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Ultra-Low Molecular Weight Photoswitchable Hydrogelators

preprint
revised on 15.09.2020 and posted on 16.09.2020 by Fayaz Larik, Lucy Fillbrook, Sandra Nurttila, Adam D Martin, Rhiannon P. Kuchel, Karrar Al Taief, Mohan Bhadbhade, Jonathon Beves, Pall Thordarson
Photoswitchable arylazopyrozoles 2 and 3 form hydrogels at a concentration of 1.2% (w/v). With a molecular weight of 258.11 g/mol, these are the lowest known molecular weight hydrogelators that respond reversibly to light. Single-crystal X-ray structures show anisotropic aggregation of 2 and 3 is driven by in-plane hydrogen bonding interactions and 𝝅 - 𝝅 stacking. Photoswitching of 2 and 3 from the E- to the Z-form by 365 nm light results in a macrocopic gel→sol transition; nearly an order of magnitude reduction in the measured elastic and loss moduli. Cryogenic transmission electron microscopy suggests that the 29±7 nm wide sheets in the E-2 gel state narrow to 13±2 nm upon photoswitching to the predominantly Z-2 solution state. In the case of 2, photoswitching 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 from 2 and 3 can be accelerated more than 20-fold upon photoswitching with 365 nm light, demonstrating these materials are suitable for light-controlled cargo release.

Funding

Performing work through actively-driven self-assembled systems

Australian Research Council

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Controlling chemistry with light-powered molecular machines

Australian Research Council

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ARC Centre of Excellence in Convergent Bio-Nano Science and Technology

Australian Research Council

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History

Email Address of Submitting Author

p.thordarson@unsw.edu.au

Institution

UNSW Sydney

Country

Australia

ORCID For Submitting Author

0000-0002-1200-8814

Declaration of Conflict of Interest

No conflict of interest

Version Notes

This is version 2 (minor spelling mistakes fixed)

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