Effective Photocatalytic Initiation of Reactive Oxygen Species by a Photoactive Covalent Organic Framework for Oxidation Reactions

Abstract

Reactive oxygen species (ROS) play a vital role in both chemistry and physiology. Developing effective photocatalysts becomes a feasible approach to trigger the generation of ROS. Herein, a photosensitive covalent organic framework (COF) was rationally designed and constructed by incorporating the photoactive triphenylamine moieties into its skeleton, characterizations of which not only showed the success formation of the highly crystalline and stable framework, but also revealed the photoactive property derived from triphenylamine-based building block. Electron paramagnetic resonance measurements displayed that the COF was an effective photocatalyst for generating ROS with one unpaired electron, that is, superoxide radical anion (O 2• − ). Subsequently, its high efficiency, selectivity, and reusability in photocatalytic aerobic oxidation of sulfides confirmed that the COF is a promising photocatalyst in the applications of ROS-involved reactions, demonstrating that precisely embedding organic photochromic groups into COFs could be a powerful strategy to fabricate metal-free heterogeneous photocatalysts for targeted reactions.

Effective Iodine Adsorption by Nitrogen-Rich Nanoporous Covalent Organic Frameworks

“…Considering that both TFBT and TAPA are triple-symmetric building blocks, and the connections of these triple-symmetric organic modules usually give the generation of two-dimensional layer frameworks, 62−66 a two-dimensional (2D) (3, 3)-connected COF structure with an AA stacking model was first constructed using Materials Studio 2017 software to simulate its crystal structure. 47,67 By setting a unit cell of TFBT-1 in the Trigonal P3 (no. 143) space group with the parameters of a = b = 25.3339 Å, c = 2.9687 Å, Pawley refinements were carried out and finally good agreement factors of R P = 1.62% and R WP = 2.08% were obtained (Figure 3c).…”

Highly Effective Generation of Singlet Oxygen by an Imidazole-Linked Robust Photosensitizing Covalent Organic Framework

“…Inspired by the strong semiconductive optical activity of the constructed PyPor-COF derived from the successful incorporation of the porphyrin moieties into its skeleton, EPR measurements were therefore carried out to detect its capability of initiating the generation of ROS including ·OH, ·O 2 – and 1 O 2 (Figures a and S6–S9). ,− When taking 2,2,6,6-tetra-methyl-1-piperidine (TEMP) as the trapping agent of 1 O 2 , while all samples did not display any ROS signal under dark conditions and PyTO did not show ROS signal even under light conditions, PyPor-COF exhibited an obvious 1 O 2 signal response after light irradiation (Figures a and S6–S8), which is much stronger than that of its porphyrin precursor, p -Por-CHO, detected under the same conditions (Figure a). Although pyrene-containing compounds usually show strong photoresponsive properties, PyTO did not present an ROS signal under light irradiation probably due to the destruction of the conjugated structure of pyrene after its oxidation to PyTO and the resulting decreases of both absorption capability of light and delocalization ability of electrons.…”

“…Although pyrene-containing compounds usually show strong photoresponsive properties, PyTO did not present an ROS signal under light irradiation probably due to the destruction of the conjugated structure of pyrene after its oxidation to PyTO and the resulting decreases of both absorption capability of light and delocalization ability of electrons. When using 5,5-dimethyl-1-pyrrole- N -oxide (DMPO) as a trapping agent of ·OH and ·O 2 – , nearly no signal was observed even under light irradiation (Figure S9), indicating that the synthesized COF is a selective photosensitizer toward the generation of 1 O 2 (Figure b). − Then, control experiments were conducted to compare the 1 O 2 generation efficiency of PyPor-COF with the commercially available singlet oxygen reagents commonly used in PDT, such as rhodamine B, methylene blue, and Ce6, at the same conditions (Figures c and S10–S12). , Surprisingly, PyPor-COF exhibited much higher singlet oxygen generation efficiency than that of rhodamine B, and it was comparable with that of methylene blue and Ce6 (Figure c).…”

“…Covalent organic frameworks (COFs) have been emerging as a group of highly promising functional materials in wide applications. − Besides the structure diversity and intriguing porosity, their intrinsic organic nature derived from the periodic covalently linked organic components also endows them with chemical tunability. By incorporating chromophore organic moieties into their skeletons, photoactive COFs were synthesized and studied for photocatalysis, charge transfer and photoelectrochemistry, and also bioimaging and therapy. − For instance, previously when we took a photoactive triphenylamine-based module as a building block, a photosensitive COF was successfully constructed and used for photocatalytic oxidation reactions . Thus, photosensitizing COFs toward the application in initiating the generation of 1 O 2 can be rationally constructed by ingenious selection of photoactive organic precursors.…”

“…24−27 For instance, previously when we took a photoactive triphenylamine-based module as a building block, a photosensitive COF was successfully constructed and used for photocatalytic oxidation reactions. 27 Thus, photosensitizing COFs toward the application in initiating the generation of 1 O 2 can be rationally constructed by ingenious selection of photoactive organic precursors.…”