With the flourishing development of (CH₃NH₃)PbI₃, three-dimensional (3D) organic–inorganic perovskites with unique structure–property flexibility have become a worldwide focus. However, they still face great challenges in effectively inducing ferroelectricity. Despite the typical 3D perovskite structure and the ability of dabco (1,4-diazabicyclo[2.2.2]octane) to trigger phase transition, unfortunately [H₂dabco]RbCl₃ adopts a nonpolar crystal structure without ferroelectricity. Within the larger RbI₃ framework, we assemble N-methyl-1,4-diazoniabicyclo[2.2.2]octane (MeHdabco) obtained by reducing the molecular symmetry of dabco into a new 3D organic–inorganic perovskite. As expected, MeHdabco bearing a molecular dipole moment turns out to be vital in the generation of polar crystal structure and ferroelectric phase transition occurring at 430 K. It is the first time that the dabco component has been successfully wrapped into a 3D cage to achieve ferroelectricity even through there is intensive research on dabco. This precise molecular design strategy based on the modification of molecular symmetry provides an efficient route to enrich the family of 3D organic–inorganic perovskite ferroelectrics. Intriguingly, the iodine-doped crystal can exhibit intense saffron yellow luminescence with a high quantum yield of 17.17% under UV excitation, extending its application in the field of ferroelectric luminescence and/or multifunctional devices.

中文翻译：

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高T _c 3D有机-无机钙钛矿铁电体的精确分子设计：[MeHdabco] RbI ₃（MeHdabco = N-甲基-1,4-二氮杂双环[2.2.2]辛烷）

随着（CH ₃ NH ₃）PbI ₃的蓬勃发展，具有独特结构-属性灵活性的三维（3D）有机-无机钙钛矿已成为全球关注的焦点。然而，它们在有效地感应铁电方面仍然面临巨大的挑战。尽管具有典型的3D钙钛矿结构和dabco（1,4-二氮杂双环[2.2.2]辛烷）触发相变的能力，但不幸的是[H ₂ dabco] RbCl ₃采用无铁电的非极性晶体结构。在更大的RbI ₃框架内，我们组装N-甲基-1,4-二氮杂双环[2.2.2]辛烷（MeHdabco）是通过将dabco的分子对称性降低为新的3D有机-无机钙钛矿而获得的。不出所料，带有分子偶极矩的MeHdabco在430 K发生的极性晶体结构和铁电相变中起着至关重要的作用。这是dabco组件首次成功包裹在3D笼中以实现铁电性即使通过对dabco的深入研究也是如此。这种基于分子对称性修饰的精确分子设计策略为丰富3D有机-无机钙钛矿铁电材料家族提供了一条有效途径。有趣的是，在紫外线激发下，碘掺杂的晶体可以显示出强烈的藏红黄色发光，量子产率高达17.17％，