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Ionochromism

From Wikipedia, the free encyclopedia

Ionochromism, similar to chromic methods such asphotochromism,thermochromism and otherchromism phenomena, is the reversible process of changing the color of a material byabsorption oremission spectra of molecules usingions.^[1]Electrochromism is similar to ionochromism as it involves the use ofelectrons in order to change the color of materials. Both electrochromic and ionochromic materials undergo a change in color by the flow of charged particles, where electrochromic materials only involve ananionic species or negatively charged species such as electrons. An example of an ionochromic dye is acomplexometric indicator. A complexometric indicator involves the presence ofmetal ions in order to facilitate color change and is often used incomplexometric titration.

Overview

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Ionochromism is the process of reacting an ionochromic material with a charged species, or a positively or negatively charged ion. Materials that have ionochromic properties exhibit reversible color change, where the absence of a stimulus such as an ionic species can result in the compound changing to its original color.^[2]Various ionic color changing mechanisms that are used in chromic processes can be used in ionochromism, including:

Halochromism
Acidochromism
Metallochromism

Molecules with Ionochromic Properties

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Ionochromic materials exist in a wide range of molecules, includingorganic molecules, pH-sensitivedyes andindicators, and other color-changing compounds withchromophores. Some of these molecules includephthalides,fluorans, and leucotriarylmethanes.^[2]

Ionochromic materials

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Compounds used in ionochromism^[2]
Compound name	pH range	Color change
Phenolphthalein	8.5-9.0	Colorless-red
Cresolphthalein	8.2-9.8	Colorless-red
Thymolphthalein	9.3-10.5	Colorless-blue
Phenol Red	6.8-8.4	Yellow-red
Cresol Red	7.2-8.8	Yellow-red
Thymol Blue	1.2-2.8	Red-yellow
Methyl Orange	3.1 4.4	Red Yellow
Methyl Red	4.4 6.2	Red Yellow