Stereochemical\nActivity and Luminescence Mechanism\nin (C<sub>4</sub>H<sub>12</sub>N)<sub>2</sub>SnCl<sub>6</sub> Doped\nwith ns<sup>2</sup> Metal Ions

Metal\nhalide luminescent materials, particularly those\ndoped with\nns<sup>2</sup> ions, exhibit exceptional optical properties. However,\nthe luminescent mechanisms associated with the stereochemical activity\nof lone-pair electrons remain insufficiently explored. In this study,\nzero-dimensional (0D) tin-based halide (C<sub>4</sub>H<sub>12</sub>N)<sub>2</sub>SnCl<sub>6</sub> is utilized as a model system to investigate\nthe effects of lattice distortion and lone-pair electron expression\non fluorescence emission characteristics by doping with 6s<sup>2</sup> and 5s<sup>2</sup> ions. The findings reveal that compared to 6s<sup>2</sup> ions, 5s<sup>2</sup> ion doping results in stronger electron–phonon\ncoupling, causing significant octahedral lattice distortion and producing\nunique dual emissions along with a large Stokes shift of 317 nm. Remarkably,\neven at temperatures as high as 360 K, (C<sub>4</sub>H<sub>12</sub>N)<sub>2</sub>SnCl<sub>6</sub>:Sb maintains its dual emission due\nto insufficient thermal activation energy to promote electron transition\nfrom excited state 1 to excited state 2. In contrast, 6s<sup>2</sup> doping exhibits a single blue emission with a small Stokes shift\nof 101 nm. Additionally, calculations of the electron localization\nfunction reveal that 5s<sup>2</sup> lone pairs exhibit static stereochemical\nexpression with specific spatial orientation, while 6s<sup>2</sup> lone pairs display dynamic behavior. These findings highlight the\ncritical role of lone-pair stereochemistry in governing the photophysical\nproperties of ns<sup>2</sup>-doped metal halides, offering new insights\ninto their luminescent mechanisms.