Tuning Photoluminescence Transformation in Manganese Halides via Halogen Substitution and Phase‐Transition Regulation for Anti‐Counterfeiting and Information Encryption

Photoluminescence (PL) switchable materials responding to external stimuli are highly desirable for advanced smart optical applications, while achieving high‐contrast and reversible switching through rational structural design remains challenging. Herein, based on coordination‐sensitive properties of Mn(II)‐based organic‐inorganic hybrid metal halides (OIMHs), we proposed two structural regulation strategies to construct PL switching materials. First, through halogen substitution, a 1D (C 9 H 14 N 2 )MnCl 3 ·Cl ( 1 ), featuring a MnCl 6 octahedron and exhibiting red emission, and a 0D (C 9 H 14 N 2 )MnBr 4 ( 2 ), featuring a MnBr 4 tetrahedron and exhibiting green emission were synthesized. Second, by employing an organic cation with coordination capability, we constructed a phase‐transition crystal (C 9 H 13 N 2 O) 2 MnBr 4 ( 3 ) with reversible red‐green PL switching through heat‐ and humidity‐driven breakage and reformation of Mn–O bonds between MnO 2 Br 4 octahedron and MnBr 4 tetrahedron. Utilizing PL transformations of the three compounds, we demonstrated multi‐level optical anti‐counterfeiting and information encryption systems, highlighting the promising potential of PL‐switchable OIMHs for advanced optical applications.