Günther Konstantin, Grabicki Niklas, Battistella Beatrice, Grubert Lutz, Dumele Oliver
Department of Chemistry & IRIS Adlershof, Humboldt University of Berlin, Brook-Taylor-Strasse 2, Berlin D-12489, Germany.
J Am Chem Soc. 2022 May 18;144(19):8707-8716. doi: 10.1021/jacs.2c02195. Epub 2022 May 6.
Controlling the electronic spin state in single molecules through an external stimulus is of interest in developing devices for information technology, such as data storage and quantum computing. We report the synthesis and operation mode of two all-organic molecular spin-state switches that can be photochemically switched from a diamagnetic [electron paramagnetic resonance (EPR)-silent] to a paramagnetic (EPR-active) form at cryogenic temperatures due to a reversible electrocyclic reaction of its carbon skeleton. Facile synthetic substitution of a configurationally stable 1,14-dimethyl-[5]helicene with radical stabilizing groups at the 4,11-positions afforded two spin-state switches as 4,11-dioxo or 4,11-bis(dicyanomethylidenyl) derivatives in a closed diamagnetic form. After irradiation with an LED light source at cryogenic temperatures, a stable paramagnetic state is readily obtained, making this system a bistable magnetic switch that can reversibly react back to its diamagnetic form through a thermal stimulus. The switching can be monitored with UV/vis spectroscopy and EPR spectroscopy or induced by electrochemical reduction and reoxidation. Variable-temperature EPR spectroscopy of the paramagnetic species revealed an open-shell triplet ground state with an experimentally determined triplet-singlet energy gap of Δ < 0.1 kcal mol. The inherent chirality and the ability to separate the enantiomers turns this helical motif into a potential chiroptical spin-state switch. The herein developed 4,11-substitution pattern on the dimethyl[5]helicene introduces a platform for designing future generations of organic molecular photomagnetic switches that might find applications in spintronics and related fields.
通过外部刺激控制单分子中的电子自旋态，对于开发信息技术设备（如数据存储和量子计算）具有重要意义。我们报道了两种全有机分子自旋态开关的合成及操作模式，由于其碳骨架的可逆电环化反应，这两种开关在低温下可通过光化学从抗磁性[电子顺磁共振（EPR）沉默]转变为顺磁性（EPR 活性）形式。在构型稳定的 1,14 - 二甲基 - [5]螺旋烯的 4,11 位进行易于合成的带有自由基稳定基团的取代，得到了两种自旋态开关，即 4,11 - 二氧代或 4,11 - 双（二氰基亚甲基）衍生物，呈封闭的抗磁性形式。在低温下用 LED 光源照射后，很容易获得稳定的顺磁性状态，使该系统成为一种双稳态磁开关，可通过热刺激可逆地变回其抗磁性形式。这种开关可以用紫外/可见光谱和 EPR 光谱进行监测，也可以通过电化学还原和再氧化来诱导。顺磁性物种的变温 EPR 光谱显示为开壳三重态基态，实验测定的三重态 - 单重态能隙Δ < 0.1 kcal/mol。固有的手性以及分离对映体的能力使这种螺旋基序成为一种潜在的手性光自旋态开关。本文在二甲基[5]螺旋烯上开发的 4,11 - 取代模式为设计下一代有机分子光磁开关引入了一个平台，这些开关可能在自旋电子学及相关领域找到应用。
