Molecular engineering of covalent organic frameworks for hydrogen evolution Albert Granados and Carolina Gimbert-Suriñach Universitat Autònoma de Barcelona, Spain The generation of hydrogen through water splitting under visible-light irradiation has been a widely studied topic since the 1970s. This complex process requires multiple key components, each playing a crucial role, including light harvesting, charge separation, and bond breaking and formation. In the context of the hydrogen evolution reaction (HER), various inorganic semiconductors, such as TiO 2 , have been extensively used due to their suitable electronic configurations and stability under photochemical conditions. However, their practical implementation is hindered by limitations in solar-to-hydrogen efficiency. Recently, organic semiconductors have emerged as promising alternatives in this field. Among them, two- dimensional covalent organic frameworks (2D-COFs) have gained significant attention due to their high crystallinity, porosity, and tunable electronic properties. These materials have demonstrated great success in photocatalytic applications, including visible-light-driven HER. A key advantage of COFs is their structural versatility, which enables precise control over their chemical and electronic properties, allowing for the rational design of enhanced photocatalytic materials with improved solar light absorption, charge separation, co-catalyst interactions, and water dispersibility. In this work, we report a versatile synthetic strategy for linear difunctional molecules (C 2 ) containing an electron- withdrawing (EW) thiazolo[5,4-d]thiazole core and two electron-donating (ED) amine groups. C2-type monomers are widely employed in COF synthesis, enabling the formation of materials with diverse geometries, including 2D-trigonal, 2D-tetragonal, and 2D-hexagonal frameworks. Our synthetic approach facilitates the precise introduction of EW and ED groups, leading to the isolation of a range of dianiline C 2 precursors with distinct electronic properties that are challenging to obtain using previously reported methods. Additionally, we have successfully synthesized COFs from these precursors and evaluated their performance in HER photocatalysis. References 1. Cô té , A. P.; Benin, A. I.; Ockwig, N. W.; O’Keeffe, M.; Matzger, A. J.; Yaghi, O. M. Science 2005 , 310 , 1166. 2. Biswal, B. P.; Vignolo-González, H. A.; Banerjee, T.; Grunenberg, L.; Savasci, G.; Gottschling, K.; Nuss, J.; Ochsenfeld, C.; Lotsch, B. V. J. Am. Chem. Soc. 2019 , 141 , 11082. 3. Ghosh, S.; Nakada, A.; Springer, M. A.; Kawaguchi, T.; Suzuki, K.; Kaji, H.; Baburin, I.; Kuc, A.; Heine, T.; Suzuki, H.; Abe, R.; Seki, S. J. Am. Chem. Soc . 2020 , 142 , 9752.
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