Dual‐Emission Switching in a Mn(II)‐Based Hybrid Bromide via Water Coordination: Synthesis, Structure, and Processing

Abstract This work presents the synthesis, characterization, and functional evaluation of a new luminescent manganese(II) hybrid halide, (pr‐ted) 2 [MnBr 4 ] , containing the organic cation (pr‐ted) + (1‐propyl‐1,4‐diazabicyclo[2.2.2]octane). The compound exhibits green photoluminescence and undergoes a reversible transformation to a red‐emitting hydrated form, (pr‐ted) 2 [MnBr 4 (OH 2 )] , upon exposure to ambient humidity. Single‐crystal X‐ray diffraction reveals differences in coordination geometry between the two phases: a tetrahedral environment in the anhydrous form and a distorted trigonal bipyramidal in the hydrated phase. This structural change is responsible for the observed red shift in emission. The interconversion is fully reversible through thermal treatment or vacuum exposure. Photoluminescence and density functional theory calculations are employed to investigate optical behavior and electronic transitions. In situ X‐ray powder diffraction confirms the humidity‐induced phase transition. Both forms exhibit solubility in polar solvents, enabling the fabrication of luminescent coatings via wet‐processing methods. Impregnation and nebulization approaches are explored. The impregnation process enables the fabrication of composites on porous materials, while the nebulization method produces homogeneous coatings on non‐porous substrates. These coatings maintain reversible luminescent switching, validating the potential of (pr‐ted) 2 [MnBr 4 ] as a responsive material for humidity sensing. The integration of humidity‐sensitive luminescent compounds into functional platforms using cost‐effective techniques is demonstrated, for applications in environmental monitoring.