Thiophenylazobenzene: An Alternative Photoisomerization Controlled by Lone‐Pair⋅⋅⋅π Interaction

• Published in: Angewandte Chemie Vol. 132; no. 1; pp. 388 - 395
• Main Authors: Slavov, Chavdar, Yang, Chong, Heindl, Andreas H., Wegner, Hermann A., Dreuw, Andreas, Wachtveitl, Josef
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 02.01.2020
• Subjects: Absorption spectra; Angles (geometry); Chemistry; Disruption; Fatigue strength; Geometry; Isomerisierungsmechanismen; Photochromie; Photochromism; Photoschalter; Thiophenylazobenzol; Zeitaufgelöste Spektroskopie
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.201909739

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. Mein eigener Weg: Thiophenylazobenzol ist ein Azoheteroaren‐Photoschalter mit beeindruckendem Ermüdungswiderstand, hoher Photoisomerisierungseffizienz und hoch selektiver Photokonvertierung. Sein (Z)‐Isomer wird in einer unüblichen orthogonalen Geometrie durch eine intramolekulare Lonepair‐π‐Wechselwirkung stabilisiert. Diese steuert die ultraschnelle Photoisomerisierung mit signifikanter Bewegung entlang der Inversions‐Reaktionskoordinate.