Spin-Polarized Radicals with Extremely Long Spin-Lattice Relaxation Time at Room Temperature in a Metal-Organic Framework

The generation of spin polarization is key in quantum information science and dynamical nuclear polarization. Polarized electron spins with long spin-lattice relaxation times (T1) at room temperature are important for these applications, but have been difficult to achieve. We report the realization of spin-polarized radicals with extremely long T1 at room temperature in a metal-organic framework (MOF) in which azaacene chromophores are densely integrated. Persistent radicals are generated in the MOF by charge separation after photoexcitation. Spin polarization of triplet generated by photoexcitation are successfully transferred to the persistent radicals. Pulse ESR measurements reveal that the T1 of the polarized radical in the MOF is as long as 274 s at room temperature. The achievement of extremely long spin polarization in MOFs with nanopores accessible to guest molecules will be an important cornerstone for future highly sensitive quantum sensing and efficient dynamic nuclear polarization.