Tribochromic compounds, exemplified by 3-dicyclopropylmethylene-5-dicyanomethylene-4-diphenylmethylenetetrahydrofuran-2-one

The title compound 2 is obtained as bright yellow metastable crystals, which on mechanical grinding change to the dark red stable form; unlike piezochromic compounds, the reverse colour change does not occur; X-ray crystallographic analyses shows that the yellow form has a folded structure while the red form has a twisted structure.