Covalent organic frameworks (COFs), as a new type of promising photocatalytic materials, is highly crystalline porous polymers composed of lightweight elements with ultra-high surface area and chemical stability, which have attracted much attention in recent years. However, COFs are metal-free polymers, the most significant disadvantage of COFs materials is the lack of bare metal active centers that can be used for photocatalytic reactions, so there are some problems such as low catalytic activity and poor selectivity. Therefore, molecular metal catalyst-modified COFs as photocatalysts are the current research hotspots for improving their photocatalytic activity. The research on photocatalytic CO2 reduction of metaled COFs is still at its initial stage. Despite the well-documented recent advances in material development and photocatalytic application of those COFs structures, the fundamental catalytic process, especially, excited-state dynamics that dominate the catalytic performance has not been fully understood. In particular, the photo-generated excitons or charge carriers can undergo transfer and recombination within a broad temporal regime, containing multiple charge separation mechanisms.
In this thesis, two metaled COFs photocatalysts Re-TpBpy and Ni-TpBpy were obtained, and their excited state kinetics were explored experimentally by advanced spectroscopic measurements and theoretical by time-dependent density functional theory (TD-DFT) calculations. Both Re-TpBpy and Ni-TpBpy exhibit excellent photocatalytic reduction activity. Our in-depth understanding of the complex charge separation and transfer processes in COFs modified with metal-molecule photocatalysts on femtosecond to second-time scales will provide important guidance for the understanding and rational design of efficient photocatalysts, as well as expand the practical applications of COFs materials and initiate the research on photocatalysis of COFs materials