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Updated: May 8, 2026

Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
Published on: February 7, 2022
Halogen bond-driven azo-hydrazone tautomerisation: a computational study
Antti Siiskonen1, Arri Priimagi2
1Faculty of Engineering and Natural Sciences, Smart Photonic Materials, Tampere University, Korkeakoulunkatu 3, Tampere, 33720, Finland.
Halogen bonding influences azo-hydrazone tautomerization in azobenzenes, potentially inverting tautomeric preference and enabling tunable sensing applications. This study explores halogen bonding effects on hydroxyazobenzenes and related compounds.
Area of Science:
- Supramolecular Chemistry
- Computational Chemistry
- Materials Science
Background:
- Azo-hydrazone tautomerization impacts azobenzene photoswitching and properties.
- Non-covalent interactions, like halogen bonding, can alter tautomeric equilibrium.
- Understanding these interactions is key for designing functional azobenzene systems.
Purpose of the Study:
- Investigate the influence of halogen bonding on azo-hydrazone tautomerization in hydroxyazobenzenes and azonaphthalene derivatives.
- Examine the role of alkoxy groups in modulating tautomerization and halogen bonding.
- Explore self-complementary halogen-bonded dimers for potential sensing applications.
Main Methods:
- Density functional theory (DFT) calculations using M06-2X/DGDZVP.
- Geometry optimizations and interaction energy calculations.
- Analysis of wavefunctions using AIMAll for interacting quantum atom analysis.
Main Results:
- Halogen bonding generally favors the hydrazone tautomer.
- Tautomeric preference can be inverted when the azo tautomer is only slightly more stable.
- Temperature affects halogen bonding strength and tautomeric equilibrium.
Conclusions:
- Halogen bonding offers a tunable mechanism to control azo-hydrazone tautomerization.
- These systems show promise for developing novel sensing platforms.
- Methoxy and nitro groups influence halogen bonding and tautomerization.
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