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.