xantochromic

Xantochromic is a term used to describe materials that display a yellow color as a result of a chromic response to an external stimulus. The word combines the Greek xanthos, meaning yellow, with chroma, color. It is applied in chemistry, materials science, and pigment technology to refer to reversible or irreversible yellowing phenomena in dyes, pigments, and related compounds.

Several mechanisms can produce xantochromism. Photochromism, where light induces a color change to yellow; thermochromism, where temperature changes drive a yellow form; redox chromism, where oxidation or reduction alters the electronic structure to yield yellow; and acid–base chromism, where protonation or deprotonation shifts absorption toward yellow. In all cases, the yellow form corresponds to absorption of portions of the spectrum that make the compound appear yellow under standard illumination.

Materials exhibiting xantochromism include certain dyes and pigments as well as organic photochromic systems. Well-studied families such as spiropyrans and diarylethenes can show yellow-colored forms in one of their reversible states. In inorganic contexts, changes in oxidation state or ligand environment of metal complexes can similarly produce yellow species.

Applications of xantochromic materials span optical data storage, chemical sensing, and smart coatings, where a yellow color indicates exposure to a stimulus or a particular chemical state. The phenomenon is related to broader chromism concepts, including photochromism, thermochromism, and electrochromism. See also xanthochromism, chromism, photochromism, thermochromism, electrochromism.