Department of Chemistry, Iowa State University, Ames, Iowa 50010, United States.
J Org Chem. 2011 Nov 4;76(21):8670-81. doi: 10.1021/jo201078w. Epub 2011 Oct 11.
In an effort to design new electron-deficient building blocks for the synthesis of conjugated materials, a series of new trans-benzobisoxazoles bearing halogen or alkynyl substituents at the 4,8-positions was synthesized. Additionally, the impact of these modifications on the optical and electronic properties was investigated. Theoretical calculations predicted that the incorporation of various alkynes can be used to tune the energy levels and band gaps of these small molecules. The targeted 4,8-disubstituted benzobisoxazoles were easily prepared in good yields using a two-step reaction sequence: Lewis acid catalyzed orthoester cyclization followed by Sonogashira cross-coupling. The experimentally determined HOMO values for these 4,8-disubstituted benzobisoxazoles ranged from -4.97 to -6.20 eV and showed reasonable correlation to the theoretically predicted values, with a percent deviation that ranged from 2.4-12.8%. However, the deviation between actual and predicted HOMO values was reduced to less than 3.5% when the theoretical values were extrapolated to the long-chain limit and compared to copolymers containing the 4,8-disubstituted benzobisoxazoles. Collectively, these results indicate that these 4,8-disubstituted trans-benzobisoxazoles can be used for the synthesis of new conjugated materials with electronic properties that are variable and predictable.
为了设计新的缺电子构建块用于合成共轭材料，我们合成了一系列在 4,8-位带有卤素或炔基取代基的新型反式苯并二恶唑。此外，还研究了这些修饰对光学和电子性质的影响。理论计算预测，各种炔烃的掺入可用于调节这些小分子的能级和带隙。通过两步反应序列，即可轻松地以良好的收率制备目标 4,8-取代的苯并二恶唑：路易斯酸催化邻酯环化，然后进行 Sonogashira 交叉偶联。这些 4,8-取代的苯并二恶唑的实验测定的 HOMO 值范围为-4.97 至-6.20 eV，与理论预测值有很好的相关性，偏差百分比范围为 2.4-12.8%。然而，当将理论值外推到长链极限并与含有 4,8-取代的苯并二恶唑的共聚物进行比较时，实际和预测 HOMO 值之间的偏差降低到 3.5%以下。这些结果表明，这些 4,8-取代的反式苯并二恶唑可用于合成具有可变和可预测电子性质的新型共轭材料。
