Structure-Property Relationships in Bithiophenes with Hydrogen-Bonded Substituents.

The use of crystal engineering to control the supramolecular arrangement of π-conjugated molecules in the solid-state is of considerable interest for the development of novel organic electronic materials. In this study, we investigated the effect of combining of two types of supramolecular interaction with different geometric requirements, amide hydrogen bonding and π-interactions, on the π-overlap between calamitic π-conjugated cores. To this end, we prepared two series of bithiophene diesters and diamides with methylene, ethylene, or propylene spacers between the bithiophene core and the functional groups in their terminal substituents. The hydrogen-bonded bithiophene diamides showed significantly denser packing of the bithiophene cores than the diesters and other known α,ω-disubstituted bithiophenes. The bithiophene packing density reach a maximum in the bithiophene diamide with an ethylene spacer, which had the smallest longitudinal bithiophene displacement and infinite 1D arrays of electronically conjugated, parallel, and almost linear N-H⋅⋅⋅O=C hydrogen bonds. The synergistic hydrogen bonding and π-interactions were attributed to the favorable conformation mechanics of the ethylene spacer and resulted in H-type spectroscopic aggregates in solid-state absorption spectroscopy. These results demonstrate that the optoelectronic properties of π-conjugated materials in the solid-state may be tailored systematically by side-chain engineering, and hence that this approach has significant potential for the design of organic and polymer semiconductors.

Zero-dimensional hybrid iodobismuthate derivatives: from structure study to photovoltaic application.

The quest for lead-free light-absorbing perovskite materials has long been the target of researchers to make the 'star' material friendly to the commercial market. After a summary of different lead-free solar absorbers, we demonstrate a zero-dimensional iodobismuthate (MA)3[BiI6]·3MACl (MA: CH3NH3) featuring isolated hexaiodobismuthate(iii) anions in the crystal analysis. The unexpectedly formed material was made via an orthogonal solvent permeation method and the decomposition of the guest solvent. We compare the BiI63- containing compound with a series of more common iodobismuthates, especially the dinuclear Bi2I93- in terms of dimensionalities via single-crystal diffraction and DFT calculations, respectively. An undocumented second-order phase transition was found between 190 K and 160 K for the dimeric MA3Bi2I9. The photovoltaic device from a thermally reorganized polycrystalline film of (MA)3[BiI6]·3MACl, which resembled the structure of (MA)3[Bi2I9] gave a power conversion efficiency of 1.09%.

Reductive Alkylation of Tertiary Lactams via Addition of Organocopper (RCu) Reagents to Thioiminium Ions.

A simple procedure for the conversion of tertiary lactams to 2-monoalkylated cyclic amines is described. The reaction sequence involves conversion of a lactam to a thioiminium ion followed by reaction with an organocopper (RCu) reagent and final reduction with triacetoxyborohydride. The reaction is high yielding and shows an excellent functional group tolerance. Its utility is demonstrated by a rapid synthesis of indolizidine 167B. The excellent chemoselectivity of the process, where only monoalkylation products are formed, is rationalized by a mechanism involving the formation of a transient enamine.

Tuning Properties of Iron Oxide Nanoparticles in Aqueous Synthesis without Ligands to Improve MRI Relaxivity and SAR.

Aqueous synthesis without ligands of iron oxide nanoparticles (IONPs) with exceptional properties still remains an open issue, because of the challenge to control simultaneously numerous properties of the IONPs in these rigorous settings. To solve this, it is necessary to correlate the synthesis process with their properties, but this correlation is until now not well understood. Here, we study and correlate the structure, crystallinity, morphology, as well as magnetic, relaxometric and heating properties of IONPs obtained for different durations of the hydrothermal treatment that correspond to the different growth stages of IONPs upon initial co-precipitation in aqueous environment without ligands. We find that their properties were different for IONPs with comparable diameters. Specifically, by controlling the growth of IONPs from primary to secondary particles firstly by colloidal and then also by magnetic interactions, we control their crystallinity from monocrystalline to polycrystalline IONPs, respectively. Surface energy minimization in the aqueous environment along with low temperature treatment is used to favor nearly defect-free IONPs featuring superior properties, such as high saturation magnetization, magnetic volume, surface crystallinity, the transversal magnetic resonance imaging (MRI) relaxivity (up to r2 = 1189 mM-1·s-1 and r2/r1 = 195) and specific absorption rate, SAR (up to 1225.1 W·gFe-1).

Superparamagnetic Nanoparticles as High Efficiency Magnetic Resonance Imaging T2 Contrast Agent.

Nanoparticle-based magnetic resonance imaging T2 negative agents are of great interest, and much effort is devoted to increasing cell-loading capability while maintaining low cytotoxicity. Herein, two classes of mixed-ligand protected magnetic-responsive, bimetallic gold/iron nanoparticles (Au/Fe NPs) synthesized by a two-step method are presented. Their structure, surface composition, and magnetic properties are characterized. The two classes of sulfonated Au/Fe NPs, with an average diameter of 4 nm, have an average atomic ratio of Au to Fe equal to 7 or 8, which enables the Au/Fe NPs to be superparamagnetic with a blocking temperature of 56 K and 96 K. Furthermore, preliminary cellular studies reveal that both Au/Fe NPs show very limited toxicity. MRI phantom experiments show that r2/r1 ratio of Au/Fe NPs is as high as 670, leading to a 66% reduction in T2 relaxation time. These nanoparticles provide great versatility and potential for nanoparticle-based diagnostics and therapeutic applications and as imaging contrast agents.

Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells.

Lead halide perovskites have over the past few years attracted considerable interest as photo absorbers in PV applications with record efficiencies now reaching 22%. It has recently been found that not only the composition but also the precise stoichiometry is important for the device performance. Recent reports have, for example, demonstrated small amount of PbI2 in the perovskite films to be beneficial for the overall performance of both the standard perovskite, CH3NH3PbI3, as well as for the mixed perovskites (CH3NH3)x(CH(NH2)2)(1-x)PbBryI(3-y). In this work a broad range of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photo electron spectroscopy (PES), transient absorption spectroscopy (TAS), UV-vis, electroluminescence (EL), photoluminescence (PL), and confocal PL mapping have been used to further understand the importance of remnant PbI2 in perovskite solar cells. Our best devices were over 18% efficient, and had in line with previous results a small amount of excess PbI2. For the PbI2-deficient samples, the photocurrent dropped, which could be attributed to accumulation of organic species at the grain boundaries, low charge carrier mobility, and decreased electron injection into the TiO2. The PbI2-deficient compositions did, however, also have advantages. The record Voc was as high as 1.20 V and was found in PbI2-deficient samples. This was correlated with high crystal quality, longer charge carrier lifetimes, and high PL yields and was rationalized as a consequence of the dynamics of the perovskite formation. We further found the ion migration to be obstructed in the PbI2-deficient samples, which decreased the JV hysteresis and increased the photostability. PbI2-deficient synthesis conditions can thus be used to deposit perovskites with excellent crystal quality but with the downside of grain boundaries enriched in organic species, which act as a barrier toward current transport. Exploring ways to tune the synthesis conditions to give the high crystal quality obtained under PbI2-poor condition while maintaining the favorable grain boundary characteristics obtained under PbI2-rich conditions would thus be a strategy toward more efficiency devices.

Carboxylic Acid Functionalized Clathrochelate Complexes: Large, Robust, and Easy-to-Access Metalloligands.

Polycarboxylate ligands are among the most important building blocks for the synthesis of metal-organic frameworks (MOFs). The ability to access these ligands in an efficient way is of key importance for future applications of MOFs. Here, we demonstrate that mono- and dinuclear clathrochelate complexes are versatile scaffolds for the preparation of polytopic carboxylate ligands. The largely inert clathrochelate complexes have a trigonal-bipyramidal shape. The synthesis of functionalized clathrochelates with two, three, four, or five carboxylic acid groups in the ligand periphery can be achieved in a few steps from simple starting materials. Apart from being easily accessible, the metalloligands display interesting characteristics for applications in metallasupramolecular chemistry and materials science: they are rigid, large (up to 2.2 nm), and robust and they can show additional functions (e.g., fluorescence or extra charge) depending on the metal ion that is present in the clathrochelate core. The utility of these new metalloligands in MOF chemistry is demonstrated by the synthesis of zinc- and zirconium-based coordination polymers. The combination of Zn(NO3)2 with clathrochelates having two or three carboxylic acid groups gives MOFs in which the clathrochelate ligands are connected by Zn4O clusters or zinc paddlewheel links. The structures of the resulting two- and three-dimensional networks could be established by single-crystal X-ray crystallography. The reaction of carboxylic acid functionalized clathrochelates with ZrCl4 gives amorphous powders that display permanent porosity after solvent removal.

Efficient luminescent solar cells based on tailored mixed-cation perovskites.

We report on a new metal halide perovskite photovoltaic cell that exhibits both very high solar-to-electric power-conversion efficiency and intense electroluminescence. We produce the perovskite films in a single step from a solution containing a mixture of FAI, PbI2, MABr, and PbBr2 (where FA stands for formamidinium cations and MA stands for methylammonium cations). Using mesoporous TiO2 and Spiro-OMeTAD as electron- and hole-specific contacts, respectively, we fabricate perovskite solar cells that achieve a maximum power-conversion efficiency of 20.8% for a PbI2/FAI molar ratio of 1.05 in the precursor solution. Rietveld analysis of x-ray diffraction data reveals that the excess PbI2 content incorporated into such a film is about 3 weight percent. Time-resolved photoluminescence decay measurements show that the small excess of PbI2 suppresses nonradiative charge carrier recombination. This in turn augments the external electroluminescence quantum efficiency to values of about 0.5%, a record for perovskite photovoltaics approaching that of the best silicon solar cells. Correspondingly, the open-circuit photovoltage reaches 1.18 V under AM 1.5 sunlight.

Base-catalyzed intramolecular hydroamination of cyclohexa-2,5-dienes: insights into the mechanism through DFT calculations and application to the total synthesis of epi-elwesine.

The base-catalyzed intramolecular hydroamination of 1-ethylaminocyclohexa-2,5-dienes is described. The transformation proceeds through isomerization of the cyclohexa-1,4-dienyl fragment into the corresponding conjugated 1,3-diene prior to the hydroamination step. Attaching a chiral glycinol ether auxiliary on the amino group allows the protonation to occur with complete diastereocontrol. The resulting lithium amide then adds onto the 1,3-dienyl moiety, affording the desired fused pyrrolidine ring along with the corresponding lithium allylic anion. Protonation of the latter then proceeds with high regiocontrol to favor the resulting allylic amines. In contrast, when the reaction was performed on primary amines, fused pyrrolidines bearing a homoallylic amino group were obtained. The stereochemical course of the process and determination of the reaction pathways were established based on calculations performed at the DFT level. Finally, application of the methodology to the enantioselective synthesis of (+)-epi-elwesine, a crinane alkaloid, is described.

A four-component organogel based on orthogonal chemical interactions.

A thermoresponsive organogel was obtained by orthogonal assembly of four compounds using dynamic covalent boronate ester and imine bonds, as well as dative boron-nitrogen bonds. It is shown that the gel state can be disrupted or reinforced by chemicals which undergo exchange reactions with the gel components.

Low-cost industrially available molybdenum boride and carbide as "platinum-like" catalysts for the hydrogen evolution reaction in biphasic liquid systems.

Rarely reported low-cost molybdenum boride and carbide microparticles, both of which are available in abundant quantities due to their widespread use in industry, adsorb at aqueous acid-1,2-dichloroethane interfaces and efficiently catalyse the hydrogen evolution reaction in the presence of the organic electron donor - decamethylferrocene. Kinetic studies monitoring biphasic reactions by UV/vis spectroscopy, and further evidence provided by gas chromatography, highlight (a) their superior rates of catalysis relative to other industrially significant transition metal carbides and silicides, as well as a main group refractory compound, and (b) their highly comparable rates of catalysis to Pt microparticles of similar dimensions. Insight into the catalytic processes occurring for each adsorbed microparticle was obtained by voltammetry at the liquid-liquid interface.

Total synthesis of (±)-cylindricine C.

A concise synthesis of (±)-cylindricine C and its C(13)-epimer is described. Starting from 1-octyne, cylindricine C and 13-epi-cylindricine C were prepared in 11% and 15% yields, respectively. The synthesis involves the preparation of the central tricyclic moiety via a radical α-iodoketone carboazidation/bis-reductive amination sequence. Inversion of the stereochemistry at C(13) and C(5) was efficiently achieved on late stage intermediates.

Concise synthesis of pyrrolidine and indolizidine alkaloids by a highly convergent three-component reaction.

The synthesis of pyrrolidine and indolizidine derivatives through radical carboazidation of alkenes with α-iodoketones, followed by reductive amination, is described. When properly substituted, further lactamization afforded pyrrolizidinones in good yield. This carboazidation/reductive amination sequence was efficiently applied to the total synthesis of three different simple alkaloids, including (±)-monomorine I.

Turn-off-and-on: chemosensing ensembles for sensing chloride in water by fluorescence spectroscopy.

The recognition and sensing of aqueous chloride by synthetic receptors is a challenging task. Herein we apply the chemosensing ensemble methodology to optically detect chloride in water at near physiological pH. Variants based on two closely related receptors have been explored. The sensors can be obtained in situ by mixing a rhodium complex, a bidentate N,N-chelate ligand, and a fluorescent dye in buffered aqueous solution. Upon mixing the sensor components, the rhodium complex binds to the N,N-chelate ligand to yield a metal-based receptor. This latter associates with the fluorophore to give a non-emissive ground-state complex. The chemosensing ensembles respond to chloride via a turn-on fluorescence signal and can be used for optical detection of chloride down to mid-micromolar concentrations.

Dimerization of dendrimeric lanthanide complexes: thermodynamic, thermal, and liquid-crystalline properties.

A series of 10 different mesomorphic semidendrimeric tridentate ligands L5-L14 grafted with terminal cyanobiphenyl groups have been synthesized. Upon reaction with Ln(NO(3))(3) (Ln = trivalent lanthanide), the central 2,6-bis(N-ethylbenzimidazol-2-yl)pyridine unit is meridionally tricoordinated to the metal to give rodlike monomeric [Ln(Lk)(NO(3))(3)] and H-shaped dimeric [Ln(2)(Lk)(2)(NO(3))(6)] complexes. For the small Lu(III) cation, the monomeric complexes are quantitatively formed in a noncoordinating CD(2)Cl(2) solution. For larger cations (Ln = Eu, Pr), the thermodynamic equilibrium 2[Ln(Lk)(NO(3))(3)] ↔ [Ln(2)(Lk)(2)(NO(3))(6)] can be evidenced across the complete ligand series. Detailed thermodynamic studies show that the dimeric complexes result from the formation of primary intermetallic nitrate bridges whose strength depends on the metallic size. For each complex, secondary nonspecific interstrand van der Waals interactions produce nonartifactual enthalpy/entropy compensation. In the absence of solvent, only the complexes with the most extended ligands L5 and L6 produce thermotropic mesophases. Layered organizations are dominant (smectic A) with the induction of nematogenic behavior at high temperature when interstrand interactions are modulated by methyl substitutions. Correlations between the trend of dimerization and the sequences of thermotropic mesophases are attempted.

Synthesis of unusual oxime ethers by reaction of tetranitromethane with B-alkylcatecholboranes.

The reaction of tetranitromethane with B-alkylcatecholboranes leads to the formation of unusual dinitrooxime ethers. A tentative mechanism is provided, which suggests the involvement of extremely fast addition of alkyl radicals to tetranitromethane. The substitution of one of the nitro groups in the oxime ethers by nucleophiles (such as secondary amines, halogens and styrene) and by radicals generated from B-alkylcatecholboranes is reported.

The role of the tangent bundle for symmetry operations and modulated structures.

An equivalence relation on the tangent bundle of a manifold is defined in order to extend a structure (modulated or not) onto it. This extension affords a representation of a structure in any tangent space and that in another tangent space can easily be derived. Euclidean symmetry operations associated with the tangent bundle are generalized and their usefulness for the determination of the intrinsic translation part in helicoidal axes and glide planes is illustrated. Finally, a novel representation of space groups is shown to be independent of any origin point.

Differential geometry: a natural tool for describing symmetry operations.

Differential geometry provides a useful mathematical framework for describing the fundamental concepts in crystallography. The notions of point and associated vector spaces correspond to those of manifold and tangent space at a given point. A space-group operation is a one-to-one map acting on the manifold, whereas a point-group operation is a linear map acting between two tangent spaces of the manifold. Manifold theory proves particularly powerful as a unified formalism describing symmetry operations of conventional as well as modulated crystals without requiring a higher-dimensional space. We show, in particular, that a modulated structure recovers a three-dimensional periodicity in any tangent space and that its point group consists of linear applications.

B-Alkylcatecholborane-mediated tandem radical conjugated addition-aldol cyclization.

A one-pot procedure involving radical conjugate addition of B-alkylcatecholboranes to enones followed by intramolecular aldol reaction is reported. Application to the stereoselective synthesis of monocyclic and bicyclic products with up to four contiguous stereogenic centers is presented.