Hattori Yohei, Suzuki Daiya, Ota Wataru, Sato Tohru, Rapenne Gwénaël, Imai Yoshitane
Division of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan.
Department of Applied Chemistry, Faculty of Science and Engineering, Kindai University, 3-4-1 Kowakae, Higashi-Osaka, Osaka 577-8502, Japan.
J Phys Chem Lett. 2024 Nov 28;15(47):11696-11700. doi: 10.1021/acs.jpclett.4c02793. Epub 2024 Nov 14.
Stable triarylmethyl radicals are the most common carbon radical building blocks and have recently attracted much attention for their luminescent properties. However, magnetic circular dichroism (MCD) discovered by Michael Faraday and magnetic circularly polarized luminescence (MCPL) have not been observed for simple triarylmethyl radicals, probably due to their photodegradability. Here we report the first observation of MCD and MCPL of triarylmethyl radicals in solution using racemic mixtures of (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) and (3,5-difluoro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (FPyBTM), which are much more photostable than simple triphenylmethyl radical derivatives. Faraday terms, which are at the origin of magnetic dichroism in nondegenerate systems, were calculated using TD-DFT, and the line shape of MCD spectra was well reproduced. This study provides new circular dichroism properties for luminescent triarylmethyl radicals in solution without separating enantiomers and also clarifies the origin of magnetic circular dichroism properties of stable organic radicals for the first time.
稳定的三芳基甲基自由基是最常见的碳自由基结构单元，最近因其发光特性而备受关注。然而，迈克尔·法拉第发现的磁圆二色性（MCD）和磁圆偏振发光（MCPL）尚未在简单的三芳基甲基自由基中观察到，这可能是由于它们的光降解性。在这里，我们报告了首次使用（3,5-二氯-4-吡啶基）双（2,4,6-三氯苯基）甲基自由基（PyBTM）和（3,5-二氟-4-吡啶基）双（2,4,6-三氯苯基）甲基自由基（FPyBTM）的外消旋混合物在溶液中观察到三芳基甲基自由基的MCD和MCPL，它们比简单的三苯甲基自由基衍生物更具光稳定性。使用TD-DFT计算了非简并系统中磁圆二色性起源的法拉第项，并很好地再现了MCD光谱的线形。这项研究为溶液中的发光三芳基甲基自由基提供了新的圆二色性特性，且无需分离对映体，同时也首次阐明了稳定有机自由基的磁圆二色性特性的起源。
