Influence of Keto–Enol\nTautomerism in Regulating\nCO<sub>2</sub> Photoreduction Activity in Porous Organic\nPorphyrinic Photopolymers

Photoassisted CO<sub>2</sub> reduction employing a metal-free\nsystem\nis both challenging and fascinating. In our study, we present a structural\nengineering strategy to tune the potential energy barrier, which,\nin turn, affects the photoreduction ability. A series of porphyrin-based\nporous organic polymers (<b>POPs</b>) were hydrothermally synthesized\nand the influence of keto–enol tautomerization on the CO<sub>2</sub> photoreduction potential has been rigorously investigated.\nAmong the screened photocatalysts, <b>POP-1</b> demonstrated\nthe highest CO<sub>2</sub>/CO conversion efficacy, producing 518 μmol\ng<sup>–1</sup> h<sup>–1</sup> of CO selectively under\nlight illumination for 2 h. Density Functional Theory computational\ninvestigations concretely highlighted the reaction mechanistic pathway\nsupporting the CO<sub>2</sub> conversion reaction. Additionally, the\nelectron density mapping underpinned the thermodynamic energy barrier\nrequirements for the progress of the reaction and elucidated the reason\nfor the enhanced photocatalytic activity seen in <b>POP-1</b>. In situ Fourier-Transform Infrared spectroscopy was carried out\nfor real-time investigations to understand the synergistic reaction\ndynamics and unlock the generation of key reaction intermediates during\nthe CO<sub>2</sub> reduction reaction process. Additionally, ultrafast\ntransient absorption spectroscopy plays a vital role in understanding\nthe surface interaction dynamics of our designed catalysts. Overall,\nthis straightforward modulation strategy not only enhances CO<sub>2</sub> reduction performance but also contributes toward presenting\na crisp and concrete understanding of the structure–property\nrelationship, opening up the possibilities for the development of\nartificial photocatalysts. The results introduce a strategy for photocatalytic\nCO<sub>2</sub> reduction using an efficient, stable, and recyclable\nmetal-free photocatalytic system.