Reversible, Red-Shifted Photoisomerization in Protonated Azobenzenes
Year: 2022
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide 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 p K a of the acid is low enough, yielding both the Z - and E -azonium as supported by UV–vis- and 1 H 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.
Source: The Journal of Organic Chemistry
Institutions: University of Münster, University of Groningen
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $5,000
OpenAlex ID: W4289593517