Triafulvalene or cyclopropenylidenecyclopropene is a fulvalene hydrocarbon with chemical formula C₆H₄, composed of two linked cyclopropene rings. Triafulvalene has never been isolated, since it can decompose via an isodesmic reaction. However, its structure, stability, and spectral properties are well-studied theoretically;^{[citation needed]} the molecule is believed planar.