Organic Cation Conformation-Modulated Dimensionality in Chiral Metal Halides for Enhancing Linear and Nonlinear Chiroptical Properties.

Dimensionality engineering has been proven as a pivotal approach to the modulation of chemical and electronic structures of organic-inorganic hybrid metal halides (OIHMHs) for advanced optoelectronic applications. However, prevailing methods primarily rely on altering chemical composition, which limits the precision and predictability of fine-tuning. Herein, we propose a new conformational modulation strategy to direct the self-assembly of chiral OIHMHs without changing their chemical compositions. By steering the conformation of the cyclic chiral cation, R/S-2-methylpyrrolidinium, we achieve precise control over the connectivity and dimensionality of inorganic units. Designing mixed conformational systems by introducing axial-conformation into equatorial-conformation structures successfully enables efficient chiral amplification and enhances linear and nonlinear chiroptical responses. The resulting OIHMHs exhibit a photoluminescence quantum yield exceeding 86%, high anisotropy factors in linear and nonlinear optical circular dichroism, circularly polarized luminescence, and an enhanced second-harmonic generation intensity by two orders of magnitude. Such a simultaneous enhancement in both linear and nonlinear chiroptical properties arises from the modulation of steric hindrance and electronic structure in organic cations mediated by molecular conformation. This work highlights the contribution of conformational modulation to structural design and performance optimization, broadening the prospects for precise modulation of high-performance optoelectronic functions in chiral OIHMHs.