A series of substituted azothiophenes was prepared and investigated toward their isomerization behavior. Compared to azobenzene (AB), the presented compounds showed red‐shifted absorption and almost quantitative photoisomerization to their (Z) states. Furthermore, it was found that electron‐withdrawing substitution on the phenyl moiety increases, while electron‐donating substitution decreases the thermal half‐lives of the (Z)‐isomers due to higher or lower stabilization by a lone pair–π interaction. Additionally, computational analysis of the isomerization revealed that a pure singlet state transition state is unlikely in azothiophenes. A pathway via intersystem crossing to a triplet energy surface of lower energy than the singlet surface provided a better fit with experimental data of the (Z)→(E) isomerization. The insights gained in this study provide the necessary guidelines to design effective thiophenylazo‐photoswitches for applications in photopharmacology, material sciences, or solar energy harvesting applications.

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.

Multi-state photoswitchable compounds are highly attractive for application in data storage or multi-responsive materials. Herein, a trisazobenzene macrocycle is presented, which can be switched selectively into three individual states.

The performance of molecular solar thermal energy storage systems (MOST) depends amongst others on the amount of energy stored. Azobenzenes have been investigated as high‐potential materials for MOST applications. In the present study it could be shown that intermolecular attractive London dispersion interactions stabilize the (E)‐isomer in bisazobenzene that is linked by different alkyl bridges. Differential scanning calorimetry (DSC) measurements revealed, that this interaction leads to an increased storage energy per azo‐unit of more than 3 kcal/mol compared to the parent azobenzene. The origin of this effect has been supported by computation as well as X‐ray analysis. In the solid state structure attractive London dispersion interactions between the C−H of the alkyl bridge and the π‐system of the azobenzene could be clearly assigned. This concept will be highly useful in designing more effective MOST systems in the future.

Continuous irradiation of the thermodynamically stable ( Z, Z)-cyclobisazobenzene does not lead to accumulation of a ( Z, E) or ( E, E) isomer as one might expect. Our combined experimental and computational investigation reveals that Z → E photoisomerization still takes place on an ultrafast time scale but induces large ring strain in the macrocycle, which leads to a very fast thermal back-isomerization, preventing photostationary accumulation of ( E)-isomers.

A stereoselective domino inverse electrondemand Diels−Alder/amine group transfer reaction catalyzed by a bidentate Lewis acid provides 1-amino-1,2-dihydronaphthalenes, a core structure in many bioactive compounds. A concerted mechanism is proposed based on experimental studies as well as DFT computations demonstrating a new general reactivity scheme. The broad scope of the reaction was evaluated by variation of all three starting compounds, phthalazines, aldehydes, and amines. Scalability was demonstrated by a gram scale reaction without diminished yield.

Single crystals of compound 3a were obtained by diffusion of n-pentane into a solution of 3a in CHCl 3 . Some single crystals of C 26 H 20 N 4 were transferred into inert oil (Fomblin Y, 1600 cst, Sigma Aldrich GmbH, Steinheim, Germany). A suitable crystal was then mounted onto a micromount sample holder (MiTeGen, Dual-Thickness MicroMounts, 100 μm) and immediately placed into a stream of cold N 2 (100K) inside the diffractometer (Bruker D8 Venture, Bruker, Karlsruhe, Germany). Mo-Kα-radiation (λ = 71.073 pm) from an Incoatec microsource was used. After unit cell determination, the reflection intensities were collected. The software of the diffractometer (Bruker Apex III) [1] was used for data collection, unit cell determination and processing of the raw data. Absorption correction was applied using SADABS. [2] The structure was solved by intrinsic phasing using SHELXT [3] , full matrix least squares refinement on |F²| using SHELXL-2014/7 [4] as implemented in the Olex2 program [5] was used for structure refinement.All non-hydrogen atoms could be refined with anisotropic displacement parameters. All hydrogen atoms were refined using AFIX codes of ShelXL-2014. The program Diamond was used for graphical representations [6] . The CCDC reference number is 1535008. R indices (all data)R 1 = 0.0837, wR 2 = 0.1394Largest diff. peak and hole 0.366 and -0.248 e -/ų

The understanding and control of the light-induced isomerization of azobenzenes as one of the most important classes of molecular switches is crucial for the design of light-responsive materials using this entity. Herein, we present the stabilization of metastable (Z)-azobenzenes by London dispersion interactions, even in the presence of comparably stronger hydrogen bonds in various solvents. The Z→E isomerization rates of several N-substituted 4,4′-bis(4-aminobenzyl)azobenzenes were measured. An intramolecular stabilization was observed and explained by the interplay of intramolecular amide and carbamate hydrogen bonds as well as London dispersion interactions. Whereas in toluene, 1,4-dioxane and tert-butyl methyl ether the hydrogen bonds dominate, the variation in stabilization of the different substituted azobenzenes in dimethyl sulfoxide can be rationalized by London dispersion interactions. These findings were supported by conformational analysis and DFT computations and reveal low-energy London dispersion forces to be a significant factor, even in the presence of hydrogen bonds.