With regard to these intriguing characteristics caused by the seven-membered ring, several groups have focused on helical molecules with seven-membered rings and revealed their intrinsic properties. Takasu et al. reported that a helical nanographene C composed of a contiguous 6-7-7-6 ring system has a large racemization barrier (E calc [B3LYP/6-31G(d,p)] = 29.2 kcal mol -1 ) (Figure ). They were able to isolate an enantiopure isomer and revealed that such heptalene-embedded helical nanographene C exhibits strong circular dichroism (CD), whereas [4]helicene with a 6-6-6-6 ring system easily undergoes racemization due to its much lower energy barrier (E calc = 4.0 kcal mol ). Thus, helical nanographene C with a heptalene skeleton can achieve configurational stablitity, which is quite rare.