Two BN Isosteres of Anthracene: Synthesis and Characterization

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• 作者：Jacob S. A. Ishibashi ; Jonathan L. Marshall ; Audrey Mazi猫re ; Gabriel J. Lovinger ; Bo Li ; Lev N. Zakharov ; Alain Dargelos ; Alain Graciaa ; Anna Chrostowska ; Shih-Yuan Liu
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：October 29, 2014
• 年：2014
• 卷：136
• 期：43
• 页码：15414-15421
• 全文大小：569K
• ISSN：1520-5126

文摘

The synthesis of two parental BN anthracenes, 1 and 2, was developed, and their electronic structure and reactivity behavior were characterized in direct comparison with all-carbon anthracene. Gas-phase UV-photoelecton spectroscopy studies revealed the following HOMO energy trend: anthracene, 鈭?.4 eV; BN anthracene 1, 鈭?.7 eV; bis-BN anthracene 2, 鈭?.0 eV. The 位_max of the lower energy band in the UV鈥搗is absorption spectrum is as follows: anthracene, 356 nm; BN anthracene 1, 359 nm; bis-BN anthracene 2, 357 nm. Thus, although the HOMO is stabilized with increasing BN incorporation, the HOMO鈥揕UMO band gap remains unchanged across the anthracene series. The emission 位_max values for the three investigated anthracene compounds are at 403 nm. The pK_a values of the N-H proton for BN anthracene 1 and bis-BN anthracene 2 were determined to be approximately 26. BN anthracenes 1 and 2 do not undergo heat- or light-induced cycloaddition reactions or Friedel鈥揅rafts acylations. Electrophilic bromination of BN anthracene 1 with Br₂, however, occurs regioselectively at the 9-position. The reactivity behavior and regioselectivity of bromination of BN anthracenes are consistent with the electronic structure of these compounds; i.e., (1) the lower HOMO energy levels for BN anthracenes stabilize the molecules against cycloaddition and Friedel鈥揅rafts reactions, and (2) the HOMO orbital coefficients are consistent with the observed bromination regioselectivity. Overall, this work demonstrates that BN/CC isosterism can be used as a molecular design strategy to stabilize the HOMO of acene-type structures while the optical band gap is maintained.