Dual‐Dimensional Compositional Engineering Driven Synergistic Color Switching and Emission Enhancement in Mn(II)‐Based Metal Halides

ABSTRACT Low‐dimensional Mn‐based organic‐inorganic metal halides (OIMHs) have attracted considerable interest for optoelectronic applications owing to their unique d–d electronic transitions, environmental friendliness, and structural tunability. Nevertheless, achieving simultaneous control over emission color and intensity within a single precursor system remains challenging. Herein, we propose a dual‐dimensional compositional engineering strategy based on the same precursor (C 6 H 14 ClN) to synergistically tune the luminescence properties of Mn‐based OIMHs via a combined computational‐experimental approach. By simply varying the molar ratio of the organic amine salt to MnCl 2 and further adding raw materials to the as‐obtained products, we achieve reversible switching between (C 6 H 14 N)MnCl 3 and (C 6 H 14 N) 3 MnCl 5 , accompanied by a transition in dimensionality from 1D) to 0D), a change in Mn 2+ coordination number from 5 to 4, and a corresponding emission color shift from red to green. Moreover, substituting Cl − with Br − optimizes the Mn···Mn distance, reducing energy transfer between Mn 2+ ions. This effect effectively suppresses non‐radiative recombination induced by the heavy‐atom effect, thereby significantly enhancing the green emission intensity of (C 6 H 14 N) 3 MnBr 5 . This work not only elucidates the composition‐structure‐luminescence relationship in low‐dimensional Mn(II)‐based OIMHs, but also provides clear compositional engineering guidelines for designing next‐generation high‐performance and emission color‐tunable metal halides.