Reversed Quantum-Well Engineering Unlocks Large Ultraviolet Chiral Nonlinear Optical Response in a Water-Resistant 2D...

Two-dimensional (2D) chiral organic-inorganic hybrid metal halides (OIHMHs) are promising for chiroptical applications. However, conventional Ge/Sn/Pb-based systems remain limited by narrow bandgaps and poor moisture stability. In this work, we report the first 2D chiral hybrid fluorozirconate, (R/S-MBA)ZrF₅ (MBA = methylbenzylammonium), addressing these limitations through reversed quantum-well engineering enabled by a high-valent Zr─F framework. It features a unique reversed Type-I quantum-well electronic structure, where the [ZrF₅] inorganic layer acts as a dielectric barrier and the band-edge states are localized on the organic MBA cations. This structure yields a wide bandgap of 4.60 eV, a short UV cutoff edge of 265 nm, and a high laser-induced damage threshold exceeding 1251.58 GW/cm², providing a broad transparency window toward the UV region. Furthermore, (R/S-MBA)ZrF₅ exhibits a large SHG circular dichroism (SHG-CD) response with an anisotropy factor of 1.05. More importantly, it overcomes the typical moisture-sensitivity of OIHMHs, maintaining its structural stability and SHG-CD response after a 7-day water immersion. Structural analysis and theoretical calculations reveal this unusual water resistance is mainly attributed to the robust Zr─F framework and an effective cavity volume of 3.6%. This work highlights reversed quantum-well engineering as a novel way to synthesize water-stable and wide bandgap chiral nonlinear optical materials.