Dynamic Fluorescent Metal-Organic Frameworks Utilizing a Flexible Saddle-Like 3D Linker

Designing single-component fluorochromic metal-organic frameworks (MOFs) with multiple stages presents a significant challenge in the field of functional and smart MOFs. In this study, this challenge is successfully addressed by designing and synthesizing a novel ligand called cyclooctatetrathiophene-tetrapyridine (COTTTP), and incorporating it into 3D MOFs known as Zn/Cd-COTTTP. By exploiting the intrinsic properties of COTTTP, specifically its ability to undergo geometry changes from a bent form to a more planar form, both COTTTP as an individual molecule and the resulting Zn/Cd-COTTTP MOFs exhibit similar fluorochromic behavior. This behavior manifests as a color change from yellow to orange to red. Characterization techniques such as single crystal X-ray diffraction, Fourier transform infrared spectroscopy, solid-state UV-vis and near-infrared spectroscopy, and X-ray photoelectron spectroscopy are employed to investigate and confirm the geometry change of COTTTP within the MOF structures. Furthermore, the introduction of an auxiliary rigid ligand to the system is explored, which effectively restricts the geometry change of COTTTP and subsequently diminishes the fluorochromic behavior. This work sheds new light on the design and application of smart porous materials, particularly in the realm of single-component fluorochromic MOFs. The successful incorporation of COTTTP and the understanding of its geometry change provide insights into the development of functional and responsive MOFs for various applications. Based on the variable 3D saddle-like configuration of cyclooctaquathiophenetetrapyridine, a dynamic real-time shift in the color of Zn/Cd-COTTTP is achieved, capable of changing from yellow to red. image