Acceptor-extended donor-acceptor COFs enable charge-polarization tuning for efficient photocatalytic C–H oxidation

Abstract

Rational modulation of charge polarization in covalent organic frameworks constitutes a fundamental strategy for optimizing photocatalytic performance, yet achieving precise and systematic control over these parameters remains a significant challenge. Moreover, the interplay in covalent organic frameworks between molecular dipole moments, electronic structure, and catalytic activity is poorly understood. Here, we demonstrate that controlled extension of the acceptor unit in donor–acceptor (D–A) type COFs provides an effective handle for tuning charge polarization. By systematically elongating the acceptor linker from phenylene to naphthalene and anthracene, we achieve progressive modulation of the molecular dipole moment, accompanied by narrowed bandgaps and suppressed charge recombination, as confirmed by combined spectroscopic and density functional theory analyses. When evaluated in the photocatalytic oxidation of tetrahydroisoquinolines, the anthracene-linked Aa-COF delivers near-quantitative product yield (98%) under mild conditions, with scalability demonstrated via gram-scale synthesis and solar-driven operation. Mechanistic studies implicate superoxide and singlet oxygen as the primary reactive species, while Fukui analysis identifies enhanced nucleophilicity as a key factor facilitating oxygen activation. This work establishes acceptor extension as a viable design principle for polarization-modulated COF photocatalysts, offering a generalizable approach for selective organic transformations under sustainable conditions.