福建师范大学陈瑾团队报道了卤素键解锁超高双折射。相关研究成果于2024年7月10日发表于国际顶尖学术期刊《德国应用化学》。

各向异性对于光学材料中的双折射（Δn）至关重要，但优化它仍然是一个艰巨的挑战（Δn>0.3）。含有π共轭组分的超分子框架因其结构多样性和固有各向异性而有望实现增强的双折射。

该文中，研究人员首先合成了 (C₆H₆NO2)⁺Cl^-（NAC）。然后用I⁺取代Cl^-，构建了卤素键合超分子骨架I⁺（C₆H₄NO₂）^-（INA）。有机部分分别是质子化和去质子化的烟酸（NA）。NAC和INA中双折射活性单元的反平行排列导致层间和层内畴之间的键合特性存在显著差异。此外，1D[I⁺（C₆H₄NO₂）^-）]链中的[O···I+···N]卤素键表现出更强的相互作用和更严格的方向性，导致链内和链间方向之间更明显的平面内各向异性。

因此，INA表现出卓越的双折射性能，在550nm处的值为0.778，是NAC（在550nm处为0.363）的两倍。该值显著超过了商业双折射晶体，如CaCO₃（546nm处为0.172），是紫外双折射晶体中报告的最高值。

该项工作提出了一种新的采用卤素键作为双折射活性单元，连接位点和模式的设计策略，为开发高性能双折射晶体开辟了新的途径。

附：英文原文

Title: Halogen Bond Unlocks Ultra-High Birefringence

Author: Jin Chen, Miao-Bin Xu, Huai-Yu Wu, Jun-Yan Wu, Ke-Zhao Du

Issue&Volume: 2024-07-10

Abstract: Anisotropy is crucial for birefringence (Δn) in optical materials, but optimizing it remains a formidable challenge (Δn > 0.3). Supramolecular frameworks incorporating π-conjugated components are promising for achieving enhanced birefringence since their structural diversity and inherent anisotropy. Herein, we first synthesized (C6H6NO2)+Cl (NAC). And then constructed a halogen bonded supramolecular framework I+(C6H4NO2) (INA) by halogen aliovalent substitution of Cl with I+. The organic moieties are protonated and deprotonated nicotinic acid (NA), respectively. The antiparallel arrangement of birefringent-active units in NAC and INA leads to significant differences in bonding characteristics between interlayer and intralayer domains. Moreover, [O···I+···N] halogen bond in 1D [I+(C6H4NO2)] chain exhibits stronger interactions and stricter directionality, resulting in a more pronounced in-plane anisotropy between the intrachain and interchain directions. Consequently, INA exhibits exceptional birefringent performance, with a value of 0.778 at 550 nm, twice that of NAC (0.363 at 550 nm). This value significantly exceeds those of commercial birefringent crystals, such as CaCO3 (0.172 at 546 nm), and is the highest reported value among ultraviolet birefringent crystals. This work presents a novel design strategy that employs halogen bonds as connection sites and modes for birefringent-active units, opening new avenues for developing high-performance birefringent crystals.

DOI: 10.1002/anie.202411503

Source: https://onlinelibrary.wiley.com/doi/10.1002/anie.202411503