Self‐Calibrated Luminescence Sensing Under Pressure in a Hybrid Manganese Halide

ABSTRACT Hybrid organic‐inorganic manganese halides have emerged as a promising class of emitters, owing to their excellent optical properties, low toxicity, and rich structural diversity. However, achieving site‐specific control over their high‐pressure optical response remains a great challenge. In this study, we report a zero‐dimensional manganese chloride, (HIm) 6 [MnCl 4 ∙MnCl 6 ] (HIm = imidazolium), which concurrently incorporates both tetrahedral and octahedral Mn 2 + centers within a single lattice. Under pressure, the red emission of [MnCl 6 ] 4− exhibits a pronounced and linear redshift and intensity attenuation. However, the green emission of [MnCl 4 ] 2− remains stable in both peak position and intensity, serving as a rigid energetic anchor. By leveraging the invariant green emission as an internal reference and the pressure‐sensitive red emission as a probe, a self‐calibrated pressure sensing system is achieved. Synchrotron high‐pressure x‐ray diffraction, in situ optical spectroscopy and density functional theory calculations demonstrate that this decoupled response originates from the large structural compressibility of the [MnCl 6 ] 4− octahedra and high rigidity of the [MnCl 4 ] 2− tetrahedra. Our findings demonstrate that hybrid organic‐inorganic crystals represent a promising class of self‐calibrated optical sensing materials for next‐generation metrology.