Broadband red-emitting one-dimensional halide (C₃H₈N₆)₂MnCl₆ with a high photoluminescence quantum yield

Organic-inorganic hybrid metal halides (OIHMs) have emerged as highly promising optoelectronic materials for light-emitting diodes, fluorescence sensing, and radiation detection due to their structurally tunable crystal structures and excellent photophysical properties. In particular, manganese-based OIHMs have attracted extensive attention because of their characteristic broadband -d-d emission, environmental benignity, and low fabrication cost. Herein, a novel one-dimensional (1D) Mn-based OIHM (C₃H₈N₆)₂MnCl₆ was successfully synthesized via a facile aqueous solution method. (C₃H₈N₆)₂MnCl₆ crystallizes in the P2₁/m space group and features 1D [Mn_nCl_5n+1]_∞^(3n+1)- chains constructed of vertex-sharing [MnCl₆]^4- octahedra, which are further isolated by [C₃H₈N₆]²⁺ cations. The (C₃H₈N₆)₂MnCl₆ crystals display a broad excitation band spanning 240-600 nm with a maximum at 415 nm and emit broadband red emission covering 540-870 nm peaking at 665 nm. The photoluminescence quantum yield (PLQY) of (C₃H₈N₆)₂MnCl₆ crystals is up to 78.82%, which is significantly higher than that of the constituted organic component melamine (5.38%). Mechanistic studies demonstrate that the red luminescence originates from the spin-forbidden d-d electron transitions of the [MnCl₆]^4- octahedra, and the 1D chain structure facilitates exciton localization, benefiting broadband emission and high PLQY. Meanwhile, the high thermal activation energy of 141.8 meV suppresses thermally activated exciton dissociation at room temperature, thereby favouring efficient radiative recombination. This work not only enriches the structural family of Mn-based OIHMs but also provides a feasible strategy for the design of high-efficiency red-emitting luminescent materials.