ABSTRACT In‐situ X‐ray diffraction (XRD) of metal‐organic framework (MOF) provides unique insights into the correlation between the dynamic structural transformation and the photophysical evolution under external stimuli. Herein, we present MOF TCPE‐Tb from the butterfly‐shaped ligand H 4 TCPE 1,1,2,2‐tetra(4‐carboxyphenyl)ethylene, which exhibited the exceptional stability (up to 500 K and 24.6 GPa). The fluorescence evolution of TCPE‐Tb directly reflected the orientation of the tetraphenylene (TPE) core with the stimuli of temperature and pressure. In the temperature range of 80–460 K, TCPE‐Tb underwent a symmetric transition from P2 1 /n to P2 1 /m and a non‐monotonic fluorescence trend (intensity: decrease‐increase‐decrease, maximum emission wavelength: 502 nm to 486 nm). In contrast, externally applied pressure shortened the intermolecular distances of the TCPE ligand, resulting in π‐π stacked excimers that triggered a 100 nm red shift (480–580 nm) with the colors blue, blue‐green, green, yellow‐green, and activated excimer‐mediated decay pathways. For the first time, in‐situ temperature‐dependent single‐crystal XRD and in‐situ high‐pressure spectroscopy revealed the underlying relationship of the detailed conformational dynamics of the TCPE ligand (dihedral angle evolution) with the photophysical behavior under the external stimuli. The responses of TPE core to the thermal‐ and mechanical‐stimuli were completely distinct, the intramolecular torsion vs. the intermolecular packing. This work established a design paradigm for mechanically robust, stimuli‐responsive MOFs, advancing the applications in multimodal sensing and adaptive optoelectronics.
Zhang et al. (Sun,) studied this question.