Participating Group (2020-2021)
Planned creation and development of organic metastable crystals using salt-cocrystal continuum phase
The regulation of proton transfer dynamics between acid–base complexes is of significant interest in the pharmaceutical industry and materials chemistry. It is generally accepted that ⊿pKa values (pKa (protonated base) – pKa (acid)) and the crystalline environment determine the extent of proton transfer, which is recognized as a ⊿pKa rule. When the pKa value is greater than 4, a salt is expected to form (all components are charged), and a pKa value below -1 leads toward cocrystals forming (all components in their neutral states). However, when ⊿pKa is in the range of -1 < ⊿pKa < 4, the crystals exist as a molecular salt, a cocrystal, or a disordered solid with partial proton transfer forms, and the location of the acidic proton is dependent on the specific crystal packing environment. In this study, we focus on the fact that the salt-cocrystal continuum is a metastable crystals, and realize the systematic creation of “multi-component soft crystals” that show changes in optical properties in response to various external stimuli.