A porphyrin-based covalent organic framework with pH-dependent fluorescence

Covalent organic frameworks have attracted great attention due to their extensive applications in energy storage, gas separation, catalysis, and photoelectric devices over the past decades. However, the design and synthesis of COFs with fluorescent units have been considered as a big challenge. Herein, we report a porphyrin-based covalent organic framework (TPE-Por-4) by the condensation of the C4-symmetric and D2h-symmetric monomers. Through a series of characterizations, its structure was confirmed. It was found that TPE-Por-4 shows unique fluorescent properties originated from both of porphyrin and tetraphenylethylene building blocks, its suspensions emit strong fluorescence and display an apparent response to pH fluctuation ranging from 2 to 4, and thus, a promising method was provided for spectroscopic monitoring of medium pH value.