Ionochromism, similar to chromic methods such as photochromism,

thermochromism Thermochromism is the property of substances to change color due to a change in temperature. A mood ring is an excellent example of this phenomenon, but thermochromism also has more practical uses, such as baby bottles which change to a differen ...

and other chromism phenomena, is the reversible process of changing the color of a material by

absorption Absorption may refer to: Chemistry and biology * Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which ...

emission spectra The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an electron making a atomic electron transition, transition from a high energy state to a lower energy st ...

of molecules using ions. Electrochromism is similar to ionochromism as it involves the use of

electrons The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

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 an anionic species or negatively charged species such as electrons. An example of an ionochromic dye is a complexometric indicator. A complexometric indicator involves the presence of

metal ions A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

in order to facilitate color change and is often used in

complexometric titration Complexometric titration (sometimes chelatometry) is a form of volumetric analysis in which the formation of a colored complex is used to indicate the end point of a titration. Complexometric titrations are particularly useful for the determinati ...

Overview

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. Various ionic color changing mechanisms that are used in chromic processes can be used in ionochromism, including: #

Halochromism A halochromic material or pH indicator is a material which changes colour when pH changes occur. The term ‘ chromic’ is defined for materials that can change colour reversibly with the presence of an external factor. In this case, the factor ...

# Acidochromism # Metallochromism

Molecules with Ionochromic Properties

Ionochromic materials exist in a wide range of molecules, including

organic molecules In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The s ...

, pH-sensitive

dyes A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

and

indicators Indicator may refer to: Biology * Environmental indicator of environmental health (pressures, conditions and responses) * Ecological indicator of ecosystem health (ecological processes) * Health indicator, which is used to describe the health o ...

, and other color-changing compounds with chromophores. Some of these molecules include

phthalides Phthalide is an organic chemical compound with the molecular formula C8H6O2. A white solid, it is the simplest benzo lactone. It is prepared from hydroxymethylbenzoic acid. Phthalides The phthalide core is found a variety of more complex chemic ...

Overview

Molecules with Ionochromic Properties

Ionochromic materials

Applications

Carbonless copy paper

Analytical chemistry

Lithographic process for printing plates

Direct thermal printing

References