Reversible, Red-Shifted Photoisomerization in Protonated Azobenzenes

Jonas Rickhoff, Niklas B. Arndt, Marcus Böckmann, Nikos L. Doltsinis, Bart Jan Ravoo, Luuk Kortekaas*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

8 Citations (Scopus)
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Azobenzenes are among the best-studied molecular photoswitches and play a key role in the search for red-shifted photoresponsive materials for extended applications. Currently, most approaches deal with aromatic substitution patterns to achieve visible light application, on occasion paired with protonation to yield red-shifted absorption of the azonium species. Appropriate substitution patterns are essential to stabilize the latter approach, as conventional acids are known to induce a fast Z- to E-conversion. Here, we show that steady-state protonation of the azo-bridge instead is possible in simple azobenzenes when the pKaof the acid is low enough, yielding both the Z- and E-azonium as supported by UV-vis- and 1H NMR spectroscopy as well as density functional theory calculations. Moreover, the steady-state protonation of para-methoxyazobenzene, specifically, yields photoisomerizable azonium ions in which the direction of switching is essentially reversed, that is, visible light produces the out-of-equilibrium Z-azonium. Although the current conditions render the visible light photoswitch unsuitable for in vivo and material application, the demonstrated understanding of simple azobenzenes paves the way for a great range of further work on this already widely studied photoswitch.

Original languageEnglish
Pages (from-to)10605-10612
Number of pages8
JournalJournal of Organic Chemistry
Issue number16
Publication statusPublished - 19-Aug-2022

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