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, ∆H_a, entropy change, ∆S_a, Gibbs free energy change, ∆G_a, and equilibrium constant of ionization process of indicators, K_a, 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.

磺酞染料是重要的一类pH指示剂，在新型传感器中有一些应用。在本文中，作者提出了一项理论研究，以阐明物理因素对磺基酞菁染料光致变色行为的影响。所研究的磺酞染料为酚红，甲酚红，溴酚蓝，并考虑了温度，压力，溶剂介电常数和组成原子的同位素类型等物理因素。同时，研究了指示剂颜色变化的pH值∆pH与指示剂酸碱平衡中的物理因素的关系。为此，焓变ΔH _a，熵变ΔS _a，吉布斯自由能变化ΔG _a。，指标电离过程的平衡常数K _a计算在不同条件下的平衡反应; 然后用热力学定律和统计热力学定律解释它们的值。结果表明，通过在任何压力下升高温度，在任何温度下升高压力，降低所用溶剂的极性以及使用组成原子的同位素，∆pH均为正值。在较高的温度和压力下，温度和压力对∆pH的影响分别较小，并且与指示剂的类型无关。由于同位素因素引起的∆pH值取决于原子的类型以及指示剂的类型。这些发现表明，物理因素对染料的盐致变色行为的重要性对于进一步研究和开发pH敏感传感器至关重要。