Piezochromism, from the Greek ''piezô'' "to squeeze, to press" and ''chromos'' "color", describes the tendency of certain materials to change color with the application of

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

. This effect is closely related to the electronic band gap change, which can be found in

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

s, semiconductors (e.g. hybrid perovskites) and hydrocarbons. One simple molecule displaying this property is 5-methyl-2- 2-nitrophenyl)amino3-thiophenecarbonitrile, also known as ROY owing to its red, orange and yellow crystalline forms. Individual yellow and pale orange versions transform reversibly to red at high pressure.

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Piezochromism
Chromism {{materials-stub