1,4-Bis(1,3-dioxo-2-indenylidene)cyclohexane: polymorphism, gas phase oxidation and enol form mediated radical formation in the solid state

Crystallization of 1,4-bis(1,3-dioxo-2-indenylidene)cyclohexane from toluene and dichloromethane solutions afforded yellow photochromic and orange non-photochromic crystals, respectively. In situ Raman spectroscopy of the photochromic form revealed the presence of an enol form. Both forms undergo sublimation assisted dehydrogenation under aerobic conditions.