Gon Masayuki, Wakabayashi Junko, Tanaka Kazuo, Chujo Yoshiki
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University Katsura, Nishikyo-ku, Kyoto, 615-8510, Japan.
Chem Asian J. 2019 May 15;14(10):1837-1843. doi: 10.1002/asia.201801659. Epub 2019 Jan 29.
A recent report illustrated superior optical properties, such as near-infrared emission, of polymers connected at the 4,4'-positions to a fused azobenzene-boron complex (BAz). In this study, it is initially demonstrated that further narrowing of the band gap can be realized through the substituent effect with bromine groups at the 5,5'-positions of BAz compared with those at the 4,4'-positions. From a series of mechanistic studies, perturbation of the energy levels was rationally explained by the difference in contributions of the inductive effect and the variable resonance effect, which was correlated with the degree of electron distribution of molecular orbitals at the substituent positions. Moreover, it was found that unique electronic states, such as delocalized HOMOs and LUMOs, should appear on the main chains of the BAz-containing copolymers with fluorene and bithiophene units, according to the optical and electrochemical data and theoretical calculations. By taking advantage of property tunability and the dramatically low LUMO energy level (near -4.0 eV) of the BAz unit, it can be said that BAz should be a conjugated building block favorable for building advanced optoelectronic devices.
最近的一份报告阐述了在4,4'-位与稠合偶氮苯-硼配合物（BAz）相连的聚合物具有优异的光学性能，如近红外发射。在本研究中，最初证明与在4,4'-位的情况相比，通过在BAz的5,5'-位引入溴原子的取代基效应可实现带隙的进一步变窄。通过一系列机理研究，能级的扰动可通过诱导效应和可变共振效应贡献的差异得到合理的解释，这与取代基位置分子轨道的电子分布程度相关。此外，根据光学和电化学数据以及理论计算发现，含BAz的与芴和联噻吩单元的共聚物主链上应出现独特的电子态，如离域的最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）。利用BAz单元的性能可调性和极低的LUMO能级（接近-4.0 eV），可以说BAz应该是构建先进光电器件的一种有利的共轭结构单元。
