Lateral Extension of π Conjugation along the Bay Regions of Bisanthene through a Diels-Alder Cycloaddition Reaction

Diels–Alder cycloaddition reactions at the bay regions of bisanthene (1) with dienophiles such as 1,4‐naphthoquinone have been investigated. The products were submitted to nucleophilic addition followed by reductive aromatization reactions to afford the laterally extended bisanthene derivatives 2 and 3. Attempted synthesis of a larger expanded bisanthene 4 revealed an unexpected hydrogenation reaction at the last reductive aromatization step. Unusual Michael addition was observed on quinone 14, which was obtained by Diels–Alder reaction between 1 and 1,4‐anthraquinone. Compounds 1–3 exhibited near‐infrared (NIR) absorption and emission with high‐to‐moderate fluorescent quantum yields. Their structures and absorption spectra were studied by density function theory and non‐planar twisted structures were calculated for 2 and 3. All compounds showed amphoteric redox behavior with multiple oxidation/reduction waves. Oxidative titration with SbCl5 gave stable radical cations, and the process was followed by UV/Vis/NIR spectroscopic measurements. Their photostability was measured and correlated to their different geometries and electronic structures. Expanded and twisted! Diels–Alder (D–A) cycloaddition at the bay regions of bisanthene gave a series of expanded quinones (see scheme). Subsequent nucleophilic addition and reductive aromatization led to new, laterally expanded and twisted, polycyclic aromatic hydrocarbons with near‐infrared absorption and emission.