSCs) with efficiency greater than 10.5 % are reported. Using a newly designed sensitizer (K77, see figure) combined with a newly formulated nonvolatile organic-solvent-based electrolyte (Z646), highly efficient DSCs (up to 9.5 %) that exhibit unprecedented long-term stability (1000 h) under both light-soaking and thermal stress are demonstrated.

A novel iridium complex, [bis-(2-phenylpyridine)(2-carboxy-4-dimethylaminopyridine)iridium(iii)] (N984), was synthesized and characterized using spectroscopic and electrochemical methods; a solution processable OLED device incorporating the N984 complex displays electroluminescence spectra with a narrow bandwidth of 70 nm at half of its intensity, with colour coordinates of x = 0.322; y = 0.529 that are very close to those suggested by the PAL standard for a green emitter.

A high molar extinction coefficient charge transfer sensitizer tetrabutylammonium [Ru(4,-carboxylic acid-4'-carboxylate-2,2'-bipyridine)(4,4'di-(2-(3,6-dimethoxyphenyl)ethenyl)-2,2'-bipyridine)(NCS)(2)], is developed which upon anchoring onto nanocrystalline TiO2 films exhibit superior power conversion efficiency compared to the standard sensitizer bistetrabutylammonium cis-dithiocyanatobis(4,4'-dicarboxylic acid-2,2'bipyridine)ruthenium(II) (N719). The new sensitizer anchored TiO2 films harvest visible light very efficiently over a large spectral range and produce a short-circuit photocurrent density of 18.84 mA/cm(2), open-circuit voltage 783 mV and fill factor 0.73, resulting remarkable solar-to-electric energy conversion efficiency (eta) 10.82, under Air Mass (AM) 1.5 sunlight. The Time Dependent Density Functional Theory (TDDFT) excited state calculations of the new sensitizer show that the first three HOMOs have ruthenium t(2g) character with sizable contribution coming from the NCS ligands and the pi-bonding orbitals of the 4,4'-di-(2-(3,6-dimethoxyphenyl)ethenyl)-2,2'-bipyridine. The LUMO is a pi* orbital localized on the 4,4'-dicarboxylic acid-2,2'-bipyridine ligand. (c) 2006 Elsevier B.V. All rights reserved.