Pushing the Length Limit of Dihydrodiboraacenes

Pushing the Length Limit of Dihydrodiboraacenes

Author: Angewandte Chemie International Edition

Acenes are polycyclic aromatic hydrocarbons made up of linearly fused benzene rings. Heteroacenes incorporate heteroatoms in their skeletons and are promising structures for organic functional materials. Boron-embedded boraacenes, for example, possess unique optoelectronic properties. However, long boraacenes (n ≥ 6) are challenging to synthesize and isolate.

Xiao-Ye Wang, Nankai University, Tianjin, China, and colleagues have pushed the length limits of boraacenes by synthesizing the longest boron-embedded heteroacenes to date—dihydrodiboraheptacene and dihydrodiboranonacene (pictured). The key step for the synthesis of both compounds is an Si/B exchange of trimethylsilyl groups with boron tribromide to construct the linear backbone from two fragments, followed by substitution with bulky aryl groups.

The boron-embedded heptacene is highly stable, whereas the boron-embedded nonacene is air-sensitive. Both compounds exhibit unique anti-Kasha luminescence (a direct emission from high excited states) and high photoluminescence quantum yields (boron-embedded heptacene: ca. 98 %; boron-embedded nonacene: 51 %). This work could potentially create new opportunities for the development of boraacene-based functional materials with useful optical properties.




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