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.