Atzori Matteo, Santanni Fabio, Breslavetz Ivan, Paillot Kévin, Caneschi Andrea, Rikken Geert L J A, Sessoli Roberta, Train Cyrille
Laboratoire National des Champs Magnétiques Intenses (LNCMI), Univ. Grenoble Alpes, INSA Toulouse, Univ. Toulouse Paul Sabatier, EMFL, CNRS, F-38043 Grenoble, France.
Dipartimento di Chimica "Ugo Schiff" e INSTM, Università degli Studi di Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino (Firenze), Italy.
J Am Chem Soc. 2020 Aug 12;142(32):13908-13916. doi: 10.1021/jacs.0c06166. Epub 2020 Jul 31.
Magnetochiral dichroism (MChD) is a nonreciprocal manifestation of light-matter interaction that can be observed in chiral magnetized systems. It features a differential absorption of unpolarized light depending on the relative orientation of the magnetic field and the light wavevector and on the absolute configuration of the system. The relevance of this effect for optical readout of magnetic data calls for a complete understanding of the microscopic parameters driving MChD with an easy-accessible and nondamaging light source, such as visible light. For this purpose, here we report on MChD detected with visible light on a chiral magnetic helix formulated as [Mn(cyclam)(SO)]ClO·HO (cyclam = 1,4,8,11-tetraazacyclotetradecane) featuring antiferromagnetically coupled anisotropic Mn ions. Alternate current susceptibility measurements revealed the existence of a single-chain magnet behavior hidden below the canted antiferromagnetism ( = 5.8 K) already evidenced by direct current magnetometry. A detailed analysis of the optical absorption gives access to the value of the zero-field splitting parameter (2.9 cm), which quantifies the magnetic anisotropy of the Mn centers. Below the magnetic ordering temperature of the material, the MChD spectra exhibit intense absolute configuration dependent MChD signals reaching record values of ca. 12% of the absorbed intensity for the two electronic transitions most influenced by the spin-orbit coupling of the Mn ion. These findings set a clear route toward the design and preparation of highly MChD-responsive molecular materials.
磁手性二色性（MChD）是光与物质相互作用的一种非互易表现形式，可在手性磁化系统中观察到。它的特点是根据磁场与光波矢的相对取向以及系统的绝对构型，对非偏振光有不同的吸收。这种效应对于磁性数据的光学读出的相关性要求我们用一种易于获取且无损伤的光源（如可见光）来全面理解驱动MChD的微观参数。为此，我们在此报告用可见光在一种手性磁螺旋体[Mn(环胺)(SO)]ClO·HO（环胺 = 1,4,8,11 - 四氮杂环十四烷）上检测到的MChD，该磁螺旋体具有反铁磁耦合的各向异性锰离子。交流磁化率测量揭示了单链磁体行为的存在，它隐藏在已经由直流磁测量法证明的倾斜反铁磁性（ = 5.8 K）之下。对光吸收的详细分析得出零场分裂参数的值（2.9 cm），该参数量化了锰中心的磁各向异性。在材料的磁有序温度以下，MChD光谱表现出强烈的与绝对构型相关的MChD信号，对于受锰离子自旋 - 轨道耦合影响最大的两个电子跃迁，其达到约吸收强度12%的记录值。这些发现为设计和制备对MChD高度响应的分子材料指明了一条清晰的途径。
