Solution-Processable Naphthalene Diimide-Based Conjugated Polymers as Organocatalysts for Photocatalytic CO₂ Reaction with Extremely Stable Catalytic Activity for Over 330 Hours

Nowadays, the photochemical conversion of CO2 to high-value products is attracting tremendous research interest. Developing artificial photocatalysts with excellent catalytic activity and long-term stability is still a challenge. This work demonstrates that solution-processable naphthalenedimide (NDI)-based conjugated polymers, PNDI-BT, PNDI-DTBT, and PNDI-BP, which are copolymerization products of NDI with bithiophene (BT), 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT), and biphenyl (BP), respectively, were capable of catalyzing the photochemical reduction of CO2 to produce CO in the presence of water without the need for metal-containing co-catalysts or sacrificial agents. In particular, the PNDI-BP-catalyzed reaction generated CH4 as well as CO. Results from time-resolved photoluminescence, photovoltage decay, electrochemical impedance spectroscopy, and transient photocurrent response experiments indicate that PNDI-BP with the largest dihedral angles along the conjugated backbone possessed the longest electron lifetime, the lowest charge-carrier recombination rate, and the smallest interfacial charge transfer resistance. Consequently, it had the best catalytic performance. Notably, PNDI-BP exhibited excellent recyclability, robust structural stability, and extremely steady catalytic activity for more than 330 h during a photocatalytic CO2 reaction. Furthermore, the solution-processability of the linear polymer allows the incorporation of porous substrates, which improve the reaction interface. The catalyst system of PNDI-BP@molecular sieves with H2O/triethylamine doubled the CO yield to 214.8 μmol·gcat–1 and enhanced the CH4 yield by ∼36 times to 61.4 μmol·gcat–1 in an 18 h reaction.