Helicene Aromaticity Deviates from the Clar Rule—On the Electronic Dissimilarity of Large Isomeric Fibonacenes

• DOI: 10.1002/anie.202403170
• Publication Date: 2024-04-03T15:25:11Z
• Authors: Ludmilla Sturm; Albert Artigas; Yoann Coquerel; Ivan H. Bechtold; Fabien Durola; Harald Bock

AbstractThis combined experimental and theoretical study illustrates the profound consequences of non‐planarity on the electronic properties of polycyclic arenes. Three isomeric [10]fibonacene tetraesters were synthesized through a robust and regiocontrolled Perkin/Mallory approach: a nearly planar [10]phenacene derivative, a moderately twisted [10]semicircle derivative, and a 3D non‐planar [10]helicene derivative. The photophysical properties of the 3D [10]helicene isomer were found to be dramatically different from the comparable ones of the [10]phenacene and [10]semicircle isomers. The aromatic properties of the [10]phenacene and [10]semicircle isomers conform well with their predictive Kekulé and Clar analyses, but the [10]helicene isomer deviates from these general topological rules, which appears to be a general phenomenon for [n]fibonacenes with n≥9.