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

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[MnCl₄∙MnCl₆] (HIm = imidazolium), which concurrently incorporates both tetrahedral and octahedral Mn^{2 +} centers within a single lattice. Under pressure, the red emission of [MnCl₆]^4- exhibits a pronounced and linear redshift and intensity attenuation. However, the green emission of [MnCl₄]^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 [MnCl₆]^4- octahedra and high rigidity of the [MnCl₄]^2- tetrahedra. Our findings demonstrate that hybrid organic-inorganic crystals represent a promising class of self-calibrated optical sensing materials for next-generation metrology.