Helical Cadmium Hybrid Halide with Dual Isostructural Phase Transitions: Coexisting Dielectric Switching and Thermoreversible Blue STE Luminescence.

Organic-inorganic hybrid metal halides have attracted widespread attention due to their structural diversity and tunable physicochemical properties. However, most existing studies rely on intrinsically emissive metal ions to achieve optical responses. In contrast, the 4d10 closed-shell electron configuration of Cd2+ endows it with no inherent d-d transition luminescence capability. In this work, we assembled the CdBr42- unit with R-3-HQ to successfully synthesize [R-3-HQ]2[CdBr4] (R-3-HQ = protonated R-3-quinuclidinol). Crystallizing in the space group P212121, two isostructural phase transitions of [R-3-HQ]2[CdBr4] occur at 301 and 361 K, accompanied by a dielectric switching response with a ratio of approximately 2.5 around 361 K. Meanwhile, the material shows blue emission originating from self-trapped excitons; the emission intensity gradually decreases with increasing temperature and recovers upon cooling, demonstrating good reversibility. Density functional theory calculations further reveal that this compound is a semiconductor material dominated by the inorganic framework. This work provides a strategy for designing multifunctional materials that integrate dielectric switching and reversible luminescence modulation.