Pressure‐Switchable Lanthanide Metal–Organic Frameworks With Dynamic Fluorescent Response

The construction of a switchable fluorescent platform with precisely defined sites that can respond to quantitative stimuli remains a challenge. Herein, we proposed two different pressure‐switchable lanthanide metal‐organic frameworks (Ln‐MOFs) platforms by introducing a three‐dimensional flexible “saddle‐shaped” cyclooctatetrathiophene unit and Tb 3+ ions with distinct coordination environments. The dynamic fluorescent behaviors of these two MOFs are strongly related to the molecular geometry of the cyclooctatetrathiophene unit. Specifically, Tb‐MOF‐1 exhibits a completely reversible response between the green emission (located at 527 nm) at 1 atm and red emission (located at 676 nm) at 14.4 GPa. For Tb‐MOF‐2, it exhibits an irreversible response among the green emission (located at 549 nm) at 1 atm, red emission (located at 616 nm) at 7.9 GPa, subsequent white emission at 13.5 GPa, and an enhanced white emission at ambient conditions after the pressure‐release treatment. Both mechanisms of the dynamic behaviors are evidenced by the single‐crystal structural analysis, in situ Fourier transform infrared spectra, in situ angle‐dispersive X‐ray diffraction, and density functional theory calculations. We demonstrate that the precise assembly of a flexible three‐dimensional linker in an ordered framework can serve as a potential strategy for the construction of a smart fluorescent material.