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Ultra‐Low Molecular Weight Photoswitchable Hydrogelators
Author(s) -
Larik Fayaz Ali,
Fillbrook Lucy L.,
Nurttila Sandra S.,
Martin Adam D.,
Kuchel Rhian P.,
Al Taief Karrar,
Bhadbhade Mohan,
Beves Jonathon E.,
Thordarson Pall
Publication year - 2021
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.202015703
Subject(s) - self healing hydrogels , rhodamine , chemistry , photochromism , photochemistry , transmission electron microscopy , visible spectrum , rhodamine b , materials science , nanotechnology , chemical engineering , polymer chemistry , fluorescence , optoelectronics , organic chemistry , photocatalysis , optics , catalysis , physics , engineering
Two photoswitchable arylazopyrozoles form hydrogels at a concentration of 1.2 % (w/v). With a molecular weight of 258.28 g mol −1 , these are the lowest known molecular weight hydrogelators that respond reversibly to light. Photoswitching of the E‐ to the Z‐form by exposure to 365 nm light results in a macroscopic gel→sol transition; nearly an order of magnitude reduction in the measured elastic and loss moduli. In the case of the meta‐arylazopyrozole, cryogenic transmission electron microscopy suggests that the 29±7 nm wide sheets in the E‐gel state narrow to 13±2 nm upon photoswitching to the predominantly Z‐solution state. Photoswitching for meta‐arylazopyrozole is reversible through cycles of 365 nm and 520 nm excitation with little fatigue. The release of a rhodamine B dye encapsulated in gels formed by the arylazopyrozoles is accelerated more than 20‐fold upon photoswitching with 365 nm light, demonstrating these materials are suitable for light‐controlled cargo release.