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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., My own way: Thiophenylazobenzene is a sulfur‐based azoheteroarene photoswitch with impressive fatigue resistance, photoisomerization efficiency, and highly selective photoconversion. Its (Z)‐isomer adopts an unusual orthogonal geometry stabilized by an intramolecular lone‐pair⋅⋅⋅π interaction governing the ultrafast photoisomerization, which requires a mechanism involving significant movement along the inversion reaction coordinate.

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.

Kraftsonden ermoglichen die Echtzeitmessung von Kraften, die an verschiedenen Stellen groser Molekule wirken, und eignen sich dazu, Strukturanderungen in Makromolekulen, z. B. Faltungsprozesse, zu erforschen.1–10 Die daraus gewonnen Informationen sind fur unser Verstandnis mechanochemischer Reaktivitat grundlegend.2, 3, 6, 7 Zu diesem Zweck konnen kleine molekulare Kraftsonden in grose Molekule eingefugt werden.2, 3, 11–13 Einige der verfugbaren Systeme beruhen auf Mechanochromie, der Anderung des UV/Vis-Absorptionsspektrums eines Molekuls als Resultat einer auseren Kraft.1, 14 Hier prasentieren wir die neuartige Idee, molekulare Kraftsonden zu verwenden, deren Punktgruppensymmetrie infolge einer mechanischen Deformation verringert wird. Dies bewirkt ausgepragte Anderungen in optischen Spektren der deformierten Molekule, welche durch computergestutzte Methoden ermittelt wurden. Die Anderungen sind reversibel und selbst bei geringen auseren Kraften zu beobachten.