Spin‐Correlated Luminescence Enabled by Bright–Dark Radical Pairing in a Diradical System

Abstract Spin‐optical modulation lies at the core of emerging technologies in spintronics, spin‐based optoelectronics, and quantum materials. Open‐shell luminescent diradicals, featuring two unpaired and synthetically tunable spins, offer a molecular platform to achieve such control. However, previous studies have been restricted to symmetric systems, where spin interactions occur between two identical, luminescent radicals. Here, we demonstrate that a non‐luminescent (dark) radical can effectively modulate the spin and photophysical behavior of a luminescent (bright) radical within an asymmetric diradical framework. The resulting molecule exhibits a unique three‐stage magnetoluminescence (ML) response at low temperatures, arising from hyperfine coupling (HFC) ( B < 0.05 T), the Δg ‐induced spin mixing (0.05–0.8 T), and spin polarization (0.8–7 T). Notably, the system exhibits pronounced ML enhancement (>14%) under ultra‐low magnetic fields ( B < 0.05 T), a previously unreported phenomenon in molecular spin‐optical systems. These findings establish asymmetric bright–dark diradicals as a powerful new motif for spin‐photon interface design, providing fresh insights into the fundamental photophysics of open‐shell systems.