Helicene is a class of chiral π-conjugated molecules with a screw-shaped skeleton formed by ortho-fused benzene rings (i.e., phenanthrene units) that has been actively studied. In addition to the chiroptical properties such as circular dichroism (CD) and circularly polarized luminescence (CPL), 2) their physical properties as molecular springs 3) and the CISS effect 4) are cutting-edge functionalities based on the helical molecular scaffold. When focusing on the lengths of [n]carbohelicene, it is assumed that the overlap of the πplanes becomes more significant by forming a layered structure; double layered at n = 7 and triple layered at n = 13. In 2015, [16]carbohelicene (A) was synthesized by Murase and Fujita, and this is the longest [n]carbohelicene ever synthesized (Figure ). The synthesis of longer helicenes has been desired simply as a synthetic challenge and various improved synthetic methods have been devised. Helicenes comprising more than triple-layered structures are particularly difficult to synthesize, because of solubility issues, and because the middle-layered core is tightly compressed, making it difficult to release the strain. Recently, several longer helicene analogues that can release the strain by virtue of their structure have been developed. For example, expanded helicenes, in which phenanthrene units are partially replaced by anthracene units to increase the diameter of helicenes, and perylene bisimide-incorporated helicenes (helicene nanoribbons) have been synthesized. These "diameter-expanded" helicene analogues display interesting dynamic behavior and chiroptical properties. Tilly's group synthesized expanded [n]helicenes (B) with three different lengths (n = 15, 19, 23), and compared the racemization barriers and dissymmetry factors. By contrast, Hirose and Matsuda have reported "π-extended"