Optically Addressable Spins in a Metal–Organic Framework

Molecular spins supporting optically detected magnetic resonance (ODMR) offer unique opportunities for quantum sensing and many-body physics by combining the sensitivity and spatial resolution offered by optical spin detection with the capacity for bottom-up assembly and chemical control. Metal–organic frameworks (MOFs) are a promising architecture to leverage such opportunities since they offer control over spin placement, tunable porosity and large internal surface areas for efficient integration with sensing targets, and a richly tunable chemical space. However, optical spin readout has not been demonstrated in a MOF. Here, we report the first successful optical detection of spins in a MOF. We use a porphyrin-based aluminum MOF (Al-PMOF), which supports efficient triplet generation on the porphyrin chromophore ligands. Using electron paramagnetic resonance, we demonstrate that these triplet states support a spin coherence time (T2) on the order of a few microseconds at 50 K. Importantly, we successfully detect optically detected magnetic resonance of these triplets using near-infrared ODMR at 77 K. Optical spin readout in a MOF paves the way for next-generation quantum sensing applications that leverage bottom-up assembly.