Enantiomer-enriched π-extended helicenes with a perylene core from binaphthol: axial-to-helical chirality transfer with a stepwise Scholl reaction mechanism

Abstract

π-Extended helicenes, as chiral nanographene molecules, possess unique chiral structures and properties, making them highly valuable for applications in advanced chiral materials. However, their enantioselective synthesis typically requires complex resolution processes or the use of expensive catalysts and labor-intensive substrates. This study introduces a cost-effective strategy that utilizes binaphthol, an axially chiral precursor, in the Scholl reaction to generate a twisted perylene core. This approach leads to the formation of an enantiomer-enriched helical structure with an enantiomeric ratio of up to 80.1 : 19.9, without the need for specialized ligands or substrates. The enantiomeric purity is further enhanced through crystal selection or thin-layer chromatography (TLC), eliminating the need for high-performance liquid chromatography (HPLC). The resulting helicenes exhibit a circular dichroism dissymmetry factor (|g_abs|) of up to 0.01, accompanied by near-infrared (NIR) emission and a fluorescence quantum yield of 41.1%. These results underscore the practicality and efficiency of binaphthol in enantioselective synthesis, expanding the scope of the Scholl reaction to produce enantiomerically enriched helicenes with excellent optical properties.