Composition Dependent Dynamic Behaviors of Non-Stoichiometric Cocrystalline Hydrogen-Bonded Organic Frameworks

Non-stoichiometric multicomponent crystals have the potential not only to fine-tune material properties but also to emerge new functionalities. In this paper, the composition-dependent dynamic transformation of non-stoichiometric cocrystalline hydrogen-bonded organic frameworks (NS-HOFs) composed of tetrakis(4-carboxyphenyl)hexahydropyrene and -pyrene derivatives (CP-Hp and CP-Py, respectively) is reported. Isostructural mono-component frameworks of CP-Hp and CP-Py (CP-Hp-1 and CP-Py-1, respectively) underwent structural transformation into the corresponding shrunk frameworks (CP-Hp-2 and CP-Py-2, respectively) by spontaneous release of the included solvent molecules, where the transformation speed of CP-Hp-1 is faster than that of CP-Py-1. NS-HOFs of CP-Hp and CP-Py, denoted by CP-HpPy-1(x), where x is the mixing ratio of CP-Hp, show the transformation into CP-HpPy-2(x), and the transformation behaviors strongly depend on the composition ratio. Interestingly, the transformation speed is not proportional to the composition ratio, while the maximum speed is observed for CP-HpPy-1(0.5). This is, to the best of these knowledge, the first example of composition-dependent structural changes in non-stoichiometric cocrystalline frameworks, demonstrating that dynamic behaviors can be modulated nonlinearly by the composition of the frameworks and shedding light on new aspects of porous soft crystals.