Guest-Induced Reversible Phase Transformation of Organic–Inorganic Phenylpiperazinium Antimony (III) Chlorides with Solvatochromic Photoluminescence

Antimony halide hybrids have been recently revealed to show reversible solvent-induced phase transformation along with solvatochromic photoluminescence (PL). However, the effects of guest molecules on such phase transformation are not yet well understood due to metastable solvent-induced phases. Here, we report the synthesis of 1-phenylpiperazinium (PhPi)-incorporated antimony chloride hybrids ((PhPi)₂SbCl₇·xH₂O) with a guest H₂O-mediated hydrogen bonding network. Upon removing H₂O molecules through vacuum treatment or solvent induction, red-emissive (PhPi)₂SbCl₇·xH₂O with a PL quantum yield (QY) of 32% is transformed into two yellow-emissive isomers (PhPi)₂SbCl₇-V (PL QY: 9%) or (PhPi)₂SbCl₇-S (PL QY: 95%), which can be reversibly transformed into (PhPi)₂SbCl₇·xH₂O by placing in open air. Due to more compact and rigid structures that suppress octahedral distortion, smaller Stokes shifts are observed for both (PhPi)₂SbCl₇-V (1.41 eV) and (PhPi)₂SbCl₇-S (1.35 eV), consistent with density function theory calculations that (PhPi)₂SbCl₇·xH₂O exhibits the largest distortion at excited states. Additionally, compared to poorly emissive (PhPi)₂SbCl₇-V, (PhPi)₂SbCl₇-S with near-unity QY is attributed to the Jahn–Teller-like deformation of excited states and a large thermal quenching barrier. Our findings highlight the role of guest molecules in tuning [SbCl₆] octahedral distortion to enhance the luminescence efficiency of Sb-based halides.