ortho‐Fluoroazobenzenes: Visible Light Switches with Very Long‐Lived Z Isomers |
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Authors: | Christopher Knie Manuel Utecht Fangli Zhao Hannes Kulla Sergey Kovalenko Prof Albert M Brouwer Prof Peter Saalfrank Prof Stefan Hecht Dr David Bléger |
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Institution: | 1. Department of Chemistry, Humboldt‐Universit?t zu Berlin, Brook‐Taylor‐Strasse 2, 12489 Berlin (Germany);2. Institut für Chemie, Universit?t Potsdam, Karl‐Liebknecht‐Strasse 24‐25, 14476 Potsdam Golm (Germany);3. Van't Hoff Institute for Molecular Sciences, University of Amsterdam, P.O. Box 94157, 1090 GD Amsterdam (The Netherlands) |
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Abstract: | Improving the photochemical properties of molecular photoswitches is crucial for the development of light‐responsive systems in materials and life sciences. ortho‐Fluoroazobenzenes are a new class of rationally designed photochromic azo compounds with optimized properties, such as the ability to isomerize with visible light only, high photoconversions, and unprecedented robust bistable character. Introducing σ‐electron‐withdrawing F atoms ortho to the N?N unit leads to both an effective separation of the n→π* bands of the E and Z isomers, thus offering the possibility of using these two transitions for selectively inducing E/Z isomerizations, and greatly enhanced thermal stability of the Z isomers. Additional para‐electron‐withdrawing groups (EWGs) work in concert with ortho‐F atoms, giving rise to enhanced separation of the n→π* transitions. A comprehensive study of the effect of substitution on the key photochemical properties of ortho‐fluoroazobenzenes is reported herein. In particular, the position, number, and nature of the EWGs have been varied, and the visible light photoconversions, quantum yields of isomerization, and thermal stabilities have been measured and rationalized by DFT calculations. |
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Keywords: | azobenzenes photochromism photoswitches substituent effects visible light |
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