Light-Harvesting Spin Hyperpolarization of Organic Radicals in a Metal-Organic Framework

Light-driven spin hyperpolarization of organic molecules is a crucial technique for spin-based applications such as quantum information science (QIS) and dynamic nuclear polarization (DNP). Synthetic chemistry provides the design of spins with atomic precision and enables the scale-up of individual spins to hierarchical structures. The high designability and extended pore structure of metal-organic frameworks (MOFs) can control interactions between spins and guest molecules. However, the effective design of polarizing radical electron spins by photoexcitation in MOFs has been unexplored. Here, we show that it is possible to effectively hyperpolarize radical electron spins by harvesting mobile excitons in MOFs. As a proof of concept, we introduce 4-carboxy TEMPO molecules as electron spins into MOF-525, which contains an array of porphyrin chromophores, and demonstrate that this light-harvesting MOF system generates a spin-polarized excited quartet state and doublet ground state even by doping a small amount of electron spins. The current material design leads to the creation of highly spin-polarized nanospaces that can be used for quantum sensing and DNP by efficiently generating high-spin polarization in MOFs doped with small amounts of electron spins to prevent spin relaxation.