The correlation between structural factors and Stokes shifts in zero-dimensional Antimony(III) halides

Zero-dimensional (0D) hybrid metal halides (HMHs) have recently garnered significant attention as promising light emitters due to their distinctively Stokes-shifted broadband emissions resulting from self-trapped excitons (STEs). However, the influence of crystalline structures on the Stokes shift remains inadequately understood. Herein, we design and synthesize a series of 0D (Ph4P)2SbCl5-xBrx (Ph4P = tetraphenylphosphonium, x = 0–5) compounds to elucidate the intrinsic relationship between structural factors and the Stokes shift in 0D Sb(III) halides. Our comprehensive investigations into their crystalline structures and photoluminescence (PL) properties unveil that the Stokes shift correlates with intra- and inter-pyramidal [SbCl5-xBrx]2- units. Specifically, a shorter vertical Sb–Cl bond within the square pyramid, coupled with a greater Sb⋯Sb distance between the pyramidal units, facilitates significant structural relaxation in excited states, resulting in a larger Stokes shift, and vice versa. Notably, this principle applies not only within identical space groups but also across different crystal systems. Furthermore, our findings are supported by analyses of the structures and PL properties of other reported 0D Sb(III) halides with square pyramidal coordination. This study elucidates the structure-dependent nature of the Stokes shift in 0D Sb(III) halides, offering a novel avenue for the design of functional 0D metal halide materials.