Octagon‐Embedded Carbohelicene as a Chiral Motif for Circularly Polarized Luminescence Emission of Saddle‐Helix Nanographenes

Abstract

AbstractWe report a new family of hexa‐peri‐hexabenzocoronene (HBC)‐based helical nanographenes incorporating π‐extended carbo[5]helicenes bearing an octagonal carbocycle. This family represents a new kind of highly distorted saddle‐helix hybrid nanographenes. For the first time, the eight‐membered ring becomes a constituent of both a carbo[5]helicene and a HBC and thus, the negative curvature is responsible for twisting both units. This novel chiral motif, namely, oct‐[5]helicene results in the largest torsion angle recorded so far for a carbo[5]helicene (θ=79.5°), as it has been suggested by DFT‐calculations and confirmed by X‐ray crystallography. Consequently, the barriers of isomerization become exceptionally high for a [5]helicene unsubstituted in the fjord region since neither racemization nor decomposition were observed at 200 °C for 1 or 3 during 5 h. Therefore, racemic resolutions allowed subsequent chiroptical studies showing the ECD and CPL responses of this novel family of chiral nanographenes.