title: Two BN isosteres of anthracene: synthesis and characterization.
abstract: 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, -7.4 eV; BN anthracene 1, -7.7 eV; bis-BN anthracene 2, -8.0 eV. The λmax of the lower energy band in the UV-vis 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-LUMO band gap remains unchanged across the anthracene series. The emission λmax values for the three investigated anthracene compounds are at 403 nm. The pKa 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-Crafts 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-Crafts 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.
authors.affiliation: Department of Chemistry, Merkert Chemistry Center, Boston College , Chestnut Hill, Massachusetts 02467-3860, United States.
authors.forename: Jacob S A
authors.initials: JS
authors.lastname: Ishibashi
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Marshall
authors.forename: Audrey
authors.initials: A
authors.lastname: Mazière
authors.forename: Gabriel J
authors.initials: GJ
authors.lastname: Lovinger
authors.forename: Bo
authors.initials: B
authors.lastname: Li
authors.forename: Lev N
authors.initials: LN
authors.lastname: Zakharov
authors.forename: Alain
authors.initials: A
authors.lastname: Dargelos
authors.forename: Alain
authors.initials: A
authors.lastname: Graciaa
authors.forename: Anna
authors.initials: A
authors.lastname: Chrostowska
authors.forename: Shih-Yuan
authors.initials: SY
authors.lastname: Liu