Water-Triggered Structural Transformation of a Hybrid Manganese Bromide for Visual Trace-Water Detection

Accurate detection of trace water is essential for ensuring the quality control of moisture-sensitive solvents, chemical processes, and advanced materials. Herein we present a water-triggered structural transformation in hybrid manganese bromide of MnBr2(C3H7NO) for visual trace-water detection. This compound was synthesized by using pure water as a solvent with high yield. One-dimensional (1D) MnBr2(C3H7NO) exhibits bright red photoluminescence with a quantum yield of 20.39%. Upon exposure to trace water, MnBr2(C3H7NO) undergoes rapid single-crystal-to-single-crystal structural transformation from a 1D chain to a 0D nonluminescent hydrated structure of MnBr2(C3H7NO)2(H2O)2, resulting in fluorescence quenching. The fluorescence response is notably nonlinear, with a low limit of detection of 87.9 ppm and signal amplification over a narrow concentration window (∼100 ppm), enabling visual detection of trace water across various organic solvents. Notably, this process is partially reversible upon mild thermal treatment, allowing recycled use. This work demonstrates a sustainable platform for instrument-free water sensing and highlights dimensionality transformation as an effective strategy for luminescent sensing materials.