Exploring the role of π-π interactions in metallic and covalent organic frameworks based photocatalysis: Design, principles and applications

Metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have gained significant attention as promising photocatalytic materials, largely due to their structurally versatile architectures, extensive surface areas, and highly customizable pore characteristics. In addition to the different factors that have been attributed to their high photocatalytic efficiency, π-π interactions are also an important factor that has been less studied. These non-covalent interactions, arising from aromatic π-electron systems, significantly influence the optoelectronic properties. In contrast to previous reviews in which π-conjugation, π-stacking, and photocarrier transfer are treated as distinct or only superficially addressed contributions, this review critically discusses π-π interaction as an integral design principle that regulates the optoelectronic properties and photocatalytic activity of MOFs and COFs. The present review draws on a systematic examination of literature sourced from major scientific databases, with a primary focus on mechanistic studies investigating the role of π-mediated interactions in MOF- and COF-based photocatalysts. We first discussed the origin of π-π interactions in MOFs and COFs, highlighting the stacking and delocalized π-conjugation. π-π interactions in MOFs are originally related to the aromatic organic linkers and their special arrangements. Whereas, in-plane π-conjugation and π-π stacking in COFs are related to enhanced charge transport and less recombination. The review further examines the effect of π-π interactions on optoelectronic properties, stability, and adsorption properties of MOFs and COFs. Moreover, this review identifies key design strategies such as π-π stacking, extended π-conjugation, donor-acceptor architectures, and surface functionalization, and discusses their mechanistic contributions, benefits, limitations, and significance in the rational development of high-performance photocatalysts. Furthermore, the important factors for engineering the π-π interactions in MOFs and COFs are also explored. Finally, the applications of π-π interactions modulated MOFs and COFs for H 2 production, CO 2 reduction and pollutant degradation are also discussed. Finally, the future directions in the field of π-π interactions-based MOFs and COFs photocatalytic systems are discussed. Overall, this review explores the π-π interactions as a parameter to design the efficient MOFs and COFs photocatalytic material for energy and environmental applications.