12b, 24b‐Diborahexabenzo[a, c, fg, l, n, qr]pentacene: A Low‐LUMO Boron‐Doped Polycyclic Aromatic Hydrocarbon. (3rd January 2022)

• Record Type: Journal Article
• Authors: Mützel, Carina; Farrell, Jeffrey M.; Shoyama, Kazutaka; Würthner, Frank
• Is Part Of: Angewandte Chemie. Volume 134:Number 8(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-03
• Subjects: Aromaticity -- Boron -- Near infrared emitter -- Pentacene -- Polycycles; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.202115746
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: Herein we devise and execute a new synthesis of a pristine boron‐doped nanographene. Our target boron‐doped nanographene was designed based on DFT calculations to possess a low LUMO energy level and a narrow band gap derived from its precise geometry and B‐doping arrangement. Our synthesis of this target, a doubly B‐doped hexabenzopentacene (B 2 ‐HBP ), employs six net C−H borylations of an alkene, comprising consecutive hydroboration/electrophilic borylation/dehydrogenation and BBr3 /AlCl3 /2, 6‐dichloropyridine‐mediated C−H borylation steps. As predicted by our calculations, B 2 ‐HBP absorbs strongly in the visible region and emits in the NIR up to 1150 nm in o‐dichlorobenzene solutions. Furthermore, B 2 ‐HBP possesses a very low LUMO level, showing two reversible reductions at −1.00 V and −1.17 V vs. Fc + /Fc. Our methodology is surprisingly selective despite its implementation of unfunctionalized precursors and offers a new approach to the synthesis of pristine B‐doped polycyclic aromatic hydrocarbons . Abstract : A doubly B‐doped hexabenzopentacene was designed based on presynthetic DFT calculations, predicting intriguing optoelectronic properties. Subsequently, the electron‐deficient, NIR‐emitting B‐doped polycyclic aromatic hydrocarbon was prepared via six net C−H borylations from an unfunctionalized alkene in a two‐pot synthetic procedure. The structure obtained by X‐ray crystallography confirmed an enhanced π‐conjugation upon cyclization compared to non‐fused derivatives.