Theoretical insights into a colorimetric azo-based probe to detect copper ions

Area of Science:

• Chemical Sensing
• Materials Science
• Computational Chemistry

Background:

• Development of selective colorimetric probes for metal ion detection is crucial for environmental and biological monitoring.
• Azobenzene derivatives offer tunable optical properties suitable for sensing applications.
• Understanding the complexation mechanism at a molecular level is key to designing efficient probes.

Purpose of the Study:

• To report a novel azobenzene-based probe (AZO 1) for selective colorimetric detection of Cu²⁺.
• To investigate the mechanism underlying the probe's color change using computational methods.
• To elucidate the role of stoichiometry, solvent, and molecular conformation in the sensing process.

Main Methods:

• Synthesis and characterization of the azobenzene-based probe (AZO 1).
• Colorimetric detection experiments to assess selectivity and response to Cu²⁺.
• Density Functional Theory (DFT) calculations to study binding energies, electronic transitions, and conformational changes.

Main Results:

• AZO 1 demonstrated high selectivity for Cu²⁺, exhibiting a visible red-to-yellow color change.
• DFT calculations indicated a 1:1 complexation is responsible for the significant color change, driven by HOMO-LUMO transitions.
• The probe's *o*-methoxy group facilitates octahedral complex formation, and conformational changes alter intramolecular charge transfer (ICT), causing the color shift.

Conclusions:

• AZO 1 is an effective colorimetric sensor for Cu²⁺ with a clear visual output.
• The study provides a detailed mechanistic understanding of the probe's response, validated by DFT.
• Molecular design considerations, including chelating groups and conformational flexibility, are critical for optimizing sensor performance.