Versatile Nickel(II) Scaffolds as Coordination‐Induced Spin‐State Switches for 19 F Magnetic Resonance‐Based Detection

19 F magnetic resonance (MR) based detection coupled with well-designed inorganic systems shows promise in biological investigations. Two proof-of-concept inorganic probes that exploit a novel mechanism for 19 F MR sensing based on converting from low-spin (S=0) to high-spin (S=1) Ni2+ are reported. Activation of diamagnetic NiL1 and NiL2 by light or β-galactosidase, respectively, converts them into paramagnetic NiL0 , which displays a single 19 F NMR peak shifted by >35 ppm with accelerated relaxation rates. This spin-state switch is effective for sensing light or enzyme expression in live cells using 19 F MR spectroscopy and imaging that differentiate signals based on chemical shift and relaxation times. This general inorganic scaffold has potential for developing agents that can sense analytes ranging from ions to enzymes, opening up diverse possibilities for 19 F MR based biosensing.