Efficient High-Refractive-Index Azobenzene Dendrimers Based on a Hierarchical Supramolecular Approach.

Real-time manipulation of light in a diffractive optical element made with an azomaterial, through the light-induced reconfiguration of its surface based on mass transport, is an ambitious goal that may enable new applications and technologies. The speed and the control over photopatterning/reconfiguration of such devices are critically dependent on the photoresponsiveness of the material to the structuring light pattern and on the required extent of mass transport. In this regard, the higher the refractive index (RI) of the optical medium, the lower the total thickness and inscription time can be. In this work, we explore a flexible design of photopatternable azomaterials based on hierarchically ordered supramolecular interactions, used to construct dendrimer-like structures by mixing specially designed sulfur-rich, high-refractive-index photoactive and photopassive components in solution. We demonstrate that thioglycolic-type carboxylic acid groups can be selectively used as part of a supramolecular synthon based on hydrogen bonding or readily converted to carboxylate and participate in a Zn(II)-carboxylate interaction to modify the structure of the material and fine-tune the quality and efficiency of photoinduced mass transport. Compared with a conventional azopolymer, we demonstrate that it is possible to fabricate high-quality, thinner flat diffractive optical elements to reach the desired diffraction efficiency by increasing the RI of the material, achieved by maximizing the content of high molar refraction groups in the chemical structure of the monomers.

New Hg(II) coordination polymers based on a thioimidazole ligand with good performance to detoxify Hg(II) and reversibly capture iodine.

In the current paper, we have successfully synthesized three new mercury coordination polymers with fascinating structures and properties via a flexible sulfur donor ligand, namely, {[Hg(µ2-Cl)(µ2-Ls)]}n[BF4]n(1), {[Hg(µ2-Cl)(µ2-Ls)]}n[ClO4]n(2), and [Hg(SCN)2(µ2-Ls)]n(3) [Ls = 1,1-bis(3-methyl-4-imidazoline-2-thione)methane]. These complexes have been characterized by means of different techniques such as single crystal X-ray crystallography, FT-IR, elemental analysis (CHNS), UV-Vis, PXRD, BET, and TGA. Suitable single crystals of all complexes were obtained using the branch tube method with a very high yield and good stability due to the high affinity of mercury to bind to the thione groups. The cationic moieties of polymers 1 and 2 were isostructural, with a HgCl2S2 coordination core structure. The voids of the quasi-hexagonal packing of the columnar chains were occupied by unbonded tetrahedral BF4- ions in 1 and perchlorate anions in polymer 2. Polymer 3 has a less distorted tetrahedral geometry than 1 and 2, with a HgS4 core structure. By considering the thiophilicity of mercury, a thioamide-based Ls ligand was used to detoxify Hg(II) into insoluble polymers 1-3. The results of an MTT assay for (HepG2) liver cells confirmed the excellent cytoprotective effect of this ligand against mercury. Based on IC50 calculations, their toxicity was in order of polymer 1 > polymer 2 > polymer 3. These polymers were also considered as adsorbents for the reversible removal of iodine from solution and the kinetics of the process has been studied in detail. Interestingly, all of them showed an excellent stability and high capacity, in order of 763.53 mg g-1, 877.10 mg g-1, and 905.31 mg g-1 for polymers 1-3, respectively.

Crystal and mesophase structure of a bicyclohexyl cyano mesogen.

The phase behaviour of 4-[trans-4-(trans-4-propylcyclohexyl)cyclohexyl]benzonitrile, C22H31N, 1, has been examined. This compound has two different solid phases, denoted I and II, and exhibits thermotropic liquid-crystalline behaviour, with a remarkable interval of stability of the mesophase between the lower melting solid phase (75 °C) and the isotropization temperature (247 °C). The crystal and molecular structures of solid phase I have been determined at 173 K. The cyclohexyl rings both adopt the chair conformation and are equatorially substituted. The packing of 1 in the crystalline state is driven by the antiparallel arrangement of cyano dipoles with the formation of close contacts involving the strong cyano acceptor and weak aromatic C-H or aliphatic C-H donors. The crystal packing is discussed and compared with X-ray diffraction data in the liquid-crystalline state. The combination of thermal analysis, optical polarizing microscopy and X-ray diffraction analysis suggests that the mesophase is a partially ordered smectic phase. The lamellar structure of the mesophase is retained in crystalline solid phase II obtained by cooling the liquid-crystalline phase.

Novel Thienyl DPP derivatives Functionalized with Terminal Electron-Acceptor Groups: Synthesis, Optical Properties and OFET Performance.

Three novel diketopyrrolopyrrole (DPP) based small molecules have been synthesized and characterized in terms of their chemical-physical, electrochemical and electrical properties. All the molecules consist of a central DPP electron acceptor core symmetrically functionalized with donor bi-thienyl moieties and flanked in the terminal positions by three different auxiliary electron-acceptor groups. This kind of molecular structure, characterized by an alternation of electron acceptor and donor groups, was purposely designed to provide a significant absorption at the longer wavelengths of the visible spectrum: when analysed as thin films, in fact, the dyes absorb well over 800 nm and exhibit a narrow optical bandgap down to 1.28 eV. A detailed DFT analysis provides useful information on the electronic structure of the dyes and on the features of the main optical transitions. Organic field-effect transistors (OFETs) have been fabricated by depositing the DPP dyes as active layers from solution: the different end-functionalization of the dyes had an effect on the charge-transport properties with two of the dyes acting as n-type semiconductors (electron mobility up to 4.4 ⋅ 10-2  cm2 /V ⋅ s) and the third one as a p-type semiconductor (hole mobility up to 2.3 ⋅ 10-3  cm2 /V ⋅ s). Interestingly, well-balanced ambipolar transistors were achieved by blending the most performant n-type and p-type dyes with hole and electron mobility in the order of 10-3  cm2 /V ⋅ s.

Enhanced photoinduced mass migration in supramolecular azopolymers by H-bond driven positional constraint.

Here we investigated the role of hydrogen bonding in the design of supramolecular azopolymers with a highly directional and constrained azobenzene-chain interaction involving the aromatic ring of the photoactive molecule, by exploiting the 2-aminopyrimidine/carboxylic acid supramolecular synthon as the tool for molecular recognition. We have shown that this approach is advantageous for producing affordable and versatile photopatternable azomaterials by complexation with polyacrylic acid (PAA). Molecular model complexes were successfully prepared and characterized by X-ray diffraction analysis and FTIR spectroscopy to reveal the multiple, non-ionic interaction occurring between the azobenzene units and the polymer chains. Surface photopatterning of thin films, driven by the typical mass migration phenomenon occurring in azopolymers, resulted strongly enhanced with increasing azobenzene content until equimolar composition. Results show that polymers with synthon-based azobenzenes markedly outperform single H-bonded systems bearing azomolecules with similar structure and electronic properties. We finally demonstrated that the azobenzene units can be easily extracted from a photopatterned film by a simple solvent rinse and without any chemical pre-treatment, leaving the periodicity of the inscribed surface relief gratings unaltered. This result was enabled by the orthogonal solubility of the components in the supramolecular system.

High-Energy-Density Materials: An Amphoteric N-Rich Bis(triazole) and Salts of Its Cationic and Anionic Species.

The synthesis and characterization of the N-rich bis(triazole) compound 1H,4'H-[3,3'-bis(1,2,4-triazole)]-4',5,5'-triamine (C4H7N9) with a N content of 69.6% by weight is reported. The compound exhibits a rich acid-base behavior because it can accept up to two protons, forming a monocation and a dication, and can lose one proton, forming an anion. Measurement of the acid constants has shown that there exist well-defined pH intervals in which each of the four species is predominant in solution, opening the way to their isolation and characterization by single-crystal X-ray analysis as salts with different counterions. Some energetic salts of the monocation or dication containing oxidizing inorganic counterions (dinitramide, perchlorate, and nitrate) were also prepared and characterized in the solid state for their sensitivity. In particular, the neutral compound shows a very remarkable thermal stability in air, with Td = 347 °C, and is insensitive to impact and friction. Salts of the dication with energetic counterions, in particular perchlorate and nitrate, show increased sensitivities and reduced thermal stability. The salt of the monocation with dinitramide as the counterion outperforms other dinitramide salts reported in the literature because of its higher thermal stability (Td = 230 °C in air) and friction insensitiveness.

Stabilization of an elusive tautomer by metal coordination.

The solid-state isolation of the different tautomers of a chemical compound can be a challenging problem. In many cases, tautomers with an energy very close to the most stable one cannot be isolated (elusive tautomers). In this article, with reference to the 4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole ligand, for which the elusive 3H-tautomer has an energy only 1.4 kcal mol-1 greater than the most stable 2H form, we show that metal complexation is a successful and reliable way for stabilizing the elusive tautomer. We have prepared two complexes of the neutral ligand with CuBr2 and ZnBr2, namely, aquabromidobis[4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]copper(II) bromide trihydrate, [CuBr(C8H7N7)2(H2O)]Br·3H2O, and dibromido[4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole][4-methyl-7-(pyrazin-2-yl)-3H-[1,2,4]triazolo[3,2-c][1,2,4]triazole]zinc(II) monohydrate, [ZnBr2(C8H7N7)2]·H2O. The X-ray analysis shows that, in both cases, the elusive 3H-tautomer is present. The results of the crystallographic analysis of the two complexes reflect the different coordination preferences of CuII and ZnII. The copper(II) complex is homotautomeric as it only contains the elusive 3H-tautomer of the ligand. The complex can be described as octahedral with tetragonal distortion. Two 3H-triazolotriazole ligands are bis-chelated in the equatorial plane, while a water molecule and a bromide ion in elongated axial positions complete the coordination environment. The zinc(II) complex, on the other hand, is heterotautomeric and contains two bromide ions and two monodentate ligand molecules, one in the 2H-tautomeric form and the other in the 3H-tautomeric form, both coordinated to the metal in tetrahedral geometry. The observation of mixed-tautomer complexes is unprecedented for neutral ligands. The analysis of the X-ray molecular structures of the two complexes allows the deduction of possible rules for a rational design of mixed-tautomer complexes.

Phase behaviour and crystal structures of 2',3'-difluorinated p-terphenyl derivatives.

The crystal structures of difluorine derivatives of p-terphenyls (nTm) have been determined by single-crystal X-ray diffraction. For the unsymmetrical substituted compounds 2',3'-difluoro-4-methyl-p-terphenyl (1T0, C19H14F2) and 4-ethyl-2',3'-difluoro-4''-methyl-p-terphenyl (1T2, C21H18F2), the crystal structure is disordered, with molecules statistically entering the crystal in up and down orientations, with full superposition of all the atoms, except for those of the terminal groups (H/methyl for 1T0 and methyl/ethyl for 1T2). For triclinic 2',3'-difluoro-4,4''-dimethyl-p-terphenyl (1T1, C20H16F2), with the space group P-1, the two crystallographically independent molecules have the same conformation, which is different from monoclinic 1T0 (space group C2) and 1T2 (space group C2/c). A common feature of the conformation of the three compounds is the noncoplanar twisted arrangement of the three rings of the p-terphenyl moiety. Two-dimensional (2D) Hirshfeld fingerprint plots are consistent with H...H and C...H contacts in the crystal packing. For the three compounds, the phase behaviour has been investigated by POM (Petra/Osiris/Molinspiration) and differential scanning calorimetry (DSC) analysis. 1T2 is mesogenic, with enantiotropic nematic behaviour.

Tautomeric and conformational switching in a new versatile N-rich heterocyclic ligand.

A new N-rich triazolo-triazole derivative, 4-methyl-7-(pyrazin-2-yl)-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole (C8H7N7), bearing a pyrazine residue at 7-position of the triazolo-triazole bicycle, was synthesized, and its acid-base and metal coordination properties were evaluated in solution. The results showed amphoteric behavior and the formation of stable complexes with Cu(ii) and Zn(ii) in pH intervals in which the ligand is neutral or deprotonated. Computational studies were performed in order to evaluate the stability of the different tautomers/conformers of the ligand, and the proton position in the neutral and acidic forms. Single crystal X-ray analysis of the free neutral ligand (2H/s-trans tautomer/conformer), and of its singly protonated (2H-3H/s-trans), doubly protonated (2H-3H-7H/s-trans) and deprotonated forms showed that the influence of the pyrazine ring on the triazolo-triazole system is mainly as electron withdrawing and chelating group, and proton acceptor. Different coordination modes have been evidenced for the neutral and deprotonated ligand. Upon metal coordination, the neutral ligand switches from 2H/s-trans to 3H/s-cis tautomer/conformer forming five-membered chelate rings, while the anionic deprotonated ligand forms six-membered chelate rings in the s-trans conformation. Altogether, five different tautomers/conformers of the ligand were isolated and characterized. In vitro tests confirmed the general antiproliferative activity of triazolo-triazole compounds and the importance of substitution in position 7 for their selectivity.

Crystal structure and mesogenic behaviour of a new fluorene derivative: 9,9-dimethyl-2,7-bis(4-pentylphenyl)-9H-fluorene.

The title compound, C37H42, is a new mesogenic compound containing the fluorene moiety. It exhibits enantiotropic nematic liquid crystalline behaviour with melting at 125 °C and isotropization at 175 °C. The crystallographically independent unit contains two molecules oriented face-to-edge with respect to each other. The two molecules have nearly the same conformation of the bis-phenyl fluorene moiety. The molecular packing in the crystal phase is nematic-like.

A new biologically active molecular scaffold: crystal structure of 7-(3-hydroxyphenyl)-4-methyl-2H-[1,2,4]triazolo[3,2-c][1,2,4]triazole and selective antiproliferative activity of three isomeric triazolo-triazoles.

A study of three isomeric compounds containing a phenolic moiety attached to the nitrogen-rich triazolo-triazole bicycle is presented. In the three isomers, the phenolic OH group is in the ortho, meta and para positions. The crystal structure analysis of the meta isomer (C10H9N5O) shows that the 2H-tautomer is present in the crystal and that the molecule adopts a substantially planar geometry. However, the conformation found in the crystal is different compared to the monoprotonated cation of the same compound previously investigated in several salts. The packing of the meta isomer is driven by the formation of strong hydrogen bonds and shows the formation of infinite planar ribbons, parallel to a, formed around 21 crystallographic axes. The three isomers were tested against some cancer cell lines and also against normal cell lines. The ortho isomer shows a weak antiproliferative activity, the meta isomer shows significant antiproliferative activity against some cancer lines and no activity against healthy cell lines, and the para isomer is active against all the tested cell lines.

Research Progress on Photosensitizers for DSSC.

Dye sensitized solar cells (DSSC) are considered one of the most promising photovoltaic technologies as an alternative to traditional silicon-based solar cells, for their compatibility with low-cost production methods, their peculiar optical and mechanical properties and the high indoor efficiency. Photosensitizers represent one of the most important components of a DSSC device and probably the most thoroughly investigated in the last twenty years, with thousands of dyes that have been proposed and tested for this kind of application. In this review we aimed to provide an overview of the three main classes of DSSC photosensitizers, namely ruthenium(II) polypyridyl complexes, Zn-porphyrin derivatives and metal-free organic dyes. After a brief introduction about the architecture and operational principles of a DSSC and the state of the art of the other main components of this type of device, we focused our discussion on photosensitizers. We have defined the numerous requirements DSSC photosensitizers should satisfy and have provided an overview of their historical development over the years; by examining specific dyes reported in the literature, we attempted to highlight the molecular design strategies that have been established for the optimization of their performance in real devices both in terms of efficiency (which recently reaches an outstanding 14.3%) and operational stability. Finally, we discussed, in the last section, the possible future developments of this intriguing technology.

Crystal structure of N,N'-bis-(2,4-di-fluoro-benzo-yloxy)benzene-1,2:4,5-tetra-carboximide.

Mol-ecules of the title compound, C24H8F4N2O8, have Ci point-group symmetry in the crystal, as they lie on crystallographic inversion centres (Z' = 1/2). The di-fluoro-phenyl ring is disordered over two orientations; the final refined occupancy factors of the two components of disorder are 0.947 (4) and 0.053 (4). In the crystal, some Car-H⋯F inter-actions are present, which involve the most acidic H atom of the mol-ecule.

Crystal structure of an ep-oxy-sterol: 9α,11α-ep-oxy-5α-cholest-7-ene-3ß,5,6α-triol 3,6-di-acetate.

The title compound, C31H48O6, is a polyoxygenated ep-oxy steroid obtained by a multi-step synthesis involving oxidation of 7-de-hydro-cholesterol. It crystallizes in the P212121 space group; however, the absolute structure of the molecule in the crystal could not be determined by resonant scattering. The configuration at the C5 and C6 positions is in both cases of the α-type, as is that of the C atoms of the ep-oxy ring. Mol-ecules in the crystal form chains parallel to the b axis by hydrogen bonding between O-H donors and carbonyl O-atom acceptors. Some atoms of the alkyl chain are disordered over two orientations, with a refined occupancy ratio of 0.511 (10):0.489 (10).

Pseudosymmetry and high Z' structures: the case of rac-(2R,2'R,5'S)-2-methyl-5'-[(1R,2R,5S,5'S)-1,4,4,5'-tetra-methyl-dihydro-3'H-3,8-dioxa-spiro-[bi-cyclo-[3.2.1]octane-2,2'-furan]-5'-yl]-3,4,1',2',3',4'-hexa-hydro-[2,2'-bi-furan]-5(2H)-one.

The title compound, C22H34O6, is one of the products obtained by oxidation of squalene with the catalytic system RuO4(cat.)/NaIO4. It crystallizes in the P-1 space group, with four crystallographically independent mol-ecules related by a pseudo-C2 symmetry axis. The structural analysis also shows that the title compound is isomeric with two products previously reported in the literature and that are obtained by the same reaction procedure. In particular, out of the seven chiral C atoms present in the mol-ecule, the title compound shows the opposite configuration at, respectively, four and two chiral centres with respect to the isomeric compounds.

Crystal structure of a new spiro-polytetra-hydro-furan compound with translational pseudosymmetry: rac-(2S,2'S,5'R)-2-methyl-5'-[(1R,2R,5S,5'R)-1,4,4,5'-tetra-methyl-dihydro-3'H-3,8-dioxa-spiro[bi-cyclo-[3.2.1]octane-2,2'-furan]-5'-yl]hexa-hydro[2,2'-bi-furan]-5(2H)-one.

The title compound, C22H34O6, is a product of oxidation of squalene with the catalytic system RuO4(cat.)/NaIO4. The asymmetric unit contains two crystallographically independent mol-ecules of very similar geometry approximately related by the non-crystallographic translation vector c/2. As a consequence, the average diffracted intensity in the hkl layers with odd l is systematically lower than in the layers with even l. In one mol-ecule, the lactone ring and part of the adjacent tetra-hydro-furan ring are disordered over two orientations with refined occupancy ratio of 0.831 (10):0.169 (10). The crystal structure is mainly governed by van der Waals forces.

Solid State Separation and Isolation of Tautomers of Fused-Ring Triazolotriazoles.

Fine control of the tautomeric forms of [1,2,4]triazolo[3,2-c][1,2,4]triazole derivatives in acidic conditions has been achieved by acting on the electronic character of the substituent at position 7 of the heterobicycle and on the counterion. Strong electron releasing or electron withdrawing substituents lead almost exclusively to a single tautomeric form, the 1H-3H or the 2H-3H, respectively. In the case of the phenol substituent, both tautomeric forms are present in comparable amount in solution; the two tautomers can also be selectively precipitated in different crystalline salts using suitable counterions.

5-Amino-1-(2',3'-O-iso-propyl-idene-d-ribit-yl)-1H-imidazole-4-carboxamide: a crystal structure with Z' = 4.

The title compound, C12H20N4O5, crystallizes in the monoclinic space group P21, with four crystallographically independent mol-ecules in the asymmetric unit. The four mol-ecules have a very similar conformation that is basically determined by the formation of two intra-molecular hydrogen bonds between the amino NH2 donors and the carbonyl and ring O-atom acceptors, forming, respectively, R(6) and R(7) ring motifs.. In the crystal, inter-molecular hydrogen bonding leads to the formation of R22(10) ring patterns, involving one amide CONH2 donor and an imidazole N-atom acceptor. The cluster of the four independent mol-ecules has approximate non-crystallographic C2 point symmetry. The structural analysis also shows that during the synthesis of the title compound, the reductive cleavage of the d-ribose ring of the inosine precursor proceeds stereoselectively, with retention of configuration.

Survey of temperature, reaction time and ultrasound irradiation power on sonochemical synthesis of two new nanostructured lead(II) coordination supramolecule compounds.

Nanoparticles of two new 0D, lead(II) coordination supramolecular compounds, [Pb(L)2(I)2] (1) and [Pb(L)(L/)(H2O)]·3H2O (2), (L=1,10-phenanthroline monohydrate, L/=2,6-pyridinedicarboxlic acid), have been synthesized by a sonochemical process and characterized by scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRPD), FT-IR spectroscopy and elemental analyses. The single crystal X-ray data of compounds show that the Pb ion is six coordinated in both 1 and 2. The thermal stability of compound 1 and 2 has been studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The role of temperature, reaction time and ultrasound irradiation power on the size and morphology of the nano-structured compound obtained from 1 and 2, have been investigated. Results indicate that an increase of temperature and sonication power and a decrease in time reaction led to a decrease of particle size. Topological analysis shows that the compound 1 and 2 are new topology for net: 1,4M5-1 and nch, respectively.

Strong and Anomalous Thermal Expansion Precedes the Thermosalient Effect in Dynamic Molecular Crystals.

The ability of thermosalient solids, organic analogues of inorganic martensites, to move by rapid mechanical reconfiguration or ballistic event remains visually appealing and potentially useful, yet mechanistically elusive phenomenon. Here, with a material that undergoes both thermosalient and non-thermosalient phase transitions, we demonstrate that the thermosalient effect is preceded by anomalous thermal expansion of the unit cell. The crystal explosion occurs as sudden release of the latent strain accumulated during the anisotropic, exceedingly strong expansion of the unit cell with αa = 225.9 × 10(-6) K(-1), αb = 238.8 × 10(-6) K(-1) and αc = -290.0 × 10(-6) K(-1), the latter being the largest negative thermal expansivity observed for an organic compound thus far. The results point out to the occurence of the thermosalient effect in phase transitions as means to identify new molecular materials with strong positive and/or negative thermal expansion which prior to this work could only be discovered serendipitously.