Push-Pull Phenoxazine-Based Sensitizers for p-Type DSSCs: Effect of Acceptor Units on Photovoltaic Performance.

Finding new efficient p-type sensitizers for NiO photocathodes is a great challenge for the development of promising low-cost tandem dye-sensitized solar cells (DSSCs). Now, the focus of researchers investigating these cells has been to create high-performance p-type systems. With this intention, herein, the design and synthesis of six new phenoxazine-based donor-acceptor (D-A)-configured organic dyes PO1-6 was reported, comprising different acceptor moieties specially designed for the sensitization of mesoporous p-type semiconductor NiO for the construction of p-type DSSCs (p-DSSCs). This work includes structural, photophysical, thermal, electrochemical, theoretical, and photoelectrochemical studies of these dyes, including evaluation of their structure-property relationships. The optical studies revealed that PO1-6 displayed adequate absorption and emission features in the range of 480-550 and 560-650 nm, respectively, with a bandgap in the order of 2.05-2.40 eV, and their thermodynamic parameters favored an efficient interfacial charge transfer involving NiO. Among the six new dyes, the device based on sensitizer PO2 carrying electron-withdrawing 1,3-diethyl-2-thiobarbituric acid achieved the highest power conversion efficiency of 0.031 % (short-circuit current density=0.89 mA cm-2 , open-circuit voltage=101 mV, and fill factor=35 %). Conclusively, the study furnishes an understanding of the intricacies involved in the structural modification of phenoxazine-based sensitizers to further ameliorate the performance of the p-type DSSCs.

Atom Economical Photocatalytic Oxidation of Phenols and Site-Selective Epoxidation Toward Epoxyquinols.

The discovery of a multiple-bond-forming process merging the singlet oxygen-mediated dearomatization of 3,4-disubstitued phenols and diastereo- and regioselective epoxidation is described. This one-pot strategy using a transition metal-free multicatalytic system comprised of rose bengal and cesium carbonate allowed the efficient formation of functionalized epoxyquinol products under mild conditions. Mechanistic investigations have been performed to shed the light on the key species involved in this transformation.

Hydrogen-Bond Acceptance of Solvents: A 19F Solvatomagnetic ß1 Database to Replace Solvatochromic and Solvatovibrational Scales.

A variety of physicochemical properties and several hydrogen-bond donors have been used to define methods and to build scales aiming at measuring the hydrogen-bond acceptance of solvents. There is a great deal of confusion in these scales and methods. Solvatochromic, solvatocalorimetric, solvatovibrational, and 19F solvatomagnetic comparison methods are critically reviewed. Only two methods, the solvatomagnetic and the solvatocalorimetric ones, are able to yield reliable solvent hydrogen-bond acceptance scales. The solvatomagnetic ß1 scale defined from the 19F chemical shift of 4-fluorophenol is extended to many solvents including ionic liquids and green solvents. The results for about 240 hydrogen-bond acceptor solvents are organized in a numerical ß1 database. The comparison of ß1 with solvatochromic scales highlights their shortcomings, in particular for the important class of amphiprotic solvents. Therefore, the use of the 19F solvatomagnetic comparison method and of the solvatomagnetic ß1 scale is recommended in solvent effect studies.

A versatile stereocontrolled synthesis of 2-deoxyiminosugar C-glycosides and their evaluation as glycosidase inhibitors.

A highly enantioselective synthesis of (R,S) or (S,S)-2,6-disubstituted dehydropiperidines has been previously achieved through Sn/Li transmetalation of the corresponding stannylated dehydropiperidines or of their precursors. Herein, we successively consider their Upjohn's syn dihydroxylation and their anti-dihydroxylation via an epoxidation reaction followed by epoxide opening reaction. The stereochemical course of these reactions was first reported including the use of appropriate protecting groups before considering the conversion of the obtained compounds into NH or NMe iminosugar hydrochlorides. A primary evaluation of the designed iminosugar C-glycosides as glycosidase inhibitors suggests candidates for the selective inhibition of α-galactosidase, amyloglycosidase and naringinase. Beyond the reported results, the method constitutes a highly modulable route for the synthesis of well stereodefined iminosugar C-glycosides, an advantage which might be used for the design of iminosugars to enhance their biological properties.

New azole antifungals with a fused triazinone scaffold.

We identified a new series of azole antifungal agents bearing a pyrrolotriazinone scaffold. These compounds exhibited a broad in vitro antifungal activity against pathogenic Candida spp. (fluconazole-susceptible and fluconazole-resistant) and were 10- to 100-fold more active than voriconazole against two Candida albicans isolates with known mechanisms of azole resistance (overexpression of efflux pumps and/or specific point substitutions in the Erg11p/CYP51 enzyme). Our lead compound 12 also displayed promising in vitro antifungal activity against some filamentous fungi such as Aspergillus fumigatus and the zygomycetes Rhizopus oryzae and Mucor circinelloides and an in vivo efficiency against two murine models of lethal systemic infections caused by Candida albicans.

A Comparative Investigation of the Role of the Anchoring Group on Perylene Monoimide Dyes in NiO-Based Dye-Sensitized Solar Cells.

The anchoring group of a sensitizer may strongly affect the overall properties and stability of the resulting dye-sensitized solar cells (DSSCs) and dye-sensitized photoelectrosynthetic solar cells (DSPECs). The properties of seven perylene monoimide (PMI) dyes have been comprehensively studied for their immobilization on nanocrystalline NiO film. The PMI dyes differ only by the nature of the anchoring group, which are: carboxylic acid (PMI-CO2 H), phosphonic acid (PMI-PO3 H2 ), acetyl acetone (PMI-acac), pyridine (PMI-Py), aniline (PMI-NH2 ), hydroxyquinoline (PMI-HQ), and dipicolinic acid (PMI-DPA). The dyes are investigated by cyclic voltammetry and spectroelectrochemistry and modeled by TD-DFT quantum chemical calculations. The mode of binding of these anchoring groups is investigated by infrared spectroscopy and the stability of the binding to NiO surface is studied by desorption experiments in acidic and basic media. The phosphonic acid group is found to offer the strongest binding to the NiO surface in terms of stability and dye loading. Finally, a photophysical study by ultrafast transient absorption spectroscopy shows that all dyes inject a hole in NiO with rate constants on a subpicosecond timescale and display similar charge recombination kinetics. The photovoltaic properties of the dyes show that PMI-HQ and PMI-acac give the highest photovoltaic performances, owing to a lower degree of aggregation on the surface.

Intriguing Effects of Halogen Substitution on the Photophysical Properties of 2,9-(Bis)halo-Substituted Phenanthrolinecopper(I) Complexes.

Three new copper(I) complexes [Cu(LX)2]+(PF6-) (where LX stands for 2,9-dihalo-1,10-phenanthroline and X = Cl, Br, and I) have been synthesized in order to study the impact of halogen substituents tethered in the α position of the chelating nitrogen atoms on their physical properties. The photophysical properties of these new complexes (hereafter named Cu-X) were characterized in both their ground and excited states. Femtosecond ultrafast spectroscopy revealed that early photoinduced processes are faster for Cu-I than for Cu-Cl or Cu-Br, both showing similar behaviors. Their electronic absorption and electrochemical properties are comparable to benchmark [Cu(dmp)2]+ (where dmp stands for 2,9-dimethyl-1,10-phenanthroline); furthermore, their optical features were fully reproduced by time-dependent density functional theory and ab initio molecular dynamics calculations. All three complexes are luminescent at room temperature, showing that halogen atoms bound to positions 2 and 9 of phenanthroline are sufficiently bulky to prevent strong interactions between the excited Cu complexes and solvent molecules in the coordination sphere. Their behavior in the excited state, more specifically the extent of the photoluminescence efficiency and its dependence on the temperature, is, however, strongly dependent on the nature of the halogen. A combination of ultrafast transient absorption spectroscopy, temperature-dependent steady-state fluorescence spectroscopy, and computational chemistry allows one to gain a deeper understanding of the behavior of all three complexes in their excited state.

Effect of the triazole ring in zinc porphyrin-fullerene dyads on the charge transfer processes in NiO-based devices.

Herein, the synthesis of three covalently linked donor-acceptor zinc porphyrin-fullerene (ZnP-C60) dyads (C60trZnPCOOH, C60trZnPtrCOOH and C60ZnPCOOH) is described, and their application as sensitizers in NiO-based dye-sensitized solar cells (DSCs) is discussed. To the best of our knowledge, this is the first example where covalently linked ZnP-C60 dyads have been used as chromophores in NiO-based DSCs. In an effort to examine whether the distance of the chromophore from the electron acceptor entity and/or the NiO surface affects the performance of the cells, a triazole ring was introduced as a spacer between ZnP and the two peripheral units C60 and -COOH. The triazole ring was inserted between ZnP and C60 in dyad C60trZnPCOOH, whereas both the anchoring group and C60 were connected to ZnP through triazole spacers in C60trZnPtrCOOH, and dyad C60ZnPCOOH did not contain any triazole linker. Photophysical investigation performed by ultrafast transient absorption spectroscopy in solution and on the NiO surface demonstrated that all the porphyrin-fullerene dyads exhibited long-lived charge-separated states due to electron shifts from the reduced porphyrin core to C60. The transient experiments performed in solution showed that the presence of triazole ring influenced the photophysical properties of the dyads C60trZnPCOOH and C60trZnPtrCOOH and in particular, increased the lifetime of the charge-separated states compared to that of the C60ZnPCOOH dyad. On the other hand, the corresponding studies on the NiO surface proved that the triazole spacer has a rather moderate impact on the charge separation (NiO-ZnP˙+-C60˙-) and charge recombination (NiO-3*ZnP-C60) rate constants. All three dyads exhibited enhanced performance in terms of photovoltaic measurements with more than threefold increase compared to the reference compound PhtrZnPCOOH in which the C60 acceptor is absent. Two different electrolytes were examined (I3-/I- and CoIII/II) and in most cases, the presence of the triazole ring enhanced their photovoltaic performance. The best performing dyad in I3-/I- was C60trZnPCOOH (PCE = 0.076%); in CoIII/II, the best performing dyad was C60trZnPtrCOOH (PCE = 0.074%).

A Ring-D-Seco-Tetranortriterpenoid from Seeds of Carapa procera Active against Breast Cancer Cell Lines.

The seeds of Carapa procera are exploited extensively in West African ethnopharmacy for the treatment of several pathologies, including inflammation. They also are effective as insect antifeedants and as a mosquito repellent. With the aim of identifying bioactive principles, an ethyl acetate extract of the defatted seeds was made and fractionated. Two principle compounds were isolated. One of these, 5,6-dehydro-7-deacetoxy-7-oxogedunin (1), while known from another genus of the Meliaceae, is newly identified from the genus Carapa and its X-ray structure is described for the first time. In addition, 1 displayed strong anti-clonogenic activity at 10 µM. The other compound, mexicanolide (2), is known from this species and showed neither cytotoxicity nor anti-clonogenicity. These differences in efficacy are discussed in relation to known structure-activity relationships of limonoids.

A database of dispersion-induction DI, electrostatic ES, and hydrogen bonding α1 and ß1 solvent parameters and some applications to the multiparameter correlation analysis of solvent effects.

For about 300 solvents, we propose a database of new solvent parameters describing empirically solute/solvent interactions: DI for dispersion and induction, ES for electrostatic interactions between permanent multipoles, α1 for solute Lewis base/solvent Lewis acid interactions, and ß1 for solute hydrogen-bond donor/solvent hydrogen-bond acceptor interactions. The main advantage over previous parametrizations is the easiness of extension of this database to newly designed solvents, since only three probes, the betaine dye 30, 4-fluorophenol, and 4-fluoroanisole are required. These parameters can be entered into the linear solvation energy relationship A = A0 + di(DI) + eES + aα1 + bß1 to predict a large number of varied physicochemical properties A and to rationalize the multiple intermolecular forces at the origin of solvent effects through a simple examination of the sign and magnitude of regression coefficients di, e, a, and b. Such a rationalization is illustrated for conformational and tautomeric equilibria and is supported by quantum-mechanical calculations.

1-Oxo-1H-phenalene-2,3-dicarbonitrile heteroaromatic scaffold: revised structure and mechanistic studies.

Synthesis of the originally proposed 8-oxo-8H-acenaphtho[1,2-b]pyrrol-9-carbonitrile led to a structural revision, and the product has now been identified as unknown compound 1-oxo-1H-phenalene-2,3-dicarbonitrile. The structural assignment was corroborated by detailed NMR studies and unambiguously confirmed by X-ray diffraction. A mechanism is proposed to explain the formation of this original heterocyclic scaffold. In addition, some new chemical transformations involving this compound are presented.

Synthesis, photovoltaic performances and TD-DFT modeling of push-pull diacetylide platinum complexes in TiO2 based dye-sensitized solar cells.

In this joint experimental-theoretical work, we present the synthesis and optical and electrochemical characterization of five new bis-acetylide platinum complex dyes end capped with diphenylpyranylidene moieties, as well as their performances in dye-sensitized solar cells (DSCs). Theoretical calculations relying on Time-Dependent Density Functional Theory (TD-DFT) and a range-separated hybrid show a very good match with experimental data and allow us to quantify the charge-transfer character of each compound. The photoconversion efficiency obtained reaches 4.7% for 8e (see TOC Graphic) with the tri-thiophene segment, which is among the highest efficiencies reported for platinum complexes in DSCs.

Bis[tris-(phenanthroline-κ(2) N,N')cobalt(II)] undeca-tungsto(VI)vanado(V)phosphate dihydrate.

In the title hydrated salt, [Co(C12H8N2)3]2[PVW11O40]·2H2O, the complete Kegggin ion is generated by crystallographic inversion symmetry, which imposes statistical disorder on the O atoms of its central PO4 group. The V atom is statistically disordered over all the metal sites of the anion. In the cation, the Co(2+) ion is coordinated by three bidentate 1,10-phenanthroline (phen) ligands, generating a distorted CoN6 octa-hedron. Possible very weak intra-molecular C-H⋯π inter-actions occur in the cation. In the crystal, the components are linked by O-H⋯O and C-H⋯O inter-actions, building a three-dimensional network featuring one-dimensional voids along the c-axis direction.

Determination of a solvent hydrogen-bond acidity scale by means of the solvatochromism of pyridinium-N-phenolate betaine dye 30 and PCM-TD-DFT calculations.

Empirical parameters of solvents describing their hydrogen-bond (HB) acidity (e.g., the Kamlet-Taft α parameter) are often difficult to determine for new solvents because they are not directly related to a single definition process. Here, we propose a simple method based on one probe, the betaine dye 30, and one reference process, the solvatochromism of this dye, measured by its first electronic transition energy, ET(30). These ET(30) values are calculated within the time-dependent density functional theory framework, using a polarizable continuum solvent model (PCM). The part of ET(30) values that is not included in the PCM calculation is taken as the HB component of the measured ET(30) values, allowing us to deduce a solvent HB acidity parameter α1. The validity of this simple model is assessed by good linear correlations between α1 and a variety of solute properties mainly depending on the solvent's HB acidity. The quality of fit observed with α1 is at least comparable with that obtained by previous solvent HB acidity scales. The simplicity of our method is illustrated by the determination of α1 and of its companion, the electrostatic solvent parameter ES, for some new green solvents derived from glycerol.

Performance of an Optimally Tuned Range-Separated Hybrid Functional for 0-0 Electronic Excitation Energies.

Using a set of 40 conjugated molecules, we assess the performance of an "optimally tuned" range-separated hybrid functional in reproducing the experimental 0-0 energies. The selected protocol accounts for the impact of solvation using a corrected linear-response continuum approach and vibrational corrections through calculations of the zero-point energies of both ground and excited-states and provides basis set converged data thanks to the systematic use of diffuse-containing atomic basis sets at all computational steps. It turns out that an optimally tuned long-range corrected hybrid form of the Perdew-Burke-Ernzerhof functional, LC-PBE*, delivers both the smallest mean absolute error (0.20 eV) and standard deviation (0.15 eV) of all tested approaches, while the obtained correlation (0.93) is large but remains slightly smaller than its M06-2X counterpart (0.95). In addition, the efficiency of two other recently developed exchange-correlation functionals, namely SOGGA11-X and ωB97X-D, has been determined in order to allow more complete comparisons with previously published data.

Electronic Band Shapes Calculated with Optimally Tuned Range-Separated Hybrid Functionals.

Using a set of 20 organic molecules, we assess the accuracy of both the absorption and emission band shapes obtained by two optimally tuned range-separated hybrid functionals possessing 0% (LC-PBE*) and 25% (LC-PBE0*) of short-range exact exchange as well as by four other hybrid functionals including or not dispersion and long-range corrections (APF-D, PBE0-1/3, SOGGA11-X, and ωB97X-D). The band topologies are compared to experimental data and to previous time-dependent density functional theory calculations. It turns out that both optimally tuned functionals vastly improve the vibronic band shapes obtained with the non-tuned LC-PBE approach but, statistically, do not yield more accurate topologies than standard hybrid functionals. In other words, optimal tuning allows to obtain more accurate excited-state energies without degrading the description of band shapes. In addition, the LC-PBE0* 0-0 energies have been determined for a set of 40 compounds, and it is shown that the results are, on average, less accurate than those obtained by LC-PBE* for the same panel of molecules. The correlation between the optimal range-separation parameters determined for LC-PBE* and LC-PBE0* is discussed as well.

Palladium-catalyzed direct arylation of luminescent bis-cyclometalated iridium(III) complexes incorporating C

We report the palladium-catalyzed direct 5-arylation of both metalated and nonmetalated thiophene moieties of iridium complexes 2, 3, and 4 with aryl halides via C-H bond functionalization. This method opens new routes to varieties of Ir complexes in only one step, allowing easy modification of the nature of the ligand. The photophysical properties of the new functionalized complexes have been studied by means of absorption and emission spectroscopy. The extension of the π-conjugated system induces a bathochromic and hyperchromic shift of the absorption spectra, an effect reproduced by first principle calculations. Indeed, the bathochromic shifts are related to a more delocalized nature of the excited-states. All complexes are photoluminescent in the red region of the spectrum. This study establishes that arylation of the thienyl ring affects strongly the electronic properties of the resulting complexes, even when the thienyl ring is remote and not directly metalated to the iridium center, as in the thienyltrifluoroacetonate complex 4.

(1R,2S,4S,4aS,8S,8aS)-4-Hy-droxy-8,8a-dimethyl-10-oxo-2,3,4,7,8,8a-hexa-hydro-1H-4a,1-(ep-oxy-methano)-naphthalen-2-yl acetate.

The title compound, C15H20O5, presents a bis-norsesquiterpene skeleton, with a trans-deca-line backbone constrained by the lactone bridge. The α-hy-droxy substituent and the methyl group belonging to the two deca-line rings are in axial positions, whereas the other methyl group and the acyl group occupy the sterically preferred equatorial positions. The mol-ecular structure is stabilized by an intra-molecular C-H⋯O hydrogen bond. In the crystal, mol-ecules are linked into chains along [010] by O-H⋯O hydrogen bonds.

First application of the HETPHEN concept to new heteroleptic bis(diimine) copper(I) complexes as sensitizers in dye sensitized solar cells.

We report here the synthesis and full chemical and physical characterizations of the first stable heteroleptic copper(I)-bis(diimine) complexes designed for implementation in dye sensitized solar cells (DSC). Thanks to the HETPHEN concept, pure and stable heteroleptic copper(I) complexes were isolated. Anchorage of the sensitizers was provided by 2,2'-biquinoline-4,4'-dicarboxylic acid (dcbqH2), while sterically challenged ligands 2,9-dimesityl-1,10-phenanthroline (L0) and N-hexyl-2,9-dimesityl-1,10-phenanthroline-[a:b]imidazo-(4'-dianisylaminophenyl) (L1) were used to complete the copper(I) coordination sphere. The resulting heteroleptic complexes C1 and C2 exhibit a broad MLCT transition spreading over a wide wavelength domain, especially when adsorbed onto nanoparticulate TiO2 photoanodes, providing a rather comprehensive visible light collection. The corresponding DSC were evaluated under AM 1.5 simulated solar light and rather weak performances were obtained owing to small J(sc) and V(oc). This is due to a combination of low extinction coefficient and poor driving forces for the various interfacial processes. However, significant improvements in the performances were monitored upon ageing in the dark, likely due to beneficial reorganization of the dye monolayers. The possibility to isolate stable asymmetric systems paves the way for structurally assisted photo-induced charge injection from the chemisorbed copper(i) based sensitizers into the conduction band of TiO2, through charge vectorialization.

Choosing a Functional for Computing Absorption and Fluorescence Band Shapes with TD-DFT.

The band shapes corresponding to both the absorption and emission spectra of a set of 20 representative conjugated molecules, including recently synthesized structures, have been simulated with a Time-Dependent Density Functional Theory model including diffuse atomic orbitals and accounting for bulk solvent effects. Six hybrid functionals, including two range-separated hybrids (B3LYP, PBE0, M06, M06-2X, CAM-B3LYP, and LC-PBE) have been assessed in light of the experimental band shapes obtained for these conjugated compounds. Basis set and integration grid effects have also been evaluated. It turned out that all tested functionals but LC-PBE reproduce the main experimental features for both absorption and fluorescence, though the average errors are significantly larger for the latter phenomena. No single functional stands out as the most accurate for all aspects, but B3LYP yields the smallest mean absolute deviation. On the other hand, M06-2X could be a valuable compromise for excited-states as it reproduces the 0-0 energies and also gives reasonable band shapes. The typical mean absolute deviations between the relative positions of the experimental and theoretical peaks in the vibrationally resolved spectra are ca. 100 cm(-1) for absorption and 250 cm(-1) for emission. In the same time, the relative intensities of the different maxima are reproduced by TD-DFT with a ca. 10-15% accuracy.