Successive construction of cucurbit[8]uril-based covalent organic frameworks from a supramolecular organic framework through photochemical reactions in water

Functional framework materials have been developed for many applications including adsorption, asymmetric catalysis, sensing, drug delivery, optical device, and so on. Here, we report the successive construction of two cucurbit[8]uril-based covalent organic frameworks (COFs) including tetraphenylethene-based COF (COF-1) and phenanthrene-based COF (COF-2) from a two-dimensional (2D) periodic cucurbit[8]uril-based supramolecular organic framework (SOF-1) as the prearranged structure via the intermolecular photocycloaddition of the coumarin units and the intramolecular photocyclization of the tetraphenylethene (TPE) units under ultraviolet (UV) irradiation (365 nm) in water. In this case, oxygen (O-2) plays an important role in the photocyclization of the TPE units into the phenanthrene units in the transform process from SOF-1 or COF-1 to COF-2. As the TPE units further form phenanthrenes after UV-irradiation, COF-2 exhibits aggregation-caused quenching effect and weak green emission, while COF-1 displays a strong yellow emission due to the aggregation-induced emission. Besides, the adaptive chirality of cationic COF-1 as a biomolecular sensor can be efficiently induced by chiral anionic biomolecules including adenosine-5 '-triphosphate (ATP) and adenosine-5 '-diphosphate (ADP) to exhibit sensitive negative circular dichroism responses in water. This supramolecular approach to construct COF from SOF via photochemical reactions may open a new opportunity for the construction and application of the water-soluble COFs with well structural controllability, unique photophysical properties, and favorable biocompatibility.