Chiral 2D double halide perovskites have become a new trend the past few years due to their lead-free character but also for their promising optoelectronic applications. In this context, we report new 2D double halide perovskite compounds, following the general chemical formula A_{(2 or 4)}Ag^IM^IIIBr₈  where A is either the cystaminium dication (Cyst²⁺, chiral conformation) or the chiral cation (S/R)-1-(4-bromophenyl)ethylammonium (S/R-4BrMBA) and M^III = Sb³⁺, Bi³⁺. Cystaminium is known for its conformational axial chirality change in the solid state,[1] resulting in the synthesis of chiral perovskites and compounds which exhibit phase transition, leading to potential switchable SHG materials.[2]  Driven by this objective, we synthesized and fully characterized the 2D (Cyst)₂AgSbBr₈ compound. DSC measurments showed that this compound exhibits three reversible phase transitions going from Phase 1 (Ph 1) to Phase 2 (Ph 2) (C2/c to C2/m, T = 40°C) upon heating, and upon cooling from Ph 2 to Phase 3 (Ph 3) (C2/m to C2, T = 60°C) and from Ph 3 back to the original compound at T < RT. Therefore, we performed temperature-dependent SHG measurements, highlighting the switchable SHG properties of such compound. The results of the measurement revealed that upon heating the transformation from Ph 1 to Ph 2 occurs via Ph 3 as a SHG signal is observed at 45°C. Upon cooling, the expected SHG signal originated by Ph 3 appears, with the maximum of it being at 11°C. (Figure 1a). The second spacer that we used was the chiral molecule S/R-4BrMBA. The effects of chirality in 2D lead halide perovskites is a newly grown field and based on the lack of chiral 2D double perovskites in the literature, a complete series of 2D bromide-based and iodide-based double perovskites was fully characterized. Thin films were prepared in order to study the chiroptical properties of the materials. The strong modulation of the structure and circular dichroism (CD) properties at the nanoscale is unprecedented, since the thin films of (S/R-4BrMBA)₄AgBiBr₈ strongly evolve from a single-phase compound with small intrinsic CD to a polymorphic material showing a strong increase in the chiroptical signal due to macroscopic effects, something which is not observed for the iodide derivatives (Figure 1b).[3] Such series of compounds will allow us to explore their chirality-induced spin selectivity (CISS) for both the fundamental understanding of the CISS effect and the practical aspect of preparing lead-free spintronic devices.