Humidity-Triggered Reversible 0–1D Phase Transition in Hybrid Antimony Halides

Stimulus-responsive inorganic-organic hybrid metal halides (IOMHs) have shown great potential in applications such as sensing and anti-counterfeiting. IOMHs can undergo a variety of structural changes when triggered by humidity; however, relevant reports of structural dimensionality change from zero dimension (0D) to one dimension (1D) are rare. This study investigates the synthesis, structure, and properties of two antimony-based IOMHs, namely 0D-(Mp)₃SbCl₆·MeCN and 1D-(Mp)₂SbCl₅ (Mp = protonated morpholine; MeCN = acetonitrile). Photophysical characterizations show that (Mp)₃SbCl₆·MeCN, when being excited at 375 nm, exhibits typical self-trapped exciton triplet state broad-band emission, with a peak at 620 nm and a quantum yield as high as 75.06%. Under humid conditions, the 0D structure of (Mp)₃SbCl₆·MeCN undergoes a phase transition, leading to the 1D structure of (Mp)₂SbCl₅. This transition is accompanied by fluorescence quenching. X-ray powder diffraction, Raman spectroscopy, and thermogravimetric analysis confirm the phase transition process and its reversibility. Based on the high contrast of fluorescence before and after phase transition, (Mp)₃SbCl₆·MeCN is demonstrated as an ideal material for fluorescence water sensing, capable of detecting trace amounts of water in tetrahydrofuran with a detection limit of 0.2% <i>v</i>/<i>v</i>.