Long-Chain Surfactant Cations Template Layered A2SbCl5 Series with Near-Unity Photoluminescence Quantum Yield

Zero-dimensional (0D) hybrid metal halides exhibit efficient intrinsic optical performance without doping, making them strong candidates for solid-state lighting and radiation detection. However, rational design is hindered by structural diversity introduced by different organic cations. Here, we report a series of hybrid antimony chlorides, (BDXA)₂SbCl₅ (Xyl = C14, C16, C18), using long-chain quaternary benzyldimethyl-Xylammonium cations to examine the effect of chain length on structure and optical properties. Single-crystal X-ray diffraction reveals the first isostructural A₂SbCl₅ series featuring 0D square pyramidal [SbCl₅]²⁻ units in a monoclinic structure stabilized by nonpolar alkyl chain interactions. The series adopts a novel structure with polar bilayers of SbCl₅ anions and ammonium cations, spaced by alkyl chains, half of which are bent for efficient packing. As chain length increases, only the bilayer spacing changes; [SbCl₅]²⁻ units remain identically arranged due to the shared benzyldimethyl headgroup. All compounds exhibit dual-band emission from singlet and triplet self-localized Sb³⁺ states, with near-unity photoluminescence quantum yields. This study introduces a family of highly efficient emitters and demonstrates that long-chain backbones offer a tunable structural design element in hybrid halides, enabling the development of functional materials for optoelectronic applications.