Spiropyran Photoisomerization Dynamics in Multiresponsive Hydrogels
Amos Meeks1, Michael M Lerch1,2, Thomas B H Schroeder1
1John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States.
Journal of the American Chemical Society
|December 29, 2021
Summary
Responsive hydrogels use spiropyrans for light-actuated applications. Acidic conditions and acrylic acid monomers promote faster spiropyran switching, crucial for hydrogel actuators and nonlinear optics.
Area of Science:
- Polymer Chemistry
- Materials Science
- Photochemistry
Background:
- Spiropyran-functionalized hydrogels enable reversible photoactuation for diverse applications.
- Understanding co-monomer effects on spiropyran switching dynamics is key for tailored hydrogel design.
- Combined stimuli (light, pH, temperature) can alter spiropyran behavior unpredictably.
Purpose of the Study:
- Investigate how co-monomer composition influences spiropyran isomerization dynamics in hydrogels.
- Elucidate the impact of pH and temperature-responsive co-monomers on spiropyran switching.
- Develop a model to explain observed fluorescence dynamics in spiropyran-hydrogels.
Main Methods:
- Synthesized spiropyran-modified hydrogels using four common precursors: acrylamide, acrylic acid, N-isopropylacrylamide, and 2-(dimethylamino)ethyl methacrylate.
- Employed UV-vis spectroscopy and time-dependent fluorescence intensity measurements.
- Developed and applied an analytical model incorporating H-aggregated merocyanine and light-triggered disaggregation.
Main Results:
- Observed unusual nonmonotonic, triexponential fluorescence dynamics in acidic/neutral gels under 405 nm irradiation.
- The established spiropyran-merocyanine interconversion model and hydrolysis could not explain these dynamics.
- The new analytical model, including H-aggregated merocyanine, accurately fitted the experimental fluorescence data.
Conclusions:
- An acidic internal gel environment, achieved with acrylic acid monomers, promotes rapid and complete conversion to the hydrophobic spiropyran form.
- Minimizing aggregate concentration is essential for efficient spiropyran switching.
- Findings are critical for optimizing spiropyran-functionalized hydrogel actuators and advancing nonlinear optical computing.
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