The influence of physical factors on the halochromic behavior of the pH-sensitive sulfonphthaleine dyes: a DFT study
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ORIGINAL PAPER
The influence of physical factors on the halochromic behavior of the pH‑sensitive sulfonphthaleine dyes: a DFT study Maryam Mojbafan1 · Farzaneh Zanjanchi1 · Mahboubeh Taherkhani1 Received: 17 February 2020 / Accepted: 30 May 2020 © Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract Sulfonphthaleine dyes are important class of pH indicators with some applications in novel sensors. In this paper, the authors present a theoretical study to elucidate the effect of physical factors on the halochromic behavior of the sulfonphthaleine dyes. The studied sulfonphthaleine dyes are phenol red, cresol red, bromophenol blue and the physical factors such as temperature, pressure, dielectric constant of solvent and isotope type of constituent atoms are taken into account. In the meantime, changes of pH of the color change of the indicators, ∆pH, with the physical factors in the acid–base equilibrium of the indicators are studied. To this end, Enthalpy change, ∆Ha, entropy change, ∆Sa, Gibbs free energy change, ∆Ga, and equilibrium constant of ionization process of indicators, Ka, are calculated for the equilibrium reaction under different conditions; then their values are interpreted by the laws of thermodynamics and statistical thermodynamics. The results show that ∆pH is positive by increasing temperature at any pressure, increasing pressure at any temperature, decreasing the polarity of the solvent used, and using isotopes of constituent atoms. The effect of temperature and pressure on ∆pH is lower respectively under higher temperatures and pressures, and it is not dependent on the indicator type. The ∆pH values due to the isotopic factor depend on the type of atom as well as that of the indicator. These findings indicate the importance of physical factors on the halochromic behavior of dyes for further research and the development of pH-sensitive sensors. Keywords DFT · Halochromic · pH indicator · Sulfonphthaleine dyes · Physical factors
Introduction Chromism has become a booming research field in various scientific domains (Bamfield 2001; Golchoubian et al. 2019; Van der Schueren et al. 2012). Some dyes show chromic properties, which means that their color changes depending on external influences such as thermochromism, photochromism and halochromism properties. (Bamfield 2001; Barachevskii et al. 2012; De Meyer et al. 2014; Kim 2006; Kulinich and Ishchenko 2019; Kulinich et al. 2018; Surati and Shah 2015; Zollinger 2003). A halochromic material is a material whose color changes, when pH changes occur. The pH indicators have this property. To this day, the halochromic behavior of many dyes (azo, sulfonphthaleine, phenolphthalein, phenolate, quinolone dyes, etc.) has been studied experimentally and theoretically (De Meyer et al. 2014, * Farzaneh Zanjanchi [email protected] 1
Department of Chemistry, Takestan Branch, Islamic Azad University, Takestan, Iran
2016; Ghanadzadeh Gilani et al. 2017; Hermosilla et al. 2017; Hosseini et al. 2014; Van der Schueren et al. 2012; Zhang et al. 200
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