Synthesis and Photophysical Properties of Aza[<i>n</i>]helicenes

Synthesis and study of aza[7]­helicene and aza[9]­helicene is presented in this paper. Photo-dehydrocyclization of the 3,6-bis-styryl derivative of carbazole leading to sterically less demanding aza[7]­helicene resulted in smooth reaction, and only the desired angular–angular product was detected. However, in the case of aza[9]­helicene, along with the expected angular–angular cyclization, three other products involving linear mode of cyclization were also isolated and characterized. In this case, the helical compound aza[9]­helicene was predominantly formed at lower concentration while the other isomers were obtained at higher concentration. All of the compounds formed by angular–angular, angular–linear, and linear–linear modes of cyclization were fully characterized, and their photophysical properties were investigated.