Saddle-Shaped Chiral Nanographenes Embedded with Dipleiadiene and Thia[6]helicene Units

Abstract

Negatively curved chiral nanographenes (NGs) have recently garnered significant interest as aesthetically unique carbon allotropes with unique topologies and extraordinary physicochemical properties. However, the construction of such π-systems bearing multiple heptagons and helical chirality remains challenging. Herein, we reported the successful preparation of a saddle-shaped chiral NG 2 incorporating two heptagons and a thia[6]helicene unit, along with a triple thia[6]helicene 4, by controlled Scholl reactions. Single crystal X-ray diffraction analysis revealed that 2 adopted a highly distorted architecture with a pronounced torsional angle of 30.3° with regard to the central benzene ring. The formation of two additional heptagons in 2 resulted in red-shifted absorption and emission, as well as enhanced fluorescence quantum yield compared to 4. The oxidation of the sulfur atoms in compounds 2 and 4 to their corresponding sulfone-incorporated analogues, 3 and 5, respectively, was found to be an efficient approach to modulate their electronic and electrochemical properties. Furthermore, the relatively high racemization barriers of these compounds enabled their chiral resolution and facilitated the characterization of their chiroptical properties.