Circularly Polarized Light Amplifies Spin Polarization for Efficient Photoredox Chemistry in a Chiral Magnetic Catalyst.

Photocatalysis offers a promising route to sustainable energy, yet the role of carrier spin in charge transport and interfacial redox chemistry remains poorly understood. Chiral and magnetic catalysts selectively transmit spin-compatible carriers, whereas non-polarized light generates mixed-spin populations, limiting carrier utilization. Herein, we demonstrate that circularly polarized light (CPL) reversibly modulates spin-dependent carrier transport in Ni-cocatalyst-decorated, cysteine-modified CdS nanorods, thereby promoting spin-sensitive carrier utilization during aqueous methanol reforming. Optimized D(-)-CdS/Ni exhibits a 71.1% higher hydrogen evolution rate under left-handed CPL (LCP) than under right-handed CPL (RCP) at identical light intensity and spectrum, achieving an apparent quantum efficiency of 74.4% at 420 nm while promoting methanol oxidation toward formic acid. CPL-coupled magnetic conductive atomic force microscopy reveals that LCP increases the apparent spin polarization from 70.9% in the dark to 89.1%, whereas RCP suppresses it to 12.8%. Spin-polarized calculations identify nonequivalent electronic channels, while spectroscopic and kinetic measurements support enhanced carrier extraction and reduced recombination under LCP. Together, these findings establish photon handedness as a reversible optical variable for modulating spin-selective transport and photoredox chemistry, offering a strategy to complement material-encoded spin filtering with dynamic optical control of carrier utilization.