Imai Tomoya, Sakamaki Daisuke, Aoyagi Shinobu, Amaya Toru
Department of Information and Basic Science, Graduate School of Science, Nagoya City University, 1 Yamanohata, Mizuho-cho, Mizuho-ku, Nagoya, Aichi, 467-8501, Japan.
Department of Chemistry, Graduate School of Science, Osaka Metropolitan University Naka-ku, Sakai, Osaka, 599-8531, Japan.
Chemistry. 2023 Dec 14;29(70):e202302670. doi: 10.1002/chem.202302670. Epub 2023 Oct 27.
Cyclic [3]spirobifluorenylene with bulky alkyl groups at the ends (1) was designed and synthesized to investigate the electron transfer phenomena in a π-conjugated system including orthogonal π-conjugated chains. The three bifluorenyl units in 1 are conjugated to each other via spiro-conjugation, resulting in the splitting of the HOMO levels to a small extent. Therefore, the SOMO-HOMO gap of the radical cation species is small, which is considered to allow the facile intramolecular electron transfer. The electronic properties of 1 and its partial structures were characterized by absorption and fluorescence measurements and electrochemical analysis. From the electrochemical oxidation, the interchain Coulombic repulsion was observed. In the TD-DFT calculations for the radical cation species of 1, the geometry-featured interchain electronic transitions were visualized by NTO calculations. The radical cation species of 1 generated by chemical oxidation with SbCl exhibited a broadened and lower-energy NIR absorption band exceeding 2000 nm. Considering the results of the TD-DFT calculations, the NIR band of the radical cation of 1 was attributed to the intramolecular electron transfer processes among the bifluorenyl units in the macrocycle. ESR experiments also indicated the delocalization of a spin of 1⋅ in the whole molecule via hole hopping in the ESR time scale at room temperature. This work demonstrates the usefulness of spiro-conjugation as a bridging unit in molecular wires to facilitate smooth electron transfer.
设计并合成了两端带有庞大烷基的环状[3]螺二芴（1），以研究包括正交π共轭链的π共轭体系中的电子转移现象。1中的三个联芴单元通过螺共轭相互共轭，导致HOMO能级在一定程度上分裂。因此，自由基阳离子物种的SOMO-HOMO能隙较小，这被认为有利于分子内的电子转移。通过吸收和荧光测量以及电化学分析对1及其部分结构的电子性质进行了表征。从电化学氧化中，观察到链间库仑排斥。在对1的自由基阳离子物种的TD-DFT计算中，通过NTO计算可视化了具有几何特征的链间电子跃迁。用SbCl进行化学氧化生成的1的自由基阳离子物种表现出超过2000nm的变宽且能量较低的近红外吸收带。考虑到TD-DFT计算的结果，1的自由基阳离子的近红外带归因于大环中联芴单元之间的分子内电子转移过程。ESR实验还表明，在室温下，在ESR时间尺度上，1·的自旋通过空穴跳跃在整个分子中离域。这项工作证明了螺共轭作为分子导线中的桥连单元以促进平滑电子转移的有用性。
