Pressure effects on metal/covalent-organic frameworks: structural and optical properties

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) with highly ordered porous structure, tunable bandgap, large specific surface area and structural diversity, provide an appealing platform for the development of stimulus response, sensing, imaging and optoelectronics. Among various tuning methods, pressure engineering using the diamond anvil cell is a highly powerful in-situ technique, which can efficiently modulate the structural and optical properties of MOFs/COFs. This is beyond the realization of traditional chemical methods. This review outlines the research progress in the experiment-oriented discovery of new phases or unique properties under high pressure, including phase transition, abnormal compression, photoluminescence (PL) discoloration and enhancement. Notably, the improvement of PL quantum yield in MOFs could be achieved by pressure-treated engineering and hydrogen-bonding cooperativity effect. We also propose and establish the relationship between structure and optical properties under high pressure. Finally, the challenge and outlook of the current fields are summarized. We hope that this review will supply guidance for comprehending the development of high-pressure MOF/COF-related research fields, and offer novel strategies for designing more high-performance MOF/COF materials to ultimately expand their applications.