Topology-Controlled Chirality and Spin Selectivity in Two-Dimensional Covalent Organic Frameworks

Controlling electron spin is fundamental to spintronics, where the chirality-induced spin selectivity (CISS) effect enables magnet-free spin-polarized transport. However, achieving robust and tunable spin polarization in solid-state materials remains a critical challenge. Here, we show that topological isomerism offers a direct strategy to modulate chirality and spin selectivity in two-dimensional (2D) covalent organic frameworks (COFs). Two Zn(salen)-based chiral COFs, TPE-KGM and TPE-SQL, were synthesized from identical precursors yet crystallized into distinct <b>kgm</b> and <b>sql</b> networks. Although compositionally identical, the <b>kgm</b> COF exhibits only weak local geometrical chirality, whereas the <b>sql</b> develops long-range structural chirality that markedly enhances spin selectivity. Circular dichroism (CD) and circularly polarized luminescence (CPL) reveal stronger chiral amplification in the <b>sql</b> topology, while magnetic conductive atomic force microscopy (mc-AFM) confirms enhanced spin polarization of 83% for TPE-SQL versus 53% for TPE-KGM, in sharp contrast to inorganic <b>kgm</b> crystals, where spin frustration and electronic chirality in <b>kgm</b> lattices typically yield higher spin polarization. Furthermore, both frameworks can be exfoliated into nanosheets and integrated with monolayer WSe₂ to form van der Waals heterostructures, achieving spin injection with degrees of circular polarization of 8.1% (TPE-SQL) and 3.9% (TPE-KGM) at 78 K. These findings establish topology as a powerful design principle for governing chirality and spin selectivity in crystalline polymers, advancing the development of chiral optoelectronic and valleytronic materials.