12b,24b-Diborahexabenzo[a,c,fg,l,n,qr]pentacene: A Low-LUMO Boron-Doped Polycyclic Aromatic Hydrocarbon

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 (B₂ -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, B₂ -HBP absorbs strongly in the visible region and emits in the NIR up to 1150 nm in o-dichlorobenzene solutions. Furthermore, B₂ -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.