Polymorphic behavior of a yellow isoxazolone dye

The crystal growth of a monotropic polymorphic system of a yellow isoxazolone dye has been studied. One of the two metastable polymorphs grows into a needle-shaped morphology; the stable form is rhombic. The metastable third polymorph grows only from the melt and has a solid–solid phase transition to the needle-shaped form within hours at any temperature below the melting point. The polymorphic phase diagram has been determined for a wide range of concentrations in three solvents.