Design of Pyrene-Based Small Molecules Constructed Organic Photocatalyst with Tunable Energy Level and Adjustable Electron Transfer for Efficient Photocatalytic CO2 Reduction

Organic semiconductor materials recently have been widely used in photocatalytic CO2 reduction due to their diverse synthesis methods, good light absorption, and tunable band structure, while their uncontrollable synthesis processes and exact structures have hindered the study for the relationships of structure–property over these organic photocatalysts. Herein, a series of pyrene-based conjugated small molecules were synthesized via the strategy of precise design. The conjugation of these pyrene-based molecules was modified by the introduction of unsaturated acetylene bonds and the benzene rings through classic cross-coupling reactions, which induces the different localization of photogenerated carriers on themselves and achieves an enhanced intermolecular electron transfer to the catalytic center of metal complexes. Based on this strategy, 1,3,6,8-tetraphenylpyrene (TPPy) exhibits a remarkable performance of 0.96 mmol g–1 h–1 with a selectivity of 79% in photocatalytic CO2 reduction, while 1,6-diphenylpyrene (BPPy) possesses an enhanced selectivity of 94% but a halved performance in photocatalytic CO2 reduction (0.44 mmol g–1 h–1) compared to the TPPy. The further characterizations and in situ studies reveal that the performance and selectivity of photocatalytic CO2 reduction are highly dependent on the optimized electron transfer and the modified energy levels, respectively. The purpose of this work is to not only promote the development of organic photocatalysts to reduce CO2 emissions but also provide new vision for the design of pyrene-based photocatalysts with tunable energy band levels and tunable electron transfer.