Tautomerism and Proton Transfer Dynamics in Azo Dyes
Summary
Azo dyes are characterised by the –N=N– chromophore and exhibit dynamic equilibria between azo and hydrazo tautomers. This tautomerism, often coupled with keto–enol interconversions in substituted systems, governs optical absorption, emissive behaviour and photostability. Proton transfer processes—both in the electronic ground state and upon photoexcitation—play a pivotal role in defining colour tuning, switching efficiency and sensor response. Solvent polarity, hydrogen‐bonding networks and external fields can shift tautomeric equilibria, modulate intramolecular proton‐transfer pathways and influence rates of excited‐state intramolecular proton transfer (ESIPT). Contemporary investigations integrate spectroscopic, crystallographic and computational techniques to elucidate the energy landscapes that underlie proton motion. Such insights are crucial for the design of advanced materials in areas ranging from optical data storage and molecular switches to responsive coatings and biological probes.
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Tautomerism and Proton Transfer Dynamics in Azo Dyes publication trend
The graph below shows the total number of articles in tautomerism and proton transfer dynamics in azo dyes across all publications each year (not limited to Nature Index journals).
Technical terms
Tautomerism: Equilibrium between isomers that differ by the position of a proton and the connectivity of double bonds.
Enol–keto tautomerism: Proton migration between hydroxyl and carbonyl groups, interconverting an enol form and its keto counterpart.
Azo–hydrazo tautomerism: Interconversion between the azo linkage (–N=N–) and the hydrazo linkage (–NH–NH–).
Excited-State Intramolecular Proton Transfer (ESIPT): Rapid transfer of a proton within a molecule following absorption of light, leading to altered emissive properties.
Proton crane: A molecular scaffold designed to convey a proton over extended intramolecular distances via sequential relay units under excitation.
References
- Tautomerism in Azo and Azomethyne Dyes: When and If Theory Meets Experiment. Molecules (2019).
- Experimental and Computational Study of Novel Pyrazole Azo Dyes as Colored Materials for Light Color Paints. Materials (2022).
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