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 example of this property used in a consumer product although thermochromism also has more practical uses, such as baby bottles, which c ...

and other

chromism In chemistry, chromism is a process that induces a change, often reversible, in the colors of compounds. In most cases, chromism is based on a change in the electron states of molecules, especially the π- or d-electron state, so this phenomenon i ...

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 su ...

emission spectra The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to electrons making a transition from a high energy state to a lower energy state. The photon energy of the ...

of molecules using

ions An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

Electrochromism Electrochromism is a phenomenon in which a material displays changes in color or Opacity (optics), opacity in response to an voltage, electrical stimulus. In this way, a smart window made of an electrochromic material can block specific wavelen ...

is similar to ionochromism as it involves the use of

electrons The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

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 is an ionochromic dye that undergoes a definite color change in presence of specific metal ions. It forms a weak complex with the ions present in the solution, which has a significantly different color from the form exis ...

. A complexometric indicator involves the presence of

metal ions A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. These properties are all associated with having electrons available at the Fermi level, as against n ...

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 determinat ...

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 # Acidochromism # Metallochromism

Molecules with ionochromic properties

Ionochromic materials exist in a wide range of molecules, including

organic molecules Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-cont ...

, pH-sensitive

dyes Juan de Guillebon, better known by his stage name DyE, is a French musician. He is known for the music video of the single "Fantasy (DyE song), Fantasy" from his first album ''Taki 183 (album), Taki 183''. This video became popular, attracting ...

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 ...

, and other color-changing compounds with

chromophores A chromophore is the part of a molecule responsible for its color. The word is derived . The color that is seen by our eyes is that of the light not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chr ...

. Some of these molecules include phthalides, fluorans, and leucotriarylmethanes.

Ionochromic materials

{, class="wikitable" , +Compounds used in ionochromism !Compound name !pH range !Color change , - ,

Phenolphthalein Phenolphthalein ( ) is a chemical compound with the chemical formula, formula carbon, C20hydrogen, H14oxygen, O4 and is often written as "HIn", "HPh", "phph" or simply "Ph" in shorthand notation. Phenolphthalein is often used as an indicator in ...

, 8.5-9.0 , Colorless-red , - , Cresolphthalein , 8.2-9.8 , Colorless-red , - , Thymolphthalein , 9.3-10.5 , Colorless-blue , - ,

Phenol Red Phenol red (also known as phenolsulfonphthalein or PSP) is a pH indicator frequently used in cell biology laboratories. Chemical structure and properties Phenol red exists as a red crystal that is stable in air. Its solubility is 0.77 grams per ...

, 6.8-8.4 , Yellow-red , - , Cresol Red , 7.2-8.8 , Yellow-red , - ,

Thymol Blue Thymol blue (thymolsulfonephthalein) is a brownish-green or reddish-brown crystalline powder that is used as a pH indicator. It is insoluble in water but soluble in alcohol and dilute alkali In chemistry, an alkali (; from the Arabic word , ...

, 1.2-2.8 , Red-yellow , - ,

Methyl Orange Methyl orange is a pH indicator frequently used in titration because of its clear and distinct color variance at different pH values. Methyl orange shows red color in acidic medium and yellow color in basic medium. Because it changes color at the p ...

, 3.1 4.4 , Red Yellow , - , Methyl Red , 4.4 6.2 , Red Yellow

References

Chromism Complexometric indicators