Electronic properties of diastereomeric Möbius shaped cyclotris[5]helicenes

Abstract

The in-depth analysis of the configurational, (chir)optical and aromatic properties of two diastereomeric singly and triply twisted Möbius-shaped macrocycles, the cyclotris[5]helicenes, in which three [5]helicene fragments with like and unlike helicity are connected by three C(sp²)–C(sp²) single bonds, led to the conclusion that global π electronic delocalization exists in these molecules. This was analyzed as a consequence of the reduced torsion angle (≤30°) at the C(sp²)–C(sp²) single bonds connecting the [5]helicene fragments. The enantiomers of both diastereomeric cyclotris[5]helicenes were thoroughly analyzed experimentally by unpolarized and circularly polarized vibrational, absorption and luminescence (fluorescence and phosphorescence) spectroscopies, all correlated with advanced DFT models, which provided insightful data on their S₀, S₁ and T₁ electronic states, and on their chirality. The theoretical analyses of aromaticity in both diastereomeric cyclotris[5]helicene macrocycles, as compared with recently reported analogues, confirmed their Möbius aromaticity.