“Stairway to Heaven” molecules based on polycyclic aromatic hydrocarbon structures bridged by fulvalene motifs were prepared from simple precursors using Lawesson's reagent. These ladder-type molecules are multi-redox systems that exhibit both reversible oxidations and reductions with electrochemical HOMO-LUMO gaps correlating with the optical ones. Representative cyclic voltammograms are shown as “clouds”. More information can be found in the Full Paper by M. B. Nielsen et al. (DOI: 10.1002/chem.202100984).

Many macromolecular data sets suffer from being more or less incomplete mainly as a result of experimental difficulties.Often axes are missing which should be inspected for systematic absences.Even data sets considered complete usually miss very low resolution reflections due to beam stop issues.Low resolution reflections are important as they to a large extent define the protein/solvent boundary.Seriously incomplete data sets can hamper many crystallographic calculations.In the order of minutes a completed data set can be produced with estimates of unobserved intensities along with estimated standard deviations based on how well the free intensities are reproduced by following the ideas of Read (1986) [1].

Polycyclic aromatic hydrocarbons (PAHs) have found strong interest for their electronic properties and as model systems for graphene. While PAHs have been studied intensively as single units, here PAHs were constructed in ladder-type arrangements using cross-conjugated fulvalene and dithiafulvalene motifs as connecting units and moving forward a convenient synthetic approach for dimerizing (thio)ketones into olefins by the action of Lawesson's reagent. Some of the PAHs can also be regarded as "super-extended" tetrathiafulvalenes (TTFs) with some of the largest cores ever explored, being multi-redox systems that exhibit both reversible oxidations and reductions. Concomitant absorption redshifts were observed when expanding the ladder-type structures from one to two to three indenofluorene units, and optical and electrochemical HOMO-LUMO gaps were found to correlate linearly. Various conformations (and solid-state packing arrangements) were studied by X-ray crystallography and computations.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Thieno-fused subporphyrazines (TPs) containing a central and axially substituted boron atom are a class of compounds with interesting optical and redox properties. Here we present our efforts towards expanding this class of compounds using various thiophene substrates that were prepared by cyanation or nitration of 3,4-dibromothiophene. Moreover, we show that one TP derivative forms a 2:1 complex in the solid state with C70.

Carbon dioxide is an intrinsically stable molecule; however, it can readily react with various nucleophilic reagents. In the presence of a cyanide source, CO2 was proven to be useful to promote addition reactions. Here we report the use of CO2 to facilitate 1,4-conjugate cyanide addition reaction to chalcones to generate organonitriles. Nitriles are key component in organic synthesis due to their utility in numerous functional group transformation, however, conjugation addition of cyanide has been a challenge in this substrate class due to side reactions. To mitigate this, we employed simple ammonium and metal cyanide sources as nucleophiles under carbon dioxide atmosphere where high selectivity toward the desired product was obtained. The presented reaction is not feasible under inert atmosphere, which highlights the important role of CO2, as a Lewis and Brøndsted acidic catalyst. Further derivatization of organonitriles compounds were performed to showcase the utility of the reaction, while an unprecedented dimerization reaction was identified and characterized, affording a cyclopentanone scaffold.

We report a Michael-type cyanation reaction of coumarins by using CO2 as a catalyst. The delivery of the nucleophilic cyanide was realized by catalytic amounts of CO2, which forms cyanoformate and bicarbonate in the presence of water. Under ambient conditions, CO2-catalyzed reactions afforded high chemo- and diastereoselectivity of beta-nitrile carbonyls, whereas only low reactivities were observed under argon or N-2. Computational and experimental data suggest the catalytic role of CO2, which functions as a Lewis acid, and a protecting group to mask the reactivity of the product, suppressing byproducts and polymerization. The utility of this convenient method was demonstrated by preparing biologically relevant heterocyclic compounds with ease.

Molecular solar thermal energy storage (MOST) systems based on photochromic molecules that undergo photoisomerization to high-energy isomers are attractive for storage of solar energy in a closed-energy cycle. One challenge is to control the discharge time of the high-energy isomer. Here we show that incorporation of a strong acceptor substituent in the seven-membered ring of the dihydroazulene/vinylheptafulvene (DHA/VHF) couple increases the half-life of the energy-releasing VHF-to-DHA back-reaction from hours to more than a day in a polar solvent. For some derivatives, the absorption maximum of the photo-active DHA is also significantly redshifted, thereby better matching the solar spectrum. Synthetic protocols and kinetics studies are presented together with a computational study of the energy densities of the systems and excitation spectra. The computations show that the increased lifetime of the high-energy isomer is counter-balanced by a lower energy storage capacity in vacuo than for the parent system, but a slightly higher energy density than for the parent system in a polar solvent.

Graphyne allotropes of carbon are fascinating materials, and their electronic properties are predicted to rival those of the "wonder material" graphene. One allotrope of graphyne, having rectangular symmetry rather than hexagonal, stands out as particularly attractive, namely 6,6,12-graphyne. It is currently an insurmountable challenge, however, to design and execute a synthesis of this material. Herein, we present synthesis and electronic properties of molecules that serve as model compounds. These oligomers, so-called radiaannulenes, are prepared by iterative acetylenic coupling reactions. Systematic optical and redox studies indicate the effective conjugation length of the radiaannulene oligomers is nearly met by the length of the trimer. The HOMO-LUMO gap suggested by the series of oligomers is still, however, higher than that expected for 6,6,12-graphyne from theory, which predicts two nonequivalent distorted Dirac cones (no band gap). Thus, the radiaannulene oligomers present a suitable length in one dimension of a sheet, but should be expanded in the second dimension to provide a unique representation of 6,6,12-graphyne.

The boron subphthalocyanine (SubPc) fluorescence is reversibly modulated by photoisomerization of a covalently attached dihydroazulene (DHA) photoswitch into a vinylheptafulvene (VHF).

The optical and switching properties of the dihydroazulene/vinylheptafulvene (DHA/VHF) photo-/thermoswitch can be finely tuned by substituent groups at specific positions. While the kinetics of the thermal ring closure of VHF into DHA have previously been shown to follow systematic trends in regard to the electron-withdrawing/donating character of substituents at DHA positions C(2), C(3), and C(7) (Hammett correlations), no such correlation has so far been established for a selection of compounds with different substituents at C(1). Functionalization at this position is at the same time known to have the strongest impact on the VHF-to-DHA conversion rate. Here we show that introduction of a benzothiazole ring at C(1) of DHA (corresponding to the vinyl position of VHF) with various electron-withdrawing/donating groups provides VHFs whose rates of ring closure follow a Hammett correlation - the more electron-withdrawing substituent on the benzothiazole, the faster ring closure reaction.

A series of boron subphthalocyanine-tetracyanobutadiene-ferrocene (SubPc-TCBD-Fc) triads was synthesized by subjecting SubPcs with a ferrocenylethynyl substituent at either the axial or peripheral position to a [2 + 2] cycloaddition reaction with tetracyanoethylene followed by retroelectrocyclization. The ferrocenylethynyl unit was introduced at the axial position (at the boron atom) by a simple aluminum chloride-mediated alkynylation reaction, while functionalization at the SubPc periphery was accomplished by a Sonogashira coupling reaction. The conversion of one alkyne unit into a TCBD unit in combination with the location of the resulting TCBD-Fc moiety was found to have a strong influence on the optical and redox properties, which is ascribed to very different ground-state interactions between the individual donor/acceptor systems. The first electrochemical oxidation could thus be anodically shifted by as much as 0.4 V from the strongest donor molecule (with most unperturbed ferrocene character) to the poorest donor molecule (with strongly perturbed ferrocene character). Six redox states could be reached reversibly for the SubPc-TCBD-Fc triads, -3, -2, -1, 0, + 1, + 2, and for one compound the formation of a tetraanion persistent at the time scale of slow scan voltammetry was observed.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

We have characterized the structure and dynamics of the carbohydrate-modifying enzyme Paenibacillus nanensis xanthan lyase (PXL) involved in the degradation of xanthan by X-ray crystallography, small-angle X-ray scattering, and hydrogen/deuterium exchange mass spectrometry. Unlike other xanthan lyases, PXL is specific for both unmodified mannose and pyruvylated mannose, which we find is correlated with structural differences in the substrate binding groove. The structure of the full-length enzyme reveals two additional C-terminal modules, one of which belongs to a new non-catalytic carbohydrate binding module family. Ca2+ are critical for the activity and conformation of PXL, and we show that their removal by chelating agents results in localized destabilization/unfolding of particularly the C-terminal modules. We use the structure and the revealed impact of Ca2+ coordination on conformational dynamics to guide the engineering of PXL variants with increased activity and stability in a chelating environment, thus expanding the possibilities for industrial applications of PXL.

Tweezer-like molecules comprised of two boron subphthalocyanine (SubPc) units were prepared by Sonogashira couplings and investigated using NMR spectroscopy for their ability to bind fullerenes (C60 and C70). The preorganization of the tweezers provided association constants of ca. 103 M-1 in toluene- d8, while a SubPc monomer did not show any association. Nevertheless, the SubPc monomer crystallized with the fullerenes as 2:1 complexes, supporting the favorable tweezer-like design for complexation, which was further corroborated by computations.

The synthesis, crystal structure and spectroscopic properties of the neodymium(III) complex [Nd(btpa) Cl-2] Cl center dot 5H(2)O with btpa being the octadentate polypyridine ligand 6,6'-bis[bis(2-pyridylmethyl) aminomethyl]- 2.2'-bipyridine are reported. The structure shows that the Nd3+ ion is coordinated to seven nitrogen atoms of btpa and two chloride ions, leaving one uncoordinated pyridine group. The coordination polyhedron is best described as a monocapped cube. The btpa ligand forms a stable 1: 1 complex with Nd(CF3SO3)(3) and other selected triflates of the lanthanides(III) ions (Ln) in anhydrous acetonitrile. The stability constants of the Ln(btpa)(3+) complexes are quite similar along the series, due to a compensation between ligand-metal interaction and lanthanide desolvation. High resolution absorption spectroscopy at 4 K shows one equivalent crystallographic position of the Nd3+ ion in the structure. The Nd-btpa complexes in the solid-state and in AN solution upon excitation wavelength from the range of ligands absorption bands display NIR luminescence with the characteristic F-4(3/2) -> I-4(J) (J = 9/2, 11/2 and 13/2) transitions of the Nd3+ ion. The decay times of the F-4(3/2) state of Nd3+ equal 1.4 (293 K) and 2.3 mu s (77 K) (lambda(exc) = 350 nm) for the complexes in the solid-state as well as 0.43 (293 K) and 0.46 mu s (77 K) (lambda(exc) = 266 nm) for AN solution. (C) 2017 Elsevier B.V. All rights reserved.

Boron subphthalocyanines comprised of three isoindole units bridged by aza-linkages are attractive light harvesters on account of their intense low-energy absorptions. Herein, we present a class of related compounds, in which one or two isoindole units are substituted for thieno[3,4-c] pyrrole units - thieno-fused subporphyrazines. Such changes have remarkable consequences for the optical properties, as was revealed by combined experimental and theoretical studies. Thus, we find that the lowest-energy absorptions cover a much broader region with a significantly redshifted end-absorption and without compromising the absorption intensities. Thieno-fused subporphyrazines also underwent more readily oxidation and reduction, indicating an increased HOMO energy and decreased LUMO energy. In addition, they were found to readily co-crystallize with Buckminsterfullerene, C-60. Altogether, these findings render this new class of chromo-phores attractive candidates for light-harvesting applications.