Harnessing Naphthalimide Scaffolds for Sustainable CO2 Utilization: A Metal-, Halide-, and Solvent-Free Photocatalytic CO2 Cycloaddition via Sequential Two-Photon Activation.

Consecutive photoinduced electron transfer (ConPET) has attracted great interest due to its ability to activate inert substrates under mild reaction conditions. The imide-functionalized rylene derivatives are well-documented in the literature as competent chromophores capable of operating via ConPET. Herein, we report the synthesis and characterization of naphthalimide-based organophotocatalyst, JS-2, for CO2 cycloaddition with epoxides to synthesize cyclic carbonates. JS-2 demonstrated remarkable efficiency with just 0.1 mol% catalyst loading at room temperature, atmospheric CO2 pressure, and under visible light irradiation, giving excellent yield and selectivity for a wide range of substrates. Detailed mechanistic investigations and density functional theory calculations confirmed that the reaction proceeds via a sequential two-photon excitation, forming the CO2 radical anion (CO2 •-) as a nucleophile. The heterogeneity and excellent recyclability across five consecutive cycles highlight the robustness and feasibility of the catalyst for practical use. To the best of our knowledge, this is the first report of a completely metal-, halide-, and solvent-free approach, employing a ConPET process and leveraging the nucleophilic reactivity of CO2 •- in epoxide ring opening for a photocatalytic CO2 cycloaddition reaction.