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Tuning azoheteroarene photoswitch performance through heteroaryl design

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Title: Tuning azoheteroarene photoswitch performance through heteroaryl design
Authors: Calbo, J
Weston, CE
White, A
Rzepa, H
Contreras-García, J
Fuchter, MJ
Item Type: Journal Article
Abstract: Photoswitchable compounds, which can be reversibly switched between two isomers by light, continue to attract significant attention for a wide array of applications. Azoheteroarenes represent a relatively new but understudied type of photoswitch, where one of the aryl rings from the conventional azobenzene class has been replaced with a five-membered heteroaromatic ring. Initial studies have suggested the azoheteroarenes - the arylazopyrazoles in particular - to have excellent photoswitching properties (quantitative switching and long Z isomer half-life). Here we present a systematic computational and experimental study to elucidate the origin of the long thermal half-lives and excellent addressability of the arylazopyrazoles, and apply this understanding to determine important structure-property relationships for a wide array of comparable azoheteroaryl photoswitches. We identify compounds with Z isomer half-lives ranging from seconds to hours, to days and to years, and variable absorption characteristics; all through tuning of the heteraromatic ring. Conformation perhaps plays the largest role in determining such properties; where the compounds with the longest isomerization half-lives adopt a T-shaped ground state Z isomer conformation and proceed through a T-shaped isomerization pathway, whereas the most complete photoswitching is achieved for compounds that have a twisted (rather than T-shaped) Z-isomer conformation. By balancing these factors, we report a new azopyrazole 3pzH, which can be quantitatively switched to its Z-isomer (>98%) with 355 nm irradiation, near-quantitatively (97%) switched back to the E isomer with 532 nm irradiation, and has a very long half-life for thermal isomerisation (t1/2 = 74 d at 25 °C). Given the large tunability of their properties, the predictive nature of their performance, and the other functional opportunities afforded by usage of a heteroaromatic system, we believe the azoheteroaryl photoswitches to have huge potential in a wide range of optically addressable applications.
Issue Date: 23-Dec-2016
Date of Acceptance: 1-Dec-2016
URI: http://hdl.handle.net/10044/1/43629
DOI: https://dx.doi.org/10.1021/jacs.6b11626
ISSN: 1520-5126
Publisher: American Chemical Society
Start Page: 1261
End Page: 1274
Journal / Book Title: Journal of the American Chemical Society
Volume: 139
Issue: 3
Copyright Statement: © 2016 American Chemical Society. This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
Sponsor/Funder: Engineering & Physical Science Research Council (EPSRC)
Funder's Grant Number: N/A
Keywords: Science & Technology
Physical Sciences
Chemistry, Multidisciplinary
General Chemistry
03 Chemical Sciences
Publication Status: Published
Conference Place: United States
Appears in Collections:Chemistry
Faculty of Natural Sciences