Tailoring the Exciton Binding Energy of 2D Conjugated Polymers for Powering Metal-Free CO2 Photoreduction

Metal-free conjugated polymer photocatalysts have provided promising environmentally friendly options in photoreduction of CO2 to high value-added chemicals. However, due to the strong Coulombic interaction of excited electron-hole pairs, most polymer photocatalysts show moderate photocatalytic performances compared with inorganic semiconductor photocatalysts. Herein, we prepared a series of 2D porphyrin-based conjugated polymers. By simply altering the aromatic acetylene linkers, we found that the exciton binding energy (E-b) of the 2D conjugated polymers could be fine-tuned. With an increasing number of acetylene units in linkers, their E-b values were reduced by 27% accompanied by promoted charge-carrier generation (about a 4-fold increase in photocurrent) and obviously enhanced catalytic activity of CO2 photoreduction. The optimized polymer, PTPP-DA, linked with diacetylene groups, affords CO and CH4 as the carbonaceous products with rates of 465 and 237 mu mol g(-1) h(-1), respectively, without any metal or photosensitizer. This work reveals the important implications of conjugated linkers on mediating the E-b values of 2D conjugated polymers and provides new insight for designing efficient metal-free polymeric photocatalysts for CO2 reduction.