Tuning the Donor−π–Acceptor Character of Arylborane–Arylamine Macrocycles

Donor−π–acceptor compounds based on arylamine and arylborane moieties connected by a π-conjugated linker are attractive materials in organic electronics and imaging applications due to the strong charge transfer character that leads to low energy absorption and solvatochromic emission properties. Here we introduce a new conjugated macrocyclic system that consists of four arylborane and two arylamine units as confirmed by single-crystal X-ray structure analysis. The acceptor character of the arylboranes is enhanced by exocyclic electron-withdrawing 2,4,6-tris­(trifluoromethyl)­phenyl (FMes) substituent as well as the mutual interaction between adjacent boranes. The absorption, solvent-dependent emission, and electrochemical properties are studied and compared to those of other macrocyclic organoboranes. Computational studies offer additional insights into the electronic structure. Due to the enhanced acceptor character of the boranes, the LUMO orbitals are lower lying, leading to more facile reduction, red-shifted absorption and emission, and larger Stokes shifts than those found for previously studied B–N macrocycles.由π共轭连接基连接芳胺与芳硼烷片段所构建的给体-π-受体（Donor−π–acceptor）化合物，因其具备强电荷转移特性，可实现低能吸收与溶剂致变色发光性能，故而在有机电子学与成像应用中极具应用潜力。本研究报道一种新型共轭大环体系，该体系包含4个芳硼烷单元与2个芳胺单元，其结构经单晶X射线衍射结构分析得以确证。芳硼烷的受体特性可通过环外吸电子取代基2,4,6-三(三氟甲基)苯基（FMes）以及相邻硼烷间的相互作用得到强化。本研究对该体系的吸收光谱、溶剂依赖型发光性能及电化学性能开展了表征，并将其与其他大环有机硼烷的对应性能进行了对比。计算化学研究进一步为其电子结构提供了理论视角。由于硼烷的受体特性得到强化，其最低未占据分子轨道（LUMO）能级更低，相较于此前研究的硼-氮大环体系，该体系的还原过程更易进行，吸收与发射光谱均发生红移，且斯托克斯位移更大。