Uio-Type Metal-Organic Framework Thin Film with Redox-Active Linkers: Development and Charge Transport Behavior

Abstract

Designing redox-active metal-organic frameworks (MOFs) that can be synthesized as thin films is a key challenge towards their application in electrocatalysis.1 In addition, highly stable MOFs are often electronically insulating in nature, resulting in poor charge transport to redox-catalysts within the MOFs. To overcome these obstacles, we have developed a novel MOF-based thin film platform, which provides electron transport pathways for molecular electrocatalysis.2 The material was rationally designed utilizing the robust Zr-based UiO/PIZOF topology3 and redox-active naphthalene diimide-based linkers (dcphOH-NDI). In addition, hydroxyl groups were included on the dcphOH-NDI linker to facilitate proton transport through the material. When grown on conducting substrates (fluorine-doped tin oxide, FTO), this material forms thin films (Zr(dcphOH-NDI)@FTO) that display reversible electrochromic behavior. Importantly, nearly all (97%) of the NDI sites are electrochemically active at applied potential. The method of charge propagation through the film was found to proceed via an electron hopping mechanism that is accompanied by counter ion transport. Finally, the MOF thin films were found to function efficiently in aqueous solutions, adding to their potential usefulness in electrocatalytic applications. The fabrication of a UiO/PIZOF-type MOF thin film with linkers having a well-defined electrochemical response, confers unprecedented versatility to utilize postsynthetic methods to introduce catalytic units into a robust and widely studied framework that is now redox-active. In the future, this will allow for the roles of charge propagation and catalysis to be carried out by separate linkers within the MOF film, enabling the individual optimization of each process. Downes, C. A.; Marinescu, S. C. ChemSusChem, 10, 4374−4392 (2017).Johnson, B. A.; Bhunia, A.; Fei, H.; Cohen, S. M.; Ott, S. J. Am. Chem. Soc., 140, 2985−2994 (2018).Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti, C.; Bordiga, S.; Lillerud, K. P. J. Am. Chem. Soc., 130, 13850−13851 (2008); Schaate, A.; Roy, P.; Preuße, T.; Lohmeier, S. J.; Godt, A.; Behrens, P. Chem. - Eur. J., 17, 9320−9325 (2011).