Two SbX5-based isostructural polar 1D hybrid antimony halides with tunable broadband emission, nonlinear optics, and semiconductor properties

Metal halide perovskites based on MX6 (M is metal and X is halogen) octahedra have developed into significant materials, extensively used in many fields, such as solid-state lighting, semiconductor, and nonlinear optics. However, the MX5 square pyramid-based hybrid metal halides beyond zero-dimensional (0D) polyhedrons and clusters are rarely reported. Herein, we reported two new isostructural hybrid antimony halides, namely (2cepyH)SbCl4 (1-Cl) and (2cepyH)SbBr4 (2-Br) (2cepy = 1-(2-chloroethyl)pyrrolidine), characterized by 1D polar polyanionic chains formed by corner-sharing SbX5 tetragonal pyramid units. Upon photoexcitation at 340 nm, 1-Cl shows broad, yellow phosphorescence emissions stemming from triplet self-trapped excitons, as proved by its long lifetime (6.85 μs) and the temperature dependences of broadband emission. To our knowledge, this should be the first observation on the broadband emissive properties in the 1D hybrid metal halide constructed by MX5 tetragonal pyramid units. Moreover, second harmonic generation measurements show that the nonlinear optical properties of 2-Br (∼3.2 × KDP) are superior to that of 1-Cl (∼1.8 × KDP). Experimental and calculated data indicate that the bandgap of 1-Cl is larger than that of 2-Br and that the polar inorganic moieties determine their band structures. Our work opens up a new way for constructing broadband emission materials with novel polar frameworks.