A physiochemical study of azo dyes: DFT based ESIPT process.

Area of Science:

• Organic Chemistry
• Photophysics
• Computational Chemistry

Background:

• Azo dyes and Schiff bases are important organic compounds with diverse applications.
• Understanding excited state intramolecular proton transfer (ESIPT) is crucial for designing fluorescent materials.
• Dual emission phenomena in organic molecules often arise from multiple ground-state isomers or excited-state processes.

Purpose of the Study:

• To synthesize and characterize novel azo linked dye derivatives.
• To investigate the mechanism of excited state intramolecular proton transfer (ESIPT) in a hydroxy Schiff base.
• To explore the potential of the synthesized hydroxy Schiff base as a fluorescence sensor for metal ions.

Main Methods:

• Synthesis and characterization of azo linked dye derivatives using NMR, mass spectrometry, and elemental analysis.
• Analysis of excited state intramolecular proton transfer (ESIPT) and dual emission properties.
• Density Functional Theory (DFT) calculations for energy, dipole moment, and charge distribution.
• Potential Energy Surface (PES) calculations to determine energy barriers for rotamer interconversion.
• Spectroscopic studies involving varying base concentration and fluorescence quenching with metal ions.

Main Results:

• Two distinct ground state isomers were identified as responsible for the observed dual emission.
• DFT and PES calculations supported the occurrence of the ESIPT process and highlighted differences in rotamer interconversion barriers between ground and excited states.
• The presence of two isobestic points confirmed the equilibrium between trans enol, anion, and cis enol forms upon base addition.
• Fluorescence quenching experiments demonstrated the selective detection of Cu(2+) ions by the hydroxy Schiff base.

Conclusions:

• The synthesized azo linked dye derivatives exhibit interesting photophysical properties.
• The hydroxy Schiff base undergoes ESIPT, driven by distinct ground state isomers, leading to dual emission.
• The molecule exists in equilibrium between different forms in the presence of base, as evidenced by isobestic points.
• The hydroxy Schiff base shows promise as a selective and sensitive fluorescence sensor for Cu(2+) detection.