The use of DFT computational method to study the effect of physical factors on the pH range of color change of Azo indicator: Methyl red and Methyl Orange
Subject Areas :ahdieh Sadeghpour 1 , Farzaneh Zanjanchi 2
1 - Department of Chemistry, Takestan Branch, Islamic Azad University, Takestan, Iran
2 - Department of Chemistry, Takestan Branch, Islamic Azad University, Takestan, Iran
Keywords: Azo color, temperature, Indicators, Halochromic, density functional theory (DFT) pH, Pressure,
Abstract :
Azo dyes are an important group of indicator that are used as pH sensors and can also be used in the structure of new sensors. In this research, a theoretical study has been conducted on the role of physical factors on the behavior of azo-halochromic dyes. The azo dyes studied in this paper are methyl red and methyl orange.The values obtained for the totomeric equilibrium constant show that the azo form of these indicators is more stable than their hydrazone form. Therefore, in this paper, only the relationship between acid-base equiblirum of azo form indicators is investigated. Also, the range of color change of pH indicators and the effect of physical factors on acid-base equiblirum of indicators will be examined. Studies show that increasing the temperature reduces the pH range of the color change of the indicators but the effect of pressure will decrease with increasing pressure, and the type of indicator will not affect this result.Studies also show that increasing polarity of the solvent and the use of isotopes of atoms will decrease the pH range of color change of the indicators. The method used in this research can be help the development of pH-sensitive sensors.
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