Centimeter-scale chiral zero-dimensional manganese halide hybrids with green emission and second-harmonic generation

Two centimeter-scale zero-dimensional manganese(II) halide hybrids, [MPPZ]MnX₄ (X = Br, Cl; MPPZ = diprotonated 1-methyl-3-phenylpiperazine), were grown by solvent evaporation. Single-crystal X-ray diffraction shows that both compounds crystallize in the chiral, noncentrosymmetric orthorhombic space group P2₁2₁2₁ and contain isolated [MnX₄]^2- tetrahedra separated by organic dications. The Br and Cl analogues emit green light at 518 and 514 nm, respectively. Microsecond lifetimes, variable-temperature photoluminescence, and electronic-structure calculations support Mn²⁺-centered d-d emission, while localized states and excitation-associated structural distortion modulate the relaxation process. Powder SHG measurements give responses of 2.13 and 1.55 × KDP for the Br and Cl compounds, respectively, consistent with their noncentrosymmetric structures. Both materials retain similar PL spectra and PXRD patterns after 90 days in air, 24 h of UV irradiation, and heating at 353 K. Proof-of-concept WLEDs based on these green emitters show color-rendering indices of 97 and 98, identifying these chiral 0D manganese halides as luminescent hybrids with measurable SHG activity.