The route to transition metal complexes with azahelicenes

Azahelicenes possess an extended conjugated π system which can endow their complexes with useful optical properties, including intense absorption bands in the visible region of the spectrum and photoluminescence. As such, azahelicene complexes may be regarded as promising functional components of light-harvesting and energy transfer systems. For this reason, mono- and diaza[5]helicenes were approached on one hand through gas-phase quanto-mechanic calculations aimed to determine the availability of the nitrogen(s) lone pair and on the other side through X-ray diffraction of their crystals, with the purpose to shed light on the intermolecular forces driving the formation of well-ordered structures in the solid state. Furthermore, N-alkylation of some of these molecules was realized, in order to relate the ease of formation of quaternary salts with the results obtained by density functional calculations. These results provide a rationale for designing new azahelicene-transition metal complexes.