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 eve ...
. This effect is closely related to the electronic
band gap
In solid-state physics and solid-state chemistry, a band gap, also called a bandgap or energy gap, is an energy range in a solid where no electronic states exist. In graphs of the electronic band structure of solids, the band gap refers to t ...
change, which can be found in
plastic
Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
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.
References
External links
Piezochromism
Chromism
{{materials-stub