Highly Conjugated Covalent Organinc Frameworks for the Photocatalytic Generation of Hydrogen

The development of new conjugated covalent organic frameworks (COFs) designed specifically to maximise hydrogen adsorption and production has been a hot topic in recent years due to the desirable properties COFs possess. High thermal and chemical stability, tuneable pore sizes and charge transport properties as well as the molecular building block approach in their synthesis all make COF’s excellent materials for hydrogen storage and production. This coupled with the lack of heavy metals within their structure and within their synthesis make COFs attractive in terms of sustainability.¹<br/><br/>The specific design of compounds with a spiro core have been studied extensivley as componenets of conjugated oligomers and polymers, and their use as organic light emitting diode (OLED) and solar cells.² However, the use of spiro component in COFs has yet to be explored extensively. The C4 type symmetry in spiro compounds coupled with C2 symmetry in linkers would provide interesting topologies when considering the dihedral angel in spiro compounds. Varying the linker length also provides a greater insight into the effects this has on pore size and hence and H2 adsorption.<br/><br/>Furthermore, introducing electron rich donor type molecules within the linkers of the framework furthers the scope of application for these COFs thus allowing them to be used as photocatalysts for photocatalytic evolution of H2 from water. The high degree of crystallinity favours charge separation and transport, which provides COFs with promising catalytic activity.³ This ties into the growing interest of organics polymeric photocatalyst as well as the growing market for new hydrogen storage and generation materials.<br/><br/>Herein we present a series of highly conjugated spiro core-based COFs designed with two main objectives, to increase hydrogen adsorption rates of COF materials and to further increase the hydrogen evolution rate (HER) seen in current COF photocatalyst materials.<br/><br/>Reference:<br/>1 N. W. Ockwig, A. P. Co, M. O. Keeffe, A. J. Matzger and O. M. Yaghi, 2005, 310, 1166–1171.<br/>2 R. Pudzich, T. Fuhrmann-Lieker and J. Salbeck, Adv. Polym. Sci., 2006, 199, 83–142.<br/>3 C. Dai and B. Liu, Energy Environ. Sci., 2020, 13, 24–52.