Synthesis of Homogeneously <i>π</i>-Extended Helicenes and Their Electronic and Photophysical Properties

Helically twisted conductive nanocarbon materials hold great potential for optoelectronic and electromagnetic molecular devices operating on the nanometer scale. With recent advances in synthetic organic chemistry, there has been increasing interest in the synthesis and characterization of compounds with large π-conjugated systems, which were previously challenging to synthesize. Our research focuses on the synthesis of homogeneously π-extended helicene derivatives and the investigation of their electronic structures. In 2018, we successfully synthesized and performed single-crystal structure analysis of a π-extended [7]helicene (2, C48H24). In 2022, we synthesized π-extended [5]helicene (1, C34H16(CH3)2) and π-extended [9]helicene (3, C62H30). Through our study of their electronic structures, we discovered that the unique electronic and photophysical properties of π-extended helicenes originate from a polyene-like electronic state within the helical framework along the helical inner rim. In this article, we present our latest findings on the synthesis of homogeneously π-extended helicene derivatives and their distinct physical properties, which arise from their molecular structures.