Photoresponsive Covalent Organic Frameworks with Diarylethene Switch for Tunable Singlet Oxygen Generation

Abstract

Incorporation of molecular switches with light, heat, and electricity responsibility into artificial solids has been developed as a successful strategy to construct stimuli-responsive functional materials. However, precise manipulation of their molecular geometries and electronic structures to control the properties of macroscopic materials still remains a fundamental challenge. Herein, a photoresponsive covalent organic framework (o-COF) with the square lattice was fabricated from the dynamic covalent chemistry reaction of ring-open dithienylethene–dialdehyde with 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (H2TAPP). UV irradiation of the dithienylethene-based units in o-COF afforded its reversible photoisomer (c-COF) in the ring-closed form. In addition to a range of diffraction, microscopic, and gas physical sorption characterizations, spectroscopic investigations with the help of theoretical simulations revealed different photocatalytic activities toward the evolution of singlet oxygen and corresponding photocatalytic oxidation of amines due to the different energy transfer pathways from the porphyrin unit to BBTP photoisomers in these two COFs. Most interestingly, such different photocatalytic behaviors for two COFs could be easily tuned in a reversible manner by adjusting the ring-closed/open form of dithienylethene units by means of UV and visible light.