Hexaarylbiimidazole
{{Short description|Class of chemical compounds}}
Hexaarylbiimidazoles (HABIs) are a class of organic compounds that are imidazole derivatives.{{cite book | title = Photochemistry, History and Commercial Applications of Hexaarylbiimidazoles: All about HABIs | author = Rolf Dessauer | publisher = Elsevier | date = 2006 | isbn = 9780080466798 }} In their natural state, HABIs are typically colorless, but when ultraviolet light breaks the bond connecting the two imidazole groups in the molecule, it produces a version that is dark blue. The transformation takes ten seconds or longer.{{cite journal | doi = 10.1021/ol801135g | title = Photochromism of a Radical Diffusion-Inhibited Hexaarylbiimidazole Derivative with Intense Coloration and Fast Decoloration Performance | date = 2008 | last1 = Fujita | first1 = Kana | last2 = Hatano | first2 = Sayaka | last3 = Kato | first3 = Daisuke | last4 = Abe | first4 = Jiro | journal = Organic Letters | volume = 10 | issue = 14 | pages = 3105–3108 | pmid = 18563908 }} By adding naphthalene to the compound, the color transition can be made in about 180 milliseconds. The cyclophane version of HABI reverts to colorless just as fast as the UV light is off.