Chem. Mater., 2021, 33, 20, 8106–8111, https://doi.org/10.1021/acs.chemmater.1c02896

Recent discoveries in organic−inorganic metal halides reveal superior semiconducting and polarization properties. Herein, we report three organic–inorganic metal halides, (PBA)₄BiBr₇·H₂O, (PBA)₄BiI₇·H₂O, and (PBA)₄InBr₇·H₂O [(PBA)⁺ = C₆H₅(CH₂)₄NH₃⁺], with band gaps of ∼3.52, ∼2.29, and ∼4.05 eV, respectively. They possess zero-dimensional structures containing the inorganic octahedra [MX₆]^3– (M = Bi, In, X = Br, I) and unbound X^– ions and crystallize in the C2 space group. (PBA)₄BiI₇·H₂O shows a second-harmonic-generation (SHG) response in the infrared region, approximately 1.3 times that of AgGaS₂; (PBA)₄BiBr₇·H₂O and (PBA)₄InBr₇·H₂O show SHG responses in the ultraviolet region, approximately 0.4 and 0.6 times that of KH₂PO₄, respectively. The large SHG responses are attributed to the synergistic contribution of the octahedral distortion of [MX₆]^3– (M = Bi, In, X = Br, I) and the ordered arrangement of the benzene ring-containing organic cation PBA⁺. Upon ultraviolet and visible-light excitations at room temperature, (PBA)₄BiBr₇·H₂O, (PBA)₄BiI₇·H₂O, and (PBA)₄InBr₇·H₂O exhibit broad red-light luminescence with large Stokes shifts of 290, 237, and 360 nm, respectively, due to self-trapped exciton emission. All of these properties demonstrate that this series of metal halides are potential multifunctional optoelectronic materials.