Strongly Polarized π-Extended 1,4-Dihydropyrrolo[3,2-b]pyrroles Fused with Tetrazolo[1,5-a]quinolines.

A straightforward route to 1,4-dihydropyrrolo[3,2-b]pyrroles comprised of two electron-withdrawing quinoline or tetrazolo[1,5-a]quinoline scaffolds has been developed. The versatile multicomponent reaction affording 1,4-dihydropyrrolo[3,2-b]pyrroles combined with intramolecular direct arylation enables assembly of these products in just three steps from anilines with overall yields exceeding 30%. The planarized, ladder-type heteroacenes possess up to 14 conjugated rings. These nominally quadrupolar materials exhibit efficient fluorescence with wavelengths spanning most of the visible spectrum from green-yellow for the dyes possessing biaryl bridges and orange-red for the fully fused systems. In many cases, the fluorescence quantum yields are large, the solvatofluorochromic effects are strong, and the fluorescence is maintained even in crystalline state. Analysis of the electronic structure of these molecular architectures using quantum chemical methods suggests that the character and position of the flanking heterocycle determine the shape of HOMO and LUMO and their extension to N-aryl substituents, influencing the values of molar absorption coefficient. An experimental study of the two-photon absorption (2PA) properties has revealed that it occurs in the 700-800 nm range with apparent deviation from the Laporte parity selection rule, which may be attributed to Hertzberg-Teller contribution to vibronically allowed 2PA transition.

Gold-Catalyzed 1,2-Aryl Shift and Double Alkyne Benzannulation.

The tandem intramolecular hydroarylation of alkynes accompanied by a 1,2-aryl shift is described. Harnessing the unique electron-rich character of 1,4-dihydropyrrolo[3,2-b]pyrrole scaffold, we demonstrate that the hydroarylation of alkynes proceeds at the already occupied positions 2 and 5 leading to a 1,2-aryl shift. Remarkably, the reaction proceeds only in the presence of cationic gold catalyst, and it leads to heretofore unknown π-expanded, centrosymmetric pyrrolo[3,2-b]pyrroles. The utility is verified in the preparation of 13 products that bear six conjugated rings. The observed compatibility with various functional groups allows for increased tunability with regard to the photophysical properties as well as providing sites for further functionalization. Computational studies of the reaction mechanism revealed that the formation of the six-membered rings accompanied with a 1,2-aryl shift is both kinetically and thermodynamically favourable over plausible formation of products containing 7-membered rings. Steady-state UV/Visible spectroscopy reveals that upon photoexcitation, the prepared S-shaped N-doped nanographenes undergo mostly radiative relaxation leading to large fluorescence quantum yields. Their optical properties are rationalized through time-dependent density functional theory calculations. We anticipate that this chemistry will empower the creation of new materials with various functionalities.

Saddle-shaped aza-nanographene with multiple odd-membered rings.

A saddle-shaped aza-nanographene containing a central 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) has been prepared via a rationally designed four-step synthetic pathway encompassing intramolecular direct arylation, the Scholl reaction, and finally photo-induced radical cyclization. The target non-alternant, nitrogen-embedded polycyclic aromatic hydrocarbon (PAH) incorporates two abutting pentagons between four adjacent heptagons forming unique 7-7-5-5-7-7 topology. Such a combination of odd-membered-ring defects entails a negative Gaussian curvature within its surface with a significant distortion from planarity (saddle height ≈ 4.3 Å). Its absorption and fluorescence maxima are located in the orange-red region, with weak emission originating from the intramolecular charge-transfer character of a low-energy absorption band. Cyclic voltammetry measurements revealed that this stable under ambient conditions aza-nanographene underwent three fully reversible oxidation steps (two one-electron followed by one two-electron) with an exceptionally low first oxidation potential of E ox1 = -0.38 V (vs. Fc/Fc+).

Hydrogen-Bonding Motifs in Adducts of Allylamine with the 10 Simplest n-Alcohols: Single-Crystal X-ray Diffraction Studies and Computational Analysis.

In this paper, we analyzed the homologous series of 10 allylamine adducts with n-alcohols from methanol to decanol. These are the first adduct structures containing aliphatic n-alcohols and an aliphatic amine as co-formers. While all of the ingredients are liquids under ambient conditions, the phases were synthesized with the use of the in situ crystallization technique assisted by IR laser-focused radiation at atmospheric pressure. The structures were characterized by single-crystal X-ray diffraction. All of the phases contain the amine and alcohol in a 1:1 ratio. The architecture of the structures, based on hydrogen-bonding interactions between NH2 and OH moieties, depends on the size of the alcohol and changes in a systematic way. The three smallest alcohol adducts contain centrosymmetric layers of molecules of the L4(4)8(8) type. The next four alcohol adducts have the T4(2) topology. The structures with the biggest alcohols contain non-centrosymmetric L6(6) layers. The structural investigations were supported by periodic DFT calculations at the B3LYP/pobTZVP level. The cohesive and adhesive energies made up of layer (E lbe) and ribbon (E rbe) binding energies were used to predict which type of architecture can be formed. The thermal stabilities of the adducts correlate with the melting points of the co-forming alcohols, with no evident relation to the adduct architecture.

Effect of Diamine Bridge on Reactivity of Tetradentate ONNO Nickel(II) Complexes.

Two new square planar ONNO nickel(II) complexes C2_core and C3_core have been synthesized and characterized by single crystal X-ray diffraction, NMR spectroscopy, thermogravimetry, and DFT calculations. The experimental results revealed the effect of the length of diamine bridge in the ligand on the behavior of the studied complexes in the reaction with N-heterocyclic aromatic amines, while DFT calculations provided a basis for the rationalization of this observation. The complex with propylenediamine bridge (C3_core) readily reacts with pyridine and its derivatives to form high-spin (paramagnetic) complexes with octahedral geometry as characterized by X-ray diffraction; electron-donating substituents on the pyridine ring facilitate the coordination of axial ligands. In contrast, the complex with ethylenediamine bridge (C2_core) does not undergo such a reaction because of the high deformation energy of the core required for the formation of C2_Py complex.

Structural reasons for the formation of multicomponent products and the influence of high pressure.

(S)-(-)-1-Phenylethanaminium 4-(2,4,6-triisopropylbenzoyl)benzoate (S-PEATPBB) undergoes a photochemical reaction in its crystalline form upon UV irradiation and forms three different products: the first product is the result of a Yang cyclization with the participation of the δ-H atom of o-isopropyl (product D) and the second and third products are obtained via a Norrish-Yang reaction with the involvement of the γ-H atom of 2-isopropyl (product P) and 6-isopropyl (product Z). These products are formed in different proportions (D > P >> Z). The path and kinetics of the reaction were monitored step-by-step using crystallographic methods, both under ambient and high-pressure conditions. The reactivity of S-PEATPBB depends strongly on the geometry of the reaction centre and the volume of the reaction cavity. Due to the geometrical preferences making the cyclization reaction easier to proceed, product D dominates over the other products, while the formation of product Z becomes difficult or almost impossible at high pressure. The reaction proceeds with an increase of the unit-cell volume, which, suppressed by high pressure, results in a significant decrease of the reaction rate. The crystal lattice of S-PEATPBB shows high elasticity. The quality of the partially reacted crystal remains the same after decompression from 0.75 GPa to 0.1 MPa.

Bowl-Shaped Pentagon- and Heptagon-Embedded Nanographene Containing a Central Pyrrolo[3,2-b]pyrrole Core.

A bowl-shaped nitrogen-doped nanographene composed of a pyrrolo[3,2-b]pyrrole core substituted with six arene rings circularly bonded with one another has been prepared via a concise synthetic strategy encompassing the multicomponent tetraarylpyrrolopyrrole (TAPP) synthesis, the Scholl reaction, and intramolecular direct arylation. This synthesis represents the first case of programmed sequential intramolecular direct arylation reactions utilizing the different reactivity of C-Br and C-Cl bonds. The target compound contains two central pentagons confined between two adjacent heptagons-the inverse Stone-Thrower-Wales topology. The presence of both five- and seven-membered rings in the final structure is responsible for interesting properties such as a perpendicularly aligned dipole moment, absorption and fluorescence in the orange-red region, weak emission originating from the charge-transfer character of a low-energy absorption band, and a high lying HOMO. In the solid state slipped convex-to-convex π-π stacking dominates.

Comprehensive Protocol for the Identification and Characterization of New Psychoactive Substances in the Service of Law Enforcement Agencies.

A non-routine, comprehensive protocol for characterization of emerging new psychoactive substances (NPS) including chemical structures, impurities, as well as crystal structures, has been developed to facilitate the work of law enforcement agencies. A set of NPS has been synthesized, identified, and characterized by various analytical methods in order to be used as certified reference standards (CRMs). Seven selected compounds (5-IT, NM-2201, MT-45, AB-CHMINACA, UR-144, 5F-PB-22, and 4-CMC) were synthesized on the laboratory scale, then the process was upscaled to semi-technical. All products were analyzed by electrospray Q/TOF-MS/MS for molecular structure identification. The presence of by-products, as well as metal impurities, arising from the performed syntheses, were characterized by reversed phase liquid chromatography (RP-HPLC) with DAD and Q/TOF-MS detection and inductively-coupled plasma with quadrupole mass spectrometer (ICP-QMS), respectively. Additionally, the crystal structures of UR-144, NM-2201, 5F-PB-22, and 4-CMC have been determined by single-crystal and powder X-ray diffraction.

New cubic cluster phases in the Mg-Ni-Ga system.

The crystal structure of new Mg9Ni6Ga14 and Mg3Ni2Ga compounds were investigated by single-crystal diffraction. Both structures can be described as three-core-shell cluster compounds. In the Mg6Ni9Ga14 structure, the [Ni6Ga6] icosahedron is encapsulated within the [Mg20] dodecahedron, which is again encapsulated within a [Ni18Ga42] fullerene-like truncated icosahedron, thus the three core-shell cluster [Ni6Ga6@Mg20@Ni18Ga42] results. In the Mg3Ni2Ga structure, the [Mg6] octahedron is encapsulated within the [Ni12Ga6] flattened icosahedron in vertices of which there are 12 nickel atoms, and six lateral edges are centered by gallium atoms, which in turn is encapsulated within a [Mg36] pseudo-rhombicuboctahedron with 12 additional atoms centering the lateral faces; thus for Mg3Ni2Ga the three-shell cluster is [Mg6@Ni12Ga6@Mg36].

Covalently Linked Bis(Amido-Corroles): Inter- and Intramolecular Hydrogen-Bond-Driven Supramolecular Assembly.

Four bis-corroles linked by diamide bridges were synthesized through peptide-type coupling of a trans-A2 B-corrole acid with aliphatic and aromatic diamines. In the solid state, the hydrogen-bond pattern in these bis-corroles is strongly affected by the type of solvent used in the crystallization process. Although intramolecular hydrogen bonds play a decisive role, they are supported by intermolecular hydrogen bonds and weak N-H⋅⋅⋅π interactions between molecules of toluene and the corrole cores. In an analogy to mono(amido-corroles), both in crystalline state and in solutions, the aliphatic or aromatic bridge is located directly above the corrole ring. When either ethylenediamine or 2,3-diaminonaphthalene are used as linkers, incorporation of polar solvents into the crystalline lattice causes a roughly parallel orientation of the corrole rings. At the same time, both NHCO⋅⋅⋅NH corrole hydrogen bonds are intramolecular. In contrast, solvation in toluene causes a distortion with one of the hydrogen bonds being intermolecular. Interestingly, intramolecular hydrogen bonds are always formed between the -NHCO- functionality located further from the benzene ring present at the position 10-meso. In solution, the hydrogen-bonds pattern of the bis(amido-corroles) is strongly affected by the type of the solvent. Compared with toluene (strongly high-field shifted signals), DMSO and pyridine disrupt self-assembly, whereas hexafluoroisopropanol strengthens intramolecular hydrogen bonds.

Easy Synthesis and Characterization of Holmium-Doped SPIONs.

The exceptional magnetic properties of superparamagnetic iron oxide nanoparticles (SPIONs) make them promising materials for biomedical applications like hyperthermia, drug targeting and imaging. Easy preparation of SPIONs with the controllable, well-defined properties is a key factor of their practical application. In this work, we report a simple synthesis of Ho-doped SPIONs by the co-precipitation route, with controlled size, shape and magnetic properties. To investigate the influence of the ions ratio on the nanoparticles’ properties, multiple techniques were used. Powder X-ray diffraction (PXRD) confirmed the crystallographic structure, indicating formation of an Fe3O4 core doped with holmium. In addition, transmission electron microscopy (TEM) confirmed the correlation of the crystallites’ shape and size with the experimental conditions, pointing to critical holmium content around 5% for the preparation of uniformly shaped grains, while larger holmium content leads to uniaxial growth with a prism shape. Studies of the magnetic behaviour of nanoparticles show that magnetization varies with changes in the initial Ho3+ ions percentage during precipitation, while below 5% of Ho in doped Fe3O4 is relatively stable and sufficient for biomedicine applications. The characterization of prepared nanoparticles suggests that co-precipitation is a simple and efficient technique for the synthesis of superparamagnetic, Ho-doped SPIONs for hyperthermia application.

Hydrogen Bonds Involving Cavity NH Protons Drives Supramolecular Oligomerization of Amido-Corroles.

trans-A2 B-Corroles with amide substituents at different positions versus the macrocyclic core have been synthesized. Their self-organizing properties have been comprehensively evaluated both in solid-state and in solution. The rigid arrangement of the amide functionality with the corrole ring led to the formation of strong intramolecular interactions and precluded intermolecular interactions. Replacement of sterically hindered C6 F5 substituents at positions 5 and 15 with smaller electron-withdrawing CO2 Me groups resulted in significant changes in the self-assembly pattern. With these substituents, tetramers formed in a crystalline state, in which one of the H-pyrrole subunits is out of the corrole plane. This allows the N-H group to form a hydrogen bond with a neighboring carbonyl group of the n-butyl amide fragment. DOSY NMR studies showed that amido-corroles bearing the OCH2 CONHnBu motif formed dimers in millimolar solutions in nonpolar solvents and the dimers existed in equilibrium with monomers. However, the corroles possessing meso-ester groups did not form dimers in polar tetrahydrofuran. Comprehensive optical studies allowed the absorption and emission features of the monomer corroles to be characterized in dilute solutions.

The role of steric hindrance in the intramolecular oxidative aromatic coupling of pyrrolo[3,2-b]pyrroles.

The presence of steric hindrance triggers different reaction pathways in the intramolecular oxidative aromatic coupling of tetraaryl-pyrrolo[3,2-b]pyrroles and leads to the formation of a fluorene moiety and a new cationic π-system linked together by a spiro carbon atom. Computational studies elegantly rationalized these results. These previously unknown functional dyes emit red light with reasonable efficiency.

Cyclic π-electron delocalization in non-planar linear acenes.

Based on the experimental data of newly determined structures of per-substituted naphthalenes by halogen atoms (F, Cl and Br) and perchloroanthracene, as well as on the molecular modeling we have shown that deviation from planarity leads to relatively small changes in the cyclic π-electron delocalization of acenes. Per-substituted naphthalenes are twisted, whereas perchloroanthracene adopts a boat conformation in the solid state. For the most distorted case - perbromonaphthalene twisted by 34.7°, the geometry-based HOMA index drops down by 0.128 of the unit only, which means ca. 15% reduction of the extent of π-electron delocalization as referred to naphthalene. To account for the changes in the aromatic stabilization energies (ASEs), exaltation of magnetic susceptibilities (Λ) and strain energies (SEs) upon bending we have proposed a set of homodesmotic reactions based on the peri-substituted systems, where the reference compounds have similar conformation to the distorted aromatics. The decrease of aromaticity is smooth, but regular in a rather large range of distortion. Notably, the most extreme case - 1,4,5,8-tetra-t-butylnaphthalene, twisted by 51.7° with an estimated strain energy of 26 kcal mol(-1) - is still aromatic. The ASE, Λ and HOMA decrease by 19.1 kcal mol(-1), 7 cgs-ppm and 0.34 of the unit, respectively, as referred to naphthalene.

Complete Series of Alkali-Metal M(BH3NH2BH2NH2BH3) Hydrogen-Storage Salts Accessed via Metathesis in Organic Solvents.

We report a new efficient way of synthesizing high-purity hydrogen-rich M(BH3NH2BH2NH2BH3) salts (M = Li, Na, K, Rb, Cs). The solvent-mediated metathetic synthesis applied here uses precursors containing bulky organic cations and weakly coordinating anions. The applicability of this method permits the entire series of alkali-metal M(BH3NH2BH2NH2BH3) salts (M = Li, Na, K, Rb, Cs) to be obtained, thus enabling their comparative analysis in terms of crystal structures and hydrogen-storage properties. A novel polymorphic form of Verkade's base (C18H39N4PH)(BH3NH2BH2NH2BH3) precursor was also characterized structurally. For all compounds, we present a comprehensive structural, spectroscopic, and thermogravimetric characterization (PXRD, NMR, FTIR, Raman, and TGA/DSC/MS).

Double head-to-tail direct arylation as a viable strategy towards the synthesis of the aza-analog of dihydrocyclopenta[hi]aceanthrylene--an intriguing antiaromatic heterocycle.

The first case of double head-to-tail direct arylation of aromatic compounds and the unusual photophysical properties of the resulting 2,2a(1,5)b(1,7)-tetraazacyclopenta[hi]aceanthrylene are reported. This molecule, comprising of two imidazo[1,2-a]pyridine units, is antiaromatic due to the changes in the efficiency of π-electron ring current and it belongs to a class of seldom encountered compounds with a dark lowest electronically excited singlet state.

Acidic C-H Bond as a Proton Donor in Excited State Intramolecular Proton Transfer Reactions.

An unprecedented type of excited state intramolecular proton transfer in a series of benzo[h]quinoline (BHQ) derivatives substituted at position 10 with strong CH acid character is described using density functional theory/time-dependent density functional theory computational approaches with a hybrid functional and the 6-311++G(d,p) triple-ξ quality basis set. Our results show that for 10-malononitrile-substituted BHQ (2CNBHQ) the excited state intramolecular proton transfer C-H···N reaction is a barrierless process. Calculations also reveal that the reaction profiles of the 4-amino-substituted 2CNBHQ show a large dependence on the polarity of the environment.

Towards Clathrates: Frozen States of Hydration of tert-Butylamine.

The dilution of tert-butylamine (tBA) with water and subsequent cooling leads to a large series of different crystalline hydrates by an in situ IR laser melting-zone procedure. The crystal structures were determined for tBA⋅n H2 O, with n=0, 1/4, 1, 7 1/4, 7 3/4, 9 3/4, 11, and 17. For the two lower hydrates (n= 1/4, 1), one- and two-dimensional hydrogen-bonded networks are formed, respectively. The higher hydrates (n>1) exhibit a clathrate-like three-dimensional water framework with the tBA molecules as part of, or sitting inside, the cages. In all cases, tBA is hydrogen-bonded to the H2 O framework. In the intermediate range (1

Synthesis of fluorescent naphthoquinolizines via intramolecular Houben-Hoesch reaction.

The repertoire of synthetic methods leading to aza-analogues of polycyclic aromatic heterocycles has been enlarged by the discovery of the rearrangement of 10-substituted benzo[h]quinolines into compounds bearing an azonia-pyrene moiety. Acid-mediated intramolecular cyclization of derivatives bearing -CH2 CN and -CH2 CO2 Et groups led to compounds bearing a 5-substituted benzo[de]pyrido[3,2,1-ij]quinolinium core. Advanced photophysical studies including time-correlated single photon counting (TCSPC) and transient absorption spectroscopy of 5-aminobenzo[de]pyrido[3,2,1-ij]quinolin-4-ium salt and 5H-benzo[de]pyrido[3,2,1-ij]quinolin-5-one showed their promising optical properties such as high fluorescence quantum yields (37-59%), which was almost independent of the solvent, and high tenability of the absorption band position upon changing the solvent. The benzo[de]pyrido[3,2,1-ij]quinolinium salt selectively stains nucleic acids (in the nucleus and mitochondria) in eukaryotic cells.