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.

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Five derivatives of cyano-containing 9-alkyl-9H-aza­[7]­helicene were synthesized and their behavior in the crystallization was investigated. Only one of the derivatives, 5,13-dicyano-9-butyl-9H-aza­[7]­helicenes, showed the phenomenon of spontaneous resolution, which was attributed to the conglomerate formation of the same helical isomer via CN···H–Ar interaction. The helical molecules with same chiral description were aligned to form a necklace-like chain of secondary superhelix architecture of the same chirality. A correlation of the position of the cyano group and spontaneous resolution phenomena has been derived.