Molecular Polarity in Conjugated Microporous Polymers for Efficient CO2 Photoreduction

Abstract

Donor–acceptor (D–A) conjugated microporous polymers (CMPs) are a promising class of metal-free photocatalysts for CO₂ reduction. However, conventional D–A CMP design strategies that prioritize the screening of isolated D and A units based solely on energy-level offsets are often insufficient, as they overlook the substantial electronic orbital reorganization induced by D–A coupling. Herein, we demonstrate that the molecular polarity of the D–A dyad serves as a descriptor for rationalizing charge transfer behavior upon photoexcitation in the structurally related D–A CMPs. Two CMPs, denoted as TP-CMP and TN-CMP, were synthesized using the same electron donor—triptycene (TATP), but different electron acceptors, 1,4,5,8-naphthalenetetracarboxylic dianhydride (NDA), and pyromellitic dianhydride (PMDA), respectively—and evaluated for CO₂ photoreduction. TP-CMP delivers a substantially higher CO production rate of 25.78 μmol h^–1g^–1 with 98.07% selectivity, outperforming TN-CMP (12.16 μmol h^–1g^–1 with 97.22%). Despite the stronger electron-withdrawing ability of NDA in TN-CMP, TP-CMP exhibits higher D–A polarity, more favorable charge separation, and a lower free-energy requirement for *COOH formation, collectively consistent with its superior CO₂-to-CO activity. This work establishes molecular polarity as an effective descriptor rather than D–A energy‑gap engineering for designing high-performance CMP-based photocatalysts for selective CO₂ photoreduction.