Chromism

Photochromism is the reversible change of color upon exposure to light. It is a transformation of a chemical species (photoswitch) between two forms through the absorption of electromagnetic radiation (photoisomerization), where each form has a different absorption spectrum. This reversible structural or geometric change in photochromic molecules affects their electronic configuration, molecular strain energy, and other properties.

thumb|A video showing how to make thermochromatic thermal cards based on Cholesteric liquid crystal|cholesteric liquid crystals 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 for baby bottles that change to a different color when cool enough to drink, or kettles that change color when water is at or near boiling point. Thermochromism is one of several types of chromism.

thumb|180px|Redox couple for a [[viologen. The 2+ species on the left is colorless, and the 1+ species on the right is deep blue or red, depending on the identity of R.]]

In chemistry, solvatochromism is the phenomenon observed when the colour of a solution is different when the solute is dissolved in different solvents.

chemical compound

optical lenses that darken on exposure to certain wavelengths of light

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 is induced by various external stimuli which can alter the electron density of substances. It is known that there are many natural compounds that have chromism, and many artificial compounds with specific chromism have been synthesized to date. It is usually synonymous with chromotropism, the (reversible) change in color of a substance due to the physic

Longer wavelength and lower frequency

A halochromic material 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 is pH. One class of compounds with this property are pH indicators.

physical effect on materials

Ionochromism, similar to chromic methods such as photochromism, thermochromism and other chromism phenomena, is the reversible process of changing the color of a material by absorption or emission spectra of molecules using ions. Electrochromism is similar to ionochromism as it involves the use of electrons 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 d