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A series of three heteroleptic ruthenium complexes containing 2,2'-bipyridine-4,4'-dicarboxamide ligands with different substituents (propyl, benzyl or 2-phenylethyl) was synthesized as possible sensitizers for dye sensitized solar cells (DSSCs). Their structure was characterized with H-1 NMR and FTIR while their optical and electrochemical properties were also investigated. The observed optical differences were associated to structural properties of the three complexes and different electron donor strength of the ancillary ligands. In particular, ruthenium complex with propyl based ligand showed higher molar extinction coefficient succeeding better light harvesting. Semitransparent dye sensitized solar cells employing quasi-solid-state electrolyte and the three ruthenium complexes were constructed under the same fabrication conditions and electrically characterized under standard conditions of light irradiance (100 mW/cm(2), AM 1.5). Their behavior was compared with that of commercially available ruthenium complex D907 with increased conjugation length of the ancillary ligand, in terms of current- voltage characteristic curves under simulated solar light and in the dark while electrochemical impedance spectroscopy was also used for local resistance to charge transfer across the TiO2-dye/electrolyte interface. The influence of ancillary ligands into ruthenium complexes was discussed in terms of the cells' efficiency. A maximum overall performance of 5.0% was monitored for ruthenium complex with propyl substituent in comparison to 5.1% that was measured for semitransparent quasi-solid state devices with commercial D907. (C) 2018 Elsevier B.V. All rights reserved.

The photophysics and solar cell efficiency of organic sensitizers comprising a cyanoacrylic acid group are greatly influenced by an equilibrium between the neutral ("non-deprotonated", COOH) and anionic ("deprotonated", COO ) forms, whose ratio depends on the solvent polarity and its H-bonding properties, dye concentration, and temperature used. Herein, we report a detailed investigation on the relationship between the portions of COOH and COO- dye forms and the photophysical and solar cell properties of an organic dipolar sensitizer, BTZA-II, bearing triphenylamine electron-donating and benzothiazole electron-withdrawing moieties. The photophysics has been studied by stationary and timeresolved fluorescence spectroscopy in apolar and polar solvents with a dye concentration ranging from 5 x 10(-7) to 5 x 10(-5) M, also upon addition of small amounts of an external acid or base to change the solvent acidity, allowing us to distinguish the contribution and lifetime of the neutral and anionic forms. The fluorescence of BTZA-II in apolar toluene originates from the neutral form, which has a lifetime of 1.9 ns. Addition of a strong base (1,8-diazabicyclo[5.4.0]undec-7-ene, DBU) shifts the equilibrium toward the less fluorescent anionic COO- form with a lifetime of 1.1 ns. The situation is different in the polar acetonitrile, where the fluorescence of the anionic form dominates (with a lifetime of 2.0 ns). Adding small amounts of acetic acid (AcOH) protonates the COO- form of the BTZA-II dye and reveals significant quenching of the fluorescence because of the increased contribution of the neutral species with a lifetime of 0.4-0.5 ns. This quenching of the neutral species in acetonitrile has been also observed in concentrated solutions and is due to excited-state proton transfer. By contrast, the photophysics of a dye Btz-NPh2, similar to BTZA-II but without the cyanoacrylic acid group, is not affected upon adding acetic acid (H-donor) or DBU base (H-acceptor), which rules out the Bronsted-base role of the benzothiazole scaffold in the aforementioned observations. Finally, dyesensitized solar cells (DSSCs) with a solid-state electrolyte were prepared from toluene and toluene + acid solutions. A significant increase in the solar cell efficiency, eta, by 58% (eta reaching a value of 4.9%) has been achieved after addition of a small, appropriate amount of acetic acid into the initial BTZA-II dye solution.

Six ruthenium(II) complexes as charge-transfer sensitizers for dye sensitized solar cells (DSSCs) are synthesized. The absorption and electrochemical properties of newly synthesized ruthenium-dye molecules contained one bipyridine (bpy) ligand with two carboxylic groups have been investigated. Among them, four ruthenium(II) complexes contain a second bpy ligand with branching and non-branching side groups containing C and H only and the remaining two ruthenium(II) complexes instead of a second bipyridine (bpy) ligand, they consisted of a pyridine (py) ligand with side groups containing -C-O-C-molecular group. Dye sensitized solar cells employing quasi-solid state electrolyte and the six ruthenium complexes are constructed and electrically characterized under standard conditions of light irradiance (1000 W/m(2), AM 1.5). Their behavior is compared with that of commercially available ruthenium complex D907 in terms of current-voltage characteristic curves under simulated light and dark while electrochemical impedance spectroscopy showed comparable results for local resistance to charge transfer across the TiO2-electrolyte interface and free electron lifetimes for two bipyridine and commercial D907 complexes. The influence of molecular side groups into ruthenium-dye molecules is discussed in terms of the cells' efficiency. (C) 2015 Elsevier Ltd. All rights reserved.

Twelve Pr3+, Sm3+, Eu3+, Gd3+, Tb3+ and Dy3+ complexes of N-(pyridin-2-ylmethylene) picolinohydrazonate (phzp-) were synthesized by the Ln3+ assisted hydrolysis of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine. Crystallographic characterization of Pr3+, Sm3+ and Eu3+ hydrazonate complexes with nitrate or trifluoroacetyleacetonate co-ligands shows them to have binuclear structures with a planar Ln2O2 core and the ligand to be in its mono-anionic form. Exception is the Pr 3+ complex with nitrate co-ligand, which is a mononuclear species containing the neutral hydrazone. Paramagnetic 1D 1H and 2D gCOSY and gNOESY-gEXSY 1H NMR spectroscopies revealed the presence of different isomers exhibiting a sterically controlled fluxional behavior. In addition, phzp- significantly enhances the luminescence of Eu 3+ and Tb3+. Magnetic measurements show antiferromagnetic coupling between the Ln3+ ions in the dinuclear complexes. The structural characterization of the complexes in both solid state and solution show the versatility of phzp- ligand to adopt various ligating motifs. © 2013 Elsevier Ltd. All rights reserved. 64 308 320 Cited By :3