Understandingthe Relation between the Structure andEmission Properties in 0D (2-ABI)₃Bi_1–<i>x</i>Sb_<i>x</i>Cl₆·H₂O: Impact of Structural Distortion and Stereoactivity of ns² Lone Pairs

Zero-dimensional (0D) organic–inorganic metal halides (OIMHs) have emerged as a fascinating class of materials, offering unprecedented opportunities for the development of low-cost solid-state lighting devices. Herein, we report two novel 0D Bi/Sb-based OIMHs, (2-ABI)₃MCl₆·H₂O (M = Bi, Sb), crystallizing in the monoclinic <i>P</i>2₁/<i>n</i> space group. Under 365 nm UV light irradiation, the Sb-analogue displays a bright and broad yellow emission band at 580 nm with a photoluminescence (PL) quantum yield of 34.6%, which may be attributed to the distortion-induced self-trapped excitons (STEs). Theoretical study of (2-ABI)₃SbCl₆·H₂O in the ground state and excited state shows specific bonds are distorted significantly indicating the role of the stereoactivity of the 5s² lone pair. To understand the effect of gradual Sb substitution on the structure and the optical properties of (2-ABI)₃BiCl₆·H₂O, a series of mixed compounds, (2-ABI)₃Bi_1–<i>x</i>Sb_<i>x</i>Cl₆·H₂O (refined <i>x</i> = 0, 0.11, 0.40, 0.53, 0.87, 1) was prepared. This work provides important insight into the correlation between the PL properties and local structure distortion in the ground and excited states induced by the expression of 5s² lone-pair electrons of Sb³⁺, thus providing an efficient tool for exploring highly emissive 0D OIMHs and further modulating their structures to enhance the luminescent properties for practical optoelectronic applications.