Molecular-Level Control of Exciton and Nonlinear Optical Properties in 1D Hybrid Antimony Halides via Cation Steric Design

Hybrid antimony halides with one-dimensional (1D) architectures have gained increasing attention due to their structural tunability and versatile optoelectronic properties. In this study, six 1D organic-inorganic metal halides (OIMHs), including (C₇H₁₈N₂)SbX₅ and (C₆H₁₆N₂)SbX₅ (X = Cl, Br, I), were synthesized using two structurally related organic cations: 1-methyl-4-(methylamino)piperidine (C₇H₁₆N₂) and 4-(methylamino)piperidine dihydrochloride (C₆H₁₆Cl₂N₂). Comparative analysis reveals that the introduction of a methyl group significantly alters the steric environment and electronic structure, leading to reduced octahedral distortion and modified hydrogen bonding interactions. Among the synthesized compounds, (C₇H₁₈N₂)SbCl₅ exhibits strong broadband self-trapped exciton emission (STEs) with long lifetime and stable excitation behavior. In contrast, (C₆H₁₆N₂)SbCl₅ exhibits no detectable photoluminescence but demonstrates significant second-harmonic generation (SHG) activity, with an intensity approximately 1.5 times that of KH₂PO₄. These findings demonstrate that subtle changes in organic cation structure can effectively modulate excitonic dynamics and nonlinear optical responses in hybrid halide systems, providing a viable strategy for designing multifunctional optoelectronic materials.