Related Experiment Video
Updated: Jul 13, 2026
09:33
Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
Published on: February 7, 2022
Photocontrolled Hydrogen Bonding in Main-Chain Azobenzene Polymers.
Ayaulym Abilova1, Rithwik Ghanta1, Abike Sholeye1
1Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
ACS Macro Letters
|July 11, 2026
Summary
Light-induced isomerization of azobenzene polymers reversibly alters material properties. Hydrogen bonding significantly impacts thermomechanical behavior, enabling tunable polymer characteristics through targeted isomer populations.
Area of Science:
- Polymer Chemistry
- Materials Science
- Photochemistry
Background:
- Azobenzene polymers exhibit light-driven property changes via trans-cis photoisomerization.
- Properties at intermediate isomer concentrations, especially in main-chain polymers, are not well understood.
- Intermolecular interactions, like hydrogen bonding, can influence photoresponsive polymer behavior.
Purpose of the Study:
- To synthesize and compare azobenzene-containing polymers with and without urethane hydrogen-bonding motifs.
- To investigate the impact of trans-cis isomerization on thermomechanical properties and polymer structure.
- To explore the role of intermolecular interactions in light-modulated polymer behavior.
Main Methods:
- Synthesis of structurally analogous azobenzene polymers.
- Fourier-transform infrared (FTIR) spectroscopy to monitor isomerization and hydrogen bonding.
- Differential scanning calorimetry (DSC) to determine glass transition temperature (Tg).
- Shear rheology to assess dynamic moduli and material solidification.
Main Results:
- Trans-cis isomerization disrupted urethane hydrogen bonding, reducing crystallinity and lowering Tg by ~30 °C.
- The effect of isomerization on Tg was well-described by a modified Fox model, indicating tunable local interactions.
- Non-hydrogen-bonding polymers required higher cis isomer content for photoinduced melting and showed minimal Tg change.
- Shear rheology demonstrated a three-orders-of-magnitude change in dynamic moduli due to altered interchain associations and segmental mobility.
Conclusions:
- Targeted isomer populations and intermolecular interactions provide a strategy for post-polymerization modulation of thermomechanical properties.
- Hydrogen bonding plays a crucial role in the photoresponsive behavior of azobenzene polymers.
- Understanding these relationships allows for the design of advanced photo-switchable materials.
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