Multiple stimulus responsive Co-AIE framework materials with reversible solvatochromic and thermochromic behaviors: molecular design, synthesis and characterization

Abstract

A novel Co-MOF (Co-tcbpe) based on the TPE derivative H₄tcbpe (H₄tcbpe = 4′,4′′′,4′′′′′,4′′′′′′′-(ethene-1,1,2,2-tetrayl)tetrakis([1,1′-biphenyl]-4-carboxylic acid)) was designed and synthesized under solvothermal conditions. It was found experimentally that Co-tcbpe is a kind of MOF material that undergoes reversible color changes in response to various stimuli (solvent and temperature conditions). For example, Co-tcbpe can show different colors in different solvents, and its color can return to its original color when it is removed from the solvent. By analyzing the FT-IR, UV-vis, and fluorescence spectra and fluorescence lifetime of the sample after solvent treatment, combined with the analysis of the 3D stacking structure of Co-tcbpe, it is speculated that the reason for solvatochromism is the hydrogen bonding interaction between the solvent molecules and the coordinated water molecules in the Co-tcbpe structure. Furthermore, Co-tcbpe also exhibited superior thermochromic phenomena (pink-dark green-yellow) under different temperature conditions. In the same way, in order to find out the reason for the thermochromism of Co-tcbpe, we also carried out its structural characterization, combined with the DSC curve and TGA analysis, and proved that the cause of thermochromism may be the desolvation process. These obvious color changes that can be observed with the naked eye also make Co-tcbpe become a new type of sensor that could respond to small organic molecules and temperature, which also provides a solid foundation for us to further study and develop the application field of MOFs based on TPE derivatives.