Amplifying Chirality-Induced Spin Selectivity in Helical Covalent Organic Frameworks through Fullerene Encapsulation

The chirality-induced spin selectivity (CISS) is fundamental to spintronics and molecular electronics; however, achieving high and tunable spin polarization remains challenging due to the difficulty in precisely engineering chiral architectures and modulating spin-orbit interactions. Here, we report a host-guest strategy to amplify the CISS effect by encapsulating fullerenes (C60 and C70) within three-dimensional (3D) helical chiral covalent organic frameworks (CCOFs). Two pairs of enantiomeric CCOFs (37 and 38) are synthesized from chiral binaphthalene dialdehydes and a tetraamine, forming right- and left-handed helical structures. The resulting fullerene@CCOF adducts, prepared via in situ self-assembly, exhibited clear chirality transfer, as evidenced by strong Cotton effects in circular dichroism spectra. Magnetic conductive atomic force microscopy (mc-AFM) revealed pronounced spin-selective charge transport in the pristine CCOFs, which was significantly enhanced upon fullerene encapsulation─boosting spin polarization from 46-50 to 77% with C60, and up to 90% with C70. The superior enhancement observed with C70 is likely due to its ellipsoidal geometry, which facilitates stronger π-π interactions and more effective spin-orbit coupling within the chiral environment. This study represents the first demonstration of CISS modulation through guest encapsulation in chiral materials, underscoring the promise of host-guest interactions as a robust platform for developing advanced spintronic materials and devices.