Synthesis of Aza[n]helicenes (n=4-7) via Photocyclodehydrochlorination of 1-chloro-N-aryl-2-naphthamides
Abstract
A series of aza[n]helicenes (n = 4-7) was synthesized using a photocyclodehydrochlorination of 1-chloro-N-aryl-2-naphthamides as a general synthetic procedure introducing the nitrogen atom to the third ring of the helicene framework. The effect of the nitrogen presence in the helicene skeleton on the physicochemical properties of the prepared aza[n]helicenes was studied and compared to those of the parent carbo-analogues.
The insertion of a nitrogen atom into the outer edge of the helicene molecule has a severe impact on certain physicochemical properties such as optical rotation, electrostatic potentials, and intermolecular interactions. On the other hand, some other properties such as UV/vis, fluorescence, and phosphorescence spectra remained almost unaffected when compared to the parent carbohelicenes.
A nitrogen atom can be also used for further derivatization, which can lead to further modification of helicene properties, as manifested here in the fluorescence changes induced by protonation.