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Investigating the halochromic properties of azo dyes in an aqueous environment by using a combined experimental and theoretical approach

By Thierry De Meyer, Karen Hemelsoet, Lien Van der Schueren, Ewald Pauwels, Karen De Clerck and Veronique Van Speybroeck

Abstract

The halochromism in solution of a prototypical example of an azo dye, ethyl orange, was investigated by using a combined theoretical and experimental approach. Experimental UV/Vis and Raman spectroscopy pointed towards a structural change of the azo dye with changing pH value (in the range pH 53). The pH-sensitive behavior was modeled through a series of ab initio computations on the neutral and various singly and doubly protonated structures. For this purpose, contemporary DFT functionals (B3LYP, CAM-B3LYP, and M06) were used in combination with implicit modeling of the water solvent environment. Static calculations were successful in assigning the most-probable protonation site. However, to fully understand the origin of the main absorption peaks, a molecular dynamics simulation study in a water molecular environment was used in combination with time-dependent DFT (TD-DFT) calculations to deduce average UV/Vis spectra that take into account the flexibility of the dye and the explicit interactions with the surrounding water molecules. This procedure allowed us to achieve a remarkable agreement between the theoretical and experimental UV/Vis spectrum and enabled us to fully unravel the pH-sensitive behavior of ethyl orange in aqueous environment

Topics: Chemistry, density functional calculations, pigments, azo compounds, dyes, SOLVATION MODELS, ELECTRON-DENSITY, BIOMOLECULAR SYSTEMS, TD-DFT, halochromism, UV, Vis spectroscopy, DENSITY-FUNCTIONAL THEORY, SPACE GAUSSIAN PSEUDOPOTENTIALS, PH-SENSITIVE FUNCTION, MOLECULAR-DYNAMICS, EXCITED-STATES, TEXTILE MATERIALS
Publisher: 'Wiley'
Year: 2012
DOI identifier: 10.1002/chem.201103633
OAI identifier: oai:archive.ugent.be:2963923
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