Yamada Takeru, Shimizu Daiki, Matsuda Kenji
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan.
Fukui Institute for Fundamental Chemistry, Kyoto University, Sakyo-ku, Kyoto 606-8103, Japan.
J Phys Chem Lett. 2024 Sep 12;15(36):9175-9182. doi: 10.1021/acs.jpclett.4c02212. Epub 2024 Aug 30.
Near-infrared (NIR)-absorbing dyes are valuable for various applications, such as bioimaging and electronic devices. This work introduces a novel approach for designing NIR dyes, oxidation of weakly coupled diradicals. Our approach features a weak exchange interaction in diradicals, which potentially leads to bonding/antibonding molecular orbitals with a small energy gap. We found that removing one of two singly occupied molecular orbital electrons of the diradicals results in an exceptionally narrow frontier orbital energy gap. We examined a series of Blatter radical dimers, and the most weakly coupled diradical prepared in this work ( ∼ 0.12 eV) with a molecular weight of 590 Da exhibited a strong NIR absorption band reaching 2200 nm upon one-electron oxidation. The optical band gaps of the radical cations strongly correlate to the exchange interaction in the precursor neutral species, offering prediction and fine-tuning of the optical band gap in the NIR region.
近红外（NIR）吸收染料在生物成像和电子设备等各种应用中具有重要价值。这项工作介绍了一种设计近红外染料的新方法，即弱耦合双自由基的氧化。我们的方法的特点是双自由基中存在弱交换相互作用，这可能导致具有小能量间隙的成键/反键分子轨道。我们发现，去除双自由基两个单占据分子轨道电子中的一个会导致异常窄的前沿轨道能量间隙。我们研究了一系列布拉特自由基二聚体，这项工作中制备的最弱耦合双自由基（~0.12 eV），分子量为590 Da，在单电子氧化后表现出一个强近红外吸收带，延伸至2200 nm。自由基阳离子的光学带隙与前体中性物种中的交换相互作用密切相关，为近红外区域光学带隙的预测和微调提供了依据。
