Double aza[4,5]helicenes with a common naphthalene core: synthesis, crystal structure and optical properties

Novel double aza- and diaza[4,5]helicenes, the two helical units of which have a common naphthalene core, have been prepared through a five-step synthetic sequence using commercially available 2,3-dihaloazines (2,3-dibromopyridine, 2,3-dichloropyrazine and 2,3-dichloroquinoxaline) as starting materials. The X-ray structures, UV-vis absorption and fluorescence spectra of the helicenes were investigated and compared to those of the parent phenanthrene, single aza[4]- and [5]carbohelicenes, and a double [4,5]carbohelicene.