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Compounds with multiple photoswitching units are appealing for complex photochemical control of molecular materials and nanostructures. Herein, we synthesized novel meta‐ and para‐ connected (related to the nitrogen of the indoline) azobenzene‐spiropyran dyads, in which the central benzene unit is shared by both switches. We investigated their photochemistry using static and time‐resolved transient absorption spectroscopy as well as quantum chemical calculations. In the meta‐compound, the individual components are photochemically decoupled due to the meta‐pattern. In the para‐compound the spiro‐connectivity leads to a bifunctional photoswitchable system with a red‐shifted absorption. The azobenzene and the spiropyran can thus be addressed and switched independently by light of appropriate wavelength. Through the different connectivity patterns two different orthogonally photoswitchable systems have been obtained which are promising candidates for complex applications of light control. [ABSTRACT FROM AUTHOR]

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The incorporation of heteroatoms into hydrocarbon compounds greatly expands the chemical space of molecular materials. In this context, B−N doping takes a center stage due to its isosterism with a C=C‐bond. Herein, we present a new and modular synthetic concept to access novel diazadiborabenzo[b]triphenylenes 7 a–h using the B−N doped biradical 16 as intermediate. Characterization of the photophysical properties revealed the emission spectra of the diazadibora benzo[b]triphenylenes 7 a–h can conveniently be tuned by small changes of the substitution on the boron‐atom. All of the diazadibora compounds show a short life‐time phosphorescence. Additionally, we were able to rationalize the excited‐state relaxation of the diazadiboraacene 7 a via intersystem crossing by quantum chemical calculations. The new synthetic strategy provides an elegant route to various novel B−N doped acenes with great potential for applications in molecular materials. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Photochemistry. In their Research Article (e202314112), Andreas Dreuw, Josef Wachtveitl, Hermann A. Wegner et al. report two novel photoswitch azobenzene‐spiropyran dyads. The study provides the basis for the development of new multichromic switches for information and energy storage or other applications...By Torben Saßmannshausen; Anne Kunz; Nils Oberhof; Friederike Schneider; Chavdar Slavov; Andreas Dreuw; Josef Wachtveitl and Hermann A. WegnerReported by Author; Author; Author; Author; Author; Author; Author; Author [Extracted from the article]

Quinoidal azaacenes with almost pure diradical character (y=0.95 to y=0.99) were synthesized. All compounds exhibit paramagnetic behavior investigated by EPR and NMR spectroscopy, and SQUID measurements, revealing thermally populated triplet states with an extremely low‐energy gap ΔEST′ of 0.58 to 1.0 kcal mol−1. The species are persistent in solution (half‐life≈14–21 h) and in the solid state they are stable for weeks. [ABSTRACT FROM AUTHOR]

Azoheteroarene photoswitches have attracted attention due to their unique properties. We present the stationary photochromism and ultrafast photoisomerization mechanism of thiophenylazobenzene (TphAB). It demonstrates impressive fatigue resistance and photoisomerization efficiency, and shows favorably separated (E)‐ and (Z)‐isomer absorption bands, allowing for highly selective photoconversion. The (Z)‐isomer of TphAB adopts an unusual orthogonal geometry where the thiophenyl group is perfectly perpendicular to the phenyl group. This geometry is stabilized by a rare lone‐pair⋅⋅⋅π interaction between the S atom and the phenyl group. The photoisomerization of TphAB occurs on the sub‐ps to ps timescale and is governed by this interaction. Therefore, the adoption and disruption of the orthogonal geometry requires significant movement along the inversion reaction coordinates (CNN and NNC angles). Our results establish TphAB as an excellent photoswitch with versatile properties that expand the application possibilities of AB derivatives. [ABSTRACT FROM AUTHOR]

The oxidative cyclodehydrogenation (often named the Scholl reaction) is still a powerful synthetic tool to construct even larger polycyclic aromatic hydrocarbons (PAHs) by multiple biaryl bond formations without the necessity of prior installation of reacting functional groups. Scholl‐type reactions are usually very selective although the resulting products bear sometimes some surprises, such as the formation of five‐membered instead of six‐membered rings or the unexpected migration of aryl moieties. There are a few examples, where chlorinated byproducts were found when FeCl3 was used as reagent. To our knowledge, the direct functionalization of PAHs during Scholl‐type cyclization by triflyloxylation has not been observed. Herein we describe the synthesis of functionalized PAHs by the formation of five‐membered rings and a regioselective triflyloxylation in one step. The triflyloxylated PAHs can be used as reactants for further transformation to even larger contorted PAHs. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Contorted two-dimensional aromatic molecules are fascinating synthetic targets because they are molecular 'cutouts' of nonplanar graphene structures, fullerenes, or carbon nanotubes. In most cases, the curvature is introduced by the implementation of either five-, seven-, or eight-membered rings into the fused aromatic plane. Curvature can also be generated for two-dimensional systems consisting of six-membered rings exclusively, by the introduction of cove or fjord regions. The synthesis of a polycyclic aromatic hydrocarbon (PAH) that contains two peripheral triptycene units and six tert-butyl substituents is described. As a result of steric repulsion, the structure is highly contorted with two phenylene blades of the peripheral triptycene units oriented almost coplanar with respect to each other at a distance of 16 Å, as has been verified by single crystal X-ray diffraction. The conformation is stable in solution even at a temperature of 150 °C. Additionally, internal tert-butyl groups could be selectively removed, allowing a UV/Vis-spectroscopic comparison of two structures with the same π-system, but different degrees of contortion. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Quantum mechanics/molecular mechanics calculations are employed to assign previously recorded experimental spectroscopic signatures of the intermediates occurring during the photo-induced repair of (6-4) photolesions by photolyases to specific molecular structures. Based on this close comparison of experiment and theory it is demonstrated that the acting repair mechanism involves proton transfer from the protonated His365 to the N3′ nitrogen of the lesion, which proceeds simultaneously with intramolecular OH transfer along an oxetane-like transition state. [ABSTRACT FROM AUTHOR]

Lange Polymerketten liegen stets verknotet vor. Analog zu Seilen werden Polymerketten durch Knoten erheblich geschwächt, und der Bindungsbruch erfolgt immer am Eingang oder Ausgang des Knotens. Ein molekulares Verständnis dieser Phänomene fehlt jedoch. Hier zeigen wir, dass der überwiegende Teil der mechanischen Energie einer verknoteten Polyethylenkette unter Zugspannung in den Torsionen entlang des gekrümmten Teils des Knotens gespeichert wird. Die Torsionen fungieren dabei als “Energietrichter”, die die mechanische Energie in direkter Nähe des Knotens lokalisieren. Auf diese Weise “würgt” der Knoten die Kette an seinem Eingang oder Ausgang, was zum Bindungsbruch bei deutlich geringeren Kräften als im Fall einer linearen, knotenfreien Kette führt. Unsere Untersuchungen erklären sowohl die Schwächung der Polymerkette als auch die Position des Bindungsbruchs und zeigen weiterhin, dass kovalente Bindungen nicht übermäßig stark gestreckt werden müssen, um zu reißen. Der Knoten platzt: Polymerketten werden durch einen Knoten erheblich geschwächt und reißen an dessen „Eingang”︁ oder „Ausgang”︁, da die Torsionen im gekrümmten Teil der Kette als Energietrichter fungieren und die mechanische Energie lokalisieren. Dadurch schnürt der Knoten die Kette in seiner Nähe ab. Demzufolge müssen Bindungen nicht übermäßig stark gestreckt werden, um in mechanochemischen Experimenten gebrochen zu werden. [ABSTRACT FROM AUTHOR]

Chem. 30/2020) Keywords: acenes; heteroaromatics; radicals; structure elucidation; synthetic methods EN acenes heteroaromatics radicals structure elucidation synthetic methods 12644 12644 1 07/15/20 20200720 NES 200720 B Diradikal-Puzzle b Der Zusammenbau der richtigen Kombination aus einem Azaacen, Phenoxylgruppen und Dithienobenzol-Regioisomeren wird mit chinoidalen Azacenen mit nahezu reinem Diradikalcharakter belohnt, die im festen Zustand über Wochen stabil und auch in Lösung haltbar sind. Acenes, heteroaromatics, radicals, structure elucidation, synthetic methods. [Extracted from the article]

Unter Arrest Zwei tert ‐ Butyl ‐ Gruppen beeinflussen die konformative Flexibilität und die Lichtemission eines Hexabenzoovalens. In ihrer Zuschrift auf S. 15823 ff. beschreiben M. Mastalerz et al., wie sich eine flexible Vorläuferverbindung durch oxidative Cyclodehydrierung zu einem orange emittierenden Hexabenzoovalen konformativ einfangen lässt. Eine selektive Dealkylierung gibt dem System seine Bewegungsfreiheit zurück – es emittiert grün. [ABSTRACT FROM AUTHOR]