Engineering Covalent Organic Frameworks for Photocatalytic CO2 Reduction: From Exciton Dissociation to Product Selectivity

Solar-driven CO2 reduction requires a photocatalyst to integrate light harvesting, exciton dissociation, long-range charge transport, CO2 adsorption and activation, and multielectron proton-coupled electron transfer within a single structural platform. Covalent organic frameworks (COFs) are attractive in this context because their π-conjugated backbones, periodic pores, linkage chemistry, stacking modes, and catalytic sites can be programmed with molecular precision. Nevertheless, the literature remains dominated by phenomenological correlations between optical response and product yield, while the causal relationships among exciton binding energy (Eb), free-carrier generation, interfacial charge transfer, intermediate adsorption, and product selectivity remain insufficiently resolved. This review develops a unified structure–activity framework in which intrinsic π-conjugation and donor–acceptor polarization regulate Eb and exciton diffusion; morphology and heterojunctions control the competition between interfacial transfer and recombination; and active-site coordination and pore microenvironments determine local electron density, proton delivery, and the adsorption energies of *COOH, *OCHO, *CO, *CHO, and *OCCO intermediates. Representative performance is benchmarked only when 13CO2 isotope tracing and appropriate blank controls are available, with external homogeneous photosensitizer systems treated separately. Among the entries retained in the condition-aware benchmark, reported CO production rates span 17.75–20,110 μmol g−1 h−1 and wavelength-specific AQYs span 0.058–5.1%; these values are not directly comparable without the associated photon flux, reactor configuration, catalyst loading, and auxiliary components. Finally, operando spectroscopy, density functional theory, microkinetic modelling, stability analysis, standardized reporting, machine-learning-assisted discovery, and device-oriented scale-up are discussed as routes toward predictive and reproducible COF photocatalyst engineering.