硼杂分子带: 可控合成与发光功能.

Molecular ribbons (MRs), namely graphene nanoribbons with well-defined chemical structures, exhibit unique electronic structures and optoelectronic properties, and thus have attracted great attention in synthetic chemistry and materials science. Incorporation of the boron atom into their π-skeletons may enable modulation of electronic structures and physical properties by utilizing the electronic characteristics of the boron atom. However, it remains very challenging to synthesize boron-doped MRs in solution, due to the instability of the boron atoms toward moister and oxygen and the reduced cyclization activity of aromatic rings caused by the electron-deficient nature of the boron atoms. Thus, the structural construction and functional exploration of boron-doped MRs is severely hampered. Recently, our group have proposed a new strategy to construct boron-doped MRs, namely controlled cyclization of conjugated organoboranes. We synthesized a series of borondoped MRs using solution-phase photocyclization reaction, and two of them feature isomeric C68B2 π-skeletons with 2.2 nm in length. We found that they have sufficient Lewis acidity, and the formed Lewis acid-based adducts display the photoinduced dual-dissociation behavior in the excited state and thus photochromism property. Moreover, despite of the highly contorted topological conformations, they exhibit hole transporting ability in organic field-effect transistors. On the other hand, we developed two new boron-doped conjugated π-units and then performed precise sequential cyclization reactions, affording three boron-doped MRs with controlled edges. Their band gaps and fluorescence properties were successfully modulated, and notably, the stimulated emission behavior and amplified spontaneous emission property were achieved for one boron-doped MR, demonstrating its potential as an optical-gain lasing material. These studies not only provide a new molecular system for organic optical materials, but also open a new direction for molecular carbons. [ABSTRACT FROM AUTHOR]