Chiral 2D Cu(I) Halide Frameworks

Hybrid multifunctional materials have great potential in a wide variety of applications due to their flexible combination of organic and inorganic components. Introducing chiral organic modules into the metal halide frameworks can effectively generate multifunctional materials, achieving new functionalities with noncentrosymmetric structures. Here, by incorporating (R)- or (S)-piperidine-3-carboxylic acid (R/S-PCA) as the templating cation, we report the synthesis and characterization of three pairs of new 2D chiral hybrid Cu(I) halides, namely, (R/S-PCA)CuBr2, (R/S-PCA)CuBr2·0.5H2O, and (R/S-PCA)CuI2. These chiral Cu(I) halides crystallize in the noncentrosymmetric space group C2 and belong to a new structural type similar to layered silicates. The optical absorption edges of these chiral materials can be tuned by changing the halide or upon the absorption of water and range from 2.70 to 3.66 eV. A dynamic conversion between (R/S-PCA)CuBr2 and (R/S-PCA)CuBr2·0.5H2O occurs through exposure to moisture or vacuum drying along with changes in the reversible bandgap and photoluminescence. Chiroptical properties such as circular dichroism, circular polarized light emission, and second harmonic generation are investigated. Density functional theory calculations (DFT) show the indirect and direct bandgap natures of these Cu(I) halides and reveal the mechanism for the broadband self-trapped exciton emission at the excited state. The fascinating structural type, chiroptical properties, and reversible hydrochromic behavior of these Cu(I)-based halides make them viable candidates for next-generation multifunctional optoelectronic materials.杂化多功能材料因可灵活结合有机与无机组分，在诸多应用场景中具备巨大应用潜力。将手性有机模块引入金属卤化物骨架，可有效制备多功能材料，并通过非中心对称结构赋予其全新功能。本研究以(R)-或(S)-哌啶-3-羧酸(R/S-PCA)作为模板阳离子，成功合成并表征了三对新型二维手性杂化Cu(I)卤化物，分别为(R/S-PCA)CuBr₂、(R/S-PCA)CuBr₂·0.5H₂O及(R/S-PCA)CuI₂。该类手性Cu(I)卤化物均结晶于非中心对称空间群C2，且属于一类与层状硅酸盐相似的新型结构类型。此类手性材料的光学吸收边可通过改变卤族元素种类或吸附水分子进行调控，带隙范围为2.70~3.66 eV。(R/S-PCA)CuBr₂与(R/S-PCA)CuBr₂·0.5H₂O之间可通过暴露于湿气或真空干燥实现动态转变，同时伴随可逆带隙与光致发光特性的变化。本研究还对该类材料的圆二色性、圆偏振发光及二次谐波产生等手性光学特性开展了表征。密度泛函理论计算(DFT)结果表明，此类Cu(I)卤化物兼具间接与直接带隙特性，并揭示了激发态下宽带自陷激子发射的机制。此类Cu(I)基卤化物所具备的新颖结构类型、手性光学特性与可逆水致变色行为，使其成为下一代多功能光电材料的极具潜力的候选体系。