Synthesis, Structure, and Chiroptical Properties of Indolo‐ and Pyridopyrrolo‐Carbazole‐Based <i>C<sub>2</sub></i>‐Symmetric Azahelicenes
Taisei Taniguchi, Yuji Nishii, Tadashi Mori, Ken‐ichi Nakayama, Masahiro Miura
Abstract
Abstract Treatment of 11,12‐bis(1,1’‐biphenyl‐3‐yl or 6‐phenylpyridin‐2‐yl)‐substituted 11,12‐dihydro‐indolo[2,3‐ a ]carbazole with an oxidizing system of Pd(II)/Ag(I) induced effective double dehydrogenative cyclization to afford the corresponding π‐extended azahelicenes. The optical resolutions were readily achieved by a preparative chiral HPLC. It was found that the pyridopyrrolo‐carbazole‐based azahelicene that contains four nitrogen atoms exhibits ca. 6 times larger dissymmetry factors both in circularly dichroism (CD) and circularly polarized luminescence (CPL), | g CD | and | g CPL | values being 1.1×10 −2 and 4.4×10 −3 , respectively, as compared with the parent indolocarbazole‐based azahelicene. Theoretical calculations at the RI‐CC2 level were employed to rationalize the observed enhanced chiroptical responses. The (chir)optical properties of the former helicene was further tuned by a protonation leading to remarkable red‐shift with a considerable enhancement of the | g CPL | value.