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Beyond Chiral Organic (p-Block) Chromophores for Circularly Polarized Luminescence: The Success of d-Block and f-Block Chiral Complexes.
Frontiers in Chemistry ( IF 5.5 ) Pub Date : 2020-05-29 , DOI: 10.3389/fchem.2020.00555
Benjamin Doistau 1 , Juan-Ramón Jiménez 1 , Claude Piguet 1
Affiliation  

Chiral molecules are essential for the development of advanced technological applications in spintronic and photonic. The best systems should produce large circularly polarized luminescence (CPL) as estimated by their dissymmetry factor (glum), which can reach the maximum values of −2 ≤ glum ≤ 2 when either pure right- or left-handed polarized light is emitted after standard excitation. For matching this requirement, theoretical considerations indicate that optical transitions with large magnetic and weak electric transition dipole moments represent the holy grail of CPL. Because of their detrimental strong and allowed electric dipole transitions, popular chiral emissive organic molecules display generally moderate dissymmetry factors (10−5glum ≤ 10−3). However, recent efforts in this field show that glum can be significantly enhanced when the chiral organic activators are part of chiral supramolecular assemblies or of liquid crystalline materials. At the other extreme, chiral EuIII- and SmIII-based complexes, which possess intra-shell parity-forbidden electric but allowed magnetic dipole transitions, have yielded the largest dissymmetry factor reported so far with glum ~ 1.38. Consequently, 4f-based metal complexes with strong CPL are currently the best candidates for potential technological applications. They however suffer from the need for highly pure samples and from considerable production costs. In this context, chiral earth-abundant and cheap d-block metal complexes benefit from a renewed interest according that their CPL signal can be optimized despite the larger covalency displayed by d-block cations compared with 4f-block analogs. This essay thus aims at providing a minimum overview of the theoretical aspects rationalizing circularly polarized luminescence and their exploitation for the design of chiral emissive metal complexes with strong CPL. Beyond the corroboration that f–f transitions are ideal candidates for generating large dissymmetry factors, a special attention is focused on the recent attempts to use chiral CrIII-based complexes that reach values of glum up to 0.2. This could pave the way for replacing high-cost rare earths with cheap transition metals for CPL applications.



中文翻译:

圆偏振发光的超越手性有机(p嵌段)发色团:d嵌段和f嵌段手性配合物的成功。

手性分子对于自旋电子学和光子学中先进技术应用的发展至关重要。最佳系统应产生大的圆偏振发光(CPL),其不对称系数(Glum),可以达到−2≤的最大值G标准激发后发出纯右旋或左旋偏振光时,lum≤2。为了满足这一要求,理论上的考虑表明,具有大的磁跃迁和弱的电跃迁偶极矩的光学跃迁代表了CPL的圣杯。由于它们的有害强,并允许电偶极跃迁的,流行的手性发光的有机分子通常显示中等不对称因素(10 -5GLUM ≤10 -3)。但是,最近在该领域的努力表明G当手性有机活化剂是手性超分子组装体或液晶材料的一部分时,lum可以显着增强。在另一种极端情况下,手性Eu III和Sm III基络合物具有禁止壳内奇偶性电但允许磁偶极跃迁,产生了迄今报道的最大不对称因子。Glum〜1.38。因此,具有强大CPL的4f基金属络合物目前是潜在技术应用的最佳选择。然而,它们遭受对高纯度样品的需求以及巨大的生产成本。在这种情况下,手性地球富集和廉价的d嵌段金属络合物受益于新的兴趣,因为尽管d嵌段阳离子显示的共价比4f嵌段类似物大,但它们的CPL信号仍可优化。因此,本文旨在为使圆偏振发光合理化的理论方面及其对具有强CPL的手性发射金属配合物的设计提供理论上的概述。除了证实f–f跃迁是产生较大不对称因子的理想候选者之外,基于III的复合物达到GLUM高达0.2。这可能为用廉价的过渡金属替代高价稀土为CPL应用铺平了道路。

更新日期:2020-07-28
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