Organic Bases-Mediated CO₂ Photoreduction Coupled with N-Heterocycle Dehydrogenation

Photocatalytic CO₂ reduction to value-added chemicals is a pivotal approach toward achieving carbon neutrality. However, conventional photocatalytic systems typically rely on sacrificial electron donors that are unsustainable and yield low-value oxidation byproducts, thereby limiting their economic viability. In this work, a dual-functional photocatalytic architecture is reported, which is based on pyrene-appended iron porphyrin and organic photosensitizer in combination with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) that achieves integrated redox transformations under visible light, addressing charge separation challenges. This system enables the simultaneous reduction of CO₂ to CO with 98% selectivity (turnover number, TON = 288), coupled with the oxidative semidehydrogenation of 1,2,3,4-tetrahydroisoquinoline (THIQ) to 3,4-dihydroisoquinoline (DHIQ) (TON = 273), indicating excellent coupling efficiency of the redox reactions. Mechanistic investigations, including spectroscopic analysis and density functional theory calculations, have elucidated the pivotal role of DBU as a base and electron-transfer mediator in redox coupling reaction that is meticulously designed. This strategy offers an effective approach to sustainable photocatalytic platforms and underscores the potential of utilizing multifunctional additives to optimize both catalytic performance and reaction selectivity.