Reversible Stimuli-Responsive Antimony-Based Hybrid Metal Halides for Information Security and Anti-Counterfeiting

Stimuli responsive luminescent materials that can be triggered by mechanical, thermal, or solvent inputs hold great potential for advanced information security and anti-counterfeiting applications. In this study, we present a family of 0D antimony based organic inorganic hybrid metal halides, C 7 H 18 N 2 SbX 5 (where C 7 H 18 N 2 represents 1-Isopropylpiperazine and X = Cl, Br, I), designed by coupling a flexible diammonium cation with highly distorted Sb halide polyhedra. Single crystal analysis reveals that C 7 H 18 N 2 SbCl 5 consists of discrete tetrameric clusters, while its Br and I counterparts contain edge sharing dimeric [Sb 2 X 10 ] units. Under UV light, the pristine C 7 H 18 N 2 SbCl 5 is nonemissive at room temperature but exhibits reversible, stimulus-induced turn-on luminescence: grinding, hydrostatic pressure, heating, or solvent treatment trigger broadband orange emission. Temperature and pressure dependent photoluminescence, along with structural analyses, show that these external stimuli induce local angular distortions in the Sb–Cl polyhedra and reorganize the hydrogen bonding network, while maintaining the overall framework. Density functional theory calculations indicate that the emission is related to Cl 3p to Sb 5s/5p transitions, with lattice distortions stabilizing self-trapped excitons and suppressing nonradiative decay. Polymer composites based on C 7 H 18 N 2 SbCl 5 exhibit thermally rewritable, solvent-controlled, and mechano-responsive luminescence patterns.