Thermochromism of the crystals of 2,3-bis(phenylthio)-1,4-naphthoquinone

The crystals of 2,3-bis(phenylthio)-1,4-naphthoquinone have the dimorphs of red and violet forms. The crystal structures of a monoclinic form (violet form) and an orthorhombic form (red form) have been determined by the X-ray diffraction method. In the orthorhombic form, two phenylthio groups are located on the same side of the naphthoquinone plane, while in the monoclinic form one phenylthio group is located on the naphthoquinone plane and the other phenylthio group is located under the plane. The violet form changes to the red form upon heating. The thermochromism of these crystals was studied, based on the crystal structures of the dimorphs and the solid state CP-NMR and IR and visible absorption spectra and die differential scanning calorimetry together with the theoretical analysis of the data of IR and visible absorption spectra.