Yang Kun, Zhang Xianhe, Harbuzaru Alexandra, Wang Lei, Wang Yang, Koh Changwoo, Guo Han, Shi Yongqiang, Chen Jianhua, Sun Huiliang, Feng Kui, Ruiz Delgado M Carmen, Woo Han Young, Ortiz Rocio Ponce, Guo Xugang
Department of Materials Science and Engineering, Southern University of Science and Technology (SUSTech), No. 1088, Xueyuan Road, Shenzhen, Guangdong 518055, China.
State Key Laboratory and Institute of Elemento-Organic Chemistry, Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, College of Chemistry, Nankai University, Tianjin 300071, China.
J Am Chem Soc. 2020 Mar 4;142(9):4329-4340. doi: 10.1021/jacs.9b12683. Epub 2020 Feb 20.
Unpaired electrons of organic radicals can offer high electrical conductivity without doping, but they typically suffer from low stability. Herein, we report two organic diradicaloids based on quinoidal oligothiophene derivative (QOT), that is, BTICN and QTICN, with high stability and conductivity by employing imide-bridged fused molecular frameworks. The attachment of a strong electron-withdrawing imide group to the tetracyano-capped QOT backbones enables extremely deeply aligned LUMO levels (from -4.58 to -4.69 eV), cross-conjugated diradical characters, and remarkable ambient stabilities of the diradicaloids with half-lives > 60 days, which are among the highest for QOT diradicals and also the widely explored polyaromatic hydrocarbon (PAH)-based diradicals. Specifically, QTICN based on a tetrathiophene imide exhibits a cross-conjugation assisted self-doping in the film state as revealed by XPS and Raman studies. This property in combination with its ordered packing yields a high electrical conductivity of 0.34 S cm for the QTICN films with substantial ambient stability, which is also among the highest values in organic radical-based undoped conductive materials reported to date. When used as an n-type thermoelectric material, QTICN shows a promising power factor of 1.52 uW m K. Our results not only provide new insights into the electron conduction mechanism of the self-doped QOT diradicaloids but also demonstrate the great potential of fused quinoidal oligothiophene imides in developing stable diradicals and high-performance doping-free n-type conductive materials.
有机自由基的未成对电子无需掺杂就能提供高电导率，但它们通常稳定性较差。在此，我们报道了两种基于醌型低聚噻吩衍生物（QOT）的有机双自由基化合物，即BTICN和QTICN，通过采用酰亚胺桥连的稠合分子骨架，它们具有高稳定性和导电性。在四氰基封端的QOT主链上连接强吸电子酰亚胺基团，可实现极深的LUMO能级排列（从-4.58到-4.69 eV）、交叉共轭双自由基特性以及双自由基化合物显著的环境稳定性，其半衰期>60天，这在QOT双自由基以及广泛研究的基于多环芳烃（PAH）的双自由基中都是最高的。具体而言，XPS和拉曼研究表明，基于四噻吩酰亚胺的QTICN在薄膜状态下表现出交叉共轭辅助的自掺杂。这种特性与其有序堆积相结合，使得QTICN薄膜具有0.34 S cm的高电导率以及显著的环境稳定性，这也是迄今为止报道的基于有机自由基的未掺杂导电材料中的最高值之一。当用作n型热电材料时，QTICN显示出1.52 μW m K的有前景的功率因子。我们的结果不仅为自掺杂QOT双自由基化合物的电子传导机制提供了新的见解，还证明了稠合醌型低聚噻吩酰亚胺在开发稳定双自由基和高性能无掺杂n型导电材料方面的巨大潜力。
