Fully-fused boron-doped olympicenes: modular synthesis, tunable optoelectronic properties, and one-electron reduction

Abstract

We report here a novel family of boraolympicenes, structurally featuring boron-doping at the concave 11a-position of their π-skeletons and synthetically prepared via a facile one-pot triply borylation-based double-fold borocyclization reaction. Despite having no bulky protecting groups, these boraolympicenes exhibit excellent chemical stability against air and moisture, ascribed to the significant π-electron delocalization over the vacant p_z orbitals of boron atoms as evidenced by both single-crystallographic and theoretical analyses. More importantly, the modular synthesis of these boraolympicenes allows the fine-tuning of their physicochemical properties, endowing them with intriguing electronic features, such as intense visible-to-NIR absorption and low-lying LUMO energy levels (∼−3.8 eV) as well as tunable molecular stacking characteristics in the crystalline state. As a model compound, a radical-anion salt of 6-phenyl-11a-boraolympicene was further generated through chemical reduction and well characterized by UV-vis-NIR absorption, ESR, and IR spectroscopy. This radical anion salt is sensitive to air and moisture but shows persistent stability under inert conditions benefiting from its stable borataalkene-containing resonant form.