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Integrating multiple anthracene motifs into aromatic oligoamide sequences gives rise to photoactive foldamers that can sequester a molecular thread forming helix-on-axle assemblies. Photoirradiation is shown to distort the helical host and drive dissociation of the supramolecular assembly and thread liberation as signalled by a photonic output, while thermal reversion regenerates the assembly. [ABSTRACT FROM AUTHOR]

Abstract: Trotz erheblicher Fortschritte bei der Synthese kovalenter organischer Netzwerke (COFs) wurde für diese Materialien bis jetzt nur sporadisch über den präzisen Aufbau von templatfreien Nano‐ und Mikrostrukturen berichtet. Auf der Suche nach farbstoffhaltigen porösen Materialien konnte ein neues konjugiertes Netzwerk, DPP‐TAPP‐COF, durch reversible Iminkondensationen zwischen 5,10,15,20‐Tetrakis(4‐aminophenyl)porphyrin (TAPP) und einem Diketopyrrolopyrrol‐Dialdehyd (DPP) synthetisiert werden, das eine verstärkte Absorption bis zu λ=800 nm aufweist. Überraschenderweise wurde für dieses COF eine spontane Aggregation zu hohlen Mikroröhren mit äußeren und inneren Durchmessern von d≈300 und 90 nm beobachtet. Detaillierte mechanistische Studien ergaben, dass sich zunächst schichtartige Agglomerate bilden, die mit der Zeit in röhrenförmige Mikrostrukturen transformiert werden. [ABSTRACT FROM AUTHOR]

An equimolar mixture of Ni(NO)·6HO and pyridine-2-aldehyde with two equivalents of NaN in methanol in the presence of NaOMe resulted in the formation of light green precipitate which upon crystallization from dimethylformamide (DMF) yielded light green single crystals [{NiNa(pic)(N)(HO)(MeOH)}· MeOH·3HO] ( 1) and [{NiNa(pic)(N)(HO)}·2DMF·HO] ( 2) (pic = pyridine-2-carboxylate) at room temperature and high temperature (100°C), respectively. Variable temperature magnetic studies revealed the existence of overall ferromagnetic behaviour with J ≈ +10 cm and D ≈ − 2 to −7 cm for 1 and 2, respectively. Negative D values as well as variation of D upon slight distortion of structure by varying reaction temperature were observed. The X-band Electron Paramagnetic Resonance (EPR) spectra of both 2 and 3 were recorded below 50 K. The structural distortion was also implicated from the EPR spectra. Density Functional Theory (DFT) calculations on both complexes were performed in two different ways to corroborate the magnetic results. Considering only Ni $^{\rm II}_{2}$ dimeric unit, results were J = +20.65 cm and D = −3.16 cm for 1, and J = +24.56 cm and D = −4.67 cm for 2. However, considering Ni $^{\rm II}_{2}$Na $^{\rm I}_{2}$ cubane as magnetic core the results were J = +16.35 cm ( 1), +19.54 cm ( 2); D = −3.05 cm ( 1), −4.25 cm ( 2). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Two new neutral copper-azido polymers [Cu3(N3)6(tmen)2]n (1) and [Cu6(N3)12(deen)2]n (2) [tmen = N,N,N, N'-tetramethylethylenediamine and deen = N,N'-diethyethylenediamine] have been synthesized by using lower molar equivalents of the chelating diamine ligands with Cu(NO3)2-3H2O and an excess of NaN3. The single crystal X-ray structure shows that in the basic unit of the 1D complex 1, the three CuII ions are linked by double end-on azido bridges with Cu-Nm-Cu angles on both sides of the magnetic exchange critical angle of 108°. Complex 2 is a 3D framework of a basic Cu6 cluster. Cryomagnetic susceptibility measurements over a wide range of temperature exhibit dominant ferromagnetic behavior in both the complexes. Density functional theory calculations (B3LYP functional) have been performed on the trinuclear unit to preside a qualitative theoretical interpretation of the overall ferromagnetic behavior shown by the complex 1. [ABSTRACT FROM AUTHOR]

Porous organic materials are an emerging class of functional nanostructures with unprecedented properties. Dynamic covalent assembly of small organic building blocks under thermodynamic control is utilized for the intriguingly simple formation of complex molecular architectures in one-pot procedures. In this Review, we aim to analyze the basic design principles that govern the formation of either covalent organic frameworks as crystalline porous polymers or covalent organic cage compounds as shape-persistent molecular objects. Common synthetic procedures and characterization techniques will be discussed as well as more advanced strategies such as postsynthetic modification or self-sorting. When appropriate, comparisons are drawn between polymeric frameworks and discrete organic cages in terms of their underlying properties. Furthermore, we highlight the potential of these materials for applications ranging from gas storage to catalysis and organic electronics., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Despite significant progress in the synthesis of covalent organic frameworks (COFs), reports on the precise construction of template-free nano- and microstructures of such materials have been rare. In the quest for dye-containing porous materials, a novel conjugated framework DPP-TAPP-COF with an enhanced absorption capability up to λ=800 nm has been synthesized by utilizing reversible imine condensations between 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) and a diketopyrrolopyrrole (DPP) dialdehyde derivative. Surprisingly, the obtained COF exhibited spontaneous aggregation into hollow microtubular assemblies with outer and inner tube diameters of around 300 and 90 nm, respectively. A detailed mechanistic investigation revealed the time-dependent transformation of initial sheet-like agglomerates into the tubular microstructures., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We demonstrate here that supramolecular interactions enhance the sensitivity towards detection of electron-deficient nitro-aromatic compounds (NACs) over discrete analogues. NACs are the most commonly used explosive ingredients and are common constituents of many unexploded landmines used during World War II. In this study, we have synthesised a series of pyrene-based polycarboxylic acids along with their corresponding discrete esters. Due to the electron richness and the fluorescent behaviour of the pyrene moiety, all the compounds act as sensors for electron-deficient NACs through a fluorescence quenching mechanism. A Stern-Volmer quenching constant determination revealed that the carboxylic acids are more sensitive than the corresponding esters towards NACs in solution. The high sensitivity of the acids was attributed to supramolecular polymer formation through hydrogen bonding in the case of the acids, and the enhancement mechanism is based on an exciton energy migration upon excitation along the hydrogen-bond backbone. The presence of intermolecular hydrogen bonding in the acids in solution was established by solvent-dependent fluorescence studies and dynamic light scattering (DLS) experiments. In addition, the importance of intermolecular hydrogen bonds in solid-state sensing was further explored by scanning tunnelling microscopy (STM) experiments at the liquid-solid interface, in which structures of self-assembled monolayer of the acids and the corresponding esters were compared. The sensitivity tests revealed that these supramolecular sensors can even detect picric acid and trinitrotoluene in solution at levels as low as parts per trillion (ppt), which is much below the recommended permissible level of these constituents in drinking water., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Detection of trace amounts of explosive materials is significantly important for security concerns and pollution control. Four multicomponent metal-organic frameworks (MOFs-12, 13, 23, and 123) have been synthesized by employing ligands embedded with fluorescent tags. The multicomponent assembly of the ligands was utilized to acquire a diverse electronic behavior of the MOFs and the fluorescent tags were strategically chosen to enhance the electron density in the MOFs. The phase purity of the MOFs was established by PXRD, NMR spectroscopy, and finally by single-crystal XRD. Single-crystal structures of the MOFs-12 and 13 showed the formation of three-dimensional porous networks with the aromatic tags projecting inwardly into the pores. These electron-rich MOFs were utilized for detection of explosive nitroaromatic compounds (NACs) through fluorescence quenching with high selectivity and sensitivity. The rate of fluorescence quenching for all the MOFs follows the order of electron deficiency of the NACs. We also showed the detection of picric acid (PA) by luminescent MOFs is not always reliable and can be misleading. This attracts our attention to explore these MOFs for sensing picryl chloride (PC), which is as explosive as picric acid and used widely to prepare more stable explosives like 2,4,6-trinitroaniline from PA. Moreover, the recyclability and sensitivity studies indicated that these MOFs can be reused several times with parts per billion (ppb) levels of sensitivity towards PC and 2,4,6-trinitrotoluene (TNT)., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)