A Supramolecular Symmetry-Breaking Strategy for Enhanced Circularly Polarized Luminescence, High-Temperature Phase Transition, and Piezoelectric Response in Chiral Manganese(II) Halides

Abstract Circularly polarized luminescence (CPL) has attracted intense interest for applications in 3D displays, optical data storage, and quantum information processing. Chiral organic–inorganic hybrid metal halides (HOMHs) have emerged as promising CPL materials owing to their structural tunability, facile solution processability, and tunable photoluminescence, yet they often suffer from small luminescence dissymmetry factors (glum) and limited functionality. Herein, we report a pair of enantiomeric host–guest compounds, [18-crown-6]2[(R/S)-C3H12N2][MnCl4] (R-Mn and S-Mn; (R/S)-C3H12N2 = (R/S)-propane-1,2-diammonium), via a supramolecular assembly strategy. The resulting two-in-one structures feature strong N–H···O hydrogen bonds that lock the chiral cations and reduce the crystal symmetry from the C2 phase of the previously reported compound without 18-crown-6 to the lowest-symmetry P1 space group. R/S-Mn exhibits CPL with |glum| = 2.6 × 10–2, more than 10 times higher than the previously reported value of 2 × 10–3. Moreover, both compounds display a reversible high-temperature solid–solid phase transition at 405 K and a measurable piezoelectric coefficient of 11 pC/N. DFT calculations reveal that the band edges and emissive states are dominated by the [MnCl4]2– units. Meanwhile, the organic cations do not contribute to the electronic transitions, indicating that the CPL arises from the chiral environment of the two-in-one supramolecular cations surrounding these nonchiral emissive centers. This work demonstrates supramolecular symmetry breaking as an effective design principle for integrating enhanced CPL, thermal responsiveness, and piezoelectricity into a single multifunctional chiral hybrid metal halide system.