Isoliquiritigenin (ISL) is an abundant dietary flavonoid with numerous pharmacological activities. However, isoliquiritigenin is poorly absorbed by the body which limits its clinical usage. Cocrystallization has attracted attention recently as a means of modifying unfavourable physicochemical properties of compounds. Herein, we report the synthesis of two new cocrystals of ISL: isoliquiritigenin-nicotinamide (ISL-NIC) and isoliquiritigenin-isonicotinamide (ISL-INM). To our knowledge, this is the first report of flavonoid cocrystals from a compound with a chalcone structure. The cocrystals are characterized by various techniques, including powder X-ray diffraction, Raman spectroscopy, differential scanning calorimetry and thermogravimetric analysis. Through single-crystal X-ray diffraction analysis, we investigate the crystal packing and intermolecular interactions of ISL cocrystals. The binary phase diagrams of ISL and the conformers are constructed for understanding the thermal behaviors of physical mixtures upon heating. Pharmacokinetic studies show that both of the ISL cocrystals outperform the pure form of ISL and its monohydrate with increases in bioavailabilities.

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