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Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
Published on: February 7, 2022
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Acid Violet 3: A Base-Activated Water-Soluble Photoswitch
Ing-Angsara Thongchai1, Zachary J Knepp1, Domenica R Fertal1
1Department of Chemistry, Lehigh University, 6 E. Packer Avenue, Bethlehem, Pennsylvania 18015, United States.
The Journal of Physical Chemistry. A
|January 18, 2024
Summary
Proton concentration controls the photoisomerization of acid violet 3 (AV3). The deprotonated form undergoes photoisomerization, while protonated forms do not, offering a pathway for pharmaceutical applications.
Area of Science:
- Dye photophysics
- Computational chemistry
- Spectroscopy
Background:
- Acidic azo dyes like acid violet 3 (AV3) possess vibrant colors but have underutilized potential in applications like photosensing and photomedicine.
- Understanding and controlling their photophysical properties is key to unlocking new applications.
Purpose of the Study:
- To explore the proton-controlled photophysics of acid violet 3 (AV3).
- To elucidate the photoisomerization mechanism of AV3 across different protonation states.
Main Methods:
- Density functional theory (DFT) was employed to predict ground- and excited-state potential energy surfaces.
- Spectroscopic experiments were used to confirm the proposed photoisomerization mechanism.
Main Results:
- The deprotonated AV3-H undergoes photoisomerization via dihedral rotation upon blue light excitation (453 nm).
- The *cis*-isomer of AV3-H reverts through a mixed rotational and inversion mechanism.
- Protonated forms (AV3 and AV3+H) do not photoisomerize due to a lack of driving force in the excited state.
- Lowered ground-state dihedral rotation reversion barrier observed when the azo bond is acidic.
Conclusions:
- Protonation state critically influences the photoisomerization pathway of AV3.
- Insights into AV3's reactivity across a wide pH range provide a roadmap for controlling its behavior.
- AV3's tunable photophysics make it a promising candidate for pharmaceutical development.
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