A Nitrogen-Doped Hexapole [7]Helicene versus Its All-Carbon Analogue

Two synthetic nanographenes (NGs), N-H7H and C-H7H, were prepared. N-H7H is doped with nitrogen, and C-H7H is the all-carbon analogue. Both are hexapole [7]helicenes (H7Hs), and their structures were identified by single-crystal X-ray diffraction. Sharp contrasts in absorption ((abs)lambda(max), 683 vs. 593 nm), emission ((em)lambda(max), 894 vs. 777 nm), and electrochemical behavior (E-ox(1), 0.28 vs. 0.53 V) were observed between N-H7H and C-H7H, and the origin of these differences was rationalized by theoretical calculations. Studies on N-H7H and C-H7H set a clear example to elucidate the remarkable effects of N-doping on the physical properties of NGs.