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

¹⁹F 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 ¹⁹F 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 ¹⁹F 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 ¹⁹F 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 ¹⁹F MR based biosensing.