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Organic photochemistry is intensely developed in the 1980s, in which the nature of excited electronic states and the energy and electron transfer processes are thoroughly studied and finally well-understood. This knowledge from molecular organic photochemistry can be transferred to the design of covalent organic frameworks (COFs) as active visible-light photocatalysts. COFs constitute a new class of crystalline porous materials with substantial application potentials. Featured with outstanding structural tunability, large porosity, high surface area, excellent stability, and unique photoelectronic properties, COFs are studied as potential candidates in various research areas (e.g., photocatalysis). This review aims to provide the state-of-the-art insights into the design of COF photocatalysts (pristine, functionalized, and hybrid COFs) for organic transformations. The catalytic reaction mechanism of COF-based photocatalysts and the influence of dimensionality and crystallinity on heterogenous photocatalysis performance are also discussed, followed by perspectives and prospects on the main challenges and opportunities in future research of COFs and COF-based photocatalysts.

A porphyrin-based covalent organic framework (COF), namely Porph-UOZ-COF (UOZ stands for the University of Zabol), has been designed and prepared via the condensation reaction of 5,10,15,20-tetrakis-(3,4-dihydroxyphenyl)porphyrin (DHPP) with 1,4-benzenediboronic acid (DBBA), under the solvothermal condition. The solid was characterized by spectroscopic, microscopic, and powder X-ray diffraction techniques. The resultant multifunctional COF revealed an outstanding performance in catalyzing a one-pot tandem selective benzylic C-H photooxygenation/Knoevenagel condensation reaction in the absence of additives or metals under visible-LED-light irradiation. Notably, the catalytic activity of the COF was superior to individual organic counterparts and the COF was both stable and reusable for four consecutive runs. The present approach illustrates the potential of COFs as promising metal-free (photo) catalysts for the development of tandem reactions.

[EN] MIL-125(Ti)-NH2 has been modified by reaction of salicylaldehyde with the terephthalate amino groups to form a salicylideneimine that act as ligand of Cu2+. The success of the postsynthetic modification was assessed by FTIR spectroscopy of the MIL-125(Ti)-NH2-Sal-Cu and by analysis by H-1 NMR spectroscopy of the organic linkers upon dissolution of MIL-125(Ti)-NH2-Sal-Cu. In comparison with parent MIL-125(Ti)-NH2 and MIL-125(Ti)-NH2-Sal, that exhibit a poor activity, the presence of the Cu-Schiff base complex in MIL-125(Ti)-NH2-Sal-Cu catalyst for the oxidation of 1-phenylethanol by tert-butylhydroperoxyde (TBHP, 3 eq.) increases notably the catalytic activity. Hot filtration test and reusability experiments confirm that the process is heterogeneous and that MIL-125(Ti)-NH2-Sal-Cu is stable under the reaction conditions. Quenching studies and EPR spectra using N-(t)butylphenylnitrone indicate the generation of (BuOO)-Bu-t. and (BuO center dot)-Bu-t under the reaction conditions. The scope of MIL-125(Ti)-NH2-Sal-Cu as oxidation catalyst by (BuOOH)-Bu-t was studied for benzyl alcohol as well as alicyclic and aliphatic alcohols and ethylbenzene. (C) 2018 Elsevier Inc. All rights reserved.